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1.
As environmental regulations become more stringent, environmentally sound waste management and disposal are becoming increasingly more important in all aquaculture operations. One of the primary water quality parameters of concern is the suspended solids concentration in the discharged effluent. For example, EPA initially considered the establishment of numerical limitations for only one single pollutant: total suspended solids (TSS). For recirculation systems, the proposed TSS limitations would have applied to solids polishing or secondary solids removal technology. The new rules and regulations from EPA (August 23, 2004) require only qualitative TSS limits, in the form of solids control best management practices (BMP), allowing individual regional and site specific conditions to be addressed by existing state or regional programs through NPDES permits. In recirculation systems, microscreen filters are commonly used to remove the suspended solids from the process water. Further concentration of suspended solids from the backwash water of the microscreen filter could significantly reduce quantity of discharge water. And in some cases, the backwash water from microscreen filters needs to be further concentrated to minimize storage volume during over wintering for land disposal or other final disposal options. In addition, this may be required to meet local, state, and regional discharge water quality. The objective of this research was an initial screening of several commercially available polymers routinely used as coagulation–flocculation aids in the drinking and wastewater treatment industry and determination of their effectiveness for the treatment of aquaculture wastewater. Based on the results of the initial screening, a further evaluation of six polymers was conducted to estimate the optimum polymer dosage for flocculation of aquaculture microscreen effluent and overall solids removal efficiency. Results of these evaluations show TSS removal was close to 99% via settling, with final TSS values ranging from as low as 10–17 mg/L. Although not intended to be used for reactive phosphorus (RP) removal, RP was reduced by 92–95% by removing most of the TSS in the wastewater to approximately 1 mg/L–P. Dosage requirements were fairly uniform, requiring between 15 and 20 mg/L of polymer. Using these dosages, estimated costs range from $4.38 to $13.08 per metric tonne of feed.  相似文献   

2.
《Aquacultural Engineering》2006,34(4):235-249
As environmental regulations become more stringent, environmentally sound waste management and disposal are becoming increasingly more important in all aquaculture operations. One of the primary water quality parameters of concern is the suspended solids concentration in the discharged effluent. For example, EPA initially considered the establishment of numerical limitations for only one single pollutant: total suspended solids (TSS). For recirculation systems, the proposed TSS limitations would have applied to solids polishing or secondary solids removal technology. The new rules and regulations from EPA (August 23, 2004) require only qualitative TSS limits, in the form of solids control best management practices (BMP), allowing individual regional and site specific conditions to be addressed by existing state or regional programs through NPDES permits. In recirculation systems, microscreen filters are commonly used to remove the suspended solids from the process water. Further concentration of suspended solids from the backwash water of the microscreen filter could significantly reduce quantity of discharge water. And in some cases, the backwash water from microscreen filters needs to be further concentrated to minimize storage volume during over wintering for land disposal or other final disposal options. In addition, this may be required to meet local, state, and regional discharge water quality. The objective of this research was an initial screening of several commercially available polymers routinely used as coagulation–flocculation aids in the drinking and wastewater treatment industry and determination of their effectiveness for the treatment of aquaculture wastewater. Based on the results of the initial screening, a further evaluation of six polymers was conducted to estimate the optimum polymer dosage for flocculation of aquaculture microscreen effluent and overall solids removal efficiency. Results of these evaluations show TSS removal was close to 99% via settling, with final TSS values ranging from as low as 10–17 mg/L. Although not intended to be used for reactive phosphorus (RP) removal, RP was reduced by 92–95% by removing most of the TSS in the wastewater to approximately 1 mg/L–P. Dosage requirements were fairly uniform, requiring between 15 and 20 mg/L of polymer. Using these dosages, estimated costs range from $4.38 to $13.08 per metric tonne of feed.  相似文献   

3.
Environmental pressure, land utilization, and economic feasibility have resulted in the development of recirculating aquaculture systems (RAS). For many RAS, sludge is collected and washed from the system to waste stabilization ponds (WSPs). However, disposal of brackishwater aquaculture sludge into WSP is often prohibited because the high salinity can interfere with treatment. Moreover, there are problems associated with WSPs because of elevated salt content, such as the common practice of reusing treated water and land application of stabilized sludge. We tested and compared the treatment of brackishwater aquaculture sludge in an upflow anaerobic sludge blanket (UASB) reactor as an alternative to a WSP. In UASB, wastewater flows upward through a blanket of granular sludge and is treated by anaerobic micro‐organisms. Reduction in organic matter and 5‐d biochemical oxygen demand by 97 and 91%, respectively, was achieved in a UASB as compared to corresponding reductions of 22 and 41% in a WSP. During the UASB digestion process, methane is produced and recovered. Overall, a reduction in potential environmentally harmful factors such as salinization, land requirements, greenhouse gas emissions, as well as transportation costs are achieved, making the UASB reactor an attractive possible alternative for saline aquaculture sludge management.  相似文献   

4.
Hydroponic plants can efficiently absorb and uptake soluble compounds in wastewater but they have low abilities to remove suspended solids due to the lack of culture media to trap solids. This paper presented an improved hydroponic method for effective treatment of the wastewater from the backwash of recirculating aquacultural systems. The ryegrass (Lolium perenne Lam) was cultured with improved media consisting of perforated plastic plates and several layers of unwoven cotton fabric. The plate/fabric/grass cells with one, three, five, and seven layers of fabric were studied. After one vertical filtration pass through the cells, the removals were 48, 59, 60 and 63% for total solids (TS), 48, 58, 63 and 69% for volatile solids (VS), and 4, 7, 14 and 25% for suspended solids (SS), respectively, for different cells with one, three, five, and seven layers of fabric. It was found that increasing the number of vertical filtration passes through the cells improved the solids removal. The 1-day treatment in the recycling irrigation and treatment system with five cells ( = 0.8 m2 grass) removed 66% TS, 71% VS, and 91% SS, and absorbed 72% total nitrogen (TN), 80% total phosphorus (TP), 63% chemical oxygen demand (COD), and 85% total ammonia nitrogen (TAN). This hydroponic plate/fabric/grass system is a simple and efficient technology for the effective eco-treatment of aquacultural wastewater with relatively high concentrations of suspended solids.  相似文献   

5.
As the application of intensive aquaculture systems continues to grow worldwide, so does the need for environmentally sound waste management and waste disposal techniques. The use of coagulants and flocculants to assist in removing suspended solids has long been a standard in the waste treatment field. Recently, The Conservation Funds Freshwater Institute has continued its research into coagulation/flocculation aids by examining the performance of alum coupled with various commercially available polymers. Alum is efficient in sequestering phosphorus through chemical precipitation and coagulation of fine solids through charge neutralization. Synthetic polymers are efficient in flocculating small particles together but do not efficiently remove dissolved phosphorus. The specific intention of this work was to use the qualities that distinguish both the alum and the polymer individually and combine the two to optimize wastewater treatment for the removal of both suspended solids and phosphorus. The alum/polymer combinations were first screened to determine which polymers worked best with our waste and with the alum. Once the screening was completed, the six best performing combinations were further evaluated with triplicate tests in a jar test apparatus to determine a standard optimal dosage based on phosphorus and suspended solids removal. Using a combination of alum/polymer, the effluent total suspended solids (TSS) removal rate was close to 99%, with final TSS values ranging from 4 to 20 mg/L. Reactive phosphorus was reduced by 92 to 99% to as low as 0.16 mg/L‐P. Finally, total phosphorus was also significantly reduced (98%), with treated effluent concentrations from 0.9 to 3.0 mg/L‐P. Although not intended for nitrogen removal, total ammonia‐nitrogen (TAN), nitrite‐nitrogen, nitrate‐nitrogen, and total nitrogen in the effluent were reduced on average by 64, 50, 68, and 87%, respectively. Removal rates for both 5 d carbonaceous biochemical oxygen demand (CBOD5) and chemical oxygen demand (COD) were also significant, with an average value of 97.3 and 96.4%.  相似文献   

6.
Effluents from aquaculture facilities vary between species and among production systems. Drainage ditches commonly convey effluents from central Arkansas baitfish ponds. Ditches could potentially reduce suspended solids prior to effluent release into receiving streams through settling. We characterized suspended solids in effluents from baitfish ponds and evaluated changes in suspended solids in drainage ditches. We also characterized drainage ditches based on width, depth, slope, and percent vegetation cover. Average (± SD) total suspended solids (TSS) at the point of discharge was 52 (± 41) mg/L, while volatile suspended solids (VSS) averaged 22 (± 23) mg/L. Screening effluents did little to alter their composition. Approximately 76% of TSS were less than 5 μm. There were no significant changes in effluent solids along drainage ditches 100 m from the point of discharge and no significant correlations between ditch characteristics and changes in either TSS or VSS. Existing ditches are quite variable and are not necessarily effective in removing solids present in baitfish effluents. Screening and use of ditches as settling basins seem impractical for effluent treatment given the characteristics of solids in baitfish effluents.  相似文献   

7.
Design information for the use of sand beds to remove suspended solids from wastewater discharged from recirculating aquaculture systems (RAS) was developed. Wastewater from a commercial RAS tilapia farm with 2% total solids and 1.6% total suspended solids (TSS) was applied to sand columns to determine infiltration rates and phosphorus capture. Various hydraulic loading rates and drying periods between application events were evaluated. Infiltration rates stabilized after five application events to 3.5 cm/day (S.D.=1.7). Practically, all suspended solids were captured at the top of the columns, creating the primary resistance to infiltration. Concrete sand removed approximately 93% of the soluble phosphorous in the wastewater and wollastonite, an economical aggregate alternative to sand, removed at least 98%. A modified Darcy equation is presented to predict infiltration based upon TSS and the number of sequential applications.  相似文献   

8.
《Aquacultural Engineering》2008,38(3):266-273
Hydroponic plants can efficiently absorb and uptake soluble compounds in wastewater but they have low abilities to remove suspended solids due to the lack of culture media to trap solids. This paper presented an improved hydroponic method for effective treatment of the wastewater from the backwash of recirculating aquacultural systems. The ryegrass (Lolium perenne Lam) was cultured with improved media consisting of perforated plastic plates and several layers of unwoven cotton fabric. The plate/fabric/grass cells with one, three, five, and seven layers of fabric were studied. After one vertical filtration pass through the cells, the removals were 48, 59, 60 and 63% for total solids (TS), 48, 58, 63 and 69% for volatile solids (VS), and 4, 7, 14 and 25% for suspended solids (SS), respectively, for different cells with one, three, five, and seven layers of fabric. It was found that increasing the number of vertical filtration passes through the cells improved the solids removal. The 1-day treatment in the recycling irrigation and treatment system with five cells ( = 0.8 m2 grass) removed 66% TS, 71% VS, and 91% SS, and absorbed 72% total nitrogen (TN), 80% total phosphorus (TP), 63% chemical oxygen demand (COD), and 85% total ammonia nitrogen (TAN). This hydroponic plate/fabric/grass system is a simple and efficient technology for the effective eco-treatment of aquacultural wastewater with relatively high concentrations of suspended solids.  相似文献   

9.
循环水养殖系统中的固体悬浮物去除技术   总被引：3，自引：2，他引：3  
循环水养殖系统(Recirculating aquaculture systems,RAS)中固体悬浮物(Suspended solids,SS)的去除效果直接影响到鱼类生长、生物净化效果、系统配置和运行成本等诸多重要因子。根据固体悬浮物产生、物理特性和分布规律,结合颗粒悬浮物去除工艺特点,对去除技术进行系统研究分析。固体悬浮物源自饲料,密度一般为1.05~1.19 g/cm3,运用重力分离、过滤和泡沫分离等工艺通过预处理、粗过滤和精处理三道工艺步骤,可分别去除不同直径的颗粒物质,在达到合理含量的前提下,获得低能耗、低成本和系统稳定运行的综合效果。固体悬浮物的去除符合目标明确、排出及时和区别对待三原则,去除工艺注重相关技术的优化集成。  相似文献   

10.
Land-based Atlantic salmon, Salmo salar, grow-out facilities utilize depuration to remediate off-flavor. Water used in this process is either discharged or repurposed as supply water in recirculating aquaculture systems (RAS). Both approaches require an understanding of water quality and waste production for water treatment decisions and compliance with pollution discharge standards; however, these data were lacking. Therefore, a study was carried out to characterize these parameters. To begin, 311 salmon (5–6 kg) originally cultured in freshwater RAS were stocked at 100 kg/m3 in an 18 m3 depuration tank. Feed was withheld 1 day before transfer and throughout the 7-day study period. Hours after stocking, total suspended solids (TSS), total phosphorus (TP), and total ammonia nitrogen (TAN) levels spiked, and concentrations declined thereafter. Delta TSS and TP were negligible by the end of the trial; however, TAN plateaued, indicating that salmon began to catabolize somatic tissue in the absence of feeding. Geosmin and 2-methylisoboreol levels in water and fish were low throughout the study. This research indicates that residual waste production occurs while depurating Atlantic salmon. Procedural refinements and recommendations were gleaned including locality for introducing depuration system water within RAS and extension of the feed withholding period before depuration.  相似文献   

11.
Saline effluents from marine land-based aquaculture production can neither be disposed in common municipal wastewater treatment plants, nor disposed as landfill. Furthermore, stricter environmental regulations require the reduction of phosphorous and organic matter levels from marine environment discharges to minimize eutrophication. Chemical coagulation with FeCl3 and AlSO4 is commonly used for removing phosphorous and suspended solids in wastewater treatment. The capacity of these coagulants for creating particle aggregations depends on the characteristics and chemistry of the treated wastewater, such as the ionic strength or mixing conditions. Marine water has a higher ionic strength than fresh or brackish water, which may be beneficial when using chemical coagulants to treat the effluents from farms operated at high salinities. The following study compared the application of FeCl3 and AlSO4, to treat the two effluents discharged from a marine land-based recirculating aquaculture system (RAS) producing salmon (Salmo salar). The aim of the study was to determine; 1) in what effluent (sludge flow vs. exchange water overflow) at the end-of-pipe treatment the coagulant application is more efficient for the removal of PO43−-P, total suspended solids (TSS), total phosphorous (TP) and total chemical oxygen demand (TCOD); and 2) the optimal coagulant dose to apply and its associated chemical sludge production. The results show that more than 89 % removal of TCOD, TSS and TP is achieved when treating the sludge flow, arguably because the sludge flow contained the largest fraction of the target masses (P and organic matter) discharged from the system. Up to 80 % of TSS removal was achieved by simple sedimentation, and with the highest coagulant dose tested, up to 95 % of TSS could be removed from the effluent. To remove 90 % of PO43−-P, FeCl3 and AlSO4 need to be dosed at a molar ratio of 2.6:1 Fe:PO43−-P and 5.7:1 Al: PO43−-P, respectively. Dosing above 90 % removal efficiency did not significantly affect removal of PO43-P and TSS, but substantially increased the volume of chemical sludge produced. Finally, FeCl3 is proposed as a better overall alternative for P removal at the end-of-pipe treatment in marine land-based RAS.  相似文献   

12.
Treatment of sludge from aquaculture is a matter of special importance and there is a need for salt-tolerant biological wastewater treatment to coincide with the development of brackish/marine aquaculture. The aims of the current study were to determine the ability of anaerobic sequencing batch reactor (ASBR) to anaerobically digest sludge from fresh-water recirculating aquaculture systems and the ability of adaptation to low saline conditions. The mesophilic ASBR were evaluated with loading rates between 0.12 and 0.41 g chemical oxygen demand (COD)/day at a 20-day hydraulic retention time (HRT) for start-up and with organic loading rates (OLR) of 0.39–0.41 g COD/L day at a 20-day HRT for saline adaptation. The average removal rate of total chemical oxygen demand (TCOD), total suspended solids (TSS) and volatile suspended solids (VSS) of the ASBR were above 97%, 96% and 91% during the stabilization period of the experimental reactors. The average daily gas production of ASBR was between 0.013 and 0.022 L/g TCOD from day 118. A sludge-mass reduction of up to 94 ± 2.3%, TCOD reduction of 44 ± 13% and VSS/SS of 39–70% were demonstrated for the reactor performance during the gas production period. However, the process of gas production was obviously inhibited, presumably by salt, and unstable due to the dissolved COD (DCOD), total ammonium nitrogen (TAN) and alkalinity of the effluents of the experimental reactors and TSS and sludge volume index (SVI) observed within the reactors. The daily gas production was observed to decrease during the saline adaptation period and stopped when the salinity of the effluents was higher than 8.7 ppt until the end of the experiment.  相似文献   

13.
Higher-energy fish feeds can reduce waste discharges and might also improve water quality in recirculating fish-culture systems. A higher-energy diet, Zeigler Salmon High Energy feed (HE; 45% protein, 20% fat, 17.4 MJ digestible energy kg-1) and a lower-energy diet, Zeigler Hi-Fat Trout Grower (LE; 38% protein, 12% fat, 14.6 MJ digestible energy kg -1) were fed ad libitum at different times to rainbow trout, Oncorhynchus mykiss (Walbaum), in a semi-closed recirculating culture system by means of demand feeders. The system contained two 10-m3 fish-culture tanks, each with a downstream microscreen (80 μn) filter. Feeding rates per day and per unit biomass were not significantly different between diets. In general, use of HE was associated with higher levels of total ammonia nitrogen (TAN) and NO2-N, lower BOD5 and total suspended solids (TSS), and lower effluent releases of suspended solids per unit feed, NO3-N per unit feed, and dissolved phosphorus per unit feed. Although total effluent P per unit feed or P fed did not differ significantly between diets, HE had significantly more of the total effluent P in the settleable solids, 85% vs. 76%. Differences in water quality in the system were probably not of great importance with respect to fish health.  相似文献   

14.
Intensive, recirculating aquaculture systems create concentrated wastes high in solid content. Geotextile has successfully dewatered aquaculture effluent; however, burlap, made from natural plant fiber, may provide similar filtering capabilities at a lower cost. The trial was designed as a 2 × 2 factorial to evaluate burlap bags and geotextile bags with or without polymer addition for dewatering Nile tilapia, Oreochromis niloticus, effluent from an intensive biofloc production system. There were no significant interactions (P > 0.05) between the main effects on the removal efficiency of total suspended solids (TSS) concentration. There were no significant differences (P > 0.05) in the main effect of textile; however, there were significant differences (P≤ 0.001) in the main effect of polymer on the removal efficiency of TSS concentration from effluent. Overall, TSS removal efficiency in textile‐only treatments was 81%, whereas textile treatments in combination with polymer removed 98%. Partial budget analysis indicated that the cost per kilogram of solids (dry weight) removed from untreated effluent was US$1.52, 1.51, 0.16, and 0.14 for the geotextile with polymer (GP), geotextile without polymer (GNP), burlap with polymer (BP), and burlap without polymer (BNP) treatments, respectively. The BP could provide an effective treatment process for removing TSS in discharged effluent.  相似文献   

15.
Intensive recirculating aquaculture systems (RAS) produce high volumes of biosolid waste. The high salinity of brackish/marine sludge limits its use in landfill sites and waste outflows and it is a source of pollution. A reduction in sludge mass would therefore minimize the potential environmental hazard and economic burden stemming from its disposal. The aims of the current study were: 1) to characterize brackish aquaculture sludge (BAS) from three RAS in order to test for potentially suitable treatments, and 2) to test the BAS's suitability for anaerobic digestion in an upflow anaerobic sludge blanket reactor (UASB). Brackish sludge from three intensive RAS was collected periodically and analyzed for a variety of physical and chemical parameters. The mean sludge electrical conductivity and pH values ranged from 4.0 to 8.6 mS cm− 1 and 7.0 to 7.7, respectively. A low sludge redox potential averaging − 80 mV and dissolved oxygen concentrations of less than 1 mg l− 1 indicated the existence of anaerobic conditions. Volatile solids comprised 56 to 76% of the dry weight and the sludge volume index ranged from 44 to 69 ml g − 1. High concentrations of total nitrogen and total carbon were also observed, resulting in a C:N ratio ranging between 8.1 and 10.3. Toxic and/or inhibitory compounds for methanogenesis such as nitrites, nitrates and sulfides were almost absent. Sludge BOD5 ranged from 10 to 30% dry weight. These data suggest that BAS may be used in anaerobic digestion and methanogenesis without pretreatment. This concept was tested by digesting aquaculture sludge in UASB reactors. Despite the high sulfate and phosphate concentrations in the BAS, these were found not to be inhibitory to methanogenesis. Up to 70% sludge-mass reduction and an average of 40% methane production were demonstrated.  相似文献   

16.
High stocking density aquaculture can result in major environmental impacts such as waste disposal with high organic matter. In order to overcome this issue, biofloc technology (BFT) has arisen as an alternative to lower effluent nutrient loading by promoting dense microbial communities that control water quality through the assimilation of inorganic nutrients. Given the central role of microorganisms in nutrients storage, the aim of this study was to evaluate the elemental composition of bioflocs and free‐living microorganisms and to determine which environmental factors are associated with the variation in their stoichiometric ratios (C:N:P) in shrimp farming systems. Samples were taken in marine shrimp farms, and the stoichiometric ratios from bioflocs and free‐living microorganisms were analysed, as well as physical and chemical water quality variables. The C:N ratios were lower, and N:P ratios were higher in the free‐living microorganisms than bioflocs. The C:P and N:P ratios of the biofloc were lower at higher temperature and total suspended solids (TSS). We concluded that the elemental composition of the bioflocs is richer in C and P and that systems with higher temperature and higher TSS have a greater ability to absorb and immobilize these elements in the bioflocs.  相似文献   

17.
Two separate geotextile bag systems were evaluated as a means for capturing and dewatering bio-solids in the effluent stream from recirculating aquaculture systems (RAS). Each geotextile bag system used a high molecular weight cationic polyacrylamide (PAM) polymer as a flocculant-aid. The two systems were operated under freshwater and brackish water conditions. A complete analysis including water quality and agronomic sludge analysis was conducted at the North Carolina State University Fish Barn – a large-scale, freshwater RAS demonstration and growout facility. An evaluation of water quality and performance of a similar geotextile bag system was also conducted at the Marine Aquaculture Research Center near Marshallberg, North Carolina, USA, under brackish conditions (15 PPT). Results indicated that performance of each of the systems was similar with TSS, COD, TN, and TP removal greater than 95%, 65%, 50%, and 38%, respectively, for both systems. Analysis of the sludge collected in the freshwater system after 70 days in a dewatering, inactive mode, showed a moisture content (MC) of 86%, or 14% dry matter (DM), indicating the system was effective at passively dewatering the bio-solids. Nutrient removal efficiency may be system specific based on the geotextile bag size and influent flow rate.Geotextile bag systems using flocculant-aids are an efficient means for capturing and dewatering waste solids from RAS effluents. Optimized geotextile bag system designs depend on flow rate, feed rate, and solids dewatering time, and fate of the treated effluent. This evaluation will aid in predicting the expected performance and determining the appropriate size of a geotextile bag system. The type of treatment required downstream from the geotextile bag system used for solids capture in a RAS wastewater treatment system will depend on the intended fate of the treated effluent.  相似文献   

18.
Studies were conducted to characterize raceway water quality, effluent water quality, and waste solids within three, raceway-type trout farms. No significant differences were found in effluent water quality between the three farms during 7 months of monitoring. Average effluent quality over the course of the day was not found to be impaired. However, effluent quality was found to change significantly during times of feeding and harvesting. In a concrete/earthen-lined farm, normalized total suspended solids (TSS) concentrations were as high as 115 and 63 mg/l during harvesting and feeding events, respectively. Total Kjeldahl nitrogen (TKN) and ortho-phosphate (OP) also increased with higher TSS loads. The majority of particles (by weight) measured in effluent samples at all three farms were evenly divided between the smallest range (1.5–30 μm) and the largest (>210 μm). For settled sludge samples, the majority of the particles were in the size range of 1.5–30 μm. Particle size in the raceway was positively correlated with fish size during feeding events, but this correlation dissipated during the 4-h period after feeding. The accumulation and characteristics of sludge in a sediment trap were also monitored over a 22-day period.  相似文献   

19.
The present case study, deals with a recently built aquaculture facility using 80–120 L s−1 spring water for trout production. The farm consists of six raceways, discharging in a common outflow channel, leading to a drum filter equipped with 80 μm gauze. About 120 L s−1 of the microscreen effluent is pumped back in the inflow channel of the six raceways. The remaining effluent is oxygenated with pure oxygen in gravity oxygenation units and led to two U-shaped raceways. The farm effluent is finally filtered by a drum filter with 63 μm mesh size. The microscreen backwash sludge is treated in a cone settler, where the sediments are extracted for agricultural manure application. The sedimentation supernatant is further led in a sub surface flow (SSF) constructed wetland prior to discharge.Due to the advanced effluent treatment within the farm, the total farm effect on the receiving effluent is kept to a minimum. The nutrient increase produced by the farm is only 0.03 mg L−1 total phosphorous (TP), 1.09 mg L−1 biological oxygen demand (BOD5) and, 0.57 mg L−1 total suspended solids (TSS) in the brook. Especially the incorporation of an intermediate microscreen prior to water recirculation, prevents leaching of dissolved nutrients from particulate matter, as large particles are effectively and as fast as possible removed from the water flow.At the pumping station, needed for water recirculation, the particle size distribution (PSD) was monitored with the previous microscreen in use and by-passed. When the screen was by-passed a significant crushing effect on PSD through pumping action was found. Through the removal of large particles, the crushing effect of the pumping station on the particles is prevented, as revealed by particle size distribution (PSD) measurement. Thus, leaching of dissolved nutrients is prevented twice.In consequence, the farm configuration can be recommended as an effective possibility for intensive trout production at sites with a small freshwater source and stringent effluent thresholds, even with the unexpected low treatment efficiencies measured for the microscreens. Both drum filters showed relative low treatment efficiencies of 33–53% for total suspended solids, respectively, while an efficiency of 70% should be expected from the measured PSD. With this impact, the farm still emitted a low nutrient amount, especially due to the highly effective offline microscreen backwash sludge treatment, where the SSF wetland efficiently reduced dissolved and particulate nutrients as nitrite (NO2-N), nitrate (NO3-N) and TSS. Thus this SSF wetland application might be suitable as a denitrification step in a closed recirculating trout farm.  相似文献   

20.
The objective of this study was to determine the solids separation efficiency of the four swirl separators and the drum filter within one of the water recirculation systems (RAS) of a salmon-smolt hatchery. Water flowrates and concentrations of total suspended solids (TSS) within the RAS were measured weekly over 5 weeks in 2004 and 4 weeks in 2005. During the study, the hydraulic retention time in the tanks was 2.8 h and the feed rate ranged between 0.16 and 0.84 kg/m3 of make-up water. The system volume replacement rate and the water flow recycle rate were respectively 21%/day and 96% in 2004, and 50%/day and 91% in 2005. A mathematical model was developed to determine the transient concentration of fine particles in the recirculation loop. By fitting the predictions of the model to the measured TSS concentrations, it was determined that about 15% of the waste generated within the RAS (assumed equal to 20% of daily feed rate) was removed by the system overflow water. Using this information and TSS data from the backwash water of the drum filter, it was calculated that the swirl separators and drum filter removed respectively 63% and 22% of the waste solids rejected by the fish.  相似文献   

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