Study On The Effects Of Air Pollutants On Water Qualitof Water Sulnetwork

A new mechanism of secondary pollution in the water quality of watersupply network was proposed. The air pollutants enter into the water supplynetwork through the inlet and exhaust valves during the intake process, alongwith the air, and influence the drinking water quality. When thenegative-pressure water hammer generated, caused by the changes of boundaryconditions, the inlet and exhaust valves will take in the air to relieve theconstant pressure decrease in the pipes. The harmful air pollutants also enterthe water supply network which is originally considered as closed, causing thewater pollution, especially the secondary pollution towards the water thatdirectly distributed to the users, and threatening the security of waterconsumption severely.The air pollutants that highly affect the water quality of water supplynetwork include heavy metal ions, polycyclic aromatic hydrocarbons andheterocyclic amine. The polycyclic aromatic hydrocarbons once into the watersupply network, with the concentrate of2000ng/m3to4000ng/m3, willthreaten the security of water consumption. Though the concentration ofheterocyclic amine in the air is lower, its carcinogenicity and teratogenicity aremuch higher than that of polycyclic aromatic hydrocarbons heterocyclic amine,which cannot be ignored as well. Analysis of the hydraulic characteristics of water supply networkindicated that direct negative–pressure water hammer wave and indirect waterhammer wave in the pipes, as results of the changes in boundary condition,would cause the rapid decrease of pipeline pressure. Protecting through inletand exhaust valves only, with the higher intake flowrate which result in theunstable statement of water flow, would influence the safety of water supply.While protecting through the one-way surge tank is costly. In the protectionagainst negative-pressure water hammer, the joint protective measure shouldbe adopted with one-way surge tank in the forepart and inlet and exhaustvalves at the end. During the normal operation, the flow patterns in thenetwork are mainly laminar flow, wavy flow and slug flow. In the partialpositions (such as valves, elbows, etc.), will appears air mass flow, foam flowand annular flow, which are transitory. The water with air pollutants will flowto the downstream pipes stably under the laminar flow, wavy flow and slugflow.The analysis and calculation of air pollutants concentration was carriedout under the hypothesis that the pollutants would completely mix with waterand flow to the downstream. As for the concentration of different inlet andexhaust valves, after the inlet pollutants enter into the pipeline, only the firstpressure decrease wave was considered, while the mutual influence ofpollutants was not taken into account the mutual influence of pollutantsthrough different inlet and exhaust valves was not taken into account. Theformulas for calculating the concentration of air pollutants in differentsituations were derived, and the law of movement and mutual influence wereanalyzed. The actual example calculation showed that the inlet pollutantsconcentration in the water supply pipelines is proportional to the instantaneousintake flow of the inlet and exhaust valves under constant air pollutantsconcentration. Due to the changes of boundary condition, which caused high negative pressure, the instantaneous intake flow of the inlet and exhaust valveswould be large and result in the high concentration of air pollutants.