A study on the optimal hydraulic loading rate and plant ratios in recirculation aquaponic system

Enhancement of nitrogen transformation in media-based aquaponics systems using biochar and zerovalent iron

Aquaponics combines aquaculture and hydroponics, offering methods to produce fish and plants. However, optimization of its nitrogen transformation processes, which would lead to higher nitrogen utilization efficiency (NUE) and lower nitrous oxide (N2O) emission, is still a daunting challenge. This study investigated these issues by using biochar and zerovalent iron (ZVI) with low (LD) and high (HD) doses. Results showed that LD improved NUE by 15%, reaching 57%, along with a significant 36% reduction in N2O emissions. Conversely, denitrifying bacteria were disturbed in HD due to incomplete denitrification, resulting in higher N2O emissions. Microbial analysis showed that the abundance of denitrifying bacteria increased from 12% to 24% in LD, compared with the control, leading to lower N2O emissions and optimized nitrogen cycling. These findings suggested that using the appropriate proportion of biochar and ZVI would be a promising approach to enhance the sustainability and productivity of aquaponics systems.

Nutrient-efficient catfish-based aquaponics for producing lamb's lettuce at two light intensities

BACKGROUND

Aquaponic systems are sustainable processes of managing water and nutrients for food production. An innovate nutrient-efficient catfish-based (Clarias gariepinus) aquaponics system was implemented for producing two cultivars of two leafy vegetables largely consumed worldwide: lamb's lettuce (Valerianella locusta var. Favor and Valerianella locusta var. de Hollande) and arugula (Eruca vesicaria var. sativa and Eruca sativa). Different growing treatments (4 × 2 factorial design) were applied to plants of each cultivar, grown at two light intensities (120 and 400 μmol m-2 s-1). During growth, several morphological characteristics (root length, plant height, leaf number, foliage diameter and biggest leaf length) were measured. At harvest, plants were weighed and examined qualitatively in terms of greenness and health status. Additionally, leaf extracts were obtained and used to determine total phenolic contents, antioxidant capacities, and levels of cytotoxicity to Caco-2 intestinal model cells.

RESULTS

After a 5-week growth period, both lamb's lettuce cultivars presented high levels of greenness and health status, at both light intensities, particularly the var. de Hollande that also showed higher average performance in terms of plant morphology. In turn, arugula cultivars showed lower levels of greenness and health status, especially the cultivar E. vesicaria var. sativa submitted to direct sunlight during growth. In addition, plant specimens submitted to higher levels of light intensity showed higher contents in antioxidants/polyphenols. Cultivars with a higher content in antioxidants/polyphenols led to higher Caco-2 cell viability.

CONCLUSION

For successful industrial implementation of the aquaponics technology, different and optimized acclimatizing conditions must be applied to different plant species and cultivars. © 2024 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Starvation and re-feeding of Gilthead seabream (Sparus aurata) and European seabass (Dicentrarchus labrax) co-cultured with glasswort (Salicornia europaea) in a polyculture aquaponic system

The aim of this study was to evaluate the effect of starvation and refeeding on the growth and food intake of gilthead seabream (Sparus aurata) and seabass (Dicentrarchus labrax) and on the growth and nitrogen uptake of glasswort (Salicornia europaea) in a polyculture aquaponic system under 12 ppt salinity for 75 days. Nine small-scale autonomous aquaponic systems were used, each containing 10 gilthead seabreams (average weight of 6.33 ± 0.73 g and average length of 5.73 ± 0.72 cm) and 10 seabasses (5.82 ± 0.77 g and 6.35 ± 0.45 cm), as well as five glasswort plants. Three fish feeding treatments were performed, a control (A), in which fish were fed daily until satiation, and two fasting treatments for 4 (B) and 7 days (C). Fish growth performance was significantly lower (p < 0.05) in the C treatment for both species compared to treatments A and B. Food consumption (FC) and feed conversion ratio (FCR) were significantly higher (p < 0.05) in treatment C. Glasswort growth performance was significantly higher in treatment C (p < 0.05). The results showed that the 4-day food-deprived fish were similar to the control fish by achieving partial compensatory growth. The more extended fasting period (7 days) resulted in significantly lower growth performance. The lipid and nitrogen retention levels in both species were significantly lower in food-deprived fish than in the control fish both before and during compensatory growth. The results suggest that a feeding schedule involving starvation-refeeding cycles is a promising feed management option for these species in polyculture aquaponic systems. The effect of food deprivation was also significantly beneficial (p < 0.05) for the growth performance of glasswort compared to the control treatment.

Optimizing nutrient utilization, hydraulic loading rate, and feed conversion ratios through freshwater IMTA-aquaponic and hydroponic systems as an environmentally sustainable aquaculture concept

Water quality in land-based fish production can be controlled through either instantaneous water exchange or costly wastewater treatment followed by recirculation. Agricultural-aquaculture integration is an excellent alternative technique for reducing nutrient discharge levels, boosting profitability, and converting fish culture wastewater into valuable products. The current study employed a solar energy system to power two separate IMTA-aquaponics systems (Nutrient Film Technique, NFT, and Floating Raft Systems, FRS) for the cultivation of Nile tilapia, African catfish, thin-lipped grey mullet, freshwater crayfish, freshwater mussels, and a variety of vegetables. Tilapia and catfish were fed exclusively on diets under the IMTA system. All wastewater from tilapia and catfish ponds, both dissolved and solid, flows sequentially to ponds containing other cultivated species. The water then flows through the IMTA system's terminal point to the NFT and FRS systems before returning to the tilapia and catfish ponds, allowing complete control of the nutrient flow throughout this entire circular system. Two 147-day production cycles were concluded. The results from the second production cycle are reported. Total biomass gain for aquatic species in the IMTA system was 736.46 kg, compared to 145.49 kg in the tilapia and 271.01 kg in the catfish monoculture systems. The current IMTA system had a cumulative feed conversion ratio (FCR) of 0.90, while the FCRs for tilapia and catfish were 1.28 and 1.42, respectively. Nile tilapia and catfish consumed 571.90 kg of feed containing 25.70 kg of nitrogen (N) and 9.70 kg of phosphorus (P), reflecting, and gaining 11.41 and 3.93 kg of dietary N and P, representing 44.40 and 40.46% dietary N and P retention, respectively. In the IMTA system, the addition of mullet and prawn as detrivores aquatic animals improves dietary N and P utilization efficiency to 59.06 and 51.19%, respectively, while the addition of mussels as herbivore animals improves dietary N and P utilization efficiency to 65.61 and 54.67%, respectively. Finally, using FRS and NFT as hydroponic systems increased dietary N and P efficiency to 83.51% N and 96.82% P, respectively. This study shows that the IMTA-Aquaponic system, as a bio-integrated food production system, can convert the majority of fish-fed residues into valuable products suitable for desert, rural, and urban areas in impoverished and developing countries.

Sustainable agriculture

Developing sustainable agricultural practices is currently becoming an increasingly relevant challenge. As the worldwide population rises and climate change affects agriculture globally, new and sustainable approaches must be adopted to ensure food security. In this editorial, we invite contributions to a BMC Plant Biology collection on 'Sustainable agriculture,' covering research on the environmental and socioeconomic factors that affect sustainable agricultural practices and their management.

Study on the plant and fish production in the aquaponic system as affected by different hydraulic loading rates

Aquaponics is the combined culture of fish and plants in recirculating aquaculture systems, considered to be an innovative, eco-friendly and sustainable technology. The effect of the hydraulic loading rate (HLR) on the performance of fish and plants in the aquapoinc system was the main aim of this study. Four hydraulic loading rates were applied, 1.2, 1.8, 2.4 and 3.0 m day-1 under stocking density tilapia fish of 5 kg m-3 and lettuce population of 25 plant m-2 for a period of January to March, 2023. Water parameters, plant and fish parameters were determined. The most important results revealed that the highest plant nutrients removal was at HLR of 2.4 m day-1. The highest value of water parameters were found at the HLR of 2.4 m day-1. Root length increased with increasing HLR. Fresh and dry shoot and root weight values were higher at 2.4 m day-1 compared to other treatments under study. Meanwhile, fish growth parameter showed higher values at the HLR of 3.0 m day-1 compared to other treatments. The highest values of weight gain, feed growth rate, specific growth rate and feed conversion ratio were 81.72 g, 1.36 g day-1, 1.88% day-1 and 1.20 g feed g-1 fish, respectively, for all treatments under study.

Aquaponics production system: A review of historical perspective, opportunities, and challenges of its adoption

The aquaponics production system integrates hydroponics and recirculatory aquaculture system for the simultaneous production of plants and fish. At a time, such as the postpandemic era, the aquaponics system represents an efficient green farming and eco-friendly alternative to sustainable agricultural production. In this review, the history and development of the production systems were traced vis-a-vis its pros and cons. Although there has been much dispute about the origin of the system, the numerous records of developmental attempts in history have all led to the current complexity of the systems and their efficiency. Water conservation, improved performance, food security, less pollution, and low energy consumption are some of the advantages identified in the use of aquaponics systems for food production. Challenges to the domestication of the system, however, include moderately high start-up capital, the need for stable electricity to operate the system, nutrient availability, as well as treatment of diseases in the system. Although the aquaponics production system could be a panacea for food security in Africa, modalities for the domestication of this technology are largely not in place, hence the need for some government interventions in this regard.

Valorization of wastewater: A paradigm shift towards circular bioeconomy and sustainability

Limitation in the availability of natural resources like water is the main drive for focussing on resource recovery from wastewater. Rapid urbanization with increased consumption of natural resources has severely affected its management and security. The application of biotechnological processes offers a feasible approach to concentrating and transforming wastewater for resource recovery and a step towards a circular economy. Wastewater generally contains high organic materials, nutrients, metals and chemicals, which have economic value. Hence, its management can be a valuable resource through the implementation of a paradigm transformation for value-added product recovery. This review focuses on the circular economy of "close loop" process by wastewater reuse and energy recovery identifying the emerging technologies for recovering resources across the wastewater treatment phase. Conventional wastewater treatment technologies have been discussed along with the advanced treatment technologies such as algal treatment, anammox technology, microbial fuel cells (MFC). Apart from recovering energy in the form of biogas and biohydrogen, second and third-generation biofuels as well as biohythane and electricity generation have been deliberated. Other options for resource recovery are single-cell protein (SCP), biopolymers as well as recovery of metals and nutrients. The paper also highlights the applications of treated wastewater in agriculture, aquaponics, fisheries and algal cultivation. The concept of Partitions-release-recover (PRR) has been discussed for a better understanding of the filtration treatment coupled with anaerobic digestion. The review provides a critical evaluation on the importance of adopting a circular economy and their role in achieving sustainable development goals (SDGs). Thus, it is imperative that such initiatives towards resource recovery from wastewater through integration of concepts can aid in providing wastewater treatment system with resource efficiency.

Recent Advances of Smart Systems and Internet of Things (IoT) for Aquaponics Automation: A Comprehensive Overview

Aquaponics is an innovative, smart, and sustainable agricultural technology that integrates aquaculture (farming of fish) with hydroponics in growing vegetable crops symbiotically. The correct implementation of aquaponics helps in providing healthy organic foods with low consumption of water and chemical fertilizers. Numerous research attempts have been directed toward real implementations of this technology feasibly and reliably at large commercial scales and adopting it as a new precision technology. For better management of such technology, there is an urgent need to use the Internet of things (IoT) and smart sensing systems for monitoring and controlling all operations involved in the aquaponic systems. Thence, the objective of this article is to comprehensively highlight research endeavors devoted to the utilization of automated, fully operated aquaponic systems, by discussing all related aquaponic parameters aligned with smart automation scenarios and IoT supported by some examples and research results. Furthermore, an attempt to find potential gaps in the literature and future contributions related to automated aquaponics was highlighted. In the scope of the reviewed research works in this article, it is expected that the aquaponics system supported with smart control units will become more profitable, intelligent, accurate, and effective.

An Overview of Soil and Soilless Cultivation Techniques—Chances, Challenges and the Neglected Question of Sustainability

Resources such as fertile soil and clean water are already limited in many parts of the world. Additionally, the conventional use of arable land is becoming increasingly difficult, which is further exacerbated by climate change. Soilless cultivation systems do not only offer the opportunity to save water and cultivate without soil but also the chance to open up urban areas such as residential rooftops for food production in close proximity to consumers. In this review, applications of soilless farming systems are identified and compared to conventional agriculture. Furthermore, aspects of economic viability, sustainability and current developments are investigated. An insight into the most important soilless farming systems—hydroponics, aquaponics and vertical farming—is provided. The systems are then differentiated from each other and, as far as possible, evaluated in terms of their environmental impact and compared with conventional cultivation methods. Comparing published data analyzing the yield of hydroponic cultivation systems in comparison to soil-based cultivation methods enables a basic overview of the profitability of both methods and, thus, lays the foundation for future research and practical applications. The most important inert substrates for hydroponic applications are presented, and their degree of sustainability is compared in order to emphasize environmental impacts and affect substrate selections of future projects. Based on an assessment of the most important soilless cultivation systems, the challenges and developments of current techniques are highlighted and discussed.

Perspectivas de una producción sostenible en acuicultura multitrófica integrada (IMTA): Una revisión

La acuicultura tradicional se enfrenta a serios problemas medioambientales, particularmente por el uso de grandes volúmenes de agua, con las consecuentes descargas de efluentes ricos en nutrientes inorgánicos y partículas orgánicas. Un ejemplo claro de esto está en que del 20 al 30% del nitrógeno presente en la proteína del alimento suministrado es aprovechado por los peces, el restante 70-80% es desechado en el cuerpo de agua producto de la excreción y el alimento no consumido, lo que favorece la eutrofización de aguas receptoras y su entorno. Por lo anterior, se requiere el desarrollo de tecnologías y prácticas de producción innovadoras, responsables, sostenibles y rentables. Una de las alternativas que está generando interés, debido a sus implicaciones ambientales, económicas y sociales, es la producción en sistemas de acuicultura multitrófica integrada (IMTA). Este concepto se basa en la integración de diferentes niveles tróficos en un mismo sistema, lo que resulta en una conversión de los residuos de cultivo de unas especies en alimentos o fertilización para otras especies. Aplicada, la producción IMTA puede mejorar la sostenibilidad de la acuicultura al reducir el impacto de los efluentes y generar mayor rentabilidad económica, debido a la producción simultanea de dos o más productos finales y al uso mínimo de fertilizantes. El objetivo de la presente revisión es presentar los fundamentos básicos de los sistemas de IMTA, como una alternativa a los sistemas de producción en piscicultura.

Improving the feasibility of aquaculture feed by using microalgae

The aquaculture industry is an efficient edible protein producer and grows faster than any other food sector. Therefore, it requires enormous amounts of fish feed. Fish feed directly affects the quality of produced fish, potential health benefits, and cost. Fish meal (FM), fis oil (FO), and plant-based supplements, predominantly used in fish feed, face challenges of low availability, low nutritional value, and high cost. The cost associated with aquaculture feed represents 40-75% of aquaculture production cost and one of the key market drivers for the thriving aquaculture industry. Microalgae are a primary producer in aquatic food chains. Microalgae are expanding continuously in renewable energy, pharmaceutical pigment, wastewater treatment, food, and feed industries. Major components of microalgal biomass are proteins with essential amino acids, lipids with polyunsaturated fatty acids (PUFA), carbohydrates, pigments, and other bioactive compounds. Thus, microalgae can be used as an essential, viable, and alternative feed ingredient in aquaculture feed. In recent times, live algae culture, whole algae, and lipid-extracted algae (LEA) have been tested in fish feed for growth, physiological activity, and nutritional value. The present review discusses the potential application of microalgae in aquaculture feed, its mode of application, nutritional value, and possible replacement of conventional feed ingredients, and disadvantages of plant-based feed. The review also focuses on integrated processes such as algae cultivation in aquaculture wastewater, aquaponics systems, challenges, and future prospects of using microalgae in the aquafeed industry.

Comparison of two commercial recirculated aquacultural systems and their microbial potential in plant disease suppression

BACKGROUND

Aquaponics are food production systems advocated for food security and health. Their sustainability from a nutritional and plant health perspective is, however, a significant challenge. Recirculated aquaculture systems (RAS) form a major part of aquaponic systems, but knowledge about their microbial potential to benefit plant growth and plant health is limited. The current study tested if the diversity and function of microbial communities in two commercial RAS were specific to the fish species used (Tilapia or Clarias) and sampling site (fish tanks and wastewaters), and whether they confer benefits to plants and have in vitro antagonistic potential towards plant pathogens.

RESULTS

Microbial diversity and composition was found to be dependent on fish species and sample site. The Tilapia RAS hosted higher bacterial diversity than the Clarias RAS; but the later hosted higher fungal diversity. Both Tilapia and Clarias RAS hosted bacterial and fungal communities that promoted plant growth, inhibited plant pathogens and encouraged biodegradation. The production of extracellular enzymes, related to nutrient availability and pathogen control, by bacterial strains isolated from the Tilapia and Clarias systems, makes them a promising tool in aquaponics and in their system design.

CONCLUSIONS

This study explored the microbial diversity and potential of the commercial RAS with either Tilapia or Clarias as a tool to benefit the aquaponic system with respect to plant growth promotion and control of plant diseases.

Freshwater-adapted sea bass Dicentrarchus labrax feeding frequency impact in a lettuce Lactuca sativa aquaponics system

The aim of this study is to investigate the effect of three daily fish feeding frequencies, two, four and eight times per day (FF2, FF4, and FF8, respectively) on growth performance of sea bass (Dicentrarchus labrax)and lettuce plants (Lactuca sativa) reared in aquaponics. 171 juvenile sea bass with an average body weight of 6.80 ± 0.095 g were used, together with 24 lettuce plants with an average initial height of 11.78 ± 0.074 cm over a 45-day trial period. FF2 fish group showed a significantly lower final weight, weight gain and specific growth rate than the FF4 and FF8 groups. Voluntary feed intake was similar for all the three feeding frequencies treatmens (p > 0.05). No plant mortality was observed during the 45-day study period. All three aquaponic systems resulted in a similar leaf fresh weight and fresh and dry aerial biomass. The results of the present study showed that the FF4 or FF8 feeding frequency contributes to the more efficient utilization of nutrients for better growth of sea bass adapted to fresh water while successfully supporting plant growth to a marketable biomass.

Improving Plant Health Through Nutrient Remineralization in Aquaponic Systems

The exploitation of readily bioavailable fish excreta as a source of plant nutrients lies at the cornerstone of aquaponics farming. Research on nutrient cycling in aquaponic systems has devoted considerable attention to the plant uptake of dissolved nutrients in fish excreta, however, the integration of particulate-bound nutrients into downstream hydroponic farming has remained elusive. The high amount of organic carbon present in fish sludge may lead to biofouling if directly incorporated into hydroponic circulation systems, reducing the utility of incorporating fish solids on a large scale. In this study, we implemented a novel treatment system capable of reducing the carbon and nitrogen load of fish solids to produce a liquid fertilizer for a downstream hydroponics unit. Lettuce (Lactuca sativa) fertilized with exclusively a commercial nutrient solution, the biofilter effluent (coupled aquaponic system), effluent from the solids treatment system, or the latter two combined were grown in nutrient flow technique gutters downstream of a recirculating aquaculture system stocked with rainbow trout (Oncorhynchus mykiss). While crop yields were lower for the aquaponic treatments compared to lettuce grown in a commercial nutrient solution, plant sap analysis demonstrated a contrasting picture with respect to internal nutrient concentrations. Lettuce grown in the commercial hydroponic solution were deficient in several mineral nutrients (Mg, Ca, Na, and Si) nor did they have higher iron concentrations despite the significantly higher EDTA-chelated aqueous iron (460 × greater than other treatments) in the nutrient solution. Nutrient uptake in the rhizosphere was not investigated on a molecular level, although stunted rhizosphere growth in the commercial nutrient solution control suggests a weakened capacity for nutrient uptake in comparison to other treatments. Alongside the remineralization of micronutrients, the solids treatment system addressed the common issue of excess carbon leading to biofouling via a total suspended solids reduction of 87.27% ± 9.95 during the coupled aquaponics cultivation period. Ultimately, these data lead to two important conclusions. Firstly, optimizing nutrient bioavailability is not synonymous to increasing the presence of a nutrient in the water column. Secondly, estimating ideal nutrient solution concentrations involves both preventing nutrient blocking and improving bioavailability.

Can Reclaimed Water Be Used for Sustainable Food Production in Aquaponics?

Aquaculture is a technology used for the production of animal protein but produces a great amount of waste that decreases productivity and adversely affects the environment. Sedimentation and filtration have been used for the treatment of the suspended fraction of these wastes although dissolved substances like nutrients can be an asset. Therefore, the management of aquaculture waste remains a challenge. Aquaponics is a technology that can eliminate dissolved N and P from aquaculture systems as they serve as nutrients for plants, which are absorbed through the roots and are incorporated into their tissues. Several reports and studies exist on the benefits of aquaponic systems for the combined production of plants and aquatic organisms and its advantages in terms of economics and environmental protection. The great majority of the studies use the wastewater from the aquatic production tanks as a source of nutrients for plants production. However, domestic or municipal wastewater is a resource that has been used extensively in other production systems such as conventional agriculture and aquaculture, yet its potential as a source of water for aquaponics has not been established. The current analysis hypothesizes that reclaimed water can be used for aquaponics. Despite the extensive use of reclaimed water in agriculture and aquaculture and the low risk to human health when properly managed, there are no academic studies that have tackled this issue. In order to overcome the generalized mistrust of the public in consuming crops irrigated with reclaimed water or fish growing in reclaimed water, it is recommended that only ornamental fish and plants would be cultivated by this method. There is an urgent need for studies to verify the safety and advantages of such cultivation technique. Finally, it is necessary to establish guidelines for the responsible use of reclaimed water in aquaponics.

LED Lighting and High-Density Planting Enhance the Cost-Efficiency of Halimione Portulacoides Extraction Units for Integrated Aquaculture

Halophytes are salt-tolerant plants that can be used to extract dissolved inorganic nutrients from saline aquaculture effluents under a production framework commonly known as Integrated Multi-Trophic Aquaculture (IMTA). Halimione portulacoides (L.) Aellen (common name: sea purslane) is an edible saltmarsh halophyte traditionally consumed by humans living near coastal wetlands and is considered a promising extractive species for IMTA. To better understand its potential for IMTA applications, the present study investigates how artificial lighting and plant density affect its productivity and capacity to extract nitrogen and phosphorous in hydroponic conditions that mimic aquaculture effluents. Plant growth was unaffected by the type of artificial lighting employed—white fluorescent lights vs. blue-white LEDs—but LED systems were more energy-efficient, with a 17% reduction in light energy costs. Considering planting density, high-density units of 220 plants m−2 produced more biomass per unit of area (54.0–56.6 g m−2 day−1) than did low-density units (110 plants m−2; 34.4–37.1 g m−2 day−1) and extracted more dissolved inorganic nitrogen and phosphorus. Overall, H. portulacoides can be easily cultivated hydroponically using nutrient-rich saline effluents, where LEDs can be employed as an alternative to fluorescent lighting and high-density planting can promote higher yields and extraction efficiencies.

Evaluation of the Water Quality and Farming Growth Benefits of an Intelligence Aquaponics System

In 2019, the degree of food self-support in Taiwan was 32.08%, which was lower than that in the previous year by 2.4%. Taiwan does not have the ability to control the availability of food in the face of a food crisis. This study used an aquaponics system to implement the mutualism of fish, flowers, vegetables, and water, as well as to implement the cyclic utilization of water, so that vegetables and fruit could be produced to relieve food shortages in the world. The simulation site of this study was located on a gentle grassy slope alongside Li-tze Lake in Changhua County, Taiwan. In the simulation, three light-tight experimental buckets, with an upper rim diameter of 130 cm, a bottom rim diameter of 125 cm, and a height of 180 cm, were embedded in the ground. The target vegetables and flowers were planted in pots at 17 cm apart, and they were planted on the water surface using the floating island principle. A solar power system enabled a motorized pump to irrigate the plants. An aerator provided adequate aeration to achieve an elementary purifying effect. The experimental results showed that, in terms of the dissolved oxygen, the mean difference of the experimental group was about 1 mg/L, that of the control group was 2 mg/L, and the maximum difference was 6.5 mg/L. As the fish died in April, the ammonia nitrogen value of the control group was 68 times higher than that of the experimental group. Due to the nitrification in July, the ammonia nitrogen decomposed into NO2, which suddenly increased to 13 mg/L and was extremely unsuitable for the existence of aquatic organisms. This amount was five to six times higher than that of the experimental group. In terms of the fish growth rate, the control group could not bear the drastic changes in the water body at the intermediate stage, and all the fish died, whereas the fish in the experimental group were not affected. The results of this study could provide useful data for gardening, aquatic products, and space design staff.

The complex microbiome in aquaponics: significance of the bacterial ecosystem

Purpose

Aquaponics is a technology that has minimal impact on the environment and which is often promoted as a solution for sustainable food production. Developing aquaponics sustainably requires a thorough understanding of the biological components of the system. Recent reports on the bacterial populations of aquaponics systems using new DNA sequencing technologies are revealing a complex and diverse microbial ecosystem. The purpose of this review is to present information on microbial composition and various factors affecting bacterial activity in aquaponics systems. Approaches for establishing a bacterial ecosystem during the setup of an aquaponics system, and microbiological safety of aquaponics products are also highlighted.

Methods

This review was developed by evaluating and synthesising current literature of peer-reviewed publications related to aquaponics and microbial communities. Based on the results from credible academic journals, publications were categorised into five groups: methods used to characterise microbiomes, biofiltration microorganisms, bacterial diversity, biofilter establishment, and safety of aquaponics products.

Results

The microbial ecosystem is essential for biological filtration of water through the mineralisation of nutrients required for plant growth in an integrated system. The aquaponics microbiome is complex, and bacterial composition varies between the different compartments of these systems. Establishing these bacterial ecosystems is essential for optimal functioning of aquaponics. At the phylum level, Proteobacteria and Bacteroidetes are dominant in aquaponics systems. Despite bacteria being fundamental to aquaponics, there are currently no reports of human pathogens in aquaponics products.

Conclusion

Knowledge of the composition of bacterial populations in aquaponics systems will enhance understanding of relationships and functions within the microbiome. This in turn will allow for the establishment of sustainable and healthy aquaponics systems for food production.

Electrifying biotrickling filters for the treatment of aquaponics wastewater

This work aimed to study the electrification of biotrickling filters by means of Microbial electrochemical technologies (MET) to develop an easy-to-assemble and easy-to-use MET for nitrogen removal without external aeration nor addition of chemicals. Four different designs were tested. The highest ammonium and nitrate removal rates (94 gN·m^-3·d^-1 and 43 gN·m^-3·d^-1, respectively) were reached by combining an aerobic zone with an electrified anoxic zone. The standards of effluent quality suitable for hydroponics were met at low energy cost (8.3 × 10^-2 kWh·gN^-1). Electrified biotrickling filters are a promising alternative for aquaponics and a potential treatment for organic carbon-deficient ammonium-contaminated waters.

Aquaponics (s.l.) Production of Spearmint (Mentha spicata) with African Catfish (Clarias gariepinus) in Northern Germany

Aquaponics production of spearmint (Mentha spicata) was evaluated under commercial grow-out conditions of African catfish (Clarias gariepinus) in Northern Germany (Mecklenburg-Western Pomerania). Fish batch production under different stocking densities in an extensive aquacultural unit (EAU) and an intensive aquacultural unit (IAU) was connected to conventional plant cultivation on ebb-and-flood planting tables and compared to a liquid fertilizer control. The best growth parameters of M. spicata were found under the intensive stocking density of C. gariepinus (IAU), resulting in a plant leaf area of 10.9 ± 2.5 cm2, leaf length of 8.6 ± 1.6 cm, and a cut fresh biomass from aboveground of 31.8 ± 13.8 g/plant, compared to the EAU (5.6 ± 2.1 cm2; 5.4 ± 1.4 cm; 17.4 ± 4.7 g/plant) and the control (5.7 ± 2.2 cm2; 5.5 ± 1.4 cm; 11.2 ± 5.3 g/plant). The fresh biomass of the whole plants was not significantly different between the EAU (165.5 ± 71.7 g/plant) and the IAU (190.7 ± 105.6 g/plant), though the latter gained more weight. The initial fish number ratio between the EAU and the IAU of 1/4 increased the M. spicata leaf area by twofold in the IAU. Our results demonstrate that aquaponics (s.l.) production of M. spicata is possible under the direct use of effluent waters from intensive African catfish cultivation without the addition of any liquid fertilizer.

Basil (Ocimum basilicum) Cultivation in Decoupled Aquaponics with Three Hydro-Components (Grow Pipes, Raft, Gravel) and African Catfish (Clarias gariepinus) Production in Northern Germany

Basil (Ocimum basilicum) was cultivated in northern Germany in three different hydroponic components: grow pipes, a raft, and an ebb-and-flood gravel substrate. The nutrients originated from the intensive production of African catfish (Clarias gariepinus) with 140 fish/m3 under decoupled aquaponic conditions. After 41 days, plants were significantly taller in the gravel components (101.8 ± 8.3 cm), followed by the grow pipes (96.7 ± 7.0 cm), and the raft (94.8 ± 8.6 cm) components (gravel > grow pipes = raft). The leaf number was high and not significantly different between the grow pipes (518.0 ± 81.4), gravel (515.1 ± 133.0), and raft components (493.7 ± 124.8; grow pipes = raft = gravel). Basil in the grow-pipe subsystems developed rapid root growth and clogged the pipes with heterogeneous plant growth. Basil production in northern Germany in grow-pipe, raft, and gravel hydro-components is possible by using effluents from intensive C. gariepinus aquaculture without additional fertilizer in the plant grow-out phase. Further research should focus on optimizing grow pipes by maintaining an optimal root–water contact area, as well as on new technologies such as aquaponics (s.l.) gardening.

Composition and quality traits of vegetables grown in a low-tech aquaponic system at different fish stocking densities

BACKGROUND

Aquaponics is considered a sustainable system for the production of fish and vegetables. However, little is known about the effects of different system variables on vegetable quality. Hence, the aims of this study were to evaluate the influence of aquaponics on the composition and quality traits of three vegetable species in relation to stocking density of the common carp (Cyprinus carpio L.), in comparison with those of plants grown in hydroponics.

RESULTS

The highest cumulative vegetable marketable yield was obtained in low-density aquaponics (APL), followed by hydroponics (HP) and high-density aquaponics (APH). Vegetable quality traits showed species-specific responses. In general, phosphorus concentration was higher in plants grown in APH and lower in those grown in HP, while the opposite was observed for nitrate concentration. In lettuce (Lactuca sativa L.), sugar content was the highest in APH, whereas for Swiss chard (Beta vulgaris L. subsp. vulgaris Cicla group), the aquaponics treatments increased only glucose content. No differences in sugar content were observed in Catalogna (Cichorium intybus L. Catalogna group). The lowest and highest phenolic acid concentrations in the aboveground biomass of Catalogna and lettuce were observed in HP and APH treatments, respectively. For Swiss chard, APH treatment resulted in the highest caffeic acid content, whereas ferulic acid was the highest in HP.

CONCLUSIONS

Aquaponics at low stocking density increased plant yield, compared to HP, without compromising vegetable quality, whereas aquaponics at high stocking density improved vegetable quality, but at the expense of yield. © 2020 Society of Chemical Industry.

Effects of Hydraulic Loading Rate on Spatial and Temporal Water Quality Characteristics and Crop Growth and Yield in Aquaponic Systems

Aquaponics is a rapidly growing food-production system integrating aquaculture and hydroponic crop production through an energy-intensive water recirculation process. Crop performance and yield in aquaponics are affected by essential and toxic nutrient levels in the root zone, which can be regulated by water flow rate. This study was conducted to examine the effects of hydraulic loading rate (HLR) on water quality and crop growth and yield in recirculating aquaponic systems set at three different loading rates: high (3.3 m3/m2/day; HFR, which is 12 times lower than recommended loading rate), medium (2.2 m3/m2/day; MFR), and low (1.1 m3/m2/day; LFR). Crop species varying in growth rate were examined for their optimal HLR: fast-growing Chinese cabbage (Brassica rapa) and lettuce (Lactuca sativa); medium-growing mustard (Brassica juncea) and chia (Salvia hispanica); and slow-growing basil (Ocimum basilicum) and Swiss chard (Beta vulgaris). Compared to LFR, HFR decreased water and leaf temperatures and total ammonium nitrogen (TAN) but increased dissolved oxygen and pH in aquaponic solution up to one and two weeks after transplant, respectively. HFR increased NO3–N concentration by 50 and 80%, respectively, compared to MFR and LFR, while reducing the exposure duration of roots to ammonia (NH3–N) and its peak concentration through rapid dissipation of the toxic compound. Lower electrical conductivity (EC) in HFR during the last two weeks of production was associated with higher plant nutrient uptake and greater biomass production. The leaf greenness, photosynthetic rate (Pn), and total plant N were significantly higher at HFR than LFR. Fish growth rate, fresh weight, and feed-conversion efficiency were also increased by HFR. The growth of fast-growing crops including total fresh weight, shoot fresh weight, leaf area, and Pn was not different between HFR and MFR, while HLR had less significant effects on the growth and performance (i.e., shoot fresh weight and whole plant photosynthesis) of slow-growing crops. In conclusion, the flow rate is an important component in aquaponic crop production as it affects spatial and temporal water characteristics and subsequently determines the growth and yield of the crops. HLR at 3.3 m3/m2/day was sufficient across the crops allowing better chemical and physical properties of the aquaponic solution for maximum yield and quality. HLR should be maintained at least at 2.2 m3/m2/day for the production of fast-growing crops but can be lowered for slow-growing crops.

Designing Aquaponic Production Systems towards Integration into Greenhouse Farming

Aquaponics is a sustainable method of food production, whereby aquaculture and hydroponics are combined in one circular system. A few aquaponics startup companies are emerging in Europe with a limited production area of a few hundred or a few thousand square meters, whereas hydroponics is a common practice in a commercially viable manner most often with production units of several hectares. In Iceland, greenhouse farmers operate on relatively small production units, often between 2000 and 5000 m2. The aim of the present study was, therefore, to develop and design aquaponic production systems towards integration into small greenhouse farming strengthening economic viability and sustainability. Since the local market in Iceland is small and import is relatively expensive due to the distance from other markets, the suitability of commercially available fish feed and the selection of plant species were assessed in relation to production efficiency and available market and resources. The effects of water flow on plant growth and on nutrient utilization in culture water were measured and evaluated. Four aquaponics test systems were designed, built and operated, and results were used to develop a pilot commercial aquaponics system implemented for greenhouse farming in Iceland. One of the test systems was a media filled flood and drain system and the other three were deep water culture systems. Tilapia (Oreochromis niloticus), one of the most popular fish in aquaculture, was reared in all systems, while different leafy greens and fruiting vegetables were grown in the hydroponics. The fish was fed with commercial aquaculture feed made for cod and charr. The feed conversion ratio (FCR) was used to assess the effectiveness of feed on fish growth. The FCR observed in this research was between 0.9 and 1.2, within the typical values for tilapia growth in aquaculture. The production of the leafy green plants (e.g., pak-choi) was approximately four times, by weight, that of the production of fish, a similar yield as shown in other researches in the field. The continuous rise of nitrate and phosphate concentrations in the aquaponic system indicated the potential to support even higher crop yield. Long daylength in the summer in Iceland is clearly beneficial for crop production in aquaponics. Based on the results, it is concluded that aquaponics can be a feasible opportunity for greenhouse farming at least to diversify the current business model. Not only can the fish provide an extra income but also the effluent from the aquaculture is easily used as fertilizer for the plants, thus the circular production system offers new innovative ideas for diversifying and value-adding the business further, for example into crayfish production and/or into educational and experience tourism.

An Experimental Brackish Aquaponic System Using Juvenile Gilthead Sea Bream (Sparus aurata) and Rock Samphire (Crithmum maritimum)

Brackish aquaponics using Mediterranean fish and plants provides an alternative opportunity for a combined production of high-quality food products with high commercial and nutritional value. This is the first study that investigates the effect of two different salinities (8 and 20 ppt) on growth and survival of Sparus aurata and Crithmum maritimum along with the cellular stress pathways using the activation of heat shock proteins (HSPs) and mitogen-activated protein kinase (MAPK) protein family members and the water bacterial abundance. In total, 156 fish were used (average initial weight of 2.55 g, length of 5.57 cm) and 36 plants (average initial height of 8.23 cm) in floating racks above the 135 L fish tanks. Survival rate for both organisms was 100%. C. crithmum grew better at 8 ppt (t-test, p < 0.05). The growth rate of S. aurata was similar for both treatments (p > 0.05). HSPs and MAPK were differentially expressed, showing tissue-specific responses. The average bacterial abundance at the end of the experiment was higher (p < 0.05) in the 20 ppt (18.6 ± 0.91 cells × 105/mL) compared to the 8 ppt (6.8 ± 1.9 cells × 105/mL). The results suggest that the combined culture of euryhaline fish and halophytes provides good quality products in brackish aquaponics systems.

Growth and Nutrient Removal Efficiency of Sweet Wormwood (Artemisia annua) in a Recirculating Aquaculture System for Nile Tilapia (Oreochromis niloticus)

The maintenance of optimal water quality for fish production is one of the major challenges in aquaculture. Aquaponic systems can improve the quality of water for fish by removing the undesirable wastes and in turn produce a second marketable crop. However, there is no information on the growth and nutrient removal capability of Artemisia annua in aquaponic systems. This study evaluated the effect of plant density on water quality, the growth of A. annua and Oreochromis niloticus in a small scale aquaponic system in Kenya. The aquaponic system consisted of three treatments representing different plant densities (D1: 48 plants/m2, D2: 24 plants/m2 and D3:0 plants/m2). The high plant density system contributed significantly (p < 0.05) to the removal of all nutrients. The removal efficiency of ammonia was significantly higher in D1 (64.1 ± 14.7%) than in D2 (44.5 ± 6.8%) and D3 (38.0 ± 12.1%). Nitrates and nitrites were inconsistent, whereas phosphorus increased gradually in all treatments. The productivity of plants was higher in D1 than D2. Fish growth rates were significantly higher in D1 (0.35 ± 0.03 g/d) and D2 (0.32 ± 0.02 g/d) than in D3 (0.22 ± 0.04 g/d). The results show that A. annua can be cultivated in aquaponic systems due to its nitrogen removal capabilities.

Performance of Water Treatment Techniques on Cocopeat Media Filled Grow Bed Aquaponics System

Aquaponics system is an innovative idea which combined both aquaculture and hydroponics systems. In this study performance of four different types of water treatment technique was investigated in cocopeat media filled grow bed aquaponics system. The techniques that had been investigated were mechanical filter, biological filter, combination of both mechanical and biological filters and grow media (cocopeat) itself as filtration media. The effectiveness these techniques were assessed through (i) water quality and nutrients level of circulated water and (ii) growth rates of plant (Gynura procumbens) and Red Nile Tilapia fish (Oreochromis niloticus) The (i) water quality (pH, temperature, total suspended solid and dissolved oxygen) (ii) nutrient level (ammonia, nitrite, nitrate) and (iii) grow rates of plant and fish were weekly measured for this study. The results revealed that cocopeat media filled grow bed only was insufficient to act as water treatment unit in the aquaponics system studied. The aquaponics system required at least a biological or mechanical filter to produce acceptable yields of fish and plant. For the long term, the combination of axial flow and biofilter with superlative ratio was suggested in order to produce the best performance of parameters studied. This integrated technique was able to maintain the water quality within the tolerance limit of fish besides supplying enough amount nutrients (especially nitrate) for the plant growth and easier maintenance work in terms of cleaning and disposal of sludge.

Effects of hydraulic retention time on the performance of algal-bacterial-based aquaponics (AA): focusing on nitrogen and oxygen distribution

The effects of hydraulic retention time (HRT) on the performance of algal-bacterial-based aquaponics (AA) were investigated in this study. Both the highest fish growth and algal biomass increase were observed in the AA system at 2-day HRT, resulting in the highest nitrogen utilization efficiency (NUE) (39.28%) in this microcosm. On the contrary, ammonia oxidation bacteria (AOB) abundance at 4-day HRT was approximately ten times higher than that at 2-day HRT, since longer HRT would benefit bacterial growth. The ¹⁵N labeling study showed that microalgae assimilation was the main pathway of NH₄⁺ removal in the AA system, and oxygen produced by microalgae could in situ support complete nitrification, thus leading to much lower NH₄⁺ concentrations at 2-day HRT. Accordingly, better water quality was achieved at 2-day HRT. Considering all the factors, HRT of 2-day was considered to be optimal for the AA system.

Decoupled systems on trial: Eliminating bottlenecks to improve aquaponic processes

In classical aquaponics (coupled aquaponic systems, 1-loop systems) the production of fish in recirculating aquaculture systems (RAS) and plants in hydroponics are combined in a single loop, entailing systemic compromises on the optimal production parameters (e.g. pH). Recently presented decoupled aquaponics (2-loop systems) have been awarded for eliminating major bottlenecks. In a pilot study, production in an innovative decoupled aquaponic system was compared with a coupled system and, as a control, a conventional RAS, assessing growth parameters of fish (FCR, SGR) and plants over an experimental period of 5 months. Soluble nutrients (NO₃^--N, NO₂^--N, NH₄⁺-N, PO₄^3-, K⁺, Ca²⁺, Mg²⁺, SO₄^2-, Cl^2- and Fe²⁺), elemental composition of plants, fish and sludge (N, P, K, Ca, Mg, Na, C), abiotic factors (temperature, pH, oxygen, and conductivity), fertilizer and water consumption were determined. Fruit yield was 36% higher in decoupled aquaponics and pH and fertilizer management was more effective, whereas fish production was comparable in both systems. The results of this pilot study clearly illustrate the main advantages of decoupled, two-loop aquaponics and demonstrate how bottlenecks commonly encountered in coupled aquaponics can be managed to promote application in aquaculture.

Biological nutrient recovery from culturing of pearl gourami (Trichogaster leerii ) by cherry tomato (Solanum lycopersicum) in aquaponic system

The possibility of using different densities of cherry tomato as a bio-filter in a simple media-based aquaponic system to recycle nutrients from pearl gourami intensive culture wastewater was evaluated. Water quality parameters including total ammonia nitrogen (TAN), nitrite (NO₂^-), nitrate (NO₃^-), phosphate (PO₄^3-), pH, and dissolved oxygen (DO) were determined in outlet of the aquaponic system during a 60-day experimental period. Cherry tomato was planted at four densities of 0 (control), 3 (T1), 6 (T2), and 9 (T3) plants per aquaponic unit with a constant fish stock density. Each treatment was equipped with aquaponic systems containing fish tank and plant growing bed. Productivity of the system was measured by recording the fish and plant growth indices. The potential in removing nitrogen of the water was the highest in T3 (with nine plants) compared to other treatments (p < 0.05). The highest concentrations of TAN (6.59 ± 0.241 mg/L), nitrite (0.42 ± 0.005 mg/L), nitrate (0.45 ± 0.162 mg/L), and phosphate (30.47 ± 0.371 mg/L) were obtained in control group, while the lowest concentrations of TAN (0.05 ± 0.091 mg/L), NO₂^- (0.11 ± 0.008 mg/L), NO₃^- (29.77 ± 0.205 mg/L), and phosphate (18.59 ± 0.185 mg/L) were detected in T3 (p < 0.05). The maximum fish weight gain was recorded in T3 (26 ± 0.014%) with 1.26 ± 0.059 FCR, and the lowest fish weight gain was measured in the control group (15 ± 0.024%) with 2.19 ± 0.446 FCR (p < 0.05). Total plant length gain was reached at the maximum value in T3 (74.70 ± 1.153 cm) in comparison to other groups (p < 0.05). It was concluded that small-scale aquaponic growing bed system can be created a sustainable ecosystem which both the plant and fish can thrive and suitable for home-made production system.

Effects of pH on nitrogen transformations in media-based aquaponics

To investigate the effects of pH on performance and nitrogen transformations in aquaponics, media-based aquaponics operated at pH 6.0, 7.5 and 9.0 were systematically examined and compared in this study. Results showed that nitrogen utilization efficiency (NUE) reached its maximum of 50.9% at pH 6.0, followed by 47.3% at pH 7.5 and 44.7% at pH 9.0. Concentrations of nitrogen compounds (i.e., TAN, NO2(-)-N and NO3(-)-N) in three pH systems were all under tolerable levels. pH had significant effect on N2O emission and N2O conversion ratio decreased from 2.0% to 0.6% when pH increased from 6.0 to 9.0, mainly because acid environment would inhibit denitrifiers and lead to higher N2O emission. 75.2-78.5% of N2O emission from aquaponics was attributed to denitrification. In general, aquaponics was suggested to maintain pH at 6.0 for high NUE, and further investigations on N2O mitigation strategy are needed.

Plant based phosphorus recovery from wastewater via algae and macrophytes

At present, resource recovery by irrigation of wastewater to plants is usually driven by the value of the water resource rather than phosphorus recovery. Expanded irrigation for increased phosphorus recovery may be expected as the scarcity and price of phosphorus increases, but providing the necessary treatment, storage and conveyance comes at significant expense. An alternative to taking the wastewater to the plants is instead to take the plants to the wastewater. Algal ponds and macrophyte wetlands are already in widespread use for wastewater treatment and if harvested, would require less than one-tenth of the area to recover phosphorus compared to terrestrial crops/pastures. This area could be further decreased if the phosphorus content of the macrophytes and algae biomass was tripled from 1% to 3% via luxury uptake. While this and many other opportunities for plant based recovery of phosphorus exist, e.g. offshore cultivation, much of this technology development is still in its infancy. Research that enhances our understanding of how to maximise phosphorus uptake and harvest yields; and further add value to the biomass for reuse would see the recovery of phosphorus via plants become an important solution in the future.