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Plumbing

PVC pipes are most commonly used for plumbing. They are available in many standard sizes, are cost-effective, easy to cut and adapt to a wide range of adapters and connectors, and also usually last a long time. Other materials could also be used, but they must be safe for both the fish and the plants, and for food production. Some general advice about pipes:

  • pipes have to be ‘just right’ – if the pipes are too small there will be a problem with leaks, and if they are too big the solids will not get flushed out because the water pressure will be too low

  • flexible pipes are to be avoided in order to reduce water flow risks and biofouling. Biofouling or biological fouling is the accumulation of microorganisms, plants, algae, or animals on wet surfaces (https://en.wikipedia.org/wiki/Biofouling).

  • the connections between the different components of the system should be as short and as straight as possible. This allows for smoother water movement. Every curve or loop represents an obstacle for smooth water flow.

Water flow and pumps

Once the aquaponic components are connected and filled with water, the water should maintain a constant and equal level in all components. However, since it must circulate, the water has to be moved by either gravity or pumping. Hydraulic systems design follows the example in Chapter 2. After drawing a process flow diagram, in the detailed design stage each pipe has to be dimensioned, the diameter chosen depending on volume flow and flow speed (calculated earlier), and defined by length, fittings and elbows/bends. Friction losses then need to be calculated. These friction losses have to be compensated for by water pressure difference between the different heights of the water level. Pumping should only be done at one point in the whole recirculation flow (with two decoupled pumps in parallel) to ensure stable flow conditions.

The pump is an extremely important component of the aquaponic system as it ensures reliable water circulation throughout the system. Water needs to be recirculated to supply microorganisms and plants with the necessary nutrients, and to provide fish with an environment free of harmful components. An inadequate or unreliable pump can lead to insufficient or excessive nutrient supply, which can harm the bacteria, fish and plants. Lack of recirculation, or recirculation that is too fast or too slow, will quickly affect all life in the aquaponic system.

There is a wide range of pumps on the market but they can be divided into two main categories: submersible pumps or inline (centrifugal) pumps. Submersible pumps are immersed in the tank water which helps to keep them cool. They are usually less efficient than inline pumps and are more suitable for smaller systems. Inline or centrifugal pumps are air-cooled pumps and are located outside the tank. They can have higher powered engines capable of pumping large quantities of water.

When sizing the pump for the aquaponic system, the flow rate has to be determined first –i.e. how much water the pump can move over a given time period. It is usually measured in litres per minute or litres per hour. The pump should be able to recirculate the entire volume of water in the system. This can vary from 3 times per hour in very intensive systems to only a few times per day in extensive systems. There is no rule of thumb. The only way to calculate the required water recirculation rate is to do a proper mass flow calculation (see Exercise 7). Generally, it is better to purchase a more powerful pump since it will allow for flow adjustments. However, such pumps are expensive.

In order to size your pump it is also important to calculate the head height by calculating all the head losses described in Exercise 7. This head loss has to be compensated for by water level difference, which will be equal to the height of the two water levels the pump has to lift the water in between. Normally the fish tank and growing bed will be at different levels. The greater the distance or the larger the head, the more energy is required to pump the water. Anything that can be done to minimize the head will make the entire system more efficient.

The final step in determining the right pump size is combining the flow rate and head height. Generally, most pumps come with a chart that combines flow rate and head height. If not, then usually the maximum flow rate (Qmax) and maximum pumping height (Hmax) are stated. If you have no pump diagram you have assume the pump has it’s optimal pumping efficiency around Hmax/2, which normally around Qmax/2. .

Design example: If you have to recirculate 10 m3/h for 2 m, then first decide if you want to use one or two pumps. If you want to use two pumps in parallel, each pump has to pump 5 m3/h for 2 m including friction losses in the pumping pipe. So you need two pumps, each with Hmax = 4 m and Qmax = 10 m3.

The cost of energy used to run the pump is an important part of the cost structure for running an aquaponic system. It is therefore important to know the electrical consumption of the pump you plan to purchase, which means knowing the number of watts the pump uses. The ideal pump will get the job done while using the smallest amount of energy possible. When purchasing a pump do not forget to also purchase a backup pump in case the first one breaks down, or operate the system with two pumps in parallel (highly recommended) and have one backup pump.

Water flow and water level regulation

The target flow velocity in pipes is around 0.7-1 m/s. If it is below 0.7 m/s there is a risk of sludge deposition, while above 1 m/s there is an unnecessary loss of energy by friction. The water flow rate in the system can be adjusted by installing:

  • a pump where the flow can be regulated

  • a regulation valve

  • an electric timer connected to the pump

  • a water level float regulator with or without a water level sensor

In aquaponic systems, especially in media growing bed systems, a bell siphon is widely used for water flow and level regulation. Bell siphons allow water from the grow bed to be automatically drained into the fish tank and the pump then takes water from the fish tank into the grow bed. In addition to the automatic regulation of water which greatly saves time and effort, bell siphons have several other benefits when used with aquaponic systems:

  • more aeration for the plants’ roots

  • constant and consistent movement of water

  • the process is automatic

  • ensures maximum efficiency

  • simple and reliable

There are other simple ways to regulate water level using bulkheads, standpipes or loop siphons (Castelo 2018).

Problems with water movement

If the water is not circulating or the flow rate is reduced, there can be several reasons; for example:

  • the pump is not working

  • the propellers of the pump are abrased/damaged by sand/growing media

  • there is not enough water in the system

  • air bubbles disrupted the water flow

  • the pipes are clogged

  • there are dead fish in the pipes

Water losses and water reserves

Some water will inevitably be lost from the system due to evapotranspiration. The main problems are water losses due to leaks (which are caused by clogging) or pump breakdowns. One must be aware that each and every hole, every seal, every pipe connection and every mechanical damage is a potential danger that can cause a leak. However, if the piping is designed correctly, and properly sealed/glued, then this should not be a problem. It is imperative to test the water flow when starting the system to ensure that there are no leaks.

Also consider what will happen if the pump stops working or if there is a power outage. Where will the water flow? Proper systems design includes a buffer volume at the lowest level of the system (usually the pump sump) to store all water overflowing from the points higher in the system. If properly designed, fish tanks will lose between 5-10 cm of water depth that can be stored by the spare volume of the pump sump and biofilter. This is the reason why the biofilter and pump sump usually look quite empty in a properly designed system. One has to install appropriate alarms and, even better, methods to automatically switch on backup pumps, connected to an electric generator. Lost water has to be topped up every day (1.5% during normal operation, failures not included). A sump tank of adequate volume is therefore needed, or a very reliable connection to another water source.

Copyright © Partners of the [email protected] Project. [email protected] is an Erasmus+ Strategic Partnership in Higher Education (2017-2020) led by the University of Greenwich, in collaboration with the Zurich University of Applied Sciences (Switzerland), the Technical University of Madrid (Spain), the University of Ljubljana and the Biotechnical Centre Naklo (Slovenia).

Please see the table of contents for more topics.


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