Treatment Of Saline Wastewater Using A Sequencing Batch Biofilm Reactor And Its Microbial Structure Analysis

At present,the majority of rural wastewater are directly discharged without treatment,which poses a threat to the rural ecological environment.In addition to the conventional pollutants such as chemical oxygen demand?COD?,total nitrogen?TN?and total phosphorus?TP?,rural wastewater in coastal areas and saline-alkali areas has a high salinity.Hence,it is particular significant to develop an integrated wastewater treatment facility with salt-tolerance,low cost and high pollutants removal efficiency.In this study,two Sequencing Batch Biofilm Reactors?SBBR?,filled with imitated aquatic spiral fiber were developed to investigate the pollutants removal process and microbial structure.After evaluating the effects of salinity,nutrient ratios?C/N/P?and hydraulic retention time?HRT?on nitrogen and phosphorus removal,the optimal operation parameters were put forward.The diversity and abundance of microbial in different locations?exterior biofilm,suspended sludge,interior biofilm?from the SBBRs at varying operating conditions were monitored by high-throughput sequencing technology.At last,an integrated wastewater treatment facility with a daily capacity of 10.0 t was developed and used in engineering.Studies have shown that the system can achieve a quick start-up in 15 days.The salinity of 10.0 g/L had almost no effect on the removal of COD,ammonia nitrogen?NH₄⁺-N?and TN,while it had a significant inhibitory effect on the removal of TP,which reduces the removal rate by about 40%removal efficiency.At the C/N/P ratio of 33.3:8.3:1.0,the removal of TN and TP were both affected,but when the C/N/P ratio is restored to 70.0:7.0:1,the removal efficiency of TN and TP could be recovered.when the HRT was 1+6 h?0.5 h in the influent phase,1.0 h in the anaerobic phase,6.0 h in the aerobic phase and 0.5 h in the effluent phase?,the effluent TP concentration is about 1.2 mg/L.The optimal C/N/P and HRT for this system were 70.0:70:1 and 3+5 h?0.5 h in the influent phase,3.0 h in the anaerobic phase,5.0 h in the aerobic phase and 0.5 h in the effluent phase?,respectively.The microbial population structure on the genus level in the SBBR system varies greatly under different operating conditions.The relative abundances of Ammonia Oxidizing Bacteria?AOB?,Phosphorus Accumulating Organisms?PAOs?and Glucose Accumulating Organisms?GAOs?in exterior biofilm and suspended sludge were higher than those in interior biofilm,while the relative abundances of Nitrite Oxidizing Bacteria?NOB?,Denitrifying Bacteria?DNB?and Denitrifying Phosphorus Accumulating Organisms?DNPAOs?in interior biofilm were the highest.The distribution of AOB,NOB and DNB in suspended sludge,exterior biofilm and interior biofilm is beneficial to the simultaneous nitrification and denitrification process,while the denitrification phosphorus removal could be achieved at low C/N/P by DNPAOs.Nevertheless,the removal of TP was mainly influenced by the competition between PAOs and GAOs.As a result,an integrated wastewater treatment facility with SBBR technology was successfully developed.When the operation period is 1.0 h in the influent phase,4.0 h in the anaerobic phase,6.0 h in the aerobic phase and 1.0 h in the effluent phase,the effluent can meet the wastewater treatment plant pollutant discharge standard“level 1B”requirements,the operating cost is about 0.54 yuan/m³.Therefore,the SBBR technology developed in this study with the characteristics of high efficiency and low consumption can provide guidance for rural sewage treatment with high salinity.