Study On Purification Of Aquaculture Wastewater Using A Biological Integrated System

The high concentration of ammonia and nitrite in aquaculture system is harmful to aquatic creatures, while the excess nitrogen and phosphorus discharged into rivers and lakes without treatment leads to eutrophication of water body in a large scale. In addition, the shortage of water resources heavily limited the development of aquaculture industry. Therefore, aquaculture wastewater purification and recycling become an important issue in aquaculture system not only on water pollution reduction but also on resource utilization economy. Purification and recirculation of aquaculture wastewater at experimental laboratory in2011-2012was studied using a Moving Bed Biofilm Reactor (MBBR) and hydrophytes-filter feeders, biological integrated system to treat the simulated wastewater of Deqing Wuyue Aquaculture and wastewater from yellow catfish culture system in laboratory. The experimental results were as follows:(1) In the process of simulated wastewater treatment using MBBR, reactor start-up quickly, operation stably, which could make the COD and ammonia removal efficiency over80%simultaneously, and TP removal rate reached50%when hydraulic retention time (HRT) was8h and DO was2.0-3.0mg/L. Under the conditions of organic loading at0.76±0.03kg/m3-d, the average removal efficiency of TN and ammonia were71.73%and98.42%, respectively, presenting the best results among all operation periods. To achieve better TN removal effect, organic loading should not be lower than0.5kg/m3. When DO was3.0±0.25mg/L, TN removal efficiency reached the maximum one, which most conductive to simultaneously nitrification and denitrification (SND). To maintain high ammonia nitrogen removal efficiency and reduce the nitrite accumulation, DO should be no less than2.0mg/L. HRT is an important parameter in MBBR operation, short HRT could make the reduction of ammonia removal efficiency, and cause possible nitrite accumulation. When MBBR was operated in sequencing mode, TP could attain better removal efficiency than in continuously operation, however, thus might lead to nitrite accumulation at the end of the operation cycle and be harm to fish. (2)14.93%-20.92%of TN and11.95%～17.92%of TP could be removed during purification of wastewater from yellow catfish culture system in lab using Ceratophyllum demersum, Myriophyllum verticillatum and Bellamya aeruginose individually or simultaneously after30days. Unfortunately, the extension of time might lead to poor removal efficiency on TN and TP. Among these treatments, Ceratophyllum demersum gave better reduction of ammonia and nitrite than the rest group, which reduced6.83mg/L ammonia and1.35mg/L nitrite to below0.5mg/L and0.1mg/L in less than18days, respectively; Myriophyllum verticillatum and Myriophyllum verticillatum+Bellamya aeruginose presented best performance on the TN removal rate, with the prolonged experiment time, the combinations showed an advantage over treatments using single material; Ceratophyllum demersum+Bellamya aeruginose indicated the best efficiency on the TP removal; the Ceratophyllum demersum+Bellamya aeruginose treatment gave the best removal efficiency in COD concentration; Ceratophyllum demersum showed best efficiency in improving DO. For aquaculture wastewater with high ammonia, nitrite and phosphorus concentration, Ceratophyllum demersum was more effective than Myriophyllum verticillatum and Bellamya aeruginose in controlling wastewater.(3) Treating the simulated wastewater using MBBR plus Ceratophyllum demersum biological system performed quite well. When HRT was8h and DO was3.0±0.25mg/L, COD and ammonia concentration in the effluent could meet the III class of the surface water quality standard (GB3838-2002). Extending the time of purifying effluent from MBBR by Ceratophyllum demersum to2days, ammonia and nitrite concentration could decrease to less than0.5mg/L and0.1mg/L, respectively, on the other hand, DO could rise to above5.0mg/L, thus meeting the requirements of healthy freshwater aquaculture. The research results showed that the integrated system used in aquaculture wastewater treatment was worthy for fish production and need to be promotion.