A Novel Zero Discharge Intensive Seawater Recirculating System for the Culture of Marine Fish

Department of Animal Sciences, Hebrew University of Jerusalem, Yerushalayim, Jerusalem, Israel
Journal of the World Aquaculture Society (Impact Factor: 0.73). 09/2003; 34(3):344 - 358. DOI: 10.1111/j.1749-7345.2003.tb00072.x


Results are presented of a zero-discharge marine recirculating system used for the culture of gilthead seabream Sparus aurata. Operation of the system without any discharge of water and sludge was enabled by recirculation of effluent water through two separate treatment loops, an aerobic trickling filter and a predominantly anoxic sedimentation basin, followed by a fluidized bed reactor. The fish basin was stocked for the first 6 mo with red tilapia Oreochromis niloticus × O. aureus at an initial density of 16 kg/m3. During this period salinity was raised from 0 to 20 parts per thousand. Then, gilthead seabream, stocked at an initial density of 21 kg/m3, replaced tilapia at day 167 and were cultured for an additional 225 d. Non steady-state inorganic nitrogen transformations occurred as a result of these salinity changes. After day 210, the system operated at all times with those water quality parameters considered critical for successful operation of mariculture systems, within acceptable limits. Thus ammonia, nitrite, and nitrate concentrations did not exceed 1.0-mg total ammonia-N/ L, 0.5-mg NO2:-N/L and 50-mg NO3-N/L, respectively. Sulfide levels in the fish basin were below detection limits and oxygen > 6 mg/L after the oxygen generator was added at day 315. Ammonia, produced in the fish basin and to a lesser extent in the sedimentation basin, was converted to nitrate in the aerobic trickling filter. Nitrate removal took place in the sedimentation basin and to a lesser extent in the fluidized bed reactor. Sludge, remaining in the sedimentation basin at the end of the experimental period, accounted for 9.2% of the total feed dry matter addition to the system. The system was disease-free for the entire year and fish at harvest were of good quality. Water consumption for production of 1 kg of tilapia was 93 L and 214 L for production of 1 kg of gilthead seabream. Additional growth performance data of gilthead seabream cultured in a similar but larger system are presented. During 164 d of operation of the latter system, maximum stocking densities reached 50 kgl M3 and fish biomass production was 27.7 kg/m3. Relatively poor fish survival and growth resulted from occasional technical failures of this pilot system.

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    • "To maintain sufficiently low levels of these compounds , a portion of system water is typically exchanged with clean water. In order to conserve resources, enhance control over fish growth and reduce dependency on a large water source, several studies over the past two decades have focused on developing a near-zero discharge RAS in which water exchange is reduced to less than 5% of the system volume per day (Gelfand et al., 2003; Shnel et al., 2002; Zohar et al., 2005 ). The large amount of sludge produced in this system is characterized by a relatively low solid content (~ 1–2.6%) (Chen et al., 1993; Mirzoyan et al., 2010; Timmons and Ebeling, 2007 ) which can be treated in-situ anaerobically (Gebauer and Eikebrokk, 2006; Mirzoyan et al., 2010; Tal et al., 2009). "

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    • "As a biological reaction, water temperature also plays a role in denitrification NO 3 − removal rates (Metcalf Eddy, 2003). The operation of other fluidized sand denitrification biofilters at higher water temperatures (19–30 • C: Arbiv and van Rijn, 1995; Gelfand et al., 2003; Shnel et al., 2002) partially explains the lower rates observed here. The Q 10 , or the factor by which the removal rate increases for every 10 • C temperature increase, has been reported for other types of denitrification systems at approximately 2 (Elgood et al., 2010; Warneke et al., 2011). "
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    ABSTRACT: The ability to consistently and cost-effectively reduce nitrate-nitrogen loads in effluent from recirculating aquaculture systems would enhance the industry's environmental stewardship and allow improved facility proximity to large markets in sensitive watersheds. Heterotrophic denitrification technologies specifically employing organic carbon found in aquaculture system waste offer a unique synergy for treatment of land-based, closed-containment production outflows. For space-efficient fluidized sand biofilters to be used as such denitrification reactors, system parameters (e.g., influent dissolved oxygen and carbon to nitrogen ratios, C:N) must be evaluated to most effectively use an endogenous carbon source. The objectives of this work were to quantify nitrate removal under a range of C:Ns and to explore the biofilter bacterial community using three replicated fluidized sand biofilters (height 3.9 m, diameter 0.31 m; fluidized sand volume plus biofilm volume of 0.206 m3) operated at a hydraulic retention time of 15 min and a hydraulic loading rate of 188 L/min-m2 at The Conservation Fund Freshwater Institute in Shepherdstown, West Virginia, USA. Nitrate reduction was consistently observed during the biofilter study period (26.9 ± 0.9% removal efficiency; 402 ± 14 g NO3-N/(m3 biofilter-d)) although nitrite-N and total ammonium nitrogen concentrations slightly increased (11 and 13% increases, respectively). Nitrate removal efficiency was correlated with carbonaceous oxygen demand to nitrate ratios (R2> 0.70). Nitrate removal rates during the study period were moderately negatively correlated with influent dissolved oxygen concentration indicating it may be possible the biofilter hydraulic retention time was too short to provide optimized nitrate removal. It is reasonable to assume that the efficiency of nitrate removal across the fluidized sand biofilters could be substantially increased, as long as organic carbon was not limiting, by increasing biofilter bed depths (to 6 - 10 m), and thus hydraulic retention time. These findings provide a low-cost yet effective technology to remove nitrate-nitrogen from effluent waters of land-based closed-containment aquaculture systems.
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    • "The concept of single-sludge denitrification in aquaculture is not new (Jewell and Cummings, 1990; Aboutboul et al., 1995; Arbiv and Van Rijn, 1995) and has been demonstrated in freshwater as well as marine systems at the experimental scale (Shnel et al., 2002; Gelfand et al., 2003; Tal et al., 2009; Martins et al., 2009). Besides a Dutch Tilapia production case (Martins et al., 2010), the feasibility of a production scaled system still has to be developed and documented. "
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    ABSTRACT: A step towards environmental sustainability of recirculated aquaculture systems (RAS) is implementation of single-sludge denitrification, a process eliminating nitrate from the aqueous environment while reducing the organic matter discharge simultaneously. Two 1700 L pilot-scale RAS systems each with a 85 L denitrification (DN) reactor treating discharged water and hydrolyzed solid waste were setup to test the kinetics of nitrate and COD removal. Nitrate removal and COD reduction efficiency was measured at two different DN-reactor sludge ages (high θX: 33–42 days and low θX: 17 - 23 days). Nitrate and total N (NO3− + NO2− + NH4+) removal of the treated effluent water ranged from 73–99% and 60 - 95% during the periods, respectively, corresponding to an overall maximum RAS nitrate removal of approximately 75%. The specific nitrate removal rate increased from 17 to 23 mg NO3−-N·(g TVS·d)−1 and the maximal potential DN rate (measured at laboratory ideal conditions) increased correspondingly from 64–68 mg NO3−-N·(g TVS·d)−1 to 247–294 mg NO3−-N·(g TVS·d)−1 at high and low θX, respectively. Quantification of denitrifiers in the DN-reactors by qPCR showed only minor differences upon the altered sludge removal practice. The hydrolysis unit improved the biodegradability of the solid waste by increasing volatile fatty acid COD content 74–76%. COD reductions in the DN-reactors were 64–70%. In conclusion, this study showed that single-sludge denitrification was a feasible way to reduce nitrate discharge from RAS, and higher DN rates were induced at lower sludge age/increased sludge removal regime. Improved control and optimization of reactor DN-activity may be achieved by further modifying reactor design and management scheme as indicated by the variation in and between the two DN-reactors.
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