Study On Enhancement Of Water Chemical Stability In Limestone Contactor

Pipe corrosion which is caused by water chemical instability increases energy consumption of delivery and water turbidity, even causes red water phenomenon. It also causes the attenuation of residual chlorine and dissolved oxygen, the growth of biofilms, the biological instability and the propagation of pathogenic bacteria in the pipe network. The measures of anti-corrosion and descaling are not as good as maintaining the chemical stability of the treated water. Thereby it is crucial to increase its chemical stability.The paper mainly concentrates on the research of the influence of limestone contactor on the chemical stability of low alkalinity and low hardness water. The specific studies are as follows:1) The influence of limestone contactor on the chemical stability of the effluent without dosing carbon dioxide.2) The relations between content of carbon dioxide and water chemical stability in low alkalinity and low hardness water. The influence of the depth, media size and filtration rate on the chemical stability of the effluent.3) The influence of degassing process on the chemical stability of the effluent.The pH value, alkalinity and hardness of the effluent increase without dosing carbon dioxide, so does the chemical stability. When the limestone contactor with the filtration rate≤4m/h, the effluent IL, IR, CCPP and AI are all in their acceptable ranges, but the Larsen ratio is still high, and its value is greater than 0.5. It also has the risk of anion damaging pipeline passive film, which triggers the "yellow water" problems.If the effluent is not carried out the treatment of removal of carbon dioxide, its pH value is low with the combination process of carbon dioxide and limestone contactor. It results that the effluent IL, IR, CCPP and AI are out of their acceptable ranges, so it is also corrosive. However, because of the increasement of alkalinity Larsen ratio can be decreased to 0.5. It indicates that the ability of anion damaging pipeline passive film declines, and electrochemical corrosion is very weak. Removing residual carbon dioxide from effluent can raise the effluent pH value to 8.0. The results show that IL, IR, CCPP, AI and LR can reach to their acceptable ranges, so as to improve the water chemical stability.