Research Of Aquaculture Wastewater Treatment By Sequencing Batch Reactor Of Submerged Biofilm Process

The composition of aquaculture wastewater is simple compared to the industrial wastewater and domestic sewage.it has low pollutant concentrations with the concentration of CODMn and TN is generally about130mg·L-1and15mg·L-1,respectively. Once the large amount of aquaculture wastewater discharge directly into the environment without treatments, it can cause severe environmental pollutions which restricts the aquaculture development. However, this wastewater can be reused after appropriate treatments in order to reduce pollution while saving water resource at the same time.With the up-to-date research achievements of aquaculture wastewater treatment techniques at home and abroad as a reference, considering the characteristics of Micro-polluted water,we present in this dissertation a new biofilm treatment to process aquaculture wastewater. Firstly we modified the activated carbon fiber (ACF) into biological activated carbon fiber (BACF), and then apply BACF-SBBR carrier to treat synthetic aquaculture wastewater. Meanwhile, we investigated the startup characteristics of the system and optimized the conditions process of the system. We examined diversity and structure of the bacterial bio-film distribution on the filler by using Miseq. Thus, we achieved theoretical support on building the recirculation aquaculture system (RAS). On this basis, we focused on the processing capability of SBBR on treating actual aquaculture wastewater in pilot-scale reactor, and examined the possibility of application of this technology. Finally, we applied this technology to engineering demonstration project.In this dissertation, we applied electrochemical modification on ACF in order to obtain a good performing of bio-film filler. We found that the surface of modified ACF became rough, the functional group increased, and both hydrophilicity and bio-affinity was improved as well. We explored under the situation (where we set1mol·L-1phosphoric acid solution as an electrolyte, a current density as1mA·cm-2, an electrolysis time as150s), biomass of modified ACF reached the maximum. Hence, we decided to choose this modified packing achieved under above situation as the carrier of SBBR in our follow up research. We disclosed that N, P and other nutrients adsorbed on ACF supply nutritional factors for growth of microorganisms. Thus the speed of bio-film is faster than other materials, and the hydrophilic is conductive to microbial attachment. However, the high hydrophilicity will lead to free of microorganisms and will be not conducive to bio-film of microorganisms.The results of lab-scale BACF-SBBR showed that film forming is quite high and the start-up time of reactor needed only20days. Optimal processing condition of SBBR was:instantaneous water,2.5hours of anaerobic,5hours of aeration,0.75hours of precipitation,0.2hours of drainage. The optimal influent pH value of system was between7and8, and the optimal influent C/N ratio was7:1. After the system had been running for3months under optimal condition, we found that the effluent concentration of CODMn was between3.25to7.03mg·L-1; the effluent concentration of ammonia nitrogen was between0.34to0.88mg·L-1; the effluent concentration of TN was between0.40to0.92mg·L-1; the effluent concentration of TP was between0.12to0.32mg·L-1.The results of pilot-scale bioreactor confirmed that SBBR process treating actual aquaculture wastewater also worked well. The optimal density of filler was0.3kg·m-3, and the optimal aeration quantity was9L·h-1.After3 months of stable operation, the system showed that it had a strong adaptability and the quality of effluent reached the standard of recycling water. We disclosed that the effluent concentration of CODMn was between5.33to8.26mg·L-1; the effluent concentration of ammonia nitrogen was between0.71to1.21mg·L-1; the effluent concentration of TN was between0.78to1.24mg·L-1; the effluent concentration of TP was between0.07to0.34mg·L-1. Both nitrate and nitrite were less than the detection limit. Concentration of suspended solids was less than8mg·L-1.The study on demonstration project revealed that the quality of effluent water was stable after5months of operation. We found that the effluent concentration of CODMn was between1.84to5.41mg·L-1; the effluent concentration of ammonia nitrogen was between0.14to0.46mg·L-1; the effluent concentration of TN was between0.15to0.49mg·L-1; the effluent concentration of TP between0.03to0.12mg·L-1. Concentration of suspended solids was less than5mg·L-1, and there was no nitrite found in the water. The water quality meets the requirements of reusing water. The running costs of this demonstration project were around0.39RMB/m3, which means that the operating costs has been saved significantly. This demonstration project has following features:(1)the requirement of area is small;(2)easy operation and management;(3)the system running costs needed are low;(4)the removal rate of pollutant is relatively high;(5) quality of effluent water meets the requirements of reusing water. All above features indicate that this technology is suitable for treating low concentrations of aquaculture wastewater. Hence, it is worthwhile to widespread used.