Study On In Situ Bioremediation Of Polluted Source Water With Biofilms

Accompanied with the rapid development of economy, acceleration of urbanization and subsequent speedy expansion of small towns, discharge of pollutants produced from point sources and non-point sources, including industrial wastewater, rural domestic sewage, domestic waste, livestock waste, pesticide and fertilizer, etc., is becoming more and more serious. This problem results in deterioration in water quality of drinking water sources in small towns which poses a great threat to human health.Based on the investigation of the water qualities status of drinking source water in Hang-Jia-Hu plain river network, the feasibility of in situ remediation of the polluted water source with biofilm attached to bio-filler media in simulated river reactor was explored in this study. Different bio-filler medium were compared by their ability to remediate the polluted source water, and the optimal parameters of in situ bioremediation were evaluated, which can provide some technical support to the security of drinking water in small towns. The main results are as follows:1) The water sources of the Hang-Jia-Hu plain are mostly river type. The complex hydraulic characteristics of the river such as the parallel flow, counter flow and stagnation would slower the water flow, diminish the water capacity, cause the cross pollution between the up and down side of the river. As a result, the water quality failed to meet the functional requirements of water environment, especially in the down side of the river.Varying degrees of polluton had been found in each investigated water source by single index evaluation method. The water quality of drinking water sources in Tiao Xi area was relatively better, which can reach grade III of 'Surface Water Environment Quality Standard' (GB3838-2002). While the water quality of drinking water source in the Great Canal river watershed were much worse, which could not meet grade V standard of GB3838-2002 and COD_Mn, ammonia nitrogen and TP were the main pollution indices.2) Two simulated river reactors were developed using elastic plastic filler and soft filler as biofilm carriers, respectively. The removal efficiencies of ammonia nitrogen, TP, COD_Mn were investigated in these simulated river reactors. The results showed that ammonia nitrogen removal efficiency in the reactor with elastic plastic filler was over 70%, which was higher than that of the reactor packed with soft filler (20%). However, higher removal efficiency of TP (49%) was achieved in the reactor packed with soft filler. Both reactors had low and TN removal efficiencies.A simulated two-stage river reactor, forepart packed with elastic plastic filler and subsequent part with soft filler, was employed to remediate the polluted source water, the effects of aeration intensity and influent flow on pollutant removal were investigated. When operated at influent flow of 8 L·d^-1 and aeration intensity of 680 L·h^-1, the reactor had a good remediation performance, with the ammonia nitrogen, TN, COD_Mn, TOC, TP and turbidity removal efficiencies of 74.7%, 12.7%, 30.5%, 31.0%, 30.7% and 81.7%, respectively. During the course of in situ remediation, the major role of aeration was to promote biofilm reformation and enhance mass transfer. When the aeration intensity was maintained at 680 L·h^-1 and the influent flow increased to 24 L·d^-1, the ammonia nitrogen, TN, COD_Mn, TP and turbidity removal efficiencies decreased to 67.3%,8.2%,23.5%,14.6% and 54.5%, respectively, while TOC removal rate stayed stable. Preliminary results revealed that excellent reactor performance was controlled by appropriate HRT. HRT was correlated with internal packing area derived from regional hydraulic loading.3) During the running of reactor, the surface characteristics of elastic plastic fillers in river reactor gradually changed from achromaticity to brown, and then to breen, with the increase of biomass and appearance of microorganisms such as alga, bacteria and metazoan. The structure of the biofilm appeared heterogeneous, interspersed with some pores and channels. Soft filler surface was attached mainly by inorganic material, while only a few algea and bacteria could be observed by microscopic examination, and the biomass decreased along with the running course. The pollutants removal rates were positively correlated with the attachment of biomass and microorganisms.