Application Of New Solutions To Food Production
Executive summary
As requested by WERC: A Consortium for Environmental Education and Technology Development, Louisiana State University (LSU) environmental engineers developed an aquaponic system as a solution to real environmental, energy, and water issues that occur on a national and global scale. The system was designed to decrease energy requirements, decrease water use, improve sustainability, and as well be economically feasible. The design was created to support the recommended fish intake of a small community of 1000 people.
Several sections of the United States, including the southwestern region, are experiencing water crisis because of population increase and limited resources. Commercial farming is a major component of the world’s water use as 70% of diverted rivers and pumped groundwater is used for irrigation [1]. Commercial farming also decreases available resources through topsoil depletion and groundwater contamination [2]. The increased demand of already restrained water reserves makes conventional farming an adverse choice for many areas of the United States.
Objectives of an aquaponics system are to raise produce and fish while reducing water and nutrient use through water recirculation. The fish in the system use the nutrients from feed to create biomass, urine and excrement, which the bacteria from the biofilter digest into a form the plants can utilize for their growth. The remainder of the fish products is filtered out of the system as waste using a clarifier, and the water is pumped back to the start of the system. Despite the efficiency of the typical aquaponics system, improvements still can be made to lower the inputs needed to run the system.
A Polygeyser® was installed into the aquaponic design to replace the biofilter and clarifier of the system. The advantage of using a Polygeyser® was that it has a low head loss and low water loss due to solids removal [3]. The biofiltration capability of the Polygeyser® was used to nitrify ammonia and allow the fish to survive in non-toxic water. The same device was used to remove solid particles 30 micrometers (μm) and larger, thereby reducing dissolved oxygen demand [4]. It was hypothesized that the possibility of pathogen growth was reduced through The Polygeyser® constant backwashing and removal of solids.
An airlift was chosen to replace a conventional pump in the aquaponic design because of its simplicity in design, dual functionality, reduced energy consumption, and reduced cost [3]. An airlift, which consists of an air compressor, a simple piece of PVC pipe, and flexible plastic tubing, was used to aerate the system and create lift to compensate for the head loss in the system. The aeration that was provided by the airlift eliminated the need for a separate degassing tank [4].
The proposed facility for the modified aquaponic system will start with a circular 30,000-gallon fish tank filled with Nilotica tilapia. The fish tank will have 36 feet (ft) diameter and water outlet at center of the bottom of the tank. This outlet will flow into a 125 cubic feet (ft3) Polygeyser®, which was selected to completely nitrify bacteria. The Polygeyser® outflow will reach the U-siphon airlift. The U-siphon airlift will create more submergence for the pipe and increase the lifting of the water. A ball valve will be installed to force all the water to flow back to the fish tank in the case of failure of the rest of the system. The positive results of the bench scale reinforce the feasibility of the full-scale design. The full scale design yields yearly energy savings of 20,000 kWh/yr ($1800/yr) when compared to an average yearly energy requirement of 98,000 kWh/yr of conventional systems.
Several sections of the United States, including the southwestern region, are experiencing water crisis because of population increase and limited resources. Commercial farming is a major component of the world’s water use as 70% of diverted rivers and pumped groundwater is used for irrigation [1]. Commercial farming also decreases available resources through topsoil depletion and groundwater contamination [2]. The increased demand of already restrained water reserves makes conventional farming an adverse choice for many areas of the United States.
Objectives of an aquaponics system are to raise produce and fish while reducing water and nutrient use through water recirculation. The fish in the system use the nutrients from feed to create biomass, urine and excrement, which the bacteria from the biofilter digest into a form the plants can utilize for their growth. The remainder of the fish products is filtered out of the system as waste using a clarifier, and the water is pumped back to the start of the system. Despite the efficiency of the typical aquaponics system, improvements still can be made to lower the inputs needed to run the system.
A Polygeyser® was installed into the aquaponic design to replace the biofilter and clarifier of the system. The advantage of using a Polygeyser® was that it has a low head loss and low water loss due to solids removal [3]. The biofiltration capability of the Polygeyser® was used to nitrify ammonia and allow the fish to survive in non-toxic water. The same device was used to remove solid particles 30 micrometers (μm) and larger, thereby reducing dissolved oxygen demand [4]. It was hypothesized that the possibility of pathogen growth was reduced through The Polygeyser® constant backwashing and removal of solids.
An airlift was chosen to replace a conventional pump in the aquaponic design because of its simplicity in design, dual functionality, reduced energy consumption, and reduced cost [3]. An airlift, which consists of an air compressor, a simple piece of PVC pipe, and flexible plastic tubing, was used to aerate the system and create lift to compensate for the head loss in the system. The aeration that was provided by the airlift eliminated the need for a separate degassing tank [4].
The proposed facility for the modified aquaponic system will start with a circular 30,000-gallon fish tank filled with Nilotica tilapia. The fish tank will have 36 feet (ft) diameter and water outlet at center of the bottom of the tank. This outlet will flow into a 125 cubic feet (ft3) Polygeyser®, which was selected to completely nitrify bacteria. The Polygeyser® outflow will reach the U-siphon airlift. The U-siphon airlift will create more submergence for the pipe and increase the lifting of the water. A ball valve will be installed to force all the water to flow back to the fish tank in the case of failure of the rest of the system. The positive results of the bench scale reinforce the feasibility of the full-scale design. The full scale design yields yearly energy savings of 20,000 kWh/yr ($1800/yr) when compared to an average yearly energy requirement of 98,000 kWh/yr of conventional systems.