Study On The Controlling Of Naidid Worms Pollution Risk In O₃-BAC Drinking Water Treatment Process

In recent years, worms are reported propagating excessively in water sources due to the large amount of nutrients input. Once worms enter water plant along with the source water, they can penetrate the whole water treatment because of their strong scalability. This can cause safety risks for aquatic organisms and microorganisms of water quality. When conditions are right, these worms can also breed excessively in water purification process, further exacerbating the risk for contamination of worms. Of which the BAC process is particularly the phenomenon of breeding. The reason for that is the carbon layer in BAC filter is rich in dissolved oxygen and microorganisms.This study began the research of worms in water purification process via the site investigation. Firstly, we analyzed the dominant species of worms in the water purification process, including these sources and pollution types; then we carried out the research on migration and distribution of worms and the development and application of pollution risk control technology, using the naidid worms in O₃-BAC drinking water treatment process in South as the research object. Those works could supply some theoretical guidance and technical support for pollution risk control technology for worms in the drinking water treatment process. The main conclusions are as follows:(1)The site sampling analysis of worms was carried out in Bi Jiashan water plant in Shenzhen. We set sampling points at the outlet of each water purification unit and carried consecutive detection for more than 4 months. The result showed Chironomus,naidid worm and nematode were the dominant species, Of which Nematode was main from external pollution sources along with the input of source water, and Chironomus, naidid worm were from internal pollution sources by second propagation. Location of the outbreak of naidid worms was in BAC filter, and chironomid larvaes in the sedimentation tank.(2)Through laboratory simulation experiments, we discovered the migration characteristics of naidid worms and confirmed drift migration was the direct reason for causing pollution of naidid worms in water purification process. Change of DO could have a larger effect on the passive drift migration of naidid .When DO decreased from 8mg/L to 5 mg/L, the scale of naidid significantly increased, of which the latter was 10 times larger than the former.(3)We used oxidants such as Cl₂, ClO₂, KMnO₄ and copper to inactivate naidid so as to inspect the inactivating efficacy of each oxidant. The inactivation results indicated that oxidants all had the inactivation function to naidid. The inactivation efficacy showed a significant dose effect and time effect. Those oxidants can all achieve 100% inactivation of naidid under the premise of ensuring the adequate value of C and CT. The inactivation effect of the four chemicals in turn was ClO₂>Cu>Cl₂>KMnO₄.(4)On the basis of research achievements of migration characteristics and oxidation inactivation of naidid, we synergistically combined oxidative inactivation with interception of sand filter, and established the technology of high efficient control for risk of naidid in the water purification process. That is technology of interception and inactivation. In the process of interception and inactivation , the interception of sand filter effectively extended the contact time of oxidative inactivation, and promoted the effect of oxidative inactivation. Oxidative inactivation could not only inactivate naidid worms, but also reduce the migration of the naidid worms which were not inactivated, strengthening the interception effect of sand filters. On the condition of pilot test, with the ClO₂ dosage of 0.2mg/L, the technology of interception and inactivation not only achieved the 100% interception efficiency of naidid worms, but obtained 100% inactivation efficiency.