Treat Aquaculture Effluent Research Articles

Effect of the number of Cyperus rotundus and medium height on the performance of batch-constructed wetland in treating aquaculture effluent

Increasing aquaculture cultivation produces large quantities of wastewater. If not handled properly, it can have negative impacts on the environment. Constructed wetlands (CWs) are one of the phytoremediation methods that can be applied to treat aquaculture effluent. This research was aimed at determining the performance of Cyperus rotundus in removing COD, BOD, TSS, turbidity, ammonia, nitrate, nitrite, and phosphate from the batch CW system. Treatment was carried out for 30 days with variations in the number of plants (10, 15, and 20) and variations in media height (10, 12, and 14 cm). The result showed that aquaculture effluent contains high levels of organic compounds and nutrients, and C. rotundus can grow and thrive in 100% of aquaculture effluent. Besides that, the use of C. rotundus in CWs with the effect of numbers of plants and media height showed performance of COD, BOD, TSS, turbidity, ammonia, nitrate, nitrite, and phosphate with 70, 79, 90, 96, 64, 82, 92, and 48% of removal efficacy, respectively. There was no negative impact observed on C. rotundus growth after exposure to aquaculture effluent, as indicated by the increase in wet weight, dry weight, and growth rate when compared to the control. Thus, adding aquaculture effluent to CWs planted with C. rotundus supports the growth and development of plants while also performing phytoremediation.

Microbial communities in full-scale woodchip bioreactors treating aquaculture effluents

Woodchip bioreactors are being successfully applied to remove nitrate from commercial land-based recirculating aquaculture system (RAS) effluents. In order to understand and optimize the overall function of these bioreactors, knowledge on the microbial communities, especially on the microbes with potential for production or mitigation of harmful substances (e.g. hydrogen sulfide; H2S) is needed. In this study, we quantified and characterized bacterial and fungal communities, including potential H2S producers and consumers, using qPCR and high throughput sequencing of 16S rRNA gene. We took water samples from bioreactors and their inlet and outlet, and sampled biofilms growing on woodchips and on the outlet of the three full-scale woodchip bioreactors treating effluents of three individual RAS. We found that bioreactors hosted a high biomass of both bacteria and fungi. Although the composition of microbial communities of the inlet varied between the bioreactors, the conditions in the bioreactors selected for the same core microbial taxa. The H2S producing sulfate reducing bacteria (SRB) were mainly found in the nitrate-limited outlets of the bioreactors, the main groups being deltaproteobacterial Desulfobulbus and Desulfovibrio. The abundance of H2S consuming sulfate oxidizing bacteria (SOB) was 5–10 times higher than that of SRB, and SOB communities were dominated by Arcobacter and other genera from phylum Epsilonbacteraeota, which are also capable of autotrophic denitrification. Indeed, the relative abundance of potential autotrophic denitrifiers of all denitrifier sequences was even 54% in outlet water samples and 56% in the outlet biofilm samples. Altogether, our results show that the highly abundant bacterial and fungal communities in woodchip bioreactors are shaped through the conditions prevailing within the bioreactor, indicating that the bioreactors with similar design and operational settings should provide similar function even when conditions in the preceding RAS would differ. Furthermore, autotrophic denitrifiers can have a significant role in woodchip biofilters, consuming potentially produced H2S and removing nitrate, lengthening the operational age and thus further improving the overall environmental benefit of these bioreactors.

Efficiency of Salicornia neei to Treat Aquaculture Effluent from a Hypersaline and Artificial Wetland

In this study, we evaluated the potential of Salicornia neei, a halophyte plant native to South America, to treat saline effluents with simulated concentration of ammonium-N (Amm) and nitrate-N (Nit) in a similar manner to land-based marine aquaculture effluents. Plants were cultivated for 74 days in drainage lysimeters under three treatments of seawater fertilized with: (1) Nit + Amm, (2) Nit, or (3) without fertilizer (Control). Over five repetitions, nitrogen removal efficiency (RE) was high in both treatments (Nit + Amm = 89.6% ± 1.0%; Nit 88.8% ± 0.9%), whereas the nitrogen removal rate (RR) was nonlinear and concentration-dependent (RRday1–4: Nit + Amm = 2.9 ± 0.3 mg L−1 d−1, Nit = 2.4 ± 0.5 mg L−1 d−1; RRday5–8: Nit + Amm = 0.8 ± 0.2 mg L−1 d−1, Nit = 1.0 ± 0.2 mg L−1 d−1). Effluent salinity increased from 40.6 to 49.4 g L−1 during the experiment, with no observed detrimental effects on RE or RR. High nitrogen removal efficiency and significant biomass production were observed (Nit + Amm = 11.3 ± 2.0 kg m−2; Nit = 10.0 ± 0.8 kg m−2; Control = 4.6 ± 0.6 kg m−2) demonstrate that artificial wetlands of S. neei can be used for wastewater treatment in saline aquaculture in South America.

Nitrate removal microbiology in woodchip bioreactors: A case-study with full-scale bioreactors treating aquaculture effluents

Woodchip bioreactors are viable low-cost nitrate (NO3−) removal applications for treating agricultural and aquaculture discharges. The active microbial biofilms growing on woodchips are conducting nitrogen (N) removal, reducing NO3− while oxidizing the carbon (C) from woodchips. However, bioreactor age, and changes in the operating conditions or in the microbial community might affect the NO3− removal as well as potentially promote nitrous oxide (N2O) production through either incomplete denitrification or dissimilatory NO3− reduction to ammonium (DNRA). Here, we combined stable isotope approach, amplicon sequencing, and captured metagenomics for studying the potential NO3− removal rates, and the abundance and community composition of microbes involved in N transformation processes in the three different full-scale woodchip bioreactors treating recirculating aquaculture system (RAS) effluents. We confirmed denitrification producing di‑nitrogen gas (N2) to be the primary NO3− removal pathway, but found that 6% of NO3− could be released as N2O under high NO3− concentrations and low amounts of bioavailable C, whereas DNRA rates tend to increase with the C amount. The abundance of denitrifiers was equally high between the studied bioreactors, yet the potential NO3− removal rates were linked to the denitrifying community diversity. The same core proteobacterial groups were driving the denitrification, while Bacteroidetes dominated the DNRA carrying microbes in all the three bioreactors studied. Altogether, our results suggest that woodchip bioreactors have a high genetic potential for NO3− removal through a highly abundant and diverse denitrifying community, but that the rates and dynamics between the NO3− removal pathways depend on the other factors (e.g., bioreactor design, operating conditions, and the amount of bioavailable C in relation to the incoming NO3− concentrations).

Denitrifying bioreactor inflow manifold design for treatment of aquacultural wastewater

Recirculating aquaculture systems (RAS) facilities subject to point-source effluent regulations need to implement cost-effective N remediation for their wastewater outflows. Relatively low-cost denitrifying “woodchip” bioreactors can effectively remove N from aquaculture effluents for at least one year, but questions remain about bioreactor lifespan for aquacultural wastewaters. Four pilot-scale bioreactors (L × W × D; 3.8 × 0.76 × 0.76 m), two with a conventional single distribution inflow manifold and two with an experimental multiple-header, feed-forward distribution manifold, were operated over 784 d to observe second-year N removal performance and to determine if the manifold design can influence bioreactor effectiveness. The study also quantified performance metrics for chemical oxygen demand, total suspended solids, and phosphorus. Manifold style did not have notable impact on bioreactor performance when treating wastewater under the facilities’ normal operating conditions, but the multiple distribution style demonstrated an 11 % increase in nitrate and 12 % increase in total suspended solids removal efficiency over the single distribution manifold toward the end of the study when bioreactors treated higher strength wastewater. Additionally, bioreactor performance in both manifold designs decreased from an average of 92 % total suspended solids removal efficiency under normal operating conditions to <76 % when treating the high-strength wastewater. The bioreactors provided N removal rates of 17−25 g NO3-N m−3 d−1 during the second year of study, demonstrating woodchip bioreactors can effectively treat aquaculture effluent for at least two years without major detrimental impacts due to clogging.

Nitrate removal from aquaculture effluents using woodchip bioreactors improved by adding sulfur granules and crushed seashells

This study examined the effects on nitrate removal when adding sulfur granules and crushed seashells to a woodchip bioreactor treating aquaculture effluents. Using a central composite design, the two components were added at three levels (0.000, 0.125 and 0.250 m3/m3 bioreactor volume) to 13 laboratory-scale woodchip bioreactors, and a response surface method was applied to find and model the optimal mixture ratios with respect to reactor performance. Adding 0.125 m3/m3 sulfur granules improved the total N removal rate from 3.27 ± 0.38 to 8.12 ± 0.49 g N/m3/d compared to pure woodchips. Furthermore, the inclusion of crushed seashells together with sulfur granules helped to maintain the pH above 7.4 and prevent a production (i.e., release) of nitrite. According to the modeled response surfaces, a sulfur granule:crushed seashell:woodchip mixture ratio containing about 0.2 m3 sulfur granules and 0.1 m3 crushed seashells per m3 reactor volume would give the best results with respect to high N removal and minimal nitrite release. In conclusion, the study showed that N removal in woodchip bioreactors may be improved by adding sulfur granules and seashells, contributing to the optimization of woodchip performance in treating aquaculture effluents.

Optimizing nitrate removal in woodchip beds treating aquaculture effluents

Nitrate is typically removed from aquaculture effluents using heterotrophic denitrification reactors. Heterotrophic denitrification reactors, however, require a constant input of readily available organic carbon (C) sources which limits their application in many aquaculture systems for practical and/or economic reasons.A potential alternative technology for removing nitrate currently applied for treating surface and drainage water is based on using wood by-products as a carbon source for denitrification.Using lab-scale horizontal-flow woodchip filters, the current study investigated the potential of optimizing woodchip reactors for treating aquaculture effluent. A central composite design (CCD) was applied to assess the effects of simultaneously changing the empty bed contact time (EBCTs of 5.0–15.0h; corresponding to theoretical hydraulic retention times of 3.3–9.9h) and bicarbonate (HCO3−) inlet concentration (0.50–1.59g HCO3−/l) on the removal rate of NO3−N, and additional organic and inorganic nutrients, in effluent deriving from an experimental recirculating aquaculture system (RAS).Volumetric NO3−N removal rates ranged from 5.20±0.02 to 8.96±0.19g/m3/day and were enhanced by adding bicarbonate, suggesting that parts of the removal was due to autotrophic denitrification. The highest N removal rate (8.96±0.05g/m3/day) was achieved at an EBCT and HCO3− combination of 15h and 1.59g HCO3−/l. Bicarbonate inlet concentration as a single factor had the strongest effect on N removal rates followed by the interaction with EBCT, and EBCT2 (quadratic term).The study thus indicates that woodchip beds may be applied and optimized for removing nitrate from aquaculture effluents. Statement of relevanceThis study is a relevant contribution to research in aquaculture as it presents an alternative method for removing nitrates from aquaculture effluents especially for less intensive fish farms. Furthermore, it shows how this method can be optimized to yield higher removal rates of nitrate.

Factors influencing the efficiency of constructed wetlands used for the treatment of intensive trout farm effluent

In this paper the factors influencing treatment performance of subsurface flow constructed wetlands (SSF wetlands) treating aquaculture effluents were identified and quantified. The financial impact of advanced aquaculture effluent treatment with SSF wetlands was calculated. It is the first long-term, commercial-scale trial of SSF wetland treatment for effluents from intensive trout farming, a highly diluted effluent at very high flow rates (mean total phosphorous concentration 0.34 mg L −1 at 14.3 L s −1). The 12-month survey provided the opportunity to generate calculation fundamentals for the commercial application of SSF wetlands for aquaculture. Treatment efficiencies of up to 75–86% for total ammonia nitrogen (TAN), biological oxygen demand (BOD 5) and total suspended solids (TSS) were achieved. The daily area retention rate per square meter wetland area was between 2.1 and 4.5 g for TAN and between 30 and 98 g for TSS. The performance of the six wetland cells comprising three replicated hydraulic loading groups (14.5, 6.9, 3.3 m 3 m −2 day −1) was monitored, offering the possibility to identify factors influencing treatment efficiency through multifactor analysis. These factors turned out to be nutrient inflow concentration, hydraulic loading rate and accumulation of TSS within the wetland bed, the only time-dependent factor. Factors such as vegetation period and fish harvesting were shown to be of significant but negligible importance. Inflow nutrient concentration is determined by production intensity, husbandry conditions, feed quality and any pre-treatment of effluent. Hydraulic load is determined by the space and budget available for SSF construction. TSS accumulation in the wetland is influenced by pre-treatment of the solid fraction prior to the wetland and determines the wetland service lifetime. From these factors the expenses of commercial wetland application can be estimated, leading to a cost increase around €0.20 kg −1 fish produced (less than 10% of production costs) and therefore confirm the commercial feasibility of SSF wetland treatment.

Treatment of rainbow trout ( Oncorhynchus mykiss) raceway effluent using baffled sedimentation and artificial substrates

The treatment performance of a 6 m wide by 67 m long by 0.8 m deep, baffled sedimentation basin receiving rainbow trout ( Oncorhynchus mykiss) raceway effluent was evaluated with and without the installation of artificial substrates (Aquamats ®). Treatment efficiency was also determined using normal rearing condition effluent loading versus cleaning and harvesting events. Total suspended solids (TSS) removal for the total basin averaged 79% and 71% during normal rearing conditions, as compared to 92% and 79% during cleaning and harvesting operations, when the Aquamats ® were installed versus removed, respectively. Total phosphorus (TP) removal by the total basin, with and without Aquamats ®, was 20% and 23% during normal rearing conditions as compared to 55% and 65% under cleaning and harvesting conditions, respectively. Higher TP removal during cleaning operations was attributed to sedimentation of particulate fractions. Dissolved nutrient removal ( ortho-phosphate (OP), total ammonia nitrogen (TAN), nitrate, nitrite, and total organic carbon (TOC)) was not consistent throughout the basin and did not improve when the Aquamats ® were installed. A short contact time and periphyton grazing by isopods may have limited the capacity of the Aquamats ®. Calculated retention times with and without Aquamats ® for the first half and total basin were 37% and 32% and 27% and 17% less than theoretical values, respectively based on a rhodamine WT dye study. Average surface overflow rates were adjusted accordingly and measured 19.1 m 3/m 2 day when the Aquamats ® were installed, versus 14.8 m 3/m 2 day when the Aquamats ® were removed for the overall basin. These rates are lower than previous recommendations for treating aquaculture effluents, but resulted in high solids removal and consistently low TSS effluent (average <2 mg/L), which may be necessary for strict discharge permits. Use of the overall basin minimized the occurrence of TSS measurements >2 mg/L by 50%. For the first half of the sedimentation basin, the overflow rate averaged 44.1 m 3/m 2 day with Aquamats ® versus 35.8 m 3/m 2 day without Aquamats ®. The majority of effluent treatment occurred within the first half of the basin, which was responsible for 84% and 94% of overall TSS removal, 42% and 100% of overall NH 3-N removal and 61% and 80% of overall TP removal during normal and cleaning/harvesting conditions, respectively.

Ammonia removal from aquaculture water by means of fluidised technology

A bench-scale fluidised bed bioreactor was used to treat aquaculture effluent intended for recycling. The reactor was loaded with ammonia-nitrogen (NH 4-N) from 0.025 to 5.675 g m −2 day −1. Maximum NH 4-N removal was 82% of influent concentration when loading was between 0.201 and 0.397 g m −2 day −1; at this level, effluent NH 4-N did not exceed 0.05 mg 1 −1.

Sieving as an effluent treatment method for aquaculture

A new device designed for sieving of fish farm effluent (trademark Triangel Filter TF 2400) was tested in order to prove if such an apparatus may be used instead of the swirl concentrator. The phosphorus reduction was estimated by water sampling and phosphorus budget and by measuring the phosphorus content in flushing water and in settled sludge. Sieving is a promising and useful method to treat aquaculture effluent, especially in ‘high-tech’ systems (recirculation, warmed water facilities) where high effluent quality and the most effective removal of solids is needed.