Reproduction And Migration Characteristics Of Worms And The Controlling Of Their Pollution In Drinking Water Treatment Process

When propagating excessively in water sources, worms can enter into water plant along with source water and then penetrate water treatment for their high stretching capability, which resulting in the pollution of drinking water quality. Worms can also propagate excessively in water treatment process under suitable conditions and increase the risk of worm pollution. At present, the controlling of worm pollution is becoming an important research topic in the field of drinking water treatment. Starting with the field investigation of worms in water plant, this paper analyzed the dominant species, origin and pollution types of worms in drinking water treatment process firstly. And then the characteristics and mechanisms on the worm growth, reproduction, migration and distribution were systematically studied by using tubifex and naidid as the model worms. Meanwhile, the study on control mechanism of worm pollution risk, the development of effective worm control method and its application were also carried on. This study aims to provide a theoretical basis and technical support on the risk control of worm pollution.3 phylums, 3 classes, 3 orders, 5 families, 8 genuses and 11 species of worms were detected in Bijiashan water plant of Shenzhen city. Nematode, naidid and chironomid larvae were the dominant species. Exogenous contamination resulted from the input accompany with source water is the main contamination type of nematode. On the contrary, endogenous contamination resulted from excessive propagation in BAC filter for naidid and in sedimentation tank for chironomid midge are their maid contamination types.According to the characteristics of tubifex and naidid reproduction modes (hermaphroditism and cross-fertilization for the former and asexual fission for the latter), life table, one of the main research methods of reproduction regular, was revised and used to discuss the effects of both temperature and dissolved oxygen on worms'reproduction process. The results showed that quantitative description of the worms'reproduction process was realized by revised life table. For tubifex, the enhance of temperature is helpful to its rapid reproduction, while under low dissolved oxygen level tubifex can maintain its population augment by lasting survival time and stopping laying eggs regularly. The population double time t is just increased from 23.75±3.22d to 25.60±4.66d while dissolved oxygen level is decreased from 5mg/L to 1mg/L. For naidid, rapid reproduction was absolved just at 23?; the tolerance ability of naidid to anoxic environment is weaker than that of tubifex and the population double time t at 1, 5 and 8 mg/L are 18.61±4.59, 8.62±1.83 and 4.97±0.16 respectively. Because of the high dissolved oxygen level and the plenty of food presented in BAC filter, excessive propagating of naidid will occur and the population double time t under experimental condition is 12.60±0.42d.The simulation experiment results of worms'migration and distribution showed that migration in sediments were the main migration mode for both tubifex and naidid, while drift migration was the direct reason that resulting in worm pollution in drinking water treatment process. The active drift capacity of tubifex is weaker than that of naidid and the highest drift rate for tubifex and naidid are 4.02% and 18.5% respectively. The results also showed that passive drift of worm would be induced by water flow. For tubifex, passive drift rate increases with the enhance of water flow velocity, while the passive drift rate of naidid fluctuates irregular with the change of water flow velocity, but can be influenced significantly by dissolved oxygen level. The pilot experiment results of worms'migration and distribution in drinking water treatment process showed that interception efficiency of coagulation and sedimentation to worms reaches almost 100%. Though sand filter has high interception and inactivation effect on naidid, its interception effect on tubifex can be influenced by filtration rate and filtration cycle. The distribution of both tubifex and naidid in BAC filter is centralized in 0⁶0cm of filter bed. In BAC filter, naidid can not only migrate from up to bottom along with filter current, but also move from bottom to up for its aerotaxis. For all the types and backwashing modes of BAC filter, only air-water backwashing of V-filter has better removal effect on naidid with removal efficiency about 80%.By comprehensive analysis of inactivation effect,·OH inducing effect, oxidative stress and lipid peroxidation occurred during inactivation process, inactivation mechanisms of oxidants and copper to worms were discussed. The results showed that KMnO4 possesses the worst inactivation effect for it has not·OH inducing effect and the toxic effect on worm is preformed only by its strong oxidizability. ClO₂ has significant·OH inducing effect and oxidative stress on worm, and can permeate into worm's body rapidly for its well liposolubility. Therefore it shows the best inactivation effect. Though both copper and chlorine have·OH inducing effect, which result in oxidative stress and lipid peroxidation, copper has better inactivation effect than chlorine for it can destroy worm's antioxidase system at the same time.Interception-inactivated technology, a highly efficient controlling technology of worm pollution risk, was established by combining interception of sand filter and inactivation of oxidant organically. During interception-inactivation, the interception of sand filter prolongs inactivated contact time, which resulting in the promoting of inactivation effect. At the same time, inactivation of oxidant can not only kill some worms, but also decrease migration ability of survival worms by which the interception effect of sand filter is strengthened. Pilot experiment results showed that interception-inactivation realized 100% interception to both tubifex and naidid while ClO2 was 0.2mg/L. Meanwhile, the inactivation efficiency of tubifex and naidid reached 72.7% and 100% respectively.