Patent Application
20250049004
The present invention is related to aquaponic systems, more particularly to, the use of filtration by means of reverse osmosis in an uncoupled aquaponic system in order to increase the production efficiency.
The term aquaponics is derived from the combination of the words “aquaculture” or the production of aquatic organisms and “hydroponics,” which consists of soilless plant production. It is a sustainable mixed system for the production of both plants and fish. It is a relatively young discipline that integrates both techniques into one.
Traditional aquaponic systems were organized into a single process cycle, integrating coupled systems, which allows directing nutrient-rich water from fish to plants (
Considering the competencies and nutritional benefits provided by aquaculture effluents for plant growth, such as nitrogen and phosphorus, and considering that both subsystems have specific requirements that are not fully compatible, there is a need to explore new proposals, including the decoupling of both systems.
Decoupled systems (
Despite the potential benefits, initially, the design with decoupling of two loops presented drawbacks. This is due to the high amounts of additional nutrients needed to be added to the hydroponic cycle since the processing water flowing from the RAS (Recirculating Aquaculture System) to the hydroponic circuit (Hp-loop) depends on evapotranspiration, i.e., moisture loss from a surface by direct evaporation along with water loss by vegetation transpiration. Nutrients also tended to accumulate in RAS systems when evapotranspiration reached critical levels, requiring periodic water purging.
Given the mentioned drawbacks, new proposals were devised, such as that of Goddek et al. (2019), which proposes decoupling by a multiloop system (
The thermal distillation technology makes aquaponic systems even more complex when considering its implementation. This additional loop may not make sense for small producers, but it may have potential for larger commercial systems, considering always higher energy expenditure.
The technologies currently used for membrane desalination are reverse electrodialysis (EDR) and reverse osmosis (RO). The choice between the two membrane separation technologies EDR or RO will depend on which is the most suitable and cost-effective for a given application, i.e., chosen aquaculture and hydroponic species, the required energy consumption proportional to the amount of salts removed from the water source, the concentration of total dissolved solids (TDS), and the quality of the source water.
Reverse osmosis (RO) is a technology based on a semipermeable membrane that separates two solutions with different concentrations. By applying pressure higher than the osmotic pressure on the side of higher concentration, a water flow occurs from the solution with higher salinity to one with lower salinity. The term semipermeable refers to a membrane that selectively allows water to pass through it at a much higher rate than the transfer rate of any component contained in the water.
In summary, desalination by semipermeable membrane (
It is desirable to have membrane desalination of aquaculture recirculation effluent with the necessary design and technological supplies to achieve a decoupled aquaponic option that maintains the necessary water quality in both biotic subsystems to increase process performance.
The present invention focuses on membrane desalination by RO of aquaculture recirculation effluent. This would result in the filtered or permeate product being low in dissolved salts, thus beneficial for diluting and treating the RAS and a rejection stream as a concentration product of nitrates and phosphates rich nutrients from the RAS directed to the Hp-loop system. In this operation, the appropriate requirements in the salt balance and pH adjustment must be achieved, as well as the correct sanitary treatment to prevent biofouling by various organic contaminants on the membrane (RO).
The present invention relates to a decoupled aquaponic system comprising: a recirculating aquaculture subsystem (RAS loop) consisting of a fish tank unit; a hydroponic subsystem (Hp-loop) consisting of a plurality of Deep Water Culture (DWC) floating raft units; and a third loop that performs reverse osmosis membrane filtration treatment connecting both subsystems. In the present decoupled aquaponic system, the fish are freshwater and the plants (vegetables, fruits, inflorescence, bulbs, stems, ornamentals, and fodder) are susceptible to be cultivated hydroponically.
With the aim of overcoming the drawbacks of previous art, the present invention proposes treating aquaculture recirculation effluent with semipermeable reverse osmosis membranes in a decoupled aquaponic system, to achieve an increase in productivity with consequent energy savings.
In this way, the following are achieved jointly: a) greater reliability to estimate future fish and plant production, b) greater stability to maintain optimal control parameters for the entire process, c) increased productive yield of both subsystems: hydroponic and especially aquaculture, and d) considerable energy savings compared to other interconnection systems between RAS and the Hp-loop.
In a preferred embodiment, the equipment of the present invention consists of three recirculation loops or 3-loops, a first loop for the aquaculture recirculation system RAS (1), a second loop for the hydroponic recirculation system Hp-loop (2), and a third loop that performs the filtration treatment by reverse osmosis membrane (OI) (3) for the desalination process and that will interconnect the two previous loops: RAS (1) and Hp-loop (2) (
The necessary conditions to implement the invention as mentioned above are as follows:
The chosen species are: Oncorhynchus mykiss sp. (rainbow trout) and Lactuca sativa sp. (lettuce).
A single tank (4) is used for the aquaculture system with a volume of 1 m3 (
The value of the hydroponic surface area (HSA) is approximately 0.98 m2 per bed or raft (
The system receives tap water in a sanitary tank (5) where it undergoes pretreatment by being pumped through a sand filter and then through another activated carbon filter. This water is then incorporated into the mixing chamber (CMIX) (6) corresponding to the RAS subsystem (1) as required.
A sieve with stainless steel mesh (7) whose minimum particle retention size is 200 μm is incorporated prior to a static (primary) conical sedimentator (8), with a gravity flow system to ensure quality water for the RAS subsystem (1), and b) a physical treatment system using ultraviolet radiation (UV) (9) to inhibit the microbiological growth of pathogens and protect fish and plants from them, with a capacity of 30 mJ/cm2.
An aerobic MBBR (Moved Bed Bio-Reactor) type bioreactor (10) is used for nitrification treatment by bacteria of the genera Nitrosomonas sp. and Nitrobacter sp. that transform ammonia-ammonium into nitrites and finally into nitrates.
A secondary sedimentator (11) of the same characteristics as the primary sedimentator (8) is included in the circuit to ensure the quality of the water circulating in the system.
Pumps are also incorporated to meet the pumping requirements for each subsystem, including the aeration system.
Two mixing or chemical conditioning chambers (CMIX) are added.
A first chamber (12) receives the reject from the osmosis, i.e., the nutrient-rich stream coming from the RAS (1), and the following are added: a) a fertilizer based on potassium 18% K2O, magnesium 3.0% MgO, sulfur 2.0% S; b) micronutrients (13) such as dissolved salts of Fe, Mg, Cu, Zn, Mo, B according to the specific deficit of the Hp-Loop system, without the addition of nitrogen (NO3—) and phosphorus (PO43—) whose presence is assessed by their contribution from the RAS; and c) saline solutions (20) to regulate the pH of the system such as solutions of Ca(OH)2, KOH, KHCO3 or citric acid for the Hp-loop. This first chamber (12) also receives discharge from the water coming from the primary sedimentator.
A second mixing chamber (6) receives the osmosis permeate, and the pH (21) suitable for the RAS is adjusted therein.
As additional equipment to the aquaponic system, the following is used:
Sludge removal is carried out without return to the system, meaning that no anaerobic mineralization loop is included for nutrient recovery in said sludge. In this way, the effect of the RO membrane on the concentration of salts reaching the Hp-loop (2) and dilution in the RAS (1) is evaluated exclusively. Such sludge comes from fish excrement and uneaten food.
The climatological data recorded daily during the 270-day duration of the experience were taken into account.
Start of sowing: for hydroponic cultivation, sowing is carried out using seedlings with leaf diameters between 3 and 8 cm from the apical view with root development to transplant to the DWC (Deep Water Culture) system, and for aquaculture cultivation, the fish have a total longitudinal size of between 10 and 12 cm to be planted in the tank containing them.
Water supply and pretreatment: tap water is stored in a sanitary tank. It is pumped to a sand filter to then pass through another activated carbon filter and then be incorporated into the RAS (1) subsystem in the corresponding mixing chamber (CMIX) (6).
Sanitization: Both subsystems, RAS (1) and Hp-loop (2), will undergo physical disinfection through ultraviolet radiation (UV) [(9)-(19)].
Greenhouse condition: the Hp-loop system (2) is located in a polyester film greenhouse with direct light transmission estimated at approximately 80%, and it has a shading system and a heat extraction and induction system by forced ventilation for the maintenance of hygrometric conditions (temperature, humidity, and ventilation).
Photoperiod requirements: both for the RAS (1) subsystem and the Hp-loop (2) subsystem, natural light requirements are obtained. Alternatively, artificial light is implemented, which is stipulated at 20 hours of light for the Hp-loop (2) and 12 hours of light for the RAS (1).
Temperature and water control: the RAS (1) subsystem has a temperature, conductivity, and pH sensor and translator online linked to a Programmable Logic Controller (PLC) coupled to a cooling equipment for maintaining the optimal temperature required by the rainbow trout (Oncorhynchus mykiss sp.) which is T (C)=15±0.3. The Hp-loop (2) subsystem has temperature, conductivity, and pH sensors online. For the cultivation of Letuca sativa sp. (lettuce), the average temperature of the recirculating water is maintained at T (C)=19±4, being controlled by the condition of the greenhouse and eventual recirculations of water input from the RAS (1) to the Hp-loop (2).
Automation and control of water currents: decoupling, permeation or RO filtration to the RAS, and concentrate or reject to the Hp-loop, including feeding the Hp-loop by the RAS, are carried out with electro-pneumatic valve actuators, which are linked to the same PLC (Programmable Logic Controller) that allows automation to operate the desalination process, including nutrient dosing.
Effluent from the system: effluent purges due to solids capture (sludge) by different sedimentation and filtration treatments are of the order of 4% of the total volume of the RAS; this sludge leaves the global aquaponic system. Effluents can be treated anaerobically by mineralization.
The complete aquaponic system can be seen schematized in
Table 1 shows the system conditioning.
The characteristic of this membrane is that it has low biofouling technology (undesirable biological encrustations of microorganisms, plants, and/or algae on wet structures) with an active membrane surface area of 7.43 m2. It includes 2 RO membranes with an intermembrane separation of 0.864 mm.
For this purpose, the specified polishing filter is used prior to the UF (Ultrafiltration) system. The characteristics of this ultrafiltration membrane are expressed in Table 3.
The control of permeate water, directed towards the RAS, and reject water, directed towards the HP-loop, is performed, with the following values found for pH, water hardness, and ion concentration. The values found can be seen in Table 4.
In
Among the advantages provided by this membrane technology by RO, it should be mentioned that it maximizes water recovery in the permeate and the higher rejection of salts, thus increasing the amount of nutrients in the Hp-loop and the quality of the permeate water in the RAS. This arises from the values found in Table 4.
Another advantage is that, compared to other experiences of decoupled aquaponic systems, it shows lower energy consumption, as observed in Table 5.
In the totalization of the energy consumption of the decoupled aquaponic system with thermal distillation treatment, it can be seen (Table 5) that the scope in which it operates is significantly higher than that corresponding to the treatment including OI membrane. While in the former, the variation is in the range of 380.96-477.46 MWh/year, in the latter, which corresponds to the present invention, it is 227.59-304.6 MWh/year.
With the implementation of the 3-loop (OI), satisfactory production is found for both subsystems as the recovery of permeate water (Table 4) returning to the RAS subsystem is maximized, and the reverse osmosis process increases the nutrient quantity in the Hp-loop subsystem.
Membrane technologies such as OI and UF have achieved synergies and complementary compatibilities, adapting to the demanding requirements of quality and quantity of recirculated water in the RAS, and demonstrating adaptability with DWC technology. They achieve benefits in volume buffering against peaks and valleys, eliminating the risk for the crop due to deficit or excess.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20230102114 | Aug 2023 | AR | national |
