Life cycle assessment (LCA), a tool used to assess the environmental impacts of products and processes, has been used to evaluate a range of aquaculture systems. Eighteen LCA studies were reviewed which included assessments of recirculating aquaculture systems (RAS), flow-through systems, net cages, and pond systems. This review considered the potential to mitigate environmental burdens with a movement from extensive to intensive aquaculture systems. Due to the diversity in study results, specific processes (feed, energy, and infrastructure) and specific impact categories (land use, water use, and eutrophication potential) were analyzed in-depth. The comparative analysis indicated there was a possible shift from local to global impacts with a progression from extensive to intensive systems, if mitigation strategies were not performed. The shift was partially due to increased electricity requirements but also varied with electricity source. The impacts from infrastructure were less than 13 % of the environmental impact and considered negligible. For feed, the environmental impacts were typically more dependent on feed conversion ratio (FCR) than the type of system. Feed also contributed to over 50 % of the impacts on land use, second only to energy carriers. The analysis of water use indicated intensive recirculating systems efficiently reduce water use as compared to extensive systems; however, at present, studies have only considered direct water use and future work is required that incorporates indirect and consumptive water use. Alternative aquaculture systems that can improve the total nutrient uptake and production yield per material and energy based input, thereby reducing the overall emissions per unit of feed, should be further investigated to optimize the overall of aquaculture systems, considering both global and local environmental impacts. While LCA can be a valuable tool to evaluate trade-offs in system designs, the results are often location and species specific. Therefore, it is critical to consider both of these criteria in conjunction with LCA results when developing aquaculture systems.

Biofilters made of Ulva and periphyton differ in their effectiveness in removing ammonia and nitrate from mariculture effluents. Our research evaluated the practicality of a combination of these two biofilters in improving the overall removal of dissolved N, where efficient removal of ammonia by the seaweed is followed by efficient removal of nitrate by periphyton. A paired Ulva-periphyton biofilter was exposed to various areal loads of ammonia and nitrate, the primary nitrogen forms in fishpond effluents. A first upstream macroalgae biofilter stocked with Ulva was fed with fishpond effluents at different areal loads of ammonia and nitrate, while a second downstream periphyton biofilter was paired for further nitrogen removal from the effluent. Ulva removed ammonia at a rate of 0.7-5.4 g TAN m(-2) d(-1), in correlation with the TAN areal load, with V-max of 5.1 and K-m of 4.4 g TAN m(-2) d(-1). Downstream periphyton was exposed to a lower TAN, but nitrate-rich effluent, and revealed similar capacities for the removal of both N forms, at removal rates of up to 1.7 and 1.8 g Nm(-2) d(-1), respectively. Compared to nitrate, areal load of TAN had a greater impact on the removal dynamics of both N forms by periphyton. Overall, the paired biofilter resulted in a nearly total depletion of ammonia (97%) and efficient nitrate removal (67%), when areal loads in fishpond effluents were below 2 and 4 g Nm(-2) d(-1) of TAN and NO3-N, respectively.

The need to expand marine fish production and improve the economic viability and sustainability of recirculating aquaculture systems led to the development of a zero-discharge, marine aquaponic system. In this study, water treatment capacity, nutrient cycling, and biomass production were evaluated in a prototype, commercial-scale marine aquaponic system that included a moving bed bioreactor (MBBR) for nitrification, a sand filter for solids removal and denitrification, and hydroponic plant beds. Red drum (Sciaenops ocellatus), two species of edible halophytes sea purslane (Sesuvium portulacastrum) and saltwort (Batts maritima), and organic solids, were successfully produced over a 9-month period. Extensive analysis of solids, organic matter, and nutrients (nitrogen and phosphorous) in water and plant biomass was used to develop detailed mass balances on the system. Simultaneous operation of the moving bed bioreactor (MBBR) and plant beds resulted in high ammonia removal rates, allowing the system to support a high fish biomass density (38.8 kg/m(3)). Passive denitrification was the main nitrate removal mechanism, contributing to approximately 59% of aqueous nitrogen removal. Conversion of a sand filter to a side-stream denitrification reactor resulted in removal of 17% of the daily aqueous nitrogen load and prevented nitrate accumulation in the system. In addition to fish and edible halophyte production, 34 kg of organic solids were harvested from the sand filter and provided to a commercial nursery that used the solids as a fertilizer. This study demonstrates that marine aquaponics is an effective way to simultaneously produce marine fish, edible halophytes, and fertilizer. Addition of biological MBBR and a denitrifying sand filter was shown to be beneficial in situations where there are space limitations for plant growth, unexpected plant losses, or to support high densities of fish.

Periphyton-based biofilters for aquaculture effluent possess multiple advantages, in water oxygenation, CO2 reduction and production of useful biomass. The performance of a marine periphyton biofilter, in terms of uptake rate and efficiency in removing different forms of nitrogen, was investigated. A periphyton biofilter was paired with an upstream macroalgae biofilter stocked with Ulva to expose the periphyton to ammonia-depleted but nitrate-rich effluent. Three trials compared the removal of total ammonia-N (TAN), nitrate (NO3-N), total N and phosphorus. The biofiltration and growth performance of (1) the periphyton downstream to the Ulva tank, (2) periphyton alone and (3) Ulva alone were compared. Biofiltration performance was evaluated at different areal loads of TAN and NO3-N. Periphyton growth performance did not depend on the effluent nutrient composition or on N loads, and yielded between 7.3 and 10.6 g dry weight m(-2)d(-1). While the Ulva preferred uptake of TAN over NO3-N, the periphyton showed no preference between them, demonstrating flexible shifts between TAN and NO3-N uptake. TAN uptake rate by the periphyton was not influenced by the effluent composition. However, periphyton NO3-N uptake rate and efficiency rose about fivefold, up to 1.4 g NO3-N m(-2)d(-1) and 63%, respectively, upon depletion of TAN areal load below 0.18 g N m(-2)d(-1) (< 0.3 mg L-1) by the Ulva pre-treatment. Normalizing nutrient uptake rate to biomass revealed similar uptake rate of TAN and phosphorus by periphyton and Ulva, while the periphyton took up nitrate much faster. By removing up to 76% of the total nitrogen, with specific removal efficiency of 97% of the TAN and of 67% of the NO3-N, the novel dual Ulva-periphyton biofilter revealed a synergistic potential in treatment of nutrient-rich mariculture effluents.

The development of marine intensive land-based aquaculture systems has been limited due to the absence of methods to manage saline wastewater. Aquaponic systems, although commonly applied to freshwater aquaculture, can potentially manage nutrient wastes while providing a secondary product. The aim of this study was to evaluate both the capacity for water treatment and the production requirements of two saltwater-tolerant plant species (Sesuvium portulacastrum and Batis maritima) when grown hydroponically in a marine aquaponic system. The presence of plants was found to significantly contribute to nitrate removal, such that mean nitrate concentrations were 10.1 ± 5.4 and 12.1 ± 6.1 mg/L NO3−-N in planted and unplanted treatments respectively. The use of coconut fibre as a planting medium also significantly contributed to nitrate removal, such that mean nitrate concentrations were 9.78 ± 5.4 and 12.4 ± 6.0 mg/L NO3−-N in coconut fibre and expanded clay treatments respectively. Daily nitrogen removal was greatest in the coconut fibre/plants treatment, ranging from −18% to 67%. Hydraulic loading rate, plant species and plant density did not significantly affect water quality or plant growth. The low flow/saltwort/low density treatment had the greatest mean daily nitrogen removal, ranging from 25% to 172%. The results indicate that the main nitrogen removal mechanisms were simultaneous nitrification–denitrification in the hydroponic plant beds and nitrogen removal through plant growth. This study demonstrates that marine aquaponics could be an effective way to manage nutrient removal in marine land-based aquaculture systems.

Life cycle assessment was used to evaluate environmental impacts of simultaneous fish and plant production through the aquaculture practice of aquaponics. In aquaponics, hydroponic plant production replaces the conventional water treatment processes of microbial nitrification and water exchanges required in recirculating aquaculture systems (RAS) to maintain water quality. The system expansion method was used to assess potential avoided burdens from coproduction of recovered solids, plant production, and water treatment. Results indicated that electricity and feed were the main contributing factors to environmental impact. Impact assessment results were highly sensitive to changes in electricity inputs, suggesting that a small reduction in electricity could contribute to a correspondingly large change in the environmental impact. Avoided burdens associated with coproducts contributed to a moderate reduction in environmental impact compared to reducing total electricity inputs or sourcing electricity from renewable sources. Of the coproducts considered, avoided water treatment contributed greatest to reductions in environmental impact due to reductions in energy use, water use, and eutrophication potential. The large reduction in water use suggests that plant production can contribute to increased recirculation rates and further reduce water inputs associated with aquaculture. Aquaponics, similar to other RASs, essentially eliminates local ecological impacts at the cost of high energy use and the addition of industrial fish feeds. Development of sustainable land-based aquaculture will encompass many production systems, including aquaponics; however, all systems will benefit from improved energy efficiency, increased accessibility to renewable energy sources, and development of sustainable fish feeds.

The water chemistry and economics of a commercial-scale inland marine integrated multi-trophic aquaculture (IMTA) system was investigated. The system used a combination of a constructed wetland, sand filter followed by a constructed wetland, and geotextile bags to treat solids waste. This study is a demonstration of a zero-discharge system where commercial nursery production of wetland plants was combined with a marine RAS to treat saline solid waste. Total suspended solids (TSS), chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) concentrations were measured. Plant and soil samples were analyzed for TN and TP. A significant (p < 0.05) difference in the effluent concentrations was not found. The variability inherent in a commercial-scale system made it difficult to isolate the individual efficiencies of the three treatment systems. Production of wetland plants was critical for aiding nutrient removal by facilitating aggregation of solids and providing conditions for denitrification. On average the nitrate concentration decreased over time due to the denitrification occurring in the plant beds. Water samples were analyzed for dissolved metals: Mn, Ni, Se, Sr, Cd, Li, Hg, Mo, Fe, B, Cu, Pb, Zn, La, Ca, K, and Mg; Mn and Fe showed a gradual increase in concentration over time. This IMTA system successfully produced Florida pompano, and the fish waste and uneaten feed provided enough nutrients to produce multiple cohorts of wetland plants over a two-year period. An economic analysis indicated that after one year of production the system would produce a profit, but the production of Florida pompano alone would not result in a positive net return. The sales of wetland plants were necessary for the system to break-even and ultimately produce a profit for the production facility in Sarasota, FL. (C) 2015 Elsevier B.V. All rights reserved.