Study On The Mechanism And Control Technology Of Bioclogging In Artificial Recharge Aquifer

Due to the lack of surface water resources and increasingly serious pollution problems, groundwater is mined heavily as an important source of water supply, which causes a series of destructive environmental geological problems. At the same time, the global rainfall events happen frequently which lead to flood disaster, and a large amount of surface runoff cause huge pressure for the urban drainage system. Aquifer storage and recovery (ASR) is a kind of underground water artificial recharge and reuse technology, which via a variety of measures, collecting the surface water and adding them into underground aquifer materials to make groundwater resources available for use. ASR is fundamental for solving excessive groundwater exploration, and achieving the joint scheduling of surface and underground water resources, and optimizing water resources allocation, as well as improving the comprehensive utilization of water resources. However, the clogging problem (especially bioclogging) in the process of artificial recharge is always a key factor which restricts artificial recharge technology for widely using. This paper mainly focused on the mechanism and control technology of bioclogging in artificial recharge aquifer. By simulating the process of artificial recharge aquifer using a series of percolation tests, the characteristics of microbial growth and metabolism in the aquifer materials were examined. Meanwhile, the influences of recharge conditions on microbial growth and metabolism were discussed. And the correlations between bacterial amount, the type of extracellular polymeric substances (EPS) and permeability of aquifer materials were discussed, and further studying for bioclogging mechanism. Based on these researches, this paper also selected Dagu river downstream saltwater intrusion area in Qingdao, Shandong province. The clogging risk of aquifer were assessed, and the prevention and control treatments were proposed. The main conclusions of the study are as follows:(1) In the process of percolation experiments, the types of microorganism were mainly aerobic bacteria and actinomycetes. The superiority strains included Methylobacterium, Janthinobacterium, Yersinia, Staphylococcus, and Acidovorax. The characteristics made the superiority strains important in bioclogging process. Meanwhile, in the process of percolation experiments, bacterial growth and metabolism mainly happened on the surface. The bacterial amount were much more near the surface. Meanwhile, bacterial growth, in the term of short rod, at the beginning of the experiments, and then increasing in number and size. At the end of the tests, a layer of dense biofilm was covered on the surface of aquifer materials.(2) Under the conditions of simulated experiments, the carbon, phosphorus concentration, salinity and temperature were the main factors affecting microbial EPS secretion, while nitrogen concentration had little effect. Carbon content as well as the interaction of carbon and phosphorus in the injection water had extremely significant influence on secretion of microbial polysaccharide, protein, and EPS concentrations.(3) The permeability of aquifer materials showed obvious heterogeneity in continuous filtration, which the degree of bioclogging gradually decreased with the increasing seepage distance. The permeability coefficient which near the inlet medium decreased most and bioclogging was the most serious. In addition, the aquifer media permeability showed a slow decreasing, rapid decreasing and leveling off with the increasing seepage time.(4) The bacteria attached to the aquifer materials underwent adaptation, logarithmic phase and decline phase, and bacteria amount presented a first increased and then decreased trend. At the same time, the trend of bacterial loosely bound EPS (LB-EPS) first increased followed by a decreasing trend, the same as the trend of tightly bound EPS (TB-EPS).(5) In the process of artificial recharge, the bioclogging mechanism contributed to different factors:at the very beginning of percolation test, the bacterial growth and volume increasing caused the decrease in permeability (0～48 h); while at the middle of experiment, bacteria and EPS both contributed to the reduction of permeability (48～144 h); and at the end of period, the large amount of LB-EPS secreted by bacteria continued to reduce the aquifer materials permeability.(6) In the process of artificial recharge using rainfall water from Jia Tuan dam, Xiao Xin river and Ma Wan bridge, the clogging types of the study area were physical and microbial clogging in the process of artificial recharge. The prevention treatments should be proposed to reduce the risk of aquifer physical and microbial clogging before the artificial recharge programs. Specific measures as follows:the rain floodâ†' MF/UFâ†'ROâ†'chlorine disinfectionâ†'dechlorination. Once aquifer clogging happens, some control measures such as changing media, backwashing and intermittent injection will solve the problems, with fully considering the purpose of the study aquifer.