Research On ABR-CRI Treatment Technology Based On Agricultural Irrigation Utilization Of Domestic Sewage In Arid Areas Of Northwest China

The agricultural irrigation resources are scarce in the arid area of northwest,but the domestic sewage in this area is large in quantity and stable in quality,which can be used as an important source of agricultural irrigation water.However,the content of some pollutants in the domestic sewage in this area exceeds the standard,so it can not be directly used for farmland irrigation,and the local domestic sewage treatment standard is high,which not only increases the cost of sewage treatment,but also fails to recover the nutrient elements(nitrogen and phosphorus)in the sewage.Therefore,it is urgent to develop a set of treatment technology for agricultural irrigation of domestic sewage,which is suitable for arid areas in Northwest China,so that the effluent can better retain the nitrogen and phosphorus in the sewage on the premise of meeting the irrigation water quality standards of all crops,so as to realize the dual resources of water and fertilizer.In view of the above problems,ABR—CRI(Anaerobic Baffled Reactor—Constructed Rapid Infiltration)combined technology was selected in the early stage,and its structure design was improved and its operation parameters were optimized.On this basis,this paper mainly studies the effect of adding elastic filler on ABR removal of pollutants and the effect of increasing filler height and mechanical ventilation on CRI removal of pollutants after two groups of ABR and three groups of CRI operate stably under the optimal conditions,so as to establish a set of treatment technology suitable for agricultural irrigation and utilization of domestic sewage in northwest arid area.Through high-throughput sequencing technology,the relationship between the effect of adding elastic filler on ABR treatment and the changes of bacterial and archaea community structure and abundance in ABR,and the relationship between the effect of increasing filler height and mechanical ventilation on CRI treatment and the changes of bacterial community structure and abundance in CRI were revealed.The conclusions are as follows(1)The average removal rates of COD,SS,Hg,Cr(VI)and Pb in ABR were increased by 3.55%,4.77%,16.28%,3.03% and 2.22% respectively by adding elastic filler,and with little effect on the removal rates of TN and TP(decreased by 0.96%and 1.39% respectively).Therefore,ABR with elastic filler should be selected as the pretreatment technology for agricultural irrigation of domestic sewage in arid areas of Northwest China,but the effluent of ABR with elastic filler does not meet the water quality standard of agricultural irrigation,so it is necessary to carry out follow-up treatment for the effluent.(2)The addition of elastic fillers increased the biomass in ABR,which intensified the competition between bacterial and archaeal communities for organic matter.Some bacterial and archaeal communities were at a dominant or inferior position in the competition for organic matter,leading to their proliferation or decline.The difference in the concentration of organic matter caused different changes in the composition,abundance and genetic relationship of bacterial and archaeal communities structure in ABR.(3)The addition of elastic filler has little effect on the nitrogen and phosphorus removal related bacteria in ABR,so the addition of elastic filler has little effect on the transformation and removal of nitrogen and phosphorus in ABR.The results showed that the average relative abundance of most bacteria in ABR related to organic degradation and methanogenesis was increased,Among them,the relative abundances of Synergistetes in the first compartment increased by 10.31%,the relative abundances of Methanobacterium in the second compartment increased by 13.24%,the relative abundances of Synergistetes,Chloroflexi and Methanobacterium in the third compartment increased by 5.13%,8.75% and 10.44% respectively,the relative abundances of Methanobacterium in the fourth compartment were increased by 4.71%,and the elastic filler could effectively intercept the suspended organic matter in the sewage,so the addition of elastic filler was conducive to the transformation and removal of organic matter by ABR.(4)The average removal rates of COD,TN,TP,Hg,As and Pb in CRI were increased by 3.77%,3.73%,25.85%,20.76%,3.75% and 83.64% respectively with the increase of filler height.The average removal rates of COD and TP in CRI increased by 3.21% and 3.05% respectively,and the average removal rate of TN decreased by 2.45% with the increase of mechanical ventilation,which was beneficial to the retention of nitrogen in wastewater.Since CRI does not discharge sludge,the removal of TP by CRI can be neglected in the long run.The effluent of three CRI groups reached the irrigation water quality standard of all crops.Therefore,CRI1 can be selected as the post-treatment technology for agricultural irrigation and utilization of domestic sewage in northwest arid area when the temperature is high and the influent organic load and hydraulic load are small,but CRI2 should be selected as the post-treatment technology for agricultural irrigation and utilization of domestic sewage in northwest arid area when the influent organic load and hydraulic load are large in winter,so as to ensure that the effluent of CRI can reach the long-term stability irrigation water quality standards for all crops.(5)Increasing the height of the filler prolonged the contact time between the sewage and the filler and the microorganisms on its surface,and increasing the mechanical ventilation changed the oxygen environment in CRI,thus affecting the growth and reproduction of some bacterial communities.Some bacterial communities were in the advantages or disadvantages in the specific nutrient concentration and oxygen environment,leading to their proliferation or decline,therefore,the composition,abundance and genetic relationship of bacterial community structure in CRI changed differently.(6)Increasing the filler height not only prolonged the contact time of wastewater with filler and its surface microorganisms,but also increased the average relative abundance of Nitrospirae at 0.8 m of CRI by 3.11%,therefore,increasing the filler height is conducive to the removal of organic matter and phosphorus and nitrification in CRI.Increasing mechanical ventilation increased the average relative abundance of Proteobacteria by 4.81% and 13.86% at 0.3 m and 0.8 m,and decreased the average relative abundance of Bacteroidetes by 2.34% and 4.59% at 0.8 m and 1.3m,respectively,therefore,increasing mechanical ventilation is conducive to the removal of organic matter and phosphorus in CRI,but not conducive to denitrification.