Aquaponics – A Process Control Approach

An aquaponics automation design was undertaken to interpret the system requirements to integrate automation to operate and optimize the system. The system was designed to increase the layers of control over the inputs and outputs to operate the system with a process control approach. The viability of these levels of control over the process was investigated by undertaking a processes design to assess types of instrumentation required and control functions that could be incorporated into the design to optimize the process. The design process incorporated sub-systems that did not rely on a main system, to increase ranges of commercially viable crops. The subsystems do not have the same environmental requirements of the main system and the subsystems environment could be calibrated to meet specific requirements of a selected crop including fruiting vegetable types. The results of the automation design have been tabulated into this article to assess the viability of increased levels of process control to obtain subsystem designs with maximized optimization.


LIST OF TABLES
water film, to supply the optimum nutritional requirement for specific plants or fruiting vegetables. As a closed system, hydroponics results in very insignificant water loss to the environment. This technology is becoming more popular with communities and governments as the preservation of water becomes more of an issue.
This is especially important in regions where water is a scarce and hence an expensive commodity. Hydroponic systems may be located within industrial complexes near to the point of consumption.
Aquaculture is the science of raising aquatic animals such as fish, prawns etc.
Aquaponics is technology developed from the aquaculture industry that integrates intensive farming of fish and utilizes plants (integrates hydroponics) in a continuous closed loop to clean the water for the fish. For aquaponics to work there must be a symbiotic, closed loop relationship between both subsystems. There are some natural symbiotic features, for example, fish produce ammonia, which is converted by bacteria into nitrates. Nitrates are toxic to fish above certain levels; however, nitrates represent a nutritional requirement of plants thereby reducing nitrate levels in the shared medium i.e. a symbiotic relationship.
However, aquaponics is a complex system of interacting parameters some of which are mutually incompatible. For example, the pH range best suited to bacteria activity differs significantly from that required by plants such as fruiting vegetables.
In effect whilst there are natural symbiotic relationships in aquaponics, there are also systems that are antibiotic.
The ideal parameters have been identified for each subsystem and the challenge has been to optimally control these parameters and address the problems of antibiotic subsystems. Supplying optimal parameters could increase the number of viable commercial crop varieties including fruiting vegetables in an aquaponics system. In order to achieve these goals process control systems have been indicates this is the first process control automated approach to aquaponics.
The use of process control and the automation that it incorporates is able to measure and maintain multiple control loops, having multiple control loops that are not dependent on others would remove some of the identified limitations by dividing the process to meet those ranges that have been researched as optimum at particular stages.
Research carried out by Dr. James Rakocy (Rakocy, 2013) looks at sizing or controlling the process by the amount of fish feed that is introduced into the system in comparison to the amount of growing area to control the process by limiting the amount of nutrients in the system.
Additional Research by Dr. James Rakocy (Rakocy, 2013) has looked at the nutrients required within the aquaponics system that includes additional items that are required and quantities to supplement plant nutrient processes to maintain conditions. that automation techniques could also be utilised to keep the process within established parameters, which should provide similar or improved results as with trialled process ranges. The addition of automation and its associated instrumentation could introduce better control over some of the inputs, which can control the ranges of the process, which ultimately controls the outputs of the system. This thesis will look at some of the known data or techniques along with the adaptation of technologies to illustrate some of the ways that automation could benefit the processes by monitoring and controlling the process to assist in optimisation.
It has been suggested by Lennard PhD (Wilson Lennard) "if nitrate concentrations were graphed therefore, they would appear as a "flat line" across the page" as an alternate approach such as if regular testing could take place and actively adjusting the feeding ratio. However there are different forms of testing or measurement and the wastewater industry has developed instrumentation that is able to measure nitrates in parts per million (ppm) in real-time. If nitrate values are measured on a constant basis then controlling the quantity of fish feed inputs to the system is only one way to control nitrate levels.
Along with controlling dissolved nitrates other nutrient levels could also be adjusted, not only by addition of fish feed but also removal of these nutrients to be recycled by supplementing nutrients to other processes. The control and stabilisation of nutrients can also be difficult in an aquaponics system, as fish are grown in batches in separate tanks to stagger production. In certain circumstances, a complete tank can be harvested to meet sales demand or reduce transport overheads. This can shock the system as the nutrient levels also change as the fish feed that supplied the levels of nutrients are not at the same input levels for optimised fish production.
Automation could aid in the control and management of the inputs and outputs, this could provide operators more stability in the system and allow regular fish harvests without interruption to nutrient levels that can effect plant and vegetable production.
This thesis is highlighting some of the systems that could be adapted to be utilised in an aquaponics system as individual components with published ranges and results from existing data. The thesis is aimed at highlighting some of the techniques used in designing a process and how automation could be implemented to aid in stabilising parameters of the process, by controlling parameters of the process`s with automation techniques. There is a lot of emphasis put on the treatment of water to obtain required water quality, by using established water treatment techniques.
There is a focus on moving nutrients within the system to allow for optimum conditions for the growing of plants such as edible fruiting vegetables. This thesis could also show that automation could aid in obtaining proven hydroponic recipes, along with the addition of recycle nutrients. Being able to recycle these nutrients just doesn't allow for clean water for fish that can be farmed intensely in an area that requires far less land space, but could also allow for intensive fruiting vegetable food production.
Aquaponics and hydroponic technology is becoming a focus in areas that have shortages in water supply. Farming techniques that are able to (Tess Russo, 2014) deploy low water use with limited or nil wastewater is considered more sustainable than conventional water reticulation systems and in many situations is becoming far more practical. One such project has been referred to as (Sophia Epstein, 2017) Growing Underground, in England old tunnels have been used to grow micro-greens with intensive farming techniques with the benefit of reduced transport costs.
Sustainable farming techniques have been recognised not by just individuals but government bodies as well, with an example of this being a rezoning of 28,000 ha of land (Australia) South of Perth Western Australia as an urban farm zone to encourage these types of projects.
Hydroponic system operators have released figures that they are able to save 99 % of water usage (Borras), yet these are under almost laboratory conditions.
Aquaponics systems that are in dry conditions with floating raft systems that are exposed to the environment (wind and associated evaporation) can still use less than half the amount of water (Watch) of traditional techniques, whilst also producing large fish quantities within the same water.
The aquaponics systems have also in some cases been certified as organic (Oi, n.d.), while this can be controversial as supplements are still required to make the solutions viable yet certification has been achieved. Although the use of automation will recycle as many nutrients as possible, during some stages in the process cycle nutrients would also be supplemented, via dosing, for the conditions to remain optimised. Another sustainable feature of aquaponics that should be noted is the technology does not use herbicides in the process, which in areas are becoming a problematic (Sedbrook, 2016) as they can leach into the waterways.
Other techniques such as energy conservation with automation techniques will also be considered by utilising products such as Variable Speed Drive`s (VSD) for motor speed control to control flow rates to desired ranges and to reduce energy consumption wastage. The consumption of energy in the process could also be offset by the production of energy onsite with the use of solar or wind sources, which could also supply batteries to offset power usage and supply a form of redundancy during times of mains electrical supply failure.
While some of these automation techniques could aid in industrial sized commercial systems these would not be practical in smaller systems and is not the focus of this research thesis, as this is targeting large-scale industrial production.

LITERATURE REVIEW
In an aquaponics system the nutrients that accumulate in the system is a result of the accumulation of waste from fish and the feed introduced to grow fish. The fish eat food that they require to remain healthy and grow, yet the food used to feed the fish and the waste it produces does not (James E Rakocy) contain all the needs of various plants. If the technologies are to support the reduction in water and remain competitive in current markets, a greater diversity of products could be required to remain competitive in commercial markets. Existing commercial aquaponics systems are able to grow a range of vegetable greens on a competitive footing yet could come under pressure during seasonal shifts when traditional market growers are able to compete during these seasonal time periods. This could also limit areas in which they are able to compete where established farming techniques could undercut Recirculating Aquaponics System (RAS) operators with the limited varieties that could be competitively grown. The additional range of products that a system is able to produce could also reduce the (Craig W. , 2015) financial risk that an investor must carry when entering into a large commercial venture as they would be able to supply a greater number of supply chains limiting market shocks.
Technologies that are able to recover or reduce water use in industry, commercial or farming techniques are becoming practical solutions as water use becomes more of a concern for governments and communities. Aquaponics systems can produce crops profitably (T. Vermeulen, n.d.), although the crops in which they are producing successfully can limit the markets in which they are able to supply and compete in. This is due to established limitations either from biological restrictions or from nutrient availability restrictions in the process, which can limit varieties of plants produced.
Most mid to small aquaponics systems will initially begin to operate their systems between pH of 6.8 and 7.2 (Ecolife), although this sets limitations on the amount of fish due to ammonia build up within the system. can be recovered in the process.
The proposed thesis will look at control techniques to make established conditions possible with an engineering approach that treats the system as a process with ranges that need to be met for the system to remain productive. Automation and control can function as both measurement and adjustment to the system on a constant basis, some of the conditions that would normally be difficult to maintain in a system would be contained within the desired range. Process control with automation is able to increase the complexity of the control parameters, which can allow Multiple Inputs and Multiple Outputs (MIMO) to be measured and controlled to achieve desired ranges. The use of ranges that have been established in aquaponics and hydroponics with known viable results can be used to develop a control solution that could overcome some of the limitations that aquaponics operators must tolerate. Currently these parameters can rely on biological process to obtain established system ranges by controlling the system by balancing the nutrients with the amount of fish feed that enters the system in comparison to the amount of plants that are in the system. This approach can restrict other components of the system and compromises are required to keep the system balanced to meet the biological requirements.
Automation techniques could also add alternate methods of controlling these nutrient levels, by adapting current or existing technologies from other industries.
These control techniques could aid in controlling both the inputs and the outputs of the system with the use of instrumentation, measurement, and automation control.
These control strategies would not just include adding additional nutrients to meet the needs of the plants but recycling those currently present in the system to reduce waste as much as possible, by streaming them into other independent control loops.
As the fish do not need certain nutrients in their diet, they are not added to the fish feed and have to be added to the water to create conditions that can grow crops successfully. Yet as there are dissolved solids in the water from the fish waste, it can be difficult to add large quantities of additional dissolved nutrients as the water quality would be diminished. As part of the process, ammonia from fish waste is also produced and must be removed, as it is toxic to fish even in very small quantities. The ammonia is converted by bacteria into different forms firstly nitrites then nitrates, which is safe to fish at certain levels. This process also produces carbon dioxide, which also introduces chemical processes. The bacteria also has optimum ranges in which it can carry out its biochemical process, which includes temperatures and a range of pH`s (Ecolife). The fish also have some particular water quality requirements that can also include the amount of (Lennard, Aquaponics System Design Parameters: Solids Filtration, Treatment and Re-use, 2012) suspended solids and preferred levels of dissolved solids within the water for them to remain healthy and productive.
Fish can survive in a variety of pH levels depending on their species with most able to survive in ranges of 6.5 to 8.5pH (Nations; FAO, Bacteria in Aquaponics, n.d.), although there are species that can live in ranges below and above this range such as tilapia, which can survive in as little as 6.0 pH. Some carp and catfish varieties can survive up to ranges of 9.0 pH. However, the nitrifying bacteria prefer to be above the 7-pH range to work efficiently, (Wilson Lennard) with optimum ranges between 7-pH to 8-pH. This factor can limit the range otherwise the water will become toxic to fish as ammonia levels will rise no matter what species of fish is used within the system. Alternatively, there would have to be a lowered number of fish density in the system, which would not be optimum for system production rates or an extremely large nitrification tank would need to be constructed to maintain the system.

Figure 1 Productive Nitrification Levels.
The process ranges of plants however differ from the requirements of certain species of fish and nitrification bacteria ( Figure 1) and the requirement can be much lower than that required in soils for the plants to have full availability to nutrients.
Nutrients such as "Mn, Cu, Zn and especially Fe are reduced at higher pH" (Bugbee), although this nutrient availability is only reduced it can be important in more (Larry Cooper, 2015) complex fruiting vegetables to consistently grow fruit that is of uniform size without deformities for the product to remain marketable.

Figure 2 Plant Nutrient Availability.
Although there are differences in the ranges between plants and bacteria, (Figures 1 and 2) these system requirements alone, do not stop commercial aquaponics operators from producing a variety of crops that are normally green leafy varieties. Although operators will look for a compromise between these ranges, even though they recognize (Chito F. Sace) "the pH was disadvantageous to vegetables." Automation techniques could also be utilized that are able to move nutrients into sub systems of the process that are not subject to the same limitations, such as pH (Konrad Mengel) which can restrict nutrient uptake by plants.

Plants
The plants in an aquaponics system utilise the nutrients that are in the water to take up the nutrients via their roots to feed the plant. The solution is made up of various nutrients and is often referred to as the hydroponic solution. The plants need 16 elements in various levels of concentration to grow at their optimum levels, which include (Latham, n.d.) "nitrogen, phosphorus, potassium, calcium, magnesium, and sulphur". While there are other nutrients supplied in smaller amounts referred to as micronutrients which include (Latham, n.d.) "iron, manganese, boron, zinc, copper, molybdenum, and chlorine are also needed but in very small amounts" while air and water are able to supply others. The plants are able to absorb these nutrients from the hydroponic solution, yet they are only available to the plant in certain pH ranges.
These pH levels are at lower pH levels than vegetables normally grown in soil, which are normally (Bickelhaupt, 2017) around the 6.0 to 7.0 range. The hydroponic solution ( Figure 3) requires the pH to be a lot lower in pH of values around 5.5 and up to 6.2, which are lower than soil (these values can vary with the type of plant to be grown). The types of plants to be grown have different nutrient requirements and different pH levels allow absorption of specific nutrients such as some of the micronutrients at lower pH levels. Access to some of these micronutrients (Larry Cooper, 2015) are important to more complex fruiting vegetables to form fruits that are not deformed and produce uniformed sizes for marketability of the product.

Bacteria
The nitrogen cycle within an aquaponics system is what turns the waste from These bacteria are slow to inhabit a system and take weeks to establish themselves at adequate levels within an aquaponics system. This factor must be considered when starting up any type of aquaculture or aquaponics system, as if these bacteria are not present. As fish are introduced into the system, ammonia can build up to toxic levels very quickly and lead to fish kills and failure of the process, yet can be mitigated by the cycling of water. The time it takes to introduce these bacteria is referred to as cycling ( Figure 4) and can be sped up with the introduction of ammonia and bacteria into the system before any fish are introduced. Once the bacteria establish themselves they can be seen as a brown (Imran Ali, 2014) slime on surface areas and will establish themselves throughout the system, where there are surface areas for them to attach.
The nitrifying bacteria also need other environmental elements for them to establish in healthy numbers, the bacteria are sensitive to light whilst establishing and prefer not to be exposed to direct sunlight. The bacteria also prefer temperatures of between The nitrification bacteria attach themselves to surface areas, which provide a home for the bacteria, the bacteria require (Burke, 2014) high specific surface areas to establish large colonies. One way to increase the surface area size is to utilise items within a specific tank that have large (James M. Ebeling P. , 2006) surface areas such as volcanic rocks, clay, bio filter balls which can be made into variable sized plastic balls.

Dissolved Oxygen
The aquaponics process relies on dissolved oxygen being present throughout the process. The fish in the aquaponics system require minimum values to be present not just to survive but also to remain (Hijran Yavuzcan Yildiz, 2017) healthy from disease in a low stress environment. The nitrification process also consumes dissolved oxygen to change the ammonia into nitrites and nitrates. Plants also compete for dissolved oxygen in the effluent. Aerated (Hendrik Monsees, 2017) aerobic mineralisation also takes oxygen for the bacteria to digest the solids, these solids can take several steps to break down, and even after they become soluble, they may not necessarily be plant available. If media beds or mineralisation (further explanation of this process component in additional sections) is utilised in the system and have oxygen demand, attention must be payed to oxygen levels to prevent any anaerobic conditions (FAO, Bacteria in Aquaponics, n.d.) in the tank, as larger organic molecules can be present using oxygen as they travel around the system.
As different components of the process use oxygen, there are also different methods of adding dissolved oxygen (Wilson Lennard, Solids Filtration, Treatment and re-use, n.d.) which should be considered that could benefit that overall part of the plant. The addition of pure dissolved oxygen to the water before it goes via the fish tanks to increase the density in the fish tanks. This thesis however is more focused on automation methods and how the process could utilise nutrients with the use of automation, however process expansion will be considered when making design choices to limit capital impacts if the process requires increases in fish production to respond to market demands. Mixing in the process by agitation was considered initially yet can be expensive as the electricity costs can be high, which has led to the development of various types of bubble diffusers (Mooers, 2013) which are able to supply a greater exchange of gases due to the larger surface area of the numerous bubbles. Blowers that are able to supply air on a constant basis once they are operating can supply these diffusers. Compressors on the other hand are able to supply air via pressure control valves and can (Kaeser, 2007) supply multiple items that may need pressurised air at various pressures. The other advantage of using compressors is that they are able to store compressed air, which has the advantage of being able to supply the system during a power outage even if only for a small period, yet potentially could prevent a fish loss during this time. A fish loss could be a there is a requirement to agitate the solution as well as supply gas exchange. Another consideration should be where they are going to be placed, as diffusers need space from the bottom of the tank, which could allow solids to settle and create an anaerobic zone. This could be designed out of the process by using technology such as diffuser mats that line the bottom of the tank to prevent oxygen deficient or dead spots being created underneath diffusers, including those areas that use finer bubbles where less agitation would be present.

pH
The pH in the system is a measure of the hydroponic fluids (water) acidic or alkalinity with 1 on the range being the most acidic and 14 being the most alkaline, while 7 is considered neutral. The pH of the system is monitored with the use of pH probes and meters, local meters or transmitters that can interface to such items as Distributed Control Systems (DCS) or Supervisory Control and Data Acquisition (SCADA) system, which can display and alarm desired ranges.
The fish, plants, and bacteria all have preferred ranges for them to survive in, they can also have preferred ranges in which they are most productive. Plants can have different pH requirements so they are able to take up different nutrients at different pH`s to grow either their leaves steams or fruits. This is similar to bacteria which will grow and survive at different pH`s yet have known values which they will perform at the most productive to oxidise ammonia or change nitrites into nitrates. As the performance of the system can rely on the levels that are present, the levels at which they are controlled is very important.
There are a number of processes in the system that influence changes to the pH levels with the following being addressed as part of the process control solution; • The amount of alkaline nutrients (Simon Goddek, 2015) that are added to the system have a natural alkaline effect.
• Another is the bacteria that break down solid waste (James E Rakocy) and ammonia that is supplied from the fish feed and its associated waste products produce Carbon Dioxide.
Carbon Dioxide dissolves in water has an acidic effect in the water and results in changes to the pH of the water, which can reduce the effectiveness of the bacteria that are aiding in the process of transforming ammonia to plant available forms.
Carbon dioxide is also toxic to fish with most species not being able to go above 20 ppm (Swann, n.d.) (tilapia can survive in up to 60 ppm).

Control pH
The pH can be monitored and be controlled through a number of strategies that could include both chemical and by carbon dioxide stripping with the use of (L Dediu, 2012)degassing tank or column/towers.
The monitoring of both carbon dioxide and alkalinity content within the water allows the operator to determine treatment of the water. If the alkalinity nutrients The other is that carbon dioxide is removed from the system if it is aerated as it naturally equalises with the air that is passed through the water. As the air passes through the water oxygen is dissolved in the water as carbon dioxide and Nitrogen are passed into the atmosphere. Carbon Dioxide can also be stripped from water by mechanical processes or with the use of carbon dioxide stripping towers, which can be calculated to size through a set of known data that is based on the number of fish and the amount of feed that is introduced into the system. Carbon Dioxide can also be (Steven T. Summerfelt, 2015) stripped out of the water by increasing the aeration at various stages of the process until it is brought within optimum ranges.
If alkalinity levels fall, it could be appropriate to increase the dosing rate to bring into the desired range (BAQUE), or leave it at current levels if it is within the desired alkalinity levels.

Sodium Control
The addition of salt into a system will eventually add up to levels that will not fall into ranges that are optimum for plant production. The levels of salt could also build-up if nutrients are being captured into a concentrate, which could also unintentionally concentrate the salt from the aquaponics effluent. Salt in the aquaponics water in (Louis A. Helfrich, 2013) small quantities is acceptable and in certain circumstances used to treat fish if diseases have entered the system. To control the salt levels in both the aquaponics and hydroponics systems, sources that introduce it should be managed. Traditional aquaponics systems use a fishmeal product or fishmeal based product to feed the fish in the system.
Fishmeal comes from waste from the fishing industry, which is cooked dried and made into a powered or pelleted product (the oils can also be separated during this process). Fishmeal has been referred to as a sustainable fishery as it is produced from waste yet this is controversial (Newman, 2014) and is contested in many forums.
The fishmeal has high levels of protein that is useful in an aquaponics system as it allows for optimum growth of the fish. The fishmeal however can also contain salt as it normally comes from salt-water waste products such as unintentional fish bycatch.
The salt and sand levels in poor quality fishmeal can approach 1 to 4% (Station) of the total meal within the feed supply. High quality fishmeal can contain less than 1% salt, although this can be lowered if the fishmeal is mixed with other products.
Fish feeds (Cant, 2007) can be based on lupins or soybean mix that has proven palatability for different fish species. These products have high protein availability and percentages, which can exceed the requirements for optimum fish growth. To The other benefit to using plant based fed products is that the lupins or soybeans also naturally contain a range of micronutrients including non-essential micronutrients that might normally need to be supplemented in an aquaponics/hydroponics systems.

Design Components
To gain a better understanding of equipment that have been successfully incorporated and designed for use in an aquaponics system including their current design parameters. An investigation was carried out to find some of the components that are already used successfully in aquaponics design solutions.

Baffles -Solids Separation
The solids within the aquaponics solution must be removed from the main stream as these can foul pipes and fittings and build up in areas and create anaerobic conditions, which can harm the system. There has been the use of baffles installed in clarifiers to separate the solid wastes from the aquaponics solution, which is referred to as the UVI clarifier (University of Virgin Islands who developed the clarifier). The UVI clarifier uses water that is pumped at a 45-degree angle towards a baffle, (James E Rakocy) approximately 50% of the solids then settle on the bottom cone section for collection at the bottom of the tank. This type of filter is designed to capture the larger solid particles that are able to settle on the bottom of the tank, although further treatment is required to remove smaller solids that are suspended in the aquaponics solution.

Swirl -Solids Separation
Solids in an aquaponics system will build up if left unchecked and will form layers of sludge in the system, which will become anoxic, which could poison or kill the fish in the system. The solids come from left over fish feed, organic matter from plants or even algae within the system, which consume dissolved oxygen and release the system of valuable nitrogen while producing other forms of toxins. In a commercial process where decreasing fish numbers to combat this issue is not realistic, the implementation of water quality techniques must be designed as part of the process to balance the system and allow for commercial scale fish stocks.
As solids are considered a resource in the aquaponics process there must be an allowance in the process to remove these for further treatment. The removal of solids allows them to be separated for mineralisation by bacteria, into a form that can be taken up by plants. The removal and treatment of these solids also allow for greater levels of water quality for the fish to survive and grow in. There are two main types of settling filters used to remove suspended solids in aquaculture systems the swirl filter or the radial flow filter.
Swirl filters are commonly used by operators with small to medium aquaponics systems and have used these with success in these systems, the influent is pumped in parallel with the tank to begin a slow swirling motion in the tank. The solids are allowed time to gently swirl in a spiral action, which assists with the solids settling at the bottom of the tank for removal. The design of the swirl filter often has a cone shape at the bottom of the filter to collect and funnel the solids down to a single point for collection. A radial flow filter as shown in Figure 6 allows flow of the effluent into baffles located in the centre of the tank and the solids settle at the bottom of the tank for removal.

Figure 6 Radial Flow Settling Filter (Technologies, n.d.).
Experiments with the use of both swirl and radial filters show that the radial settling design removes a greater amount of total suspended solids, than the swirl filters. The results from this study showed that the radial filter removed (John Davidson, 2005) 77.9 % of the total suspended solids, while the swirl separator removed 37.1 % of the total suspended solids.

Mineralisation
A mineralisation tank is utilised to treat the solids in the aquaponics solution.
Mineralisation can be done by either of two methods the aerobic or anaerobic process.
The anaerobic mineralisation or digestion of solids by bacteria is done without the presence of oxygen. The bacteria in the (Conrado Moreno-Vivián, 1999) anaerobic process can use nitrogen instead of oxygen to carry out digestion, which is counter intuitive to aquaponics as nitrogen is a resource. The anaerobic process also releases toxins and bacterial strains that are deadly to fish, for this reason it has been discounted as part of a possible design solution.
The bacteria in the aerobic process use oxygen to grow, reproduce, and feed on the organic solids that are present in the aquaponics solution. The aerobic process uses oxygen, which would already be present in the aquaponics solution, as it is required to be maintained for fish and plants. The oxygen levels are maintained by introducing air into the system, by either agitating the liquid or injecting bubbles of air into the fluid with either an air blower or compressed air.
In wastewater treatment, an extended aeration aerobic process normally takes has taken the process offline to treat solids over a longer period. If the solids are withheld in the process stream for treatment, the fish are not being supplied with a constant supply of clean water that could possibly lead to fish deaths due to the buildup of ammonia in the water.  There are also mechanical operated designs (Figure 8) that used a rotating biological discs that rotate at 1 to 3 RPM`s in the solution with half of these in the solution and half out of the solution. The discs are exposed to air, which provides oxygen to the biofilm that is present on the surfaces of the disc as it rotates both in and out of the solution. The rotating bio discs are constructed with discs, which supply an increase in the surface area. This type of nitrification tank design has the advantage that it allows for gas exchange as it rotates through the air, this includes the exchange of oxygen into the solution but also carbon dioxide to be removed into the atmosphere.

Nitrification
Up flow fluidised sand bio-filters are similar to a pool sand filter although are built on a larger scale can also be used as a nitrification tank within an aquaponics system. These tanks pump water up through sand or small plastic beads that have a (James M. Ebeling P. , 2006) large surface area of over 4000 m2/m3. This type of filter uses large pumps to pump the solution through the sand and can be subject to fouling from solids within the solution, besides taking additional power to operate the pumps this system can also be susceptible to mechanical failures.
The Upflow Sand bio filters however have the advantage of being able to be scaled to suit large commercial aquaponics systems to treat ammonia that are produced within these systems.  The bio-filtering material is suspended in the tank and aerated to supply an available source of oxygen to the nitrifying bacteria that grows on the bio-filtering media. The media is contained within the tank by sleeves on the outlet of the tank, yet allows the solution to flow to next part of the process with little or no maintenance.
This type of nitrification has some benefits as the media can be (Palayesh, 2015) packed from 30 % to 60-70% density within the tank, which allows for easy growth of the reactor by adding more media into the tank, which increases the surface area of the bio-filter. The other advantage of an MBBR is that as the media is agitated it allows the outside of the media to be scrubbed and excess biomass comes loose and prevents the media from clogging with biomass. This process is able to self-maintain the biomass, which is captured with a downstream clarifier for further removal and treatment in the mineralisation tank. The media that is used for this type of process has an internal surface area normally referred to as the protected area, which can exceed the 400 m2/m3 (Watertech, n.d.).

Nutrient Removal
Controlling the amount of nutrients in comparison to the amount of fish food entering the system versus the amount of plant growth area to control the nutrient levels within the aquaponics system has been used to (Wilson Lennard, Aquaponic System Design Parameters) size aquaponics systems. This data is relevant in the sizing of the process and the components that can feature in water treatment, however this thesis is focused on automation and control. Automation functions that can be utilised to control the parameters such as nutrient levels within the aquaponics system will be researched to find alternate control solutions than just the amount of fish feed entering the system to control the nutrient content in the system.
There are established data on solutions (Rakocy, 2013) that are contained within successful commercial aquaponics systems (which mostly grow green vegetables, as the nutrient mix is suitable for this purpose). There are also established hydroponic mixes that are used commercially to grow fruiting vegetables, although some of these mixes can be proprietary especially if the resulting fruit is consistent in size and shape as these are much more easily marketed, making the process solution competitive. As the author is approaching the aquaponics system as a process with established ranges that need to be met, this will involve the use of effective yet efficient mechanical or electrical processes. This is not just to keep the nutrient levels constant within the system but also to move nutrients to a separate hydroponic system, which can control the nutrients at established solution levels.
The removal of nutrients from the aquaponics system has some obvious benefits besides keeping the aquaponics system at safe and consistent nutrient levels for fish production. They can also be used to supplement the hydroponics system that operates at different nutrient levels or at a solution that requires different pH levels, which can make use of established nutrient recipes to grow different types of fruiting vegetables on commercial scales.
Nutrients can be stored, for use when required such as between a plant or crop cycle then re-introduced into the system as a batch with the required nutrient mix, thus supplying an additional resource from fish production and reducing additional nutrient inputs into the hydroponic system.
When comparing the nutrient solutions used in an aquaponics and hydroponics one of the most obvious differences between them is that the hydroponic solution has a larger quantity of nutrients, in comparison to available nutrients in aquaponics systems (this is required to grow complex fruiting vegetables instead of green leafy vegetables). Nitrate levels are much higher in hydroponics solution in comparison to the aquaponics nutrient recipe, as the aquaponics system also must take into account that the fish are part of the process. As the process control in this part of the process relies on nutrient removal, the recipes are considered when selecting a means to move the nutrients within the process. include chlorine), which could contaminate the water and kill the bacteria that prevent ammonia and nitrites building up to toxic levels. This could lead to a fish kill if this type of contamination event was to take place in the aquaponics system.

Electro dialysis
Another technology the author considered is the use of electro dialysis, which can operate at low pressures and has quite a low energy consumption when in operation. The system is used in water treatment where the total suspended solids (Amit Sonune, 2004) can be quite high without negative effects on the system. Electro dialysis is cleaned simply by reversing the polarity to clean the system without the use of any chemicals known as Electro Dialysis Reversal (EDR). This system would be able to reduce the nitrates in the aquaponics solution from anywhere between 50% to over 90% (Elyanow, 2005

Selective Electro Dialysis
As a more novel approach may be required to obtain the level of control required to move nutrients within the system, further research was required to find an electro dialysis system that could be adapted to the process. The membranes used in the electro dialysis (M. Pirsaheb, 2015) process has been the focus of research in recent years to reduce nitrates from well water to aid in reducing nitrates to safe drinking levels. The nitrates that contaminated the well water entered the environment from fertilisers used in farming techniques and practices, which can led to (Alyce M. Richard, 2014) medical issues from drinking the water with these high nitrate levels.
The process that was developed to overcome this nitrate issue in the water is This is not as efficient in the overall removal of nitrates in comparison to an EDR system, it should be highlighted that to control the nutrient limits within the system is to lower the nitrates, not eliminating them altogether. It should be also noted that with having control over the solids within a mineralisation tank allows for control over most of the nutrients entering the system from waste products.
The nitrates however enter the system mostly in an initial ammonia dissolved form, which would only allow control to take place by controlling what enters the system (fish feed). Having an alternate method of controlling the dissolved or liquid nutrient allows for greater control of the system and allows recycling and distribution of these nutrients in a plant available form. The pH of the concentrate would also be much lower, because the process uses an acidic base on the concentrate side of the membrane to prevent calcium build up, and keep it operating at optimum levels.

Recycling Nutrients
Traditionally aquaponics nutrients that are contained in solid waste are removed from the system through a series of settling tanks that can be of a baffle design or clarifier design such as swirl or radial clarifiers. These designs have been trialled in many environments (Jason J. Danaher, 2013) including aquaponics and has proven to successfully remove solids to preferred levels. There are other techniques such as mechanical separators that can remove solids from the aquaponics cycle very efficiently with up to 75 -90% (James M. Ebeling) of the solids being removed with these designs. As the process would be constantly altering, with fish harvests or crop rotations and natural seasonal changes that could affect growth rates and requirements of both fish and plants, the requirement for solids recycling in the system would be constantly changing. This would change the amount of solids that would be required to be removed from the process or the amount that could be treated and incorporated back into the system. A combination of these techniques are used to remove the solids into an offline process for treatment. If the process did not require the addition of solids, mechanical means could then be used to remove these totally from the system.
In conjunction with mechanical removal, there are also existing techniques from the wastewater industry that are able to decant water from the solids nutrient stream. When additional dissolved nutrients can be utilized, the decanting process could be put in line with the process making the process able to be both online and offline for effective removal, treatment or reintroduction of nutrient solids. The solids that are totally removed from the process as waste should be treated as a value-adding product, not just as waste and could be on sold as organic fertilizer or to compost manufacturers to enrich their products with nutrients.
Normally a Recirculating Aquaponics System (RAS) would be treated as a single closed loop, which must allow for all environmental conditions for biological processes to take place. As process control and automation can add additional functionality to the process, it could be broken up into more than one closed loop, with nutrient exchange taking place between the loops to supply cleaning of the fish water but also provide conditions that allow a variety of plants to grow including fruiting vegetables to their full potential.
Recycling of the solids waste from fish that contain nutrients could be in the form of treating waste as a resource in an offline / online process then reintroducing as much as possible back into the process, as the system uses it (mineralization).
Control over the main system nutrients either by removal to the sub system or removal to recycling have some advantages to the main system.
1. The aquaponics system can be regulated with addition of nutrients from more than one source (increase-recycled nutrients reintroduced after a fish harvest to prevent any losses in leafy green plant production).
2. The aquaponics system could also have a much greater survival rate of fish (excess nutrients could be removed when larger quantities of fish/feed are present in the system).
Having control over the nutrients in a sub system that is not reliant on requirements of the main system also has some advantages.

Nutrient Redistribution
Technology from the wastewater industry (Carlos Felipe Hurtado, 2016) has been utilised in applications for the aquaponics and aquaculture industry in the past, mainly to clean water of excess nutrients or remove salt from water. The technology has included the use of reverse osmosis units and low operating cost equipment such as electro dialysis or reverse electro dialysis, which is able to automatically clean its membrane by reversing the process. This has predominantly been used to clean water so it can be used in a process or recycled back into the process to lower water usage rates.
However, the automation solution proposed in further sections of this thesis is focusing on controlling nutrient levels by lowering them to established ranges by removal of dissolved nutrients from the aquaponics solution to be reused in the hydroponic sub system. These would be at pre-determined nutrient levels required for the aquaponics system to remain successful, not to remove nutrients totally from the process. One such technology that could be adapted to this purpose is Selective Electro Dialysis (SED). SED has been developed for many industries, which includes

Typical Process Ranges
To design a process control solution known optimized values must be recognized to determine instrumentation that could be implemented into the systems.
As there are also requirements for particular fish species one will be chosen as a base point to be used to design parameters to, as the author lives in Australia a non-evasive species such as Silver Perch is selected as a basepoint to determine levels which are illustrated in Figure 11. with a process referred to as (Self, 2013) plant tissue testing.

Additional Component Research
The recycling of nutrients would be beneficial and a method to control these could be to isolate the solids by a number of passive process`s (settling) then remove them to a single mineralization tank where solids could be removed as required by mechanical means. This however presents a challenge, as the tank would need to be decantered of excess water while the dissolved solids are at lower levels in the system. Technology to allow this to take place has been developed by the wastewater industry which uses a floating decanter within the tank, which would allow removal of product to take place without the tank having to be full (gravity fed). Allowing the tank not to be full would allow for a greater amount of control over the amount of solids and how they are removed, treated or recycled back into the system.
This however also presents another challenge as the solids could be in greater concentrations than are normally present in aquaponics waste streams and typical methods of mechanical removal such as drum filters (micro-screen) might not be suitable, as this type could clog with excessive concentrations of solids. The microscreen typically has a cloth filter that is sized between 40-100 microns (Bregnballe, 2015), which removes waste from the process by mechanical means. In this process design, the aim is to remove the waste by passive means (settlers and baffles) and only use mechanical means when total removal based on measured values is required.
As the mineralization tank can be online or offline with the process a different type of filter would be required to contain levels within the mineralization tank if dissolved solids are at measured saturation point within the system. A filter that was developed for the pulp and paper/food and beverage/textile/agricultural industries to treat wastewater could be adapted for this purpose. The filter is able to cycle the solids concentrate from and back to the mineralization tank, remove solids to a single stream, and remove filtered water to another stream ( Figure 10), which could be returned back to the process. This filter is also chemical free and is self-cleaning as part of its normal operation, it is also able to remove solids down to the 10-15 micron size. The filter also advertises a high water recovery with up to "99% able to be returned back into the process, while also being energy efficient with a 0.25 to 2 PSI pressure drop across the filter" (DOW, n.d.).

Figure 13 Skid Mounted Equipment (DOW, n.d.).
This filter has been developed on a skid ( Figure 13) with its own Human Machine Interface and associated programmable PLC, yet can also be integrated into a SCADA system with signals such as start and stop already incorporated into the design. Other programmable features such as timers or tank levels and self-cleaning functions are already available and could be utilized to adapt this alternate equipment into the design.

Discussion
Conducting a study on the individual requirements and designing an alternate control solution that meets the identified ranges could highlight that some of the compromises that are currently required to operate a Recirculating Aquaponics System (RAS) could be overcome and make it possible to grow vegetables with established hydroponics recipes. The systems may not necessarily be restricted to compromising between the different biological requirements of fish, plants, or bacteria but could be separated into alternate control loops. This could allow control loop requirements for segregation such as pH levels, which could be achieved by only transferring nutrients between control loops instead of allowing flow from one control loop to another. This segregation between loops also allows for temperatures of one system not relying on another system, which could allow for fish production or plant production to be independently supplied with optimum ranges.

STANDARD DESIGN METHODS
The second part of the thesis is to identify a control solution to some of the current limitations that are present in current systems. This will be achieved by using established design techniques such as an initial Process Flow Diagram (PFD), which will be followed up by a Piping & Instrumentation Diagram (P&ID) with an associated instrumentation/tag and alarm list, which will represent a design solution.
The design solution will have an automation solution not represented by hardware, but by Human Machine Interface screenshots that represent levels, or nutrients levels.
The field instruments that would be present in a practical process will be software driven to act as a simulation of the process. The automation control functions will be find design inadequacies after an event, which normally has financial consequences.
This design process is able to identify disturbances that could lead to product deviation and identify hazards that could affect the environment. Identifying process issues and designing engineering controls to prevent or mitigate issues is carried out in multiple forms or design tools. Failure Mode Effect Analysis (FMEA) is one such tool in a designer's toolbox and is recognized as an international standard (IEC 60812), which describes techniques to analyse processes that can effect the reliability of a process or determine what possible hazards could be present.
The use of FMEA has been utilized by industries to aid in carrying out HAZOP design processes, the use of these design processes can lead to inherently reliable processes. Piping and Instrumentation Diagrams also referred to as Process and Instrumentation Diagram (P&ID) are used in the process industry to show an overview of the process. The P&ID also identifies instruments that could be required for measurement and any associated alarms that are present to warn operators and mitigate failures in the process.

Figure 14 System Selection.
The integration of automation into systems that typically do not have high levels of automation can be challenging. A number of techniques could be utilized to determine design items that could identify control to be incorporated into the process.

Aquaponics is such an industry where Programmable Logic Controller's (PLC`s) and
monitoring have been incorporated although higher levels of automation such as SCADA or DCS control are not standardized. To design a functioning process and the associative automation a Process Flow Diagram was used to identify major components that are to be incorporated into the process. The Process Flow Diagram also aided in developing the Piping and Instrumentation Diagram that contains the instrumentation and alarms that the process needs to function.
As the different components must interact to complete an operating process, the components chosen must be able to function with the other design choices. In unison with the design choices, a Failure Mode Effect Analysis (FMEA) was done at this stage and at the implementation stage of the design, to assist in making design choices.
As air/oxygen is supplied to the process to account for the biological oxygen demand for the plants, mineralization bacteria, nitrification bacteria and fish that all require oxygen it will weigh heavily on the design choices made.
The Failure Mode Effect Analysis (results shown in further section as ongoing process to select instrumentation) has highlighted that a fish kill caused by power failure is a large risk to the process. One way to assist in preventing this is to select power sources that could provide some additional redundancy. One is the power source itself could be selected to have a hybrid system such as storage batteries to provide a source during a mains power failure (also stored renewables to reduce energy costs). The other is to use compressors in the process and use it to fill air storage bottles to supply air to the fish during a power failure event.
As power would also be a large operating cost, where possible the tanks and process will be gravity fed from one tank to another and must be considered when making design choices to reduce ongoing power usage. Doing an energy budget is currently outside the scope of this thesis but further detailed design to this concept would make further consideration to offset power and equipment selections.

Process Flow Diagram
The Diagram is represented in Figure 15.
Having an overall view of the process aided in the selection and design of instrumentation and alarms that need to be generated at certain points to allow control to be optimized. Design processes are able to identify disturbances that could lead to product deviation and identify hazards that could affect the environment. Identifying process issues and designing engineering controls to prevent or mitigate issues can be carried out in multiple forms or design tools. Failure Mode Effect Analysis (FMEA) is one such tool and is recognized as an international standard (IEC 60812), which describes techniques to analyze processes that can effect the reliability of a process or determine what possible hazards could be present.
The use of FMEA has been utilized by industries to aid in carrying out HAZOP design processes, the use of these design processes can lead to inherently reliable processes. Piping and Instrumentation Diagrams also referred to as Process and Instrumentation Diagram (P&ID) are used in the process industry to show an overview of the process. The P&ID also identifies instruments that could be required for measurement and any associated alarms that are present to warn operators and mitigate failures in the process. The use of these design tools have identified and mitigated the risks within the initial design concept to prevent these technical errors with engineering controls designed into the process.

Failure Mode and Effect Analysis in Aquaponics
Aquaponics operators that have taken on commercial operations have often The FMEA review results are documented into a table to record any responses and to determine the RPN score. Design notes were also taken at this stage as the analysis also identified possible design solutions. Recording the outcomes of the analysis will aid in the design process as it allows validation data to be collected that can be referred to for verification as the design develops.  The results of the FMEA (Table 1) highlighted some safety issues that also need to be addressed in further analysis such as a hazardous area review for the safe storage of fish feeds that contain oils. It also identified some changes that could be implemented to increase reliability of the process, either by redesigning subsystem components or by adding additional instrumentation to monitor identified process limits, yet also design techniques to control the limitations.

Failure Mode and Effect Analysis Automation and Aeration Control Strategies
The Failure Mode Effect Analysis (FMEA) ( Table 1) has highlighted that there is instrumentation and controls that could mitigate or prevent some of the technical failures that have occurred in aquaponics processes in the past. One of these highlighted was the use of aeration within the process as it can be stored as a reserve for a mains power failure. The other is that the stored air could be utilized to operate multiple parts of the process to prevent anaerobic conditions. This could allow some innovation to take place and adapt technologies mainly used in processes or those that could be adapted from the wastewater industry to carry out similar functions.
The process control industry has used Fail Open (FO) and Fail Close (FC) valves (Marlin, 2005) to return a process to a safe state during a disturbance or failure to the process. A simple relay or contactor that is energized by the mains supply could control an extra low voltage supply that feeds a solenoid, when power is lost to the process the contactor de-energizes returning the Fail Open valve ( Figure 16) to a position where air could flow from the stored air in the compressed air bottles. This could supply additional dissolved oxygen to the fish tanks for short periods, until the power is restored or an emergency source could be provided. Diffusers suitable for this application could be utilized to supply this gas exchange.
Automation can be configured to supply dissolved oxygen as required (bubbles) with the use of control from a SCADA/DCS system. The system could control an output from the measurement of dissolved oxygen levels from instruments placed in areas with known BOD and COD.
In plant beds, disease such as Pythium can be caused by anaerobic conditions, which are present when (Sutton, 2006) less dissolved oxygen is available. This can also be caused by higher temperatures in the aquaponics/hydroponic solution that lead to lower levels of oxygen being present. Traditionally aquaponics growers will install air stones, which will dissolve oxygen into the aquaponics solution, although there are diffusers that are able to supply ultra-fine or fine bubbles (Kossay, 2006) that have an overall greater surface area that maximize gas exchange. The use of evenly spread diffusers within the floating beds would be able to supply an evenly spread amount of gas exchange, lowering the risk of anaerobic conditions developing in isolated positions of the beds.

Failure Mode and Effect Analysis Instrumentation Adaptation
The Failure Mode Effect Analysis (FMEA) ( Table 1) also identified that there could be a requirement to monitor some of the parameters that are in the aquaponics process, which could include adapting instrumentation technologies that were developed for the wastewater treatment process.
The FMEA ( Table 1) identified features that could be incorporated onto the P&ID such as instrumentation used to measure solids for the measurement of Total Dissolved Solids (TDS) and Total Suspended Solids (TSS). The TSS in an aquaponics system is required to be monitored but also kept in control as the solids "cause suboptimal water quality characteristics" (Danaher, 2009). Having monitoring within the process allows processes not only to be monitored but also adjusted to known researched ranges that are optimal for production. This could be by streaming parts of the process that contain solids to a sub-system that is designed to remove excess solids from the process. As the PFD for this proposed design currently has an inline filter for the process, an additional flow path was added to make use of this filter by bypassing the process flow if suspended solids exceeded recommended values.
Instruments that monitor solids are commercially available and development has been mostly refined to meet stringent regulations, required by the wastewater industries , which can be (Tom Davies, 2017) "accountable to a range of state authorized bodies such as Department of Environment Regulations (DER) and Department of Health (DoH)". These regulations include the accurate measurement of contaminants to meet drinking water standards. The instruments that are available are capable of monitoring TSS down to or lower than the 1 mg/L range. Various makes and models that are able to supply (Teltherm Instruments, 2017) (BTG Australia Pty, 2004) complex models with local displays with built in relays that are able to trigger local alarms. The measurement of TDS has also been developed mainly for use in the wastewater industry and can be in various ranges with resolution of 1 ppm or lower not uncommon. Monitoring the TDS and TSS in the system would be related to the amount of solids that are re-introduced into the system. As the current process design has a mineralization tank that contains the solids, an additional sludge levelmonitoring instrument will be added to the design. The sludge level monitor has a controller with programmable outputs, which could be utilized to operate a filter to remove excess solids and prevent the dissolved solids from exceeding optimum levels.

Failure Mode and Effect Analysis Discussion
The discussion points from the Failure Mode Effect Analysis (FMEA) are listed below - • The FMEA identified risks to the process and impacts to the surrounding environment. It was documented in the FMEA that aquaponics systems could result in spills.
• Where possible gravity feed will be used to supply the system and pumps would only be used to supply flow if there was a requirement to boost pressure or pump back uphill in the process.
• The use of bunding, which could be a simple curb structure surrounding the process area was also documented to contain liquid in the greenhouse or water treatment areas (EPA, 2017) to prevent nutrient rich water from entering the environment. With the addition of a sump drain and pump installed in the floor area, the liquid could be easily removed after a spill event.
• The FMEA also identified that if there are shocks to the system such as changes of temperature or pH imbalances, there would be reduced optimization in the nitrification process, which could lead to ammonia and nitrites reaching excessive levels. The calculations to size nitrification tanks and the relationship with protein (FAO, Calculating the amount of ammonia and biofilter media for an aquaponic unit) entering the system are well documented, however allowing this component of the system to be oversized could prevent toxic build-up of ammonia or nitrates if the system was exposed to unexpected or uncontrollable system shock events.
• The FMEA also documented that there are hazards in the process such as Carbon Dioxide that is heavier than air. The accumulation of gases could potentially accumulate and injure workers in the process and could go unnoticed until an incident took place.
• Other hazards to the process that required monitoring also bought about some additional instrumentation to control the parameters before they re-entered the process, allowing the ranges downstream to have an additional layer of control upstream in the process.
• The FMEA also documented results for further consideration as the design begins to develop such as handrails around floating beds, which would be further considered if the tanks were recessed into the floor.

Piping and Instrumentation Diagrams
The Instrumentation and alarm list is attached as an Appendix 1 to this thesis, to support the items within the design that are drawn further on the Piping and Instrumentation Diagrams in Figures 17 and 18

HMI Screenshots
An aquaponics automation design was undertaken to interpret the system requirements to integrate automation to operate the system. The system was designed to increase the layers of control over the inputs and outputs to operate the system with a process control approach. The viability of these levels of control over the process was investigated by doing a design of the process to assess types of instrumentation required and control functions that could be incorporated into the design to optimize the process.
The design process incorporated sub-systems that did not rely on a main system, to increase ranges of commercial viable crops. The subsystems do not have the same environmental requirements of the main system and the subsystems environment could be calibrated to meet specific requirements of a selected crop including fruiting vegetable types. The results of the automation design have been tabulated into this thesis to assess the viability of increased levels of process control to obtain subsystem designs with maximized optimization.

Figure 19 Tank HMI Layout.
A Main Tank Alarm (featured as tag FA199 on the instrumentation list Appendix 1) has been depicted as a large red light on the screenshot to replicate a software version for the hardware. The output for this hardware would be a relay that operated a flashing beacon and audible alarm, although as this is a software version a large red light has been used to represent this operation. Once the pump is started, there must be flow from both the flow switches, if not after 10 seconds the Main Tank Alarm will be triggered, as there could be a blocked pipe or water levels are becoming inadequate. Either of these circumstances could flood or drain a tank. This was identified in the FMEA design process as having s significant financial risk to the operator of the process factory. Failure of both of these flow switches to activate in 10 seconds will also trigger an additional small light next to the tank to identify which tank has triggered the alarm for fast recognition by the operator to take action. There would also be an alarm banner displaying the monitored issue to the operator.  and the tank blockage alarms are triggered. This could cause the level to be out of range that has also initiated an additional warning on the alarm banner. The emergency stop alarm has also been initiated indicating that an operator (which could be expected if the Main Warning beacon had been activated in the process area) has depressed the local emergency button stopping the tank 1 pump.  There is also a slider to operate a valve that controls the flow re-entering the process from mineralization process, note this is currently exceeding the limits for the fish species and an alarm has been triggered which should result in the operator using the slider to decrease the flow from mineralization to reduce the total dissolved solids within the process. functions available on the screen to allow for control.     The hydroponic Human Machine Interface ( Figure 31) has a lot more control features if comparing with the aquaponics page. The sliders that control analogue outputs are able to control the dosing rates of certain nutrients to make the desired nutrient levels required by the crop that is being grown.

Aquaponics Automation by Decoupling Requirements
The aquaponics cycle is a biological process between plants, fish and bacteria, yet these all have unique optimum ranges for survival. The introduction of automation to the aquaponics cycle introduces additional forms of control by manipulating the inputs of the system to aid in controlling the process outputs. To understand the level of equipment that must be introduced into the process and the level of software development that would be required, a comprehensive design was undertaken to define the requirements of an aquaponics system that had full automation similar to a process controlled operation.
Process control is able to reduce inefficiencies with constant monitoring and reduce (Evans, 2016) process variability. Process Control automation is able to apply repeatable results as ranges or parameters of the process can be programmed or measured, which can be controlled for (Bozich, 2010) predictable results. Aquaponics have existing known parameters that optimize (Richard V. Tyson, 2011) results for fish and bacteria, yet plants that produce fruiting vegetables also have known optimum conditions that include lower pH for nutrient uptake and nutrient levels.
According to Scattini ) "The use of process control and the automation that it incorporates is able to measure and maintain multiple control loops, having multiple control loops that are not dependent on others would remove some of the identified limitations by dividing the process to meet those ranges that have been researched as optimum at particular stages of the process."

Aquaponics Subsystems
The wastewater treatment component of the process allows biological bacterium and there relevant processes to take place, which change waste ammonia to nitrites and nitrates. The fish effluent requires pH`s of 7.2 to 7.8 (FAO, n.d.) for the bacteria to transform the ammonia nitrates. Once changed to nitrates the nitrogen is in a form (Sawyer, 2013), which can be taken up by plants as a food source in turn cleaning the water for re-use by the fish.
The wastewater treatment also allows solids to be removed or reintroduced back into the system as dissolved solids (Hijran Yavuzcan Yildiz, 2017) that supply plants additional nutrients. The fish species to be grown have limitations on the amount of (Zealand, 2000)Total Dissolved Solids and other water quality requirements that must be met if the produce is to be resold. The dissolved solids are able to be removed to a storage tank in a concentrated form, which allows for decoupling of the pH`s between the fish effluent and the effluent concentrate to optimize both the main systems and the subsystems requirements. The nutrient concentrate is to be reintroduced into a hydroponic sub-system to reduce fertilizer requirements that would be required to produce the chosen crop. The hydroponic system ranges are controlled by instrumentation measurement and the delta in nutrients are met by adjustment to meet desired nutrient ranges depending on the crop of vegetables to be grown.
Supplying the optimum requirements into multiple subsystems and separating control loops between fish, bacteria, and plants is achieved with increased levels of process control automation. To determine the amount of effort to implement this level of control on an aquaponics process a preliminary design was required. This design determined the complexity of measurement and types of automation control that would be required to keep parameters ranges under control. Achieving these levels of control could assist commercial aquaponics operators to benefit by being able to produce an increased range of produce that does not rely on a single control loop or a single control loop that needs to compromise to sustain all requirements. Process control that increases the level of control over secondary loops could maximize the recycling of nutrients from waste, lower fertilizer costs and increase the viability of a technology that reduces water usage within its system.

Viability of Process Control Automation in Aquaponics
To gain an understanding of what is required to automate components of the process, the author has created an initial design (Noel Scattini, Aquaponics Automation -Design Techniques, 2017) to identify equipment required to add control functions to the process with additional levels of control with automation.
Automation to operate a process has many types of equipment from hardware that could include flow switches, instrumentation, various types of control valves, analysers and Variable Speed Drives. To operate the process within desired ranges software functions are provided from a distributed control system or SCADA to control the system within desired parameters.
The instrumentation hardware and SCADA software can be broken down into further sections either passive devices or active devices. Passive devices are those that provide a readout or indication (ANSI, 2009) which is represented as a local gauge or a software representation on the Human Machine Interface. Other passive devices could include monitoring functions that can be used to determine ranges that are outside of the optimized range.
Active devices are those that operate a function or an auxiliary device (ANSI, 2009); these auxiliary functions could be from hardware such as control valves, relays and solenoids. The output normally initiates a variable that modulates the device or process to a predetermined set point, which in this design would be a range that has been documented as optimum for the particular control loop.

Process Control Equipment used for Optimization
Flow switches are commonly used in process control to identify that flow is taking place within piping which in the process has heating, pumping costs could be a considerable higher percentage). In an aquaponics wastewater system, clarifiers are used to settle out the solids produced by fish waste. The clarifiers allow solids to be removed for either total removal or in this design to a mineralization tank (Lennard, 2012) for further biological treatment.
Having flow control over the solids from the clarifiers has the benefit of limiting the total amount of effluent being removed from the main process stream for further treatment as additional energy would be required to treat or pump the additional effluent.
Instrumentation is introduced as passive devices to measure the process constantly. The instrumentation used to aid in process control includes pH and nitrate analyzers to relay measurements, which are displayed on the Human Machine Interface. The monitoring also includes more complex analyzers that are able to carry out multiple measurements to monitor the minerals or nutrients that are available in the process. The number of instruments and types of alarms and alarm tags were listed onto an instrumentation and alarm list to identify the level of automation that would be required to control the process.

Process Configuration
To compare the design and number of devices that can be put into perspective with similar designs such as those that contain batch processing a design configuration was selected that contained multiple tanks. The aquaponics process consists of eight fish rearing tanks and a wastewater treatment processes that treats the effluent from the fish tanks. The design of the project would have to be scaled to suit a large commercial operation, yet this design has incorporated numbers of devices to operate it as a process with automation. The biological wastewater treatment component of the processes also included a degassing tower that can accommodate an additional fan to force air through the degassing tower. The fan however is not expected to be required in the processes day to day operations (designed with but not fitted), this type of fan is required in processes that have high stock densities. The fan however could be fitted in process operations that risk high density farming practices or processes that require additional cooling during summer as it has a (James M. Ebeling P. , 2006) cooling effect on the water.
The instrumentation list does not include the stand-alone instruments on the skid-mounted equipment for the adapted filters. The filters do however allow for start stop functions, along with fault functions to interface with the SCADA/DCS system.
The design was established with known existing ranges that have been documented from past research as being optimized for different components of the process, this includes ideal bacterial pH ranges, also ranges of nutrients that are required for the plants to produce fruiting vegetables. These are separated into subsystem control loops to reach optimized production rates to the established known ranges. To separate these alternate control loops, technologies from alternate industries have been adapted to obtain these established ranges.

Results of Integrating Process Control Functions
The data (Tables 2 and 3 below) represents an overview of different components of the process and what is required to automate sections of the process.
This data represents items that would be required to establish cost data, to do cost analysis of integrating the equipment into the process. The data could be used to establish data for integrating equipment into an existing process and a comparison of cost savings could be analysed against additional viable commercial crops or the risk mitigations that benefit the process operator. This data could also be used to establish design data for a new process, which would be expected to be easier to integrate as the system could be designed with the process features initially in the design.
The results are divided into two sections one that has an overview of the hardware components and two a section that has an overview of software components. The two sections list the relevant results, which elaborate on some of the uses of hardware and software, additionally the level of complexity required to automate the processes with process control functions is explained in detail.

Software Data Analysis
The results are tabulated from the instrumentation and alarm list that was incorporated onto a piping and instrumentation diagram that represents the process.
The results of software requirements equipment selection to be incorporated into the design was selected and the quantities quantified in Table 2 to represent the overall requirements of this process layout. The alarms and associated levels of priority are also listed in Table 2. The alarms also have event alarms which may note when a pump is started or stopped for later reference which could be used to determine operating or failure times of pumps to introduce maintenance measures in the future operations to increase the reliability of the process.  Other software components of the design included tags from analogue signals that operate displays on the Human Machine Interface to display ranges of measured devices. The alarms could be driven from analogue or digital devices from measurement being out of range from an analogue signal. Digital signals to operate alarms could be from an initiation of an emergency stop in the field or from a relatively basic instrument such as a float level switch.
The software besides including analogue and digital interfaces to operate displays can also include more complex software features. The hydroponics pump has requirements to operate for a period on then another period off, to flush unused nutrients from the root zone, and rehydrate the zone for a set period. This operation required a start tag on the Human Machine Interface that initiated timers to carry out this function; this is also commonly referred to as a software sequencer or PLC sequencer. Additional functions using inputs from flow switches and the start functions of pumps have been utilised to initiate flow alarms to individual tanks and alarm a main audible and visual alarm, these individual tank alarms are able to identify and localise the fault.

Hardware Data Analysis
The process also requires hardware devices either to control measured values for them to remain in optimum known ranges or to obtain those measured values. The results of the design have been accumulated into Table 3 for discussion. The devices in Table 3 represent totals of hardware devices to operate the process with a DCS/SCADA system. The devices included instruments that incorporate basic operations that communicate with digital signals and measurement analyser to supply values such as pH ranges. Complex instrumentation such as nutrient analysers could be described as small field laboratories that contain multiple outputs to send analogue outputs to the SCADA/DCS system to represent ranges of measured nutrient values.
The variable speed drives are utilised in the process to carry out speed control with indication displayed on the SCADA/DCS Human Machine Interface with speed control also displayed. The variable speed drives are able to control the motor speed that in turn controls the flow, in areas of the process to optimise the process or alternately only use energy required to carry out function to save on energy costs.

Discussion and Future Work
The completion of an automation design allows the requirements of a process to be understood before implementing a project. To gain a better understanding of the fertiliser's savings that would be made to an operator a test process that incorporates the Selective Electro Dialysis filter would be required to obtain quantifiable test results that could be scaled, of the nutrients that can be distributed to the plants in the hydroponics tanks before implementing a major project.
The results of further work would allow for cost savings in fertilisers in comparison to size of known processes to be calculated and the value of return understood on capital investments required to implement this technology. Although process systems could vary in size with items such as the number of fish rearing tanks, a complete instrumentation list has been developed and the list could be adjusted to meet the requirements of individual process systems. This type of overall installation of this industrial automation equipment is aimed at supplying large commercial operations that have large overheads such as high fertilizer or pumping costs, or alternately need to compete with diverse crop ranges.
An additional function that the instrumentation and control provides, besides the measurement of ranges required for optimum production rates, is the additional control allows for subsystem separation and optimization. The additional functions also allow for implementation of risk mitigations to prevent failures in the process and increase reliability.

CONCLUSION
Conducting a study on the individual requirements and designing an alternate control solution that meets the identified ranges could highlight that some of the compromises that are currently required to operate a Recirculating Aquaponics Systems could be overcome and make it possible to grow fruiting vegetables with established hydroponics recipes. The systems may not necessarily be restricted to compromising between the different biological requirements of fish, plants, or bacteria but could be separated into alternate control loops.
Further work studied a control solution that utilised an alternate design, which would allow the nutrients to be distributed to an alternate control loop that is independent to the main aquaponics system.
This research included newer methods to balance the Total Dissolved Solids entering the aquaponics system to balance those being removed. The thesis also investigated methods to collect concentrated nutrients to control the water quality in This design process could also be carried out before the commissioning stages of the process. The commissioning process can have a very different set of risks to the process that must be considered before introducing fluids or forms of energy to the process, which have their own set of associated risks.
The results from the automation design showed that there was a large number of software tags required to automate the process, with built in process control functions. The instruments selected to integrate process control functions into the process included relatively cheap instruments such as flow switches that can be purchased for small costs. There was also more complex instrumentation required to measure minerals or nutrients to monitor the ranges for correct dosing. These are more expensive yet some of these can monitor multiple nutrient levels and can carry out functions that are similar to a small laboratory, and display results in real time.
Although expensive, the constant monitoring of these nutrients supplies constant nutrient ranges that could be calibrated to specific plants requirements.
Benefits besides cost savings of fertilizers should also be considered as the