Nitrogen transformations in aquaponic systems: A review

In recent years, aquaponic systems have gained significant popularity as soilless agriculture systems for organic fruits and vegetables production with concomitant remediation of aquaculture effluent. Aquaponics is a potential sustainable food production system that integrates aquaculture with hydroponics in which nitrogen-rich effluent from the fish production is utilized for plant growth. Because nitrogen is one of the most important inputs in an aquaponic system, it is critical to investigate the nitrogen transformations in the system for enhanced recovery of resources. Since studies on nitrogen transformations and nitrogen utilization efficiency (NUE) in aquaponic systems have been very limited, this review critically examines the important fates of nitrogen from input to outputs (e.g., ammonia nitrogen generation, nitrification, nitrate assimilation and nitrogen loss) to improve NUE in aquaponic systems. Various factors affecting the nitrogen transformations are also discussed. Furthermore, an example of nitrogen imbalance between nitrate uptake and nitrate generation rates in an aquaponic system was demonstrated. This review aims to advance our current understanding of nitrogen transformations and outlines future research needs in aquaponic systems, a sustainable model for efficient water and nutrient managements, and food production.     

Alternative Solids Removal for Warm Water Recirculating Raft Aquaponic Systems

Aquaponics is an integrated fish and plant recirculating production system. The University of the Virgin Islands' raft aquaponic system uses a cylindro‐conical clarifier as a primary solids removal device; however, a swirl separator may offer advantages. The objectives of the 8‐wk experiment were to compare water quality parameters, Nile tilapia, Oreochromis niloticus, production and water spinach, Ipomoea aquatica, production in a raft aquaponic system using a clarifier or swirl separator for primary treatment of solids in the waste stream . No significant differences (P ≥ 0.05) existed between treatments for temperature, oxygen, pH, total suspended solids, alkalinity, electrical conductivity, total ammonia‐nitrogen, nitrite‐nitrogen, nitrate‐nitrogen, macronutrients, and micronutrients concentrations in the culture water. There were no significant differences (P ≥ 0.05) between treatments for Nile tilapia production, average weight, survival, or feed conversion ratio. There were no significant differences (P ≥ 0.05) between treatments for water spinach production or plant tissue analysis. In conclusion, the swirl separator used in this experiment performed similar to the clarifier and water spinach grew vigorously in the raft aquaponic system .     

A comparison of reciprocating flow versus constant flow in an integrated, gravel bed, aquaponic test system

Murray cod, ^{Maccullochella peelii peelii}, and Green oak lettuce, Lactuca sativa, were used to test for differences between two aquaponic flood regimes; reciprocal flow (hydroponic bed was periodically flooded) and constant flow (hydroponic bed was constantly flooded), in a freshwater aquaponic test system, where plant nutrients were supplied from fish wastes, while plants stripped nutrients from the wastewater before it was returned to the fish. The Murray cod had FCRs and biomass gains that were statistically identical in both systems. Lettuce yields were good and a significantly greater amount of both biomass and yield occurred in the constant flow treatment. Constant flow treatments exhibited greater pH buffering capacity, required fewer bicarbonate (buffer) additions to control pH and maintained lower conductivity levels than reciprocal flow controls. Water consumption in the two systems was statistically identical. Overall, results suggest that a constant flow flooding regime is as good as, or better than, a reciprocating flooding regime in the aquaponic test system used.     

循环水系统结合鱼菜、紫外处理对镜鲤生长及水质的影响

为探索绿色环保的循环水养殖模式,设计循环水鱼菜共生系统(鱼菜组)、紫外灯鱼菜共生系统(鱼菜紫外灯组)及循环水养殖系统(循环水组),比较三种不同处理方式对镜鲤(Cyprinuscarpio var.specularis)、叶用莴苣(Lactuca sativa var.ramosa)生长和养殖水质的影响。结果显示,鱼菜组、鱼菜紫外灯组处理对镜鲤的生长无显著影响,但会显著影响镜鲤形态学指标,鱼菜组镜鲤肠体比显著低于循环水组。体成分方面,鱼菜组全鱼粗蛋白、粗脂肪显著高于循环水组,鱼菜组肝脏粗蛋白显著低于循环水组。鱼菜紫外灯组的细菌总数显著低于鱼菜组。水质方面,鱼菜组、鱼菜紫外灯组可显著降低系统中氨氮、硝酸盐氮及总磷总氮含量,鱼菜紫外灯组硝酸盐氮、总磷及总氮含量显著高于鱼菜组。综上所述,循环水系统耦合水培蔬菜单元可改善系统水质,改善鱼体成分,并且结合紫外灯处理可降低水体细菌总数。     

A comparison of reciprocating flow versus constant flow in an integrated, gravel bed, aquaponic test system

Murray cod, Maccullochella peelii peelii, and Green oak lettuce, Lactuca sativa, were used to test for differences between two aquaponic flood regimes; reciprocal flow (hydroponic bed was periodically flooded) and constant flow (hydroponic bed was constantly flooded), in a freshwater aquaponic test system, where plant nutrients were supplied from fish wastes, while plants stripped nutrients from the wastewater before it was returned to the fish. The Murray cod had FCRs and biomass gains that were statistically identical in both systems. Lettuce yields were good and a significantly greater amount of both biomass and yield occurred in the constant flow treatment. Constant flow treatments exhibited greater pH buffering capacity, required fewer bicarbonate (buffer) additions to control pH and maintained lower conductivity levels than reciprocal flow controls. Water consumption in the two systems was statistically identical. Overall, results suggest that a constant flow flooding regime is as good as, or better than, a reciprocating flooding regime in the aquaponic test system used.     

Implementation of an experimental nutrient film technique-type aquaponic system

Aquaponics has been considered as having great potential as an organic production method of aquatic organisms and vegetables, because the nutrient-rich water from aquatic organisms is utilized for plant growth. The essential elements of an aquaponic system consist of the following five: a tank to maintain aquatic organisms; a clarifier or sedimentation; a biofilter; a hydroponic component; and a sump pump. In this paper, we propose the design and implementation of a nutrient film technique-type aquaponic system, which does not include the sump pump. Aquaponic systems were tested during one production cycle of the Carolina cucumber (Cucumis sativus) and Parris Island lettuce (Lactuca sativa). The aquatic organism employed was tilapia (Oreochromis niloticus). Nine systems were utilized with the aquaponic technique, and the remaining three were utilized with only the hydroponic technique as controls in plant production. The proposed aquaponic system worked efficiently during the entire crop cycle without any problems or deficiencies from lack sump. No changes were made in the flow of water in the aquaponic system during the growing season. Tilapia survival was 97.2 ± 2.4 %. Specific growth and food conversion ratios were 4.95 and 0.99, respectively. In plant survival, there were no significant differences (p > 0.05) between both production techniques. In lettuce, foliar wet weight, foliar dry weight, and yield were higher (p < 0.05) in hydroponics. In cucumber, fruit number and yield were higher (p < 0.05) in the hydroponic system. Fruit length, width, and weight exhibited no differences (p > 0.05).     

Comparison of nutrient costs from fish feeds and inorganic fertilizers for aquaponics systems

One potential advantage of aquaponic systems is reduced resource consumption compared to separate fish and plant rearing systems, but little has been published on the costs of providing nitrogen and phosphorus nutrients by fish in comparison to the purchase of inorganic fertilizers. The cost of providing nitrogen and phosphorus from six commercial fish feeds was compared to 9 commercial agricultural fertilizers. Waste production from fish was corrected for excretion of urea and the impact of feed wastage. For a typical aquaponic system without mineralization of fecal solids, the soluble nitrogen and phosphorus excretion ranged from 36.9 to 44.0 g/kg feed and 1.4–3.7 g/kg feed, respectively. The cost to provide 1 kg of nutrients from feeds ranged from $15-$29/kg for nitrogen and from $115 - $583/kg for phosphorus. Compared to the purchase of these elements from inorganic fertilizers, the feeds were 7–14 times more expensive for nitrogen and 17–88 times more expensive for phosphorus. The feed/fertilizer cost ratio (FFCR^feed) required to replace the nitrogen and phosphorus in 1 kg of feed ranged from 2 to 4 times for monoammonium phosphate to 14–17 times for anhydrous ammonia and triple superphosphate. Based on the specific conditions and assumptions in this work, the economic value of nutrients provided by fish in aquaponic systems has been greatly over-stated.     

Optimizing Koi Carp,Cyprinus carpio var. Koi (Linnaeus, 1758), Stocking Density and Nutrient Recycling With Spinach in an Aquaponic System

Fish waste water nutrient recycling in an aquaponic system was studied under different stocking densities of Koi Carp, Cyprinus carpio var. koi, along with spinach, Beta vulgaris var. bengalensis. Fish growth performance, plant growth, nutrient dynamics, and nutrient removal and their dependence on different stocking densities, namely 1.4, 2.1, and 2.8, were observed, of the different combinations, fish stocked at 1.4 kg/m³ had the best growth. Percent nutrient removal (NO₃–N, PO₄–P, and K) was significantly higher at 1.4 kg/m³. Thus, 1.4 kg/m³ stocking density can be suggested as optimum for Koi Carp production in spinach aquaponic systems.     

Characterisation of aquaponic producers and small-scale facilities in Spain and Latin America

Aquaponics is a sustainable food production system combining hydroponics and aquaculture. Although the domestic/small-scale aquaponic production has proliferated worldwide, there is scarce knowledge about how it is performed. The objective of this study was to determine the profile and motivations of aquaponic producers, the characteristics of the facilities and the performance of the production. The average aquaponic producer is a middle-aged man, with a certain level of studies and a moderate household income. The main motivations reported were the production of high-quality, healthy food, the concern for the environment and the autonomy gained. These motivations conditioned the purposes of the aquaponic facilities (mainly education, production of food for self-consumption and as a hobby), which, excepting small sales, did not have an economic motive. Due to their characteristics, aquaponic facilities are particularly adapted for urban agriculture (many of them were located on rooftops) and most of those studied were constructed recently. The nutrient film technique was the most used hydroponic subsystem, followed by media beds, where mostly a polyculture of leaf and fruit vegetables and aromatics are produced. Tilapia was the most common fish species used. In general, there is a lack of proper knowledge and expertise about these complex systems in order to efficiently operate them.

     

A Comparison of Three Different Hydroponic Sub-systems (gravel bed, floating and nutrient film technique) in an Aquaponic Test System

Murray Cod, Maccullochella peelii peelii (Mitchell), and Green Oak lettuce, Lactuca sativa, were used to test for differences between three hydroponic subsystems, Gravel Bed, Floating Raft and Nutrient Film Technique (NFT), in a freshwater Aquaponic test system, where plant nutrients were supplied from fish wastes while plants stripped nutrients from the waste water before it was returned to the fish. The Murray Cod had FCR's and biomass gains that were statistically identical in all systems. Lettuce yields were good, and in terms of biomass gain and yield, followed the relationship Gravel bed > Floating > NFT, with significant differences seen between all treatments. The NFT treatment was significantly less efficient than the other two treatments in terms of nitrate removal (20% less efficient), whilst no significant difference was seen between any test treatments in terms of phosphate removal. In terms of dissolved oxygen, water replacement and conductivity, no significant differences were observed between any test treatments. Overall, results suggest that NFT hydroponic sub-systems are less efficient at both removing nutrients from fish culture water and producing plant biomass or yield than Gravel bed or Floating hydroponic sub-systems in an Aquaponic context. Aquaponic system designers need to take these differences into account when designing hydroponic components within aquaponic systems.     

Towards commercial aquaponics: a review of systems,designs, scales and nomenclature

Aquaponics is rapidly developing as the need for sustainable food production increases and freshwater and phosphorous reserves shrink. Starting from small-scale operations, aquaponics is at the brink of commercialization, attracting investment. Arising from integrated freshwater aquaculture, a variety of methods and system designs has developed that focus either on fish or plant production. Public interest in aquaponics has increased dramatically in recent years, in line with the trend towards more integrated value chains, greater productivity and less harmful environmental impact compared to other production systems. New business models are opening up, with new customers and markets, and with this expansion comes the potential for confusion, misunderstanding and deception. New stakeholders require guidelines and detail concerning the different system designs and their potentials. We provide a definitive definition of aquaponics, where the majority (>?50%) of nutrients sustaining the optimal plant growth derives from waste originating from feeding aquatic organisms, classify the available integrated aquaculture and aquaponics (open, domestic, demonstration, commercial) systems and designs, distinguish four different scales of production (≤?50, >?50–≤?100 m², >?100–≤?500 m², >?500 m²) and present a definite nomenclature for aquaponics and aquaponic farming allowing distinctions between the technologies that are in use. This enables authorities, customers, producers and all other stakeholders to distinguish between the various systems, to better understand their potentials and constraints and to set priorities for business and regulations in order to transition RAS or already integrated aquaculture into commercial aquaponic systems.     

Comparison of Four Artificial Light Technologies for Indoor Aquaponic Production of Swiss Chard,Beta vulgaris,and Kale,Brassica oleracea

To date, most aquaponic research has been conducted outdoors in tropical climates or in greenhouses in subtropical climates. For more northerly latitudes, aquaponic production will require supplemental light in greenhouses or insulated buildings. Two separate 3‐wk growth trials were conducted to evaluate the effects of four different lighting technologies on the growth of Swiss chard, Beta vulgaris (Trial 1) and kale, Brassica oleracea (Trial 2) in aquaponic systems. Light technologies evaluated included fluorescent (FLO), metal halide (MH), induction (IND), and light‐emitting diode (LED). Four 1175‐L systems were used with all four light types represented in each system in a complete block design. Juvenile Nile tilapia, Oreochromis niloticus (241 g) were stocked in each system and fed a floating 32% protein diet at a rate of 60 g/m² of plant grow space per day. In Trial 1, Swiss chard plants grown under LED lights for 3 wk achieved significantly higher (P ≤ 0.05) average individual weights (117.7 g), higher production per unit of area (3535 g/m²), and higher production per unit of energy (32.3 g/m²/kwh) than Swiss chard grown under the other three light types, which did not differ significantly (P > 0.05) from each other. In Trial 2, kale grown under LED lights achieved significantly higher (P ≤ 0.05) average individual weights (102.9 g), higher production per unit of area (2136.6 g/m), and higher production per unit of energy (381.5 g/m²/kwh) than kale grown under the other three light types, which did not differ significantly (P > 0.05). The results of the two trials are in agreement and indicate that LED lights were superior to MH, FLO, and IND lights in terms of absolute plant growth as well as growth per unit of energy consumed.     

Waste treatment in recirculating aquaculture systems

Recirculating aquaculture systems (RAS) are operated as outdoor or indoor systems. Due to the intensive mode of fish production in many of these systems, waste treatment within the recirculating loop as well as in the effluents of these systems is of primary concern. In outdoor RAS, such treatment is often achieved within the recirculating loop. In these systems, extractive organisms, such as phototrophic organisms and detritivores, are cultured in relatively large treatment compartments whereby a considerable part of the waste produced by the primary organisms is converted in biomass. In indoor systems, capture of solid waste and conversion of ammonia to nitrate by nitrification are usually the main treatment steps within the recirculating loop. Waste reduction (as opposed to capture and conversion) is accomplished in some freshwater and marine indoor RAS by incorporation of denitrification and sludge digestion. In many RAS, whether operated as indoor or outdoor systems, effluent is treated before final discharge. Such effluent treatment may comprise devices for sludge thickening, sludge digestion as well as those for inorganic phosphate and nitrogen removal. Whereas waste disposed from freshwater RAS may be treated in regional waste treatment facilities or may be used for agricultural purposes in the form of fertilizer or compost, treatment options for waste disposed from marine RAS are more limited. In the present review, estimations of waste production as well as methods for waste reduction in the recirculating loop and effluents of freshwater and marine RAS are presented. Emphasis is placed on those processes leading to waste reduction rather than those used for waste capture and conversion.     

Biological filtration properties of selected herbs in an aquaponic system

This study was conducted to determine the biological filtration capabilities of some culinary herbs co‐cultured with lemon fin barb hybrid in a nutrient film technique (NFT) recirculating aquaponic system. Lemon fin barb hybrid (Hypsibarbus wetmorei ♂ × Barbonymus gonionotus ♀) fingerlings were stocked in twelve 2‐tonne fibreglass tanks at 25 fish per tank and co‐cultured with Chinese celery (Apium graveolens var. secalinum Alef.), coriander (Coriandrum sativum) and peppermint (Mentha × piperita) for seven weeks. The impacts of the waste generated by the fish on the water quality, the filtration capability of the herbs and the ability of fish and herbs to retain nutrients (NPK) were also estimated. All the herbs showed water purifying potentials to varying degrees as significantly lower levels of nitrogenous compounds (NH₃‐N, NO₃‐N, NO₂‐N) were observed after the herbal filtration. The plant growth seemed to be affected by their ability to absorb nutrients and consequently purify the culture medium. Interestingly, the lemon fin barb hybrid also showed significant differences in terms of weight gain, but the nutrient retention among fish treatments was not statistically different. The plants absorbed less phosphorus and potassium than the fish. After computing for the total system percentage of NPK recovered, nitrogen was the most retained nutrient. The peppermint showed superiority in terms of gross biomass and water purifying potential compared to the Chinese celery and coriander.     

基于个体生态模型在渔业生态中应用研究进展

近年来, 基于个体的生态模型(individual-based model, IBM)被广泛应用到海洋生态环境中, 被认为可能是研究鱼类生态过程的唯一合理手段。基于个体生态模型以众多的生物个体为模拟对象, 考虑个体之间的差异、环境条件的时空变化对个体发育的影响,这一研究为基于生态系统的渔业管理, 以及资源补充量预测分析提供了科学的研究方法和手段。本文主要介绍了IBM的基本概念, 以及在渔业上的研究方法和技术, 总结了IBM在鱼类输运、生长死亡和捕食相关的应用研究现状以及IBM在渔业上未来发展趋势, 并对IBM在渔业上应用的问题和不足进行了分析和讨论。本论文的总结与分析将为国内开展我国近海鱼类早期生活史的研究, 以及基于生态系统的渔业资源评估管理提供参考。     

Profitability of multi‐loop aquaponics: Year‐long production data,economic scenarios and a comprehensive model case

This case study examined the productivity and economic performance of a double recirculation aquaponic system in Germany with a total interior area of about 540 m². Calculations were carried out as an ex post analysis based on one‐year production data. The initial situation was not profitable; therefore, two scenarios were developed, which envisaged a significantly improved productivity of the fish as well as of the plant unit and a more than threefold enlargement of the greenhouse to make maximum use of the fish effluent. An ex ante analysis was performed and showed that the second scenario was profitable with a payback period of about 12 years. On the basis of this scenario, a simple but comprehensive model case with the complete set of economic key indicators showed that aquaponics is feasible if it exploits its potential, regardless of the high initial investment costs. The model case would cover an overall space of about 2,000 m², which is suitable for professional aquaponics in urban and peri‐urban areas with their limited space availability. Furthermore, multi‐loop aquaponics with its inherent circles fits into the circular city concept and implements resource‐efficient and sustainable food production into the urban fabric, which is important with increasing urbanization.     

Pathological indicators in sows relevant to animal welfare in modern housing systems

Methods and problems are discussed evaluating pathological indicators potentially related to animal welfare in modern husbandry systems of brood sows. A variety of interrelationships of diseases and genetic dispositions concerning the locomotive and cardiovascular system interferes with the required forensic evidence between individual sickness and housing and/or neglected care. There are no defined pathological processes indicating disproportionate husbandry as well as insufficient ability of physical exercise. Highly restricted possibilities to move caused by modern housing may result in pathologically manifest alterations. Technopathic diseases (induced by housing systems) may be prevented by enhanced care concerning the health control of animals and the functioning of the technical equipment as well as by appropriate prophylaxis. Farmers and veterinary surgeons should co-operate for the needs of animal welfare. One of the resulting conclusions is to plan for and to provide more labour for specific care necessary to maintain animal welfare. One should consider such management calculations with major precaution in which the size of working units relative to manpower gets increasingly maximized.     

Efficient and economical way of operating a recirculation aquaculture system in an aquaponics farm

ABSTRACT

In this article, optimal control methods based on a metabolite-constrained fish growth model are applied to the operation of fish production in an aquaponic system. The system is formulated for the twin objective of fish growth and plant fertilization to maximize the benefits by optimal and efficient use of resources from aquaculture. The state equations, basically mass balances, required by the optimization algorithms are given in the form of differential equations for the number of fish in the stock, their average weight as mediated through metabolism and appetite, the water recirculation and waste treatment, hydroponic nutrient requirements and their loss functions. Six parameters, that is, water temperature, flow rate, stock density, feed ration size per fish, energy consumption rate and the quality of food (percentage of digestible proteins) are used to control the system under dynamic conditions. The time to harvest is treated as a static decision variable that is repeatedly adjusted to find the profit-maximizing solution. By modeling the complex interactions between the economic and biological systems, it is possible to obtain the most efficient decisions with respect to diet composition, feeding rates, harvesting time and nutrient releases. Some sample numerical results using data from a tilapia-tomato farm are presented and discussed.