Study On The Pilot-Scale Ozone-Sand/Carbon Filter For Advanced Treatment Of Water In Luanhe River

With increasingly severe contamination of water resources and proposing of newly developed standard for drinking water, applying conventional treating processes appears to be difficult to meet the national standards for drinking water safety. Accordingly, to provide safe and eligible water to domestic uses has been becoming an important issue. This study intensively investigated the performance of one of the key treatment units– pilot-scale biological activated carbon filter for advanced treatment of drinking water on the basis of micro-polluted water resources in Luanhe River (summer and autumn) in Jieyuan Water Treatment Plant in Tianjin city. The treating effectiveness and affected factors of ozone-sand/carbon filter were deeply examined and the biological enhancement technology of ozone-sand/carbon was also experimentally studied.The resources of drinking water in Tianjin city mainly comes from Yin-Luan projects. It has been found that the source water in Luanhe River was contaminated by organic pollutants in terms of large amounts of small molecular organic matters. These types of organic matters have a strong potential in formation of disinfection by-products (DBPs) and are subject to be eliminated via conventional treatment technologies. Based on the experimental results, it was concluded that setting ozne-sand/carbon filter following the conventional units is capable of effectively removing particles (turbidity) as well as organic matters.This study examined the role of ozone and optimum ozone dosage in advanced treatment based on the pilot-scale experiments. The results demonstrated that the addition of ozone was able to efficiently decrease the amounts of permanganate index (COD_Mn) and UV₂₅₄, while simultaneously lead to the increase of assimilable organic carbon (AOC) and biodegradable dissolved organic carbon (BDOC). Therefore, it was concluded that the ozone oxidants could not be set as a single process followed by conventional units. Instead, sand/carbon filter should be subsequently set so that the increased AOC and BDOC concentration could be effectively reduced.The performance of ozne-sand/carbon filter for removing pollutants from raw water in Luanhe River treated by conventional processes was fully investigated at ambient conditions, including removal efficiency of pollutants such as UV₂₅₄, COD_Mn, DBPs precursors, AOC, bacteria and microcystins. These parameters could reach the standards of national water quality for uses.In order to further enhance the performance and prolong the applying lifes of the ozne-sand/carbon filter via optimizing the microbial metabolisms, the system was biologically enhanced by applying artificial screened and cultured microorganisms for pilot-scale ozne-sand/carbon filter could not only enhance the microbial degradation of organic matters, but also substantially increase the removing efficiency of organic pollutants. The results showed that, compared to single ozne-sand/carbon filter without biological enhancements, the average TOC removal obtained was stablized at the rate of 49.83%, accounting for a net increase of 15% for the same system with biological enhancements. The removal efficiency of THMs and HAAs was also increased by 10-26% and 20-45%, respectively.Ames tests suggested that the results were feminine and the bacteria in the treated effluent have a low affording ability to chlorine. These bacteria could be more easily removed by disinfection process, thus, proving the biological safety of the ozne-sand/carbon filter. The studies on biological stability illustrated that AOC removal efficiency of 86.5% was obtained for ozne-sand/carbon filter with biological enhancement. This value represented 26.5% higher than that for ozne-sand/carbon filter without biological enhancement.The influencing factors of the ozne-sand/carbon filter were analysied and compared. The sand layer set at the bottom of the filter could enhance turbidity removal, i. e. fine particles including carbon powders, bacteria and flocs were obviously removed, thus, increasing the biological safety of the effluents. The optimum heights of sand layers were also determined based on experiments.Meanwhile, operational conditions such as filtration velocity and back washing styles as factors were examined and parameters including filtration velocity, working period and backwashing intensity were experimentally determined, providing reasonable conductions for the process design and operation.The dependence effects of the ozne-sand/carbon filter performance on dissolved oxygen (DO), temperature, retention time demonstrated that the system could remove organic pollutants with a maximum efficiency of 19.3% for COD_Mn and 15.79% for UV₂₅₄ at low temperature, respectively. The optimum retention time of the process was determined to be 20min.The mathematical models that described functional dependence of COD_Mn on carbon layer height were constructed at two filtration velocity conditions upon the basis of computation and simulation with theoretical equations and experimental data. This simulation establishes a clue for us to design or operate a sand/carbon filter.