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Nitrogen migration law and recycling strategy in an innovative recirculating aquaculture system: Enhancing performance through electrocoagulation
Abstract
In this study, electrocoagulation (EC), a green and efficient water treatment technology, was used to improve the performance of the Litopenaeus vannamei (L. vannamei) RAS. The main objective was to investigate the nitrogen migration law of the innovative L. vannamei RAS, establish a nitrogen recovery strategy, and promote the sustainable development of the L. vannamei RAS. It was found that 34.22 % of input nitrogen (NInput) accumulated in live shrimp, 3.83 % and 0.69 % of NInput existed in shed shrimp shell and dead shrimp, 41.31 % of NInput was removed by the water treatment equipment, 9.75 % of NInput was removed through water exchange, and 2.89 % of NInput accumulated in the RAS. Under the action of the EC, the removal of nitrogen by a microscreen drum filter (MDF), moving-bed biofilm reactor (MBBR) and foam separator (FS) increased by 26.39 %, 9.52 %, and 9.10 %, respectively. Moreover, a Chlorella vulgaris culture system was used to recycle the waste nitrogen of the L. vannamei RAS, with a nitrogen recovery rate of 80.84 %. These findings indicate that EC can significantly enhance the nitrogen removal of RAS, and the Chlorella vulgaris can be used for the efficient recovery of the waste nitrogen from RAS.
... Compared to traditional farming models, recirculating aquaculture has attracted much attention due to its environmental sustainability, high yields, controllability, and high product quality [4]. There have been several studies of the high-density aquaculture of L. vannamei using a recirculating aquaculture system (RAS) [1,[4][5][6]. ...
... In addition to preventing the waste of resources, DO management in an RAS needs to ensure the healthy growth of breeding organisms and the efficient operation of the MBBR [7,21]. In previous studies, the DO concentration was typically maintained at 6.5-7.5 mg/L during the high-density aquaculture of L. vannamei [4,6,22]. Based on the studies referred to above, and, considering the normal growth of shrimp and the water-treatment performance of the biofilm during high-density aquaculture, it is recommended to maintain the DO concentration of the AP effluent at 6.9 ± 0.4 mg/L. ...
... In a recent study, Kır et al. (2023) indicated that the OCR of 16 ± 1.5 g L. vannaeus in water with a salinity of 30 ppt and temperature of 27 • C was equivalent to approximately 0.3 g O 2 /(kg shrimp h) [9]. The OCR of the APs was close to that of the shrimp because the RAS in this study gave prominence to the removal of suspended solids, as shown by Du et al. (2021) [4], and Xu et al. (2021Xu et al. ( , 2022 [6,18]. The water in the APs was clear, resulting in the low oxygen consumption of microorganisms [4]. ...
This study investigated the dissolved oxygen (DO) variation pattern in a Litopenaeus vannamei recirculating aquaculture system (RAS) and established an oxygen-utilization rate (UROxygen) model, pure oxygen addition (QOxygen) model, and control model that linked a microscreen drum filter (MDF) with a U-tube oxygenator. The main objective was to promote the application of the U-tube oxygenator and achieve the efficient, accurate, and automated management of DO in an RAS. To avoid wasting oxygen and ensure production safety, it was recommended to maintain the effluent of the aquaculture pond at 6.9 ± 0.4 mg/L. The modeled relationship between the RAS flow (QRAS), QOxygen, and UROxygen was UROxygen = 0.9626 × (−105.3406 + 0.9911QRAS + 10.6202QOxygen − 0.05964QRASQOxygen − 1.2628 × 10−3QRAS2 − 0.1821QOxygen2 + 6.8888 × 10−5QRAS2QOxygen + 6.3993 × 10−4QRASQOxygen2). The modeled relationship between QRAS, daily feeding rate (MFeeding), and QOxygen was QOxygen = 1.09 × (−12.8633 − 0.02793QRAS + 0.9369 MFeeding − 8.9286 × 10−4MFeedingQRAS + 5.6122 × 10−5QRAS2 − 2.3281 × 10−3MFeeding2). The modeled relationship between the MDF backwashing period (TMDF) and QOxygen was QOxygen = −11.57ln(TMDF) + 78.319. This study provided a theoretical basis and novel methods for the management of DO in an RAS, thus promoting the healthy and stable development of an L. vannamei RAS.
Designing good recirculating aquaculture systems (RASs) is challenging in shrimp aquaculture. In this study, two sets of RASs were constructed using sea cucumber nursery tanks for rearing Litopenaeus vannamei. Recirculating aquaculture was supported by key technologies such as sewage collection and aeration systems adapted to the rectangular tanks and technologies for the removal of sewage, shrimp shells, and dead individuals. Six-hundred and eighty-five thousand juveniles were selected for rearing in the newly constructed RASs, where the average stocking density was 1013 shrimp/m3. During the recirculating aquaculture period of 53 days, the water temperature of the tanks was 24–31 °C, the salinity was 25–32‰, the pH was 6.4–8.2, the DO was ≥ 4.9 mg/L, the concentration of total ammonia nitrogen (TAN) was maintained between 0.17 and 4.9 mg/L, the concentration of nitrite nitrogen (NO2-N) was between 0.12 and 4.7 mg/L, and the total number of Vibrio bacteria remained between 330 and 9700 cfu/mL. At the end of the experiment, the final average weight of individual shrimp was 13.43 g, and the average yield reached 12.92 kg/m3. The great improvement in growth performance marks a breakthrough in RAS technology of shrimp, and it supports the use of an innovative methodology for the retrofitting and utilization of idle sea cucumber nursery tanks.
Aquaculture wastewater has become a global concern, especially to the aquatic environment. Aquaculture industries rely on the consumption of water and generate an abundant amount of wastewater. Aquaculture wastewater has characteristics of high organic materials and nutrients. However, the potential of resource reclamation from this wastewater awaits to be explored further. Aquaculture wastewater contains algae, which can be harvested using biodegradable coagulants for further utilization. It is also nutrient‐rich and can be reclaimed as fertilizer or used as co‐cultivation of algae. However, limited research has focused on the potential of valuable materials recovery from aquaculture wastewater. This review paper discusses the estimation of wastewater generation from aquaculture industries and the characteristics of the effluent. It discusses the potential for valuable material recovery from wastewater, including aquaculture industries wastewater. This paper summarizes several valuable materials that can be recovered from wastewater to achieve cleaner production in industrial processes and discusses the challenges and prospects in recovering valuable materials from aquaculture effluent for future applications. This review could provide insights to increase the economic value of wastewater, especially aquaculture wastewater, and to enrich knowledge related to the resource reclamation from wastewater.
The aim of this study was to provide technical means and data support for enhancing the filtration pretreatment capacity of a recirculating aquaculture system. A continuous flow electrocoagulation (EC)–filtration system was designed and its application in the pretreatment of marine aquaculture wastewater was studied. The influences of anode combination modes, hydraulic retention times (HRTs) of the EC reactor and filter pore sizes on the water treatment capacity were investigated. Results showed that EC could significantly enhance the treatment efficiency of the filtration equipment used in subsequent steps. Al-Fe electrodes used as anode led to better processing capacity of this system, and the optimum anode was 3Al + Fe. With the increase of HRT and decrease of filter pore size, the enhanced effect of the EC process on the filter was more obvious. When the current density was 19.22 A/m2, the anode was 3Al + Fe, the HRT was 4.5 min and the filter pore size was 45 μm, the removal efficiency of the system for Vibrio, chemical oxygen demand, total ammonia nitrogen, nitrite nitrogen (NO2−-N), nitrate nitrogen (NO3−-N) and total nitrogen was 69.55 ± 0.93%, 48.99 ± 1.42%, 57.06 ± 1.28%, 34.09 ± 2.27%, 18.47 ± 1.88% and 55.26 ± 1.42%, respectively, and the energy consumption was (26.25 ± 4.95) × 10−3kWh/m3. HIGHLIGHTS
The combination technology of EC and filtration was used for the pretreatment of aquaculture wastewater.;
The filtration capacity of physical filtration equipment was improved through the EC–flocculation.;
Al-Fe combined anode was used to improve the treatment capacity of the EC–filtration system.;
Iron and phosphorus (P) are the important micro- and macro-nutrient for microalgae growth, respectively. However, the effect of iron and P on microalgae growth in co-culture associating with the formation of dominate algae has not been investigated before. In the current study, Anabaene flos-aquae, Chlorella vulgaris and Melosira sp. were co-cultivated under the addition of different initial iron and P to reveal the effect of iron and phosphorus on the growth of microalgae. The results showed that the mean growth rate of A. flos-aquae, C. vulgaris and Melosira was 0.270, 0.261 and 0.062, respectively, indicating that the A. flos-aquae and C. vulgaris algae are liable to be the dominant algae while the growth of Melosira was restrained when co-cultured. The ratio of Fe to P has a significant impact on the growth of microalgae and could be regarded as an indicator of algae growth. Microalgae showed a much more obvious uptake of iron compared to that of P. The information obtained in the current study was useful for the forecast of water quality and the control of microalgae bloom.
As in any agroecosystem, also in aquaponics the nitrogen (N) balance represents an important tool to evaluate sustainability, and to identify factors that can improve N use efficiency (NUE) and reduce N losses. In this respect, fish stocking density has been little investigated, hence this research aimed to evaluate the N balance of a low technology aquaponic (AP) system managed at two fish densities in comparison with a hydroponic system (HP). In the fish tanks common carp at two initial stocking densities were reared (2.5 and 4.6 kg m–3 in low and high AP, hereafter named APL and APH, respectively) and the vegetated sector was cultivated with a leafy vegetable crop succession (Catalogna chicory, lettuce, Swiss chard). The N balance considered N input as fish feed or fertiliser, and N content in the initial water and the N output as N in the incremented fish biomass, in the harvested vegetables, in the sediments, and in the remaining water. Total N loss was estimated by difference. The total N input and the N loss through gas emission in the atmosphere were much higher in AP than in HP, particularly at high stocking density. The opposite trend was observed for the N input recovered in vegetable aboveground biomass. The N input recovered as fish biomass was slightly higher in APL compared to APH. The better results of APL than APH suggest that in low-tech AP system lower initial fish density should be adopted at the system start up to maximise both production and N recovery.
Recirculating aquaculture systems (RAS) are a new alternative to traditional aquaculture approaches, allowing full control over the fish production conditions, while reducing the water demand. The reduction of water exchange leads to an accumulation of dissolved organic matter (DOM) that can have potential effects on water quality, fish welfare and system performance. Despite the growing awareness of DOM in aquaculture, scarce scientific information exists for understanding the composition and transformation of DOM in RAS. In this study, a non-targeted approach using ultra-performance liquid chromatography coupled to a hybrid quadrupole-time of flight mass spectrometer (UPLC-QTOF-MS) was used to characterize compositional changes of low molecular weight (LMW) DOM in RAS, when operated under two different feed types. A total of 1823 chemicals were identified and the majority of those contained a CHON chemical group in their structure. Changes in the composition of LMW-DOM in RAS waters were observed when the standard feed was switched to RAS feed. The DOM with the use of standard feed, consisted mainly of lignin/CRAM-like, CHO and CHOS chemical groups, while the DOM that used RAS feed, was mainly composed by unsaturated hydrocarbon, CHNO and CHNOS chemical groups. The Bray-Curtis dissimilarity cluster demonstrated differences in the composition of DOM from RAS and was associated to the type of feed used. When the RAS feed was used, the Kendrick mass defect plots of –CH2- homologous units in the pump-sump (after the water treatment) showed a high removal capacity for CHNO, CHNOS and halogenated chemicals with high Kendrick mass defect, KMD > 0.7. To our knowledge, this is the first report of LMW-DOM characterization of RAS by high-resolution mass spectrometry (HRMS).
By keeping tropical shrimp, like Litopenaeus vannamei, in recirculating aquaculture systems (RAS), valuable food for human consumption can be produced sustainable. L. vannamei tolerates low salinities, and therefore, the systems can operate under brackish water conditions. The stabilization of the microbial community in RAS might be difficult under high organic loads, and therefore, water treatment measures like UV irradiation or ozone application are commonly used for bacterial reduction. To investigate the impact of these measures, the effects of UV irradiation and ozone application were studied in small‐scale brackish water RAS with a salinity of 15‰ stocked with L. vannamei. UV reactors with 7 and 9 W were used, and by ozonizers with a power of 5–50 mg/hr, the redox potential in the water was adjusted to 350 mV. Ozone had a stabilizing effect on the microbial composition in the water and on biofilms of tank surfaces and shrimp carapaces, prevented an increase of nitrite and accelerated the degradation of nitrate in the water. UV irradiation led to changes in the microbial composition and was less effective in optimizing the chemical water quality. Thus, the use of ozone could be recommended for water treatment in brackish water RAS for shrimp.
Aquaculture wastewater contains a huge amount of substances that can cause environmental pollution. However, microalgae can absorb these compounds and convert them into useful biomass. In this study, Chlorella minutissima was grown in the wastewater resulting from saline aquaculture. The microalgae were found to effectively utilize nitrogen and phosphorus in the wastewater for its growth. During wastewater treatment, the cell density increased almost fivefold compared to the initial value (OD680 0.502). Moreover, batch culture resulted in the maximum biomass concentration and productivity of 4.77 g/L and 0.55 g/L/day, respectively. The contents of total nitrogen and total phosphorus in wastewater decreased by 88% and over 99%, respectively. In addition, the content of N-NO3 was reduced by 88.6%, N-NO2 by 74.3%, and dissolved orthophosphates (V) by 99%. At the beginning and throughout the experiment, the content of N-NH4 in wastewater remained below 0.05 mg/L. Furthermore, a high lipid content of 46.4% (w/w) was also obtained from the studied microalgae.
In aquaculture systems, insufficient nutrients impede shrimp growth while excessive amounts of nutrient inputs lead to environmental degradation and unnecessary high investment. A study of in-out nutrient budgets in an intensive Litopenaeus vannamei farm was conducted in this work to measure the amount of nitrogen (N) and phosphorus (P) input and output from the system. The feed conversion ratio (FCR) was obtained to determine the level of nutrient input performance. Between September and December 2017, monthly water and sediment samples were taken within one crop cycle. Nutrient concentrations in sediment and water increased over 90 days. The total nitrogen concentration in the pond water and effluents were in accordance with wastewater quality control for aquaculture; however, the total phosphorus concentration failed to meet the water quality control from the water input through the end of the crop cycle. The nutrient budget model showed that the input/output contained 107.8 kg N and 178.4 kg P. Most of the N input came from shrimp diets (80%) while most of the P came from fertilizer (57%). Both N (46%) and P (54%) mainly deposited in the sediment as an output process. The FCR of this farm is 2.0. Based on the 1.8 FCR scenario, this farm could reduce 147 kg of feed in total, which accounts for 9.04 kg N and 2.21 kg P reduction. The farmer could save $1027 USD crop− 1 ($1 USD = 32.7 baht), as well as reducing uneaten food at the bottom of the pond. This study offers a simple and straightforward model that can practically reduce environmental impacts and increase the profitability of farms.
The combined treatment systems have become a potential alternative to treat highly polluted industrial wastewater to achieve high quality treated effluents. The current review focuses on the treatment systems compromising electrocoagulation (EC) as a pretreatment step followed by a biological treatment step. The reasons for applying EC as a pretreatment process were mainly to (1) detoxify the wastewater by removing inhibitors of the biotreatment step or (2) to remove the major part of the COD or (3) the dissolved materials that could cause fouling to membrane bioreactors or (4) to increase the activity of the microorganisms. This combination represents a new and promising application characterized by higher performance and removal efficiency. The main published findings related to this application are presented and analyzed. Besides, the statistical models used to optimize the process variables and the kinetics of microorganism growth rate are discussed herein. Most of the previous investigations were conducted in a laboratory scale level with biologically treated water as a feed to the EC process. Only a few works applied a hybrid system consisting of the biological step and the EC step. In all studies, improved performance and higher removal efficiencies of the combined process were achieved particularly when applying aluminum electrodes, providing more than 95% removal efficiency. Many researchers have reported that they had faced a significant problem in the operation of the electrocoagulation process associated with the reduction of electrodes' efficiency caused by deposits of the coagulation complex. This problem needs to be effectively resolved.
The rapid development of aquaculture has sustained aquatic food production but has also led to a host of environmental problems, ranging from eutrophication of aquatic ecosystems to global acidification. China has become the world's largest producer and consumer of aquaculture products. Nitrogen is an essential nutrient in aquaculture ecosystems, and the quantitative environmental fate and impact of nitrogen during aquaculture processes have notable environmental consequences but have received little attention. Here, we established a nitrogen cycling model for China's aquaculture ecosystem to investigate the creation and fate of reactive nitrogen over a decadal time scale. A nitrogen balance analysis showed that reactive nitrogen input in the aquaculture ecosystem increased from 9.43 Tg N yr-1 in 1978 to 18.54 Tg N yr-1 in 2015, while aquaculture production increased from 0.034 to 1.33 Tg N yr-1 during the same period. The environmental fate analysis showed that nitrogen emissions, accumulation, sediment deposition, and export into the oceans increased by 9.05-fold, 0.24-fold, 9.04-fold, and 2.56-fold, respectively. Finally, we investigated four scenarios representing different consumption levels of aquatic products and provided policy recommendations (larger aquaculture size, standardized aquaculture production model, nutritional element management and balanced dietary structure, etc.) on improved management practices in aquaculture ecosystems.
Sustaining good water quality in aquaculture ponds is vital. Without an aerator, the dissolved oxygen in ponds comes primarily from mass transfer at the water-ambient atmosphere interface. As sediment can seriously affect water quality, this study used indoor experiments to examine the nutrient (nitrogen and phosphorus) release mechanisms and fluxes from sediment in aquaculture ponds with moving water but no aeration. The results showed that the ammonia nitrogen (NH3-N) concentration in the overlying water was inversely proportional to flow velocity and that a higher flow velocity tended to result in a lower concentration in the overlying water, a steeper vertical gradient of concentration within the bed sediments, and a faster release rate from the sediments. The sediment disturbed by flowing water released more nitrate nitrogen (NO3-N) and nitrite nitrogen (NO2-N) into the overlying water and NO2-N could become oxidized into NO3-N. In still water, NO3-N was released gradually and some anaerobic NO3-N was nitrified into NO2-N. Phosphorus release from the sediments was controlled by the adsorption-desorption balance, with the phosphorus concentration in the overlying water dropping gradually to a steady value from its initial maximum. The relationship between NH3-N release flux and flow rate is described by a cubic function.
Although co-cultivation of algae with aquaculture products has the potential to reduce water use and pollutant discharges while producing energy feedstocks and other end-products, little research has been carried out in this area. Maintaining axenic conditions (algal monocultures without other microorganisms) in algal culturing systems using aquaculture wastewater as a nutrient source would not be practical. This study examined the effects of the use of aquaculture wastewater as a nutrient source on biomass development of three algae cultures (indigenous mixed species consortium, Chlorella sp. and Scenedesmus) under axenic and non-axenic conditions. Biomass development was assessed by cell growth, chlorophyll, starch and lipid production. The presence of aquaculture microorganisms decreased biomass productivity in Chlorella but not in the other algae cultures. Non-axenic conditions had no effect on overall starch and chlorophyll production; however, significantly higher lipid contents were achieved under non-axenic conditions for Chlorella and the indigenous culture. The higher algal lipid content for these cultures under non-axenic conditions may have been due to competition with bacteria for nutrients. The presence of bacteria was required for effective removal of organics, while effective nitrogen removal was observed in all systems containing algae. Results from this study also show that algae harvesting should be timed to coincide with the peak production of the desired target end-product (biomass, chlorophyll, starch or lipid).
After 29 days without water exchanges, 55% of the total nitrogen (N) inputs were retained as shrimp biomass in 1 m3 cultures of juvenile Litopenaeus vannamei with artificial substrates (Aquamats®), in comparison to 37.2 to 44.8% without Aquamats. The N discharged with the effluent was 1.8-2.3% of the inputs, and the sediments contained 35.9-37.3% of the N inputs without Aquamats and 14.7 to 13.6% with Aquamats. In these, close to 16% of the N inputs were in the periphyton, indicating that additional substrates are an attractive alternative for nutrient recycling in shrimp farms operating as closed systems.
Total suspended solids (TSS) are the major factors that reduce water quality in a recirculating aquaculture system (RAS). In the present study, electrocoagulation (EC) was used for the first time to increase the particle size of TSS in RAS and improve the filtration efficiency of the microscreen drum filter (MDF) without reducing the filtration pore size. When the aquaculture water was treated using an electrocoagulation diameter increasing reactor (EDIR) for 2 min, with current density at 50 A/m² and influent flow at 300 L/h, the D50 of TSS increased by 86.43%. An electrocoagulation diameter increasing reactor and microscreen drum filter (EDIR-MDF) linkage control system was constructed, and its application in the RAS of Litopenaeus vannamei was investigated. The working principle of the EDIR-MDF linkage control system is that the output current of EDIR (IEDIR) was feedback controlled by the backwashing interval period of MDF (TMDF). Results showed that the EDIR-MDF linkage control system increased the average removal efficiency of RAS for TSS, chemical oxygen demand (COD), ammonia, and nitrite by 24.07%, 24.30%, 8.94%, and 1.39%, respectively, and resulted in average energy consumption and anode loss of EDIR of 2.38 kWh/d (1.68 RMB/d) and 370 g/d (2.22 RMB/d).
Microalgal bioremediation of recirculating aquaculture system (RAS) wastewater represents an alternative for wastewater treatment with the potential to generate valuable biomass. This study evaluated the effects of removing biological contamination and suspended solids from Nordic area RAS wastewater through filtration with 0.45 μm filters on the performance and nutritional value of microalgae. All three tested green microalgae (Haematococcus pluvialis, Monoraphidium griffithii, and Selenastrum sp.) were able to grow in raw (unfiltered) and filtered RAS wastewater. Cultivation in raw RAS wastewater decreased the ω-3 and ω-6 fatty acid content of H. pluvialis as compared to filtered wastewater, while no differences in cell density, nutrient removal, or fatty acid and amino acid contribution were seen for any microalgae between the treatments. Filtration of wastewater significantly reduced the content of actinobacterial fatty acid biomarkers in microalgal cultures compared to raw wastewater. The difference in actinobacterial fatty acid content between raw and filtered wastewater was species-specific. Our results suggest that with careful selection of microalgal species, RAS wastewater can be used for the production of high-quality microalgal biomass for further applications, such as aquaculture feeds, with no need to remove indigenous biological contaminants and suspended solids.
Organic matter is a widely occurring pollutant in freshwater sources due to the extensive use of synthetic organic compounds in industry and the natural occurrence of organic matter in the Earth’s crust. Organic matter causes adverse effects on the performance of water treatment plants, such as accelerated bacterial growth and increased consumption of chemical coagulants. Organic matter also has the ability to chelate some heavy metals forming refractory complexes that resist coagulation. The current research combines electromagnetic radiation (microwave) and electrocoagulation technologies to purify water from OM-heavy metal complexes created using iron and ethylenediaminetetraacetic acid (EDTA). The organic matter-iron solution was introduced to a microwave field to break down the complex, followed by electrolysis of the solution using an aluminum-base EC cell. Microwave power (50.0-300.0 W), temperature (50.0-150.0 oC) and irradiation period (5.0-15.0 minutes) were measured. During the electrolysing stage, initial pH (4.0-8.0), current density (1.0-2.0 mA.cm-2) and space between electrodes (5.0-20.0 mm), were examined. The results showed that the electromagnetic radiation-electrocoagulation technology removed up to 92 % of the organic matter-iron complex in comparison to 69.6 % removal using a traditional electrocoagulation method. The best operational conditions were established as follows: 10 minutes of microwave irradiation at 100Wat a temperature of 100 oC, followed by 20.0 minutes of electrolysing at an initial pH of 6.0, the space between electrodes5.0 mm and current density of 1.50 mA.cm-2.
Litopenaeus vannamei or Pacific white shrimp is one of the main shrimp species cultivated around the world. Despite its easy handling, there is no detailed description of its metabolic performance. This work developed a novel mathematical model for L. vannamei growth based on mass conservation and chemical equations for feed oxidation, allowing to calculate shrimp specific growth rate, specific rate of feed consumption, specific rate of ammonia nitrogen excretion, and oxygen specific consumption rate. Results, when compared to literature data, indicate a correlation higher than 99%, demonstrating that the proposed approach can successfully predict the growth based on the assessed parameters. Through this strategy it is possible to optimize the management of shrimp cultivation, especially in relation to dissolved oxygen, availability of feed and ammonia excretion, according to each stage of shrimp growth. Based on the environmental conditions maintained during the present study, the result of the present mathematical model can be a potential tool for reducing costs and environmental impacts in aquaculture shrimp farm.
Coagulants are widely used for solids (uneaten food, faeces, etc.) management in recirculating aquaculture systems (RAS), but no recent research has been performed on the effectiveness of different coagulants in treatment of aquaculture sludge. This study examined the effectivity of selected inorganic (polyaluminium chloride, PAC) and organic products (polyamine- and starch-based) as coagulant agents for solids management in RAS. Reductions in residual concentrations of total phosphorus (tot-P), phosphate‑phosphorus (PO4-P), suspended solids (SS) total nitrogen (tot-N), nitrate‑nitrogen (NO3-N), ammonium‑nitrogen (NH4-N), aluminium (Al) and chemical oxygen demand (COD) in reject water were determined. The effect of process parameters (coagulant type, dose, mixing and sedimentation time) on sludge treatment was also evaluated. The PAC products tested were most effective at concentrating pollutants (Tot-P, PO4-P, SS, COD) in RAS sludge into the solid phase. The organic products tested, especially a high-molecular-weight polyamine product (pAmine1), achieved good performance and can be considered a valid alternative to inorganic salts. At optimum dose, PAC (dose 32 mg/L) and pAmine1 (dose 15 mg/L) removed, respectively, 99.4% and 82.8% of turbidity, 98.2% and 65.4% of PO4-P and 97.7% and 73.6% of SS. The mixing time applied in flocculation and the time allowed for sedimentation had significant effects on coagulant performance, with the organic coagulants being most affected. Flocculation times of 5–15 min and sedimentation times of 15–60 min showed good results and can be used as a starting point in process optimisation with both inorganic and organic coagulants. The use of coagulants for treatment of RAS sludge enhances flock formation and improves particle settling characteristics, substantially decreasing nutrient, organics and solids concentration in reject water.
In order to study the effects of carbon source addition on the bacterial community, water quality and shrimp growth in the recirculating aquaculture system of Litopenaeus vannamei, sucrose with 50% of the daily feed was added daily to the system from the middle stage of culture. The bacterial communities in biofilters, aquaculture waters and shrimp intestines were measured using an Illumina MiSeq platform. The addition of sucrose did not significantly improve the regulation of nitrogen in the water, although there was a tendency to increase shrimp production. The addition of sucrose also had little effect on the bacterial community of water and intestine, but had significant effects on the bacterial community in the biofilter. Carbon addition transformed the dominant bacterial taxa of the biofilter from the Proteobacteria dominated by Rhodobacteraceae to the Planctomycetes dominated by Planctomycetaceae. In this study, the characteristics of the bacterial community and the effects of carbon source addition in the recirculating aquaculture system of L. vannamei are presented, which provides a basis for microbial management in the recirculating aquaculture system of L. vannamei. In view of the unknown role of numerous bacterial groups, the function of the bacterial community needs further study.
In order to investigate the culture characteristics of two indoor intensive Litopenaeus vannamei farming modes, recirculating aquaculture system (RAS) and water exchange system (WES), this study was carried out to analyze the water quality and nitrogen budget including various forms of nitrogen, microorganism and chlorophyll-a. Nitrogen budget was calculated based on feed input, shrimp harvest, water quality and renewal rate, and collection of bottom mud. Input nitrogen retained in shrimp was 23.58% and 19.10% respectively for WES and RAS, and most of nitrogen waste retained in water and bottom mud. In addition, most of nitrogen in the water of WES was TAN (21.32%) and nitrite (15.30%), while in RAS was nitrate (25.97%), which means that more than 76% of ammonia and nitrite were removed. The effect of microalgae in RAS and WES was negligible. However, bacteria played a great role in the culture system considering the highest cultivable cultivable bacterial populations in RAS and WES were 1.03×1010 cfu mL−1 and 2.92×109 cfu mL−1, respectively. Meanwhile the proportion of bacteria in nitrogen budget was 29.61% and 24.61% in RAS and WES, respectively. RAS and WES could realize shrimp high stocking culture with water consuming rate of 1.25 m3 per kg shrimp and 3.89 m3 per kg shrimp, and power consuming rates of 3.60 kw h per kg shrimp and 2.51 kw h per kg shrimp, respectively. This study revealed the aquatic environment and nitrogen budget of intensive shrimp farming in detail, which provided the scientific basis for improving the industrial shrimp farming.
Recirculating aquaculture systems (RASs) are intensive aquaculture facilities models that depend on diverse water treatment equipment to maintain good water quality and produce safe and healthy high‐quality aquatic products. This article combines the main farming‐mode of water purification recirculating processes with recent cultivation‐mode scientific research and the current development of the recirculating aquaculture industry. Harmful substances are present in aquaculture wastewater due to large quantities of residual particulate matter such as residual feed, faeces and small suspended solid particles, as well as ammonia, nitrite, bacteria and carbon dioxide (CO2), in the water. These harmful substances seriously affect the quality of aquatic products, so water treatment equipment is needed to remove these substances, add oxygen (O2) to the water and adjust the temperature of the water to ensure a high‐quality environment for fish survival. This article reviews the equipment for physical filtration (e.g. solid–liquid separation equipment, microscreen drum filter and foam fractionator) that could remove suspended solids during the water treatment of RASs and the equipment for biological filtration (e.g. fluidized sand biofilter (FSB), moving‐bed biofilm reactor (MBBR) and rotating biological contactor (RBC)) that could remove ammonia nitrogen, nitrite and other hazardous substances from wastewater, as well as equipment for water disinfection and sterilization, O2 addition, CO2 removal and temperature control. Comprehensive analysis and discussion of water treatment efficiency are provided for reference to create efficient high‐end recirculation aquaculture models and increase the precision and intelligence degree of recirculating water treatment technologies in the future.
In order to explore physicochemical and biological effects on detachment and activity recovery of aging biofilm by enzyme and surfactant treatments, two kinds of biofilm processes, i.e. biological aeration filter (BAF) and moving bed biofilm reactor (MBBR), and multiple indicators including water quality, biofilm morphology, activity and microbial community structure, were employed. Results showed that detachment of aging biofilm was mainly attributed by extracellular polymeric substance (EPS) solubilization and dispersion, and activity recovery of aging biofilm mainly depended on biological effects of dominant bacteria. Phosphorus metabolism related bacteria, such as Microbacterium and Micropruina, were responsible for BAF biofilm regeneration. More abundant microbial community structure of MBBR regenerated biofilm was found, and biofilm activity was not only related to phosphorus metabolism related bacteria, but also to denitrifying bacteria. Rhamnolipid performed best on aging biofilm detachment and regeneration, giving a clue for effective activation of aging biofilm in wastewater treatment systems.
Resource use was investigated at 34 Litopenaeus vannamei and five Penaeus monodon farms in Thailand and 30 L. vannamei and 24 P. monodon farms in Vietnam. Farms varied in water surface areas for production, reservoirs, canals, and settling basins; in pond size and depth; and in water management, stocking density, feeding rate, amendment input, aeration rate, crop duration, and crops per year. Production of L. vannamei averaged 17.3 and 10.9 m.t./ha/yr, and feed conversion ratio averaged 1.49 and 1.33 in Thailand and Vietnam, respectively. On average, production of 1 m.t. of L. vannamei required 0.58 ha land, 5,400 m³ water, 60 GJ energy, and 1218 kg wildfish in Thailand and 1.76 ha land, 15,100 m³ water, 33.7 GJ energy, and 1264 kg wildfish in Vietnam. Resource use per metric ton of shrimp declined with greater production intensity. In Thailand, P. monodon was produced at 0.2–0.4 m.t./ha/yr, with no inputs but water and postlarvae. In Vietnam, P. monodon production averaged 3.60 m.t./ha/yr. Production of 1 m.t. of P. monodon required 0.80 ha land, 36,000 m³ water, 47.8 GJ energy, and 1180 kg wildfish, and resource use per ton production declined with increasing production intensity. © 2016 The Authors. Journal of the World Aquaculture Society published by Wiley Periodicals, Inc. on behalf of the World Aquaculture Society.
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.
This study examined the operation of an intensive tropical shrimp farm in relation to the nitrogen (N) budget and the N components of the discharged effluent. Weekly samples were taken for total N (TN) concentration from the farm intake and discharge water over a 10-month period. A N budget was calculated based on TN data, continuous datalogger records of water exchange volumes, and farm records for feed addition, harvest and sediment removal. TN levels in the intake water were low throughout the 10 months and only contributed 5% of the N input to the farm. Most of the N (90%) entered the farm ponds as formulated shrimp food. Within the ponds, 22% of the input N was converted to harvested shrimp, 14% remained in the sediment, while most of the remainder (57%) was discharged to the environment. Only 3% of input N was unaccounted for, and assumed to be lost to the atmosphere via denitrification or volatilization of ammonia. More intensive sampling of effluent (three times a day) was done over 7-day periods in February (late summer) and July–August (winter) to provide detailed information on the N composition. All parameters varied substantially both within and between days. Forty-two to forty-five percent of the discharged N was in particulate form, mostly phytoplankton. The dissolved N fraction had two main components: dissolved organic N (DON), which comprised 37–43% of TN, and total ammonia N (TAN), which comprised 12–21% of TN. Comparison between the results of this and previous studies suggests that little progress has been made in improving nitrogen utilization efficiency of intensive Penaeus monodon shrimp farming over the past decade. Thus a major challenge facing this industry is to improve both environmental and economic performance by developing and implementing an integrated approach to reducing nitrogen waste.
Study on the three-phase recirculating aquaculture model of Litopenaeus vannamei
- Du
- Y Du
- T Qiu
- L Zhou
- F Chen
- J Xu
- Y Li
- J Sun
Y. Du, T. Qiu, L. Zhou, F. Chen, J. Xu, Y. Li, J. Sun, Study on the three-phase
recirculating aquaculture model of Litopenaeus vannamei, Fishery Modernization
48 (3) (2021) 9 (In Chinese).