Screening and evaluation of polymers as flocculation aids for the treatment of aquacultural effluents

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.     

Optimization of chitosan flocculation for phytoplankton removal in shrimp culture ponds

The removal of phytoplankton cells from aquaculture systems generally results in the reduction of nitrogenous waste and improves water quality. With this study, the effects of chitosan concentration, environmental condition and pH adjustment on flocculation of phytoplankton in marine shrimp (Litopenaeus vannamei) culture tanks were investigated. The remaining phytoplankton and suspended solids in the system were indicators for evaluating the efficiency of chitosan on flocculation. The results indicate that the flocculation efficiency of chitosan was highest (>85%) and remained fairly constant at a chitosan concentration of 40–80 mg L^?1 and a pH range of 7–9 after chitosan addition. With this novel technique including 40 mg L^?1 chitosan addition, pH adjustment to 6.5 and then to 8.5, high efficiency and consistency of flocculation were achieved. This technique could also be applied with various water alkalinity up to 400 mg CaCO₃ L^?1. The experiment for phytoplankton removal by chitosan flocculation in the recirculating aquaculture system showed that flocculation efficiency remained constant even though flocculation was repeated several times.     

Optimization of chitosan flocculation for phytoplankton removal in shrimp culture ponds

The removal of phytoplankton cells from aquaculture systems generally results in the reduction of nitrogenous waste and improves water quality. With this study, the effects of chitosan concentration, environmental condition and pH adjustment on flocculation of phytoplankton in marine shrimp (Litopenaeus vannamei) culture tanks were investigated. The remaining phytoplankton and suspended solids in the system were indicators for evaluating the efficiency of chitosan on flocculation. The results indicate that the flocculation efficiency of chitosan was highest (>85%) and remained fairly constant at a chitosan concentration of 40–80 mg L⁻¹ and a pH range of 7–9 after chitosan addition. With this novel technique including 40 mg L⁻¹ chitosan addition, pH adjustment to 6.5 and then to 8.5, high efficiency and consistency of flocculation were achieved. This technique could also be applied with various water alkalinity up to 400 mg CaCO₃ L⁻¹. The experiment for phytoplankton removal by chitosan flocculation in the recirculating aquaculture system showed that flocculation efficiency remained constant even though flocculation was repeated several times.     

The start-up and saline adaptation of mesophilic anaerobic sequencing batch reactor treating sludge from recirculating aquaculture systems

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.     

Evaluation of geotextile filtration applying coagulant and flocculant amendments for aquaculture biosolids dewatering and phosphorus removal

Wastes contained in the microscreen backwash discharged from intensive recirculating aquaculture systems were removed and dewatered in simple geotextile bag filters. Three chemical coagulation aids (aluminum sulfate (alum), ferric chloride, and calcium hydroxide (hydrated lime)), were tested in combination with a long-chain polymer flocculation aid (HyChem CE 1950 at 25 mg/L) to determine the most cost effective and efficient treatment combination. Three different coagulants were tested to determine if coagulant choice impacts nutrient and carbonaceous biochemical oxygen demand (cBOD₅) leaching into the filtrate and the final composition of the bag-captured biosolids at the end of each period. If nutrient leaching into the bag filtrate could be minimized through coagulant selection, then geotextile bags could provide a convenient and effective method to dewater waste biosolids and provide them in a form that fish farmers could readily transport, store, or send for disposal.Results from replicate geotextile bag filter tests indicate that when alum, ferric chloride, and hydrated lime (plus a polymer) were amended to a backwash flow, both suspended solids capture and solids thickening were improved; i.e., total suspended solids removal rates of 95.8, 95.1, and 96.0%, respectively, were achieved along with final dewatered filter cake percent solids concentrations of 22.1, 19.3, and 20.9%, respectively. Alum, ferric chloride, and hydrated lime (plus a polymer) amended geotextile bags were not as effective in chemical oxygen demand (COD) and cBOD₅ removal, resulting in removal rates of 69.6, 67.2, and 35.3%, respectively, and 56.6, 9.3, and ?47.4%, respectively. Further, the use of lime as a coagulant resulted in filtrate COD and cBOD₅ concentrations that exceeded inlet concentrations. Total nitrogen removal applying alum, ferric chloride, and lime were also less than effective, resulting in removal rates of 39.1, 46.7, and ?8.9%, respectively. Filtrate total nitrogen concentrations were primarily in the inorganic form (total ammonia nitrogen) suggesting mineralization of ammonia as solids were stored within geotextile bags under anaerobic conditions. Alum, ferric chloride, and lime amended bags were moderately efficient at total phosphorus removal, resulting in removal rates of 67.6, 47.0, and 77.3%, respectively. Alum was identified as the most cost effective chemical for coagulation, but hydrated lime was the most effective at dissolved phosphorus precipitation and removal.     

Hydroponic plate/fabric/grass system for treatment of aquacultural wastewater

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.     

Use of vegetated drainage ditches and low-grade weirs for aquaculture effluent mitigation: II. Suspended sediment

Total suspended solids are a priority pollutant under the Clean Water Act and a point of concern for aquaculture facilities. The use of ubiquitous vegetated ditches on the aquaculture landscape may serve as an environmentally and economically sustainable practice for reducing suspended sediment contributions to downstream environments. This study assessed effects of consecutive low-grade weirs on suspended solids retention and settling rates of aquaculture pond effluent in a single drainage ditch. Two control and nine treatment discharges were conducted in September and October 2012 at the Mississippi State University South Farm Aquaculture Facility. All discharges decreased total and volatile suspended solid loads. Total suspended solids were decreased 72–94%, with a significant removal rate of 0.02 ± 0.01 mg L⁻¹ min⁻¹ in both control (F = 6.12, P < 0.001) and treatment discharges (F = 16.02, P < 0.001). Volatile suspended solids comprised 2–80% of total suspended solids and had a significant removal rate of 0.02 ± 0.001 mg L⁻¹ min⁻¹ in both control (F = 10.46, P < 0.001) and treatment discharges (F = 6.28, P < 0.001). There was no significant difference in overall settling rates between control and treatment discharges; however, prior to weir 1, both total and volatile suspended solid concentrations increased in control discharges. Treatment discharges decreased both total and volatile suspended solids significantly (P < 0.001) prior to weir 1. Further analysis revealed flow rate to be a significant (P < 0.001) variable in total suspended solid removal while initial concentrations affected reduction rates of volatile suspended solids significantly (P < 0.001). These results suggest that the use of low-grade weirs could be a viable best management practice that easily integrates within the aquaculture landscape and creates hydraulic conditions conducive to sediment retention.     

Waste and particle management in a commercial, partially recirculating trout farm

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.     

Efficiency of producing bioflocs with aquaculture waste by using poly-β-hydroxybutyric acid as a carbon source in suspended growth bioreactors

With additional organic carbon, fish waste can be used as a substrate to produce bioflocs, a protein source for aquaculture animals. In choosing a carbon source, one should consider convenience, cost and biodegradability. This study investigates the efficiency of poly-β-hydroxybutyric acid (PHB), a biologically degradable polymer, as a carbon source to produce bioflocs in suspended growth bioreactors (SGRs), PHB-SGRs, compared with glucose (GLU-SGRs). The C:N ratio in PHB-SGRs could be maintained around 15:1. The volatile suspended solids (VSS) yield was 2.94 ± 0.72 gVSS/g fish waste for PHB-SGRS and 4.90 ± 0.23 gVSS/g fish waste for GLU-SGRs. The recycling rate of nitrogen in aquaculture solid waste was 56 ± 2% and 87 ± 7% for the PHB-SGRs and Glu-SGRs. No significant differences were found in the bioflocs produced and in the crude protein content of the produced bioflocs between PHB-SGRs and GLU-SGRs. PHB-SGRs and GLU-SGRs could remove dissolved inorganic nitrogen from aquaculture wastewater, with average values of 11.82 ± 8.95 and 16.27 ± 3.95 mg/g TSS/d. Because the calculation of the added amount of carbon and the multiple additions of carbon was avoided, PHB is considered to be a good choice as an organic carbon source for this process, even though not all parameters used for assessment were better than those of GLU-SGRs.     

Water quality and sludge characterization at raceway-system trout farms

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.     

Microscreen effects on water quality in replicated recirculating aquaculture systems

This study investigated the effects of three microscreen mesh sizes (100, 60 and 20 μm) on water quality and rainbow trout (Oncorhynchus mykiss) performance compared to a control group without microscreens, in triplicated recirculating aquaculture systems (RAS). Operational conditions were kept constant during a 6-week period where the microscreens were manually rinsed three times a day. The effects of microscreen cleaning frequency and nitrification performance were subsequently assessed.Compared to the control group, microscreens removed particles, reduced particulate organic matter, and increased β-values. Particulate parameters reached steady-state in all treatment groups having microscreens at the end of the trial. The time to reach equilibrium seemingly increased with increasing mesh size but the three treatment groups (100, 60 and 20 μm) did not significantly differ at the end of the trial. Increased backwashing frequency over a 24-h period had no further significant effects on the parameters measured. The results demonstrated the role and importance of a microscreen, and showed that mesh size, within the range tested, is less important at long operations under constant conditions.Fish performed similarly in all treatments. Preliminary screening of trout gills did not reveal any pathological changes related to microscreen filtration and the resulting water quality. Biofilter performance was also unaffected, with 0′-order nitrification rates (k_0a) being equivalent for all twelve systems (0.148 ± 0.022 g N m⁻² d⁻¹).Mechanisms for RAS equilibrium establishment, within and between systems with different mesh sizes, are discussed.     

The performance and impact of a bubble-wash bead filter in a recirculating green water larval culture system for delta smelt (Hypomesus transpacificus)

Delta smelt are cultured at the UC Davis Fish Conservation and Culture Lab (FCCL) for research purposes. The culture systems used are based on recirculation technology to ensure optimum water quality for the fish at each life stage. Larval culture takes place in recirculation systems with green water to which a Nannochloropsis algal concentrate is added to maintain a turbidity of approximately 9 NTU. A bubble-wash bead filter is used to remove total suspended solids (TSS) from the recirculation system. The performance of the bubble-wash bead filter has been evaluated by testing the TSS and particle size distribution in two parallel systems operated in the same way. The need for bubble-wash bead filter backwashing and the impact of the backwash method were evaluated also.The results show that the bubble-wash bead filter removed a great deal of the TSS, including the algae added to maintain the turbidity. An improper backwash method could result in a short term but significantly high TSS peak in the system immediately after the backwash event. Testing over an extended filtration period with a prolonged backwash interval showed that the TSS in the system remained stable up to 150 h post backwash, at which time it increased rapidly. The TSS accumulation in the system with a bubble-wash bead filter that was not backwashed was greater than that in a parallel system without a bubble-wash bead filter. No significant mortality increase was found in the system without a bubble-wash bead filter for 34 days, which provides a possible alternative in order to lower the rearing cost. Nevertheless, there are benefits of using a bead filter, and these are discussed in the paper.     

Temperature-dependent and surface specific formaldehyde degradation in submerged biofilters

This study investigated formaldehyde removal in submerged fixed media biofilters in commercial and pilot scale recirculation aquaculture systems. Steady removal of formaldehyde (F) was observed immediately after simulated therapeutic treatment in closed systems and complete removal occurred within 1–4 days depending on water temperature. Formaldehyde removal was dependent on available biofilter surface area, and comparable rates of surface specific removal (SSR) were observed in two different systems. SSR was positively correlated to temperature (Q₁₀ = 3.4) with estimates of 2.1 mg F/(m² h) at 5.7 °C to 6.5 ± 0.2 mg F/(m² h) at 14.5 °C. The estimates for SSR of formaldehyde can be used to predict actual treatment and effluent concentration with more accuracy. Furthermore, the results allow calculation on biofilter removal capacity of formaldehyde, applicable for developing biofilters ensuring sufficient formaldehyde removal in effluent water.     

Effect of different biofloc levels on microbial activity,water quality and performance of Litopenaeus vannamei in a tank system operated with no water exchange

In zero-exchange superintensive culture systems, flocculated particles (bioflocs) accumulate in the water column. Consequently, some control over the concentration of these particles must be performed. The objective of this study is to evaluate the effects of three concentrations of bioflocs on microbial activity, selected water quality indicators and performance of Litopenaeus vannamei in a tank system operated with no water exchange. A 44-day study was conducted with juvenile (6.8 g) shrimp stocked in twelve 850 L tanks at a stocking density of 459 shrimp m⁻³. Biofloc levels were expressed as three presets of total suspended solids (TSS) concentrations, as follows: 200 mg L⁻¹ (T200), 400–600 mg L⁻¹ (T400–600), and 800–1000 mg L⁻¹ (T800–1000). TSS levels were controlled by attaching a 40 L settling tank to each culture tank. Reduction of TSS to concentrations close to 200 mg L⁻¹ decreased the time of bacterial cell residence and significantly reduced the nitrification rates in the water (P < 0.05). The tanks in the T200 treatment had a greater variability of ammonia and nitrite (P < 0.05), which led to the need to increase the C:N ratio of the organic substrate to control ammonia through its assimilation into heterotrophic bacterial biomass. But the higher production of heterotrophic bacteria in T200 (P < 0.05) increased the dissolved oxygen demand. Nitrification rates were higher (P < 0.05) in tanks with TSS concentrations above 400 mg L⁻¹, and ammonia and nitrite were significantly lower than in the T200 tanks. We suggest that ammonia and nitrite in the T400–600 and T800–1000 tanks were controlled primarily by nitrifying bacteria, which provided higher stability of these parameters and of dissolved oxygen. Regarding shrimp performance, the reduction of TSS to levels close to 200 mg L⁻¹ was associated with better nutritional quality of bioflocs. Nevertheless, differences in biofloc levels and nutritional quality were not sufficient to affect the weight gain by shrimp. The rate of shrimp survival and the final shrimp biomass were lower (P < 0.05) when the TSS concentrations were higher than 800 mg L⁻¹. Analysis of the shrimps’ gills showed a higher degree of occlusion in the T800–1000 treatment (P < 0.05), which suggests that the shrimp have an intolerance to environments with a solids concentration above 800 mg L⁻¹. Our results show that intermediate levels of bioflocs (TSS between 400 and 600 mg L⁻¹) appear to be more suitable to superintensive culture of L. vannamei since they create factors propitious for maintaining the system’s productivity and stability     

Hydrodynamic characterization and performance evaluation of an aerobic three phase airlift fluidized bed reactor in a recirculation aquaculture system for Nile Tilapia production

The hydrodynamic characterization and the performance evaluation of an aerobic three phase fluidized bed reactor in wastewater fish culture treatment are presented in this report. The objective of this study was to evaluate the organic matter, nitrogen and phosphorous removal efficiency in a physical and biological wastewater treatment system of an intensive Nile Tilapia laboratory production with recirculation. The treatment system comprised of a conventional sedimentation basin operated at a hydraulic detention time HDT of 2.94 h and an aerobic three phase airlift fluidized bed reactor AAFBR operated at an 11.9 min HDT. Granular activated carbon was used as support media with density of 1.64 g/cm³ and effective size of 0.34 mm in an 80 g/L constant concentration. Mean removal efficiencies of BOD, COD, phosphorous, total ammonia nitrogen and total nitrogen were 47%, 77%, 38%, 27% and 24%, respectively. The evaluated system proved an effective alternative for water reuse in the recirculation system capable of maintaining water quality characteristics within the recommended values for fish farming and met the Brazilian standards for final effluent discharges with exception of phosphorous values.     

Nitrate removal effectiveness of fluidized sulfur-based autotrophic denitrification biofilters for recirculating aquaculture systems

There is a need to develop practical methods to reduce nitrate–nitrogen loads from recirculating aquaculture systems to facilitate increased food protein production simultaneously with attainment of water quality goals. The most common wastewater denitrification treatment systems utilize methanol-fueled heterotrophs, but sulfur-based autotrophic denitrification may allow a shift away from potentially expensive carbon sources. The objective of this work was to assess the nitrate-reduction potential of fluidized sulfur-based biofilters for treatment of aquaculture wastewater. Three fluidized biofilters (height 3.9 m, diameter 0.31 m; operational volume 0.206 m³) were filled with sulfur particles (0.30 mm effective particle size; static bed depth approximately 0.9 m) and operated in triplicate mode (Phase I: 37–39% expansion; 3.2–3.3 min hydraulic retention time; 860–888 L/(m² min) hydraulic loading rate) and independently to achieve a range of hydraulic retention times (Phase II: 42–13% expansion; 3.2–4.8 min hydraulic retention time). During Phase I, despite only removing 1.57 ± 0.15 and 1.82 ± 0.32 mg NO₃–N/L each pass through the biofilter, removal rates were the highest reported for sulfur-based denitrification systems (0.71 ± 0.07 and 0.80 ± 0.15 g N removed/(L bioreactor-d)). Lower than expected sulfate production and alkalinity consumption indicated some of the nitrate removal was due to heterotrophic denitrification, and thus denitrification was mixotrophic. Microbial analysis indicated the presence of Thiobacillus denitrificans, a widely known autotrophic denitrifier, in addition to several heterotrophic denitrifiers. Phase II showed that longer retention times tended to result in more nitrate removal and sulfate production, but increasing the retention time through flow rate manipulation may create fluidization challenges for these sulfur particles.     

Performance of sequencing microbead biofilters in a recirculating aquaculture system

Biological filtration, or biofiltration, is the key technology in recirculating aquaculture systems. Sequencing microbead biofilters, in which the media maintains a continuous up-and-down movement, are based on traditional microbead filters but offer superior filtration properties. The performance characteristics of a sequencing microbead biofilter installed in a recirculating aquaculture system for rearing Barcoo perch at 29 ± 1 °C were examined. The total ammonia-nitrogen (TAN) concentrations and the nitrite-nitrogen concentrations during a 52-day culture period were maintained blow 1.6 mg/L and 0.9 mg/L. In order to ensure efficient biofiltration, the optimal actual application of hydraulic retention time was determined to be approximately 3–5 min. The water flow produced by the reciprocating motion of the media served to wash away suspended solids, ensuring the occurrence of optimal nitrification processes. Additionally, the reciprocating motion of the media enhanced ammonia treatment efficiency significantly by improving the transport of nutrients and nitrification activity. Compared to a static situation the ammonia removal rate increased by 27% based on the application of up-and-down reciprocating movement. The biofilm on the microbead forms as a compact, complex, and homogeneous structure, consisting of numerous microscopic thin sheets. Additionally, a multitude of pores, interstitial voids, and vertical channels were widely observed to convey obviously advantageous properties in support of fluid passage, thus enhancing mass transfer and ultimately contributing to biofiltration effectiveness. The optimum biofilm thickness for providing efficient biofiltration was determined to be approximately 70 μm for this filter.     

Screening and Evaluation of Alum and Polymer Combinations as Coagulation/Flocculation Aids to Treat Effluents from Intensive Aquaculture Systems

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%.     

Nursery of young Litopenaeus vannamei post-larvae reared in biofloc- and microalgae-based systems

A 13-day nursery trial was conducted to evaluate the performance of young Litopenaeus vannamei post-larvae (from PL₆ to PL₁₈) reared in both biofloc and microalgae-based systems at a stocking density of 67 PLs L⁻¹. The effects of different concentrations of total suspended solids (TSS) on PL performance were also evaluated. One experimental group was reared in a conventional microalgae-based system with daily water exchange and daily addition of microalgae (herein called microalgae treatment). The other two experimental groups were reared using biofloc technology (BFT) with daily dextrose addition and no water exchange, but in the “Biofloc-500” treatment, TSS were maintained at around 500 mg L⁻¹, while in the “Biofloc-700” treatment, TSS were maintained at around 700 mg L⁻¹. Water quality variables remained within the appropriate range for larval culture. In microalgae treatment, ammonia control was likely associated with its assimilation into microalgae biomass and daily water exchange. In biofloc tanks, however, the addition of dextrose stimulated the production of bacterial biomass from ammonia. This system required only 12.9% of the water used by the microalgae treatment since water was not exchanged during the culture. The nursery of young PLs resulted in similar (P > 0.05) performance in all treatments: survival >94%, PL length ∼ 11.5 mm, and PL dry weight ∼ 1.2 mg. In addition, the salinity stress test (>90.0%) was not significantly different among treatments. Our results indicate that BFT can be as effective as the microalgae-based system for the nursery of young L. vannamei post-larvae. We also found that post-larvae performance was similar (P > 0.05) between biofloc treatments, indicating that organisms can tolerate environments with large quantities of solids.     

Application of sediment microbial fuel cell for in situ reclamation of aquaculture pond water quality

Performance of sediment microbial fuel cell (SMFC) with external resistance (SMFC-1) as well as short-circuited mode (SMFC-2) was evaluated at different operating temperatures (28–30 °C and 21–25 °C) and in presence and absence of aeration at the cathode. The performance was evaluated in terms of chemical oxygen demand (COD) removal and total kjeldahl nitrogen (TKN) removal for offering in situ treatment of aquaculture pond water. SMFC-2 demonstrated maximum COD and TKN removal efficiencies both in the absence and presence of aeration near cathode as compared to SMFC-1. With aeration at cathode, the COD and TKN removal efficiencies were 79.4% and 92.6% in SMFC-1 and 84.4% and 95.3% in SMFC-2, respectively. Without aeration and at lower operating temperature, the COD and TKN removals were slightly lower, yet satisfying aquaculture quality norms. SMFCs demonstrated effective in situ remediation of aquaculture water and can drastically save the operating cost of aquaculture.