Studies On The Treatment Technology Of Abrupt Cadmium Pollution In The Drinking Source Water Of Longjiang River

In recent years, the abrupt heavy metal pollution incidents happened frequently in the drinking source water in China, which caused a serious threat to the local ecological environment and the local people’s health. Facing the problem of heavy metal pollution of drinking source water which was more and more serious, how to deal with it scientificly and effectively has become a top priority. Based on the cadmium(Cd) pollution emergency treatment of Longjiang River in Guangxi province in2012, this study explored the affecting factors and optimal technological conditions to remove the cadmium pollution in the water of Longjiang River by the combination of hydroxide precipitation and coagulation technology which regarded the polyaluminium chloride (PAC) as flocculants, and the stability and migration law of the flocs was investigated after adopting the technology to dispose the cadmium pollutional water. In addition, the feasibility and reliability of the technology which was used in the emergency treatment of the cadmium pollutional water was proved through the successful application of the technology in the cadmium pollution emergency treatment of Longjiang River. The main research conclusions of this study are as follows:(1) Coagulation and sedimentation experiments indicated that the main affecting factors of the cadmium removal efficiency were the initial pH of water, the adding dosage of PAC and the hydraulic conditions, when the combination of hydroxide precipitation and coagulation technology, which regarded the PAC as flocculants, was used to dispose the simulate cadmium pollution water of Longjiang River. The optimal technological conditions of cadmium removal by PAC were pH0=9.0, the dosage of PAC was40mg/L, N1=400r/min,T1=30s,N2=250r/min,T2=5min,N3=100r/min,T3=3min,N4=50r/min,T4=3min, and the standing time was1h. Under the optimal technological conditions, PAC could remove the cadmium in the simulate cadmium pollution water effectively.(2) The stability experiment of flocs containing cadmium indicated that the initial pH of water and disturbance had great effects upon the cadmium release or dissolving out from the flocs. In the neutral and alkaline water environment, the flocs dissolved out little cadmium, which suggests that the flocs had good stability; While in the acidic water environment, the flocs dissolved out more cadmium, which suggests that the flocs had poor stability. And the stability of flocs is poor in the disturbed water environment, with the high amount of cadmium release; If reduced the pH value of water to acid when disturbed the water, the amount of cadmium dissolved out and released from the flocs would be higher, and the stability of the flocs would be poorer. Therefore, the monitoring during the floods should be strengthened in the post project analysis for eco-environmental impact of Longjiang River.(3) The results from the closely monitoring, during the floods after cadmium pollution emergency treatment of Longjiang River, indicated that the cadmium concentration of water from the Longjiang River and Liujiang River decreased to the background level gradually; Most sediments containing cadmium migrated to the down-stream with mud, sand, water and adherent algae, and their environmental risk to water-quality eliminated gradually; The cadmium concentration of bottom mud from Longjiang River also decreased, and restored to the background levels gradually.(4) The abrupt cadmium pollution incident of Longjiang River in2012was disposed successful and the ecological environmental risk of the sediments containing cadmium reduced gradually after the treatment, which effectively proved that the combination of hydroxide precipitation and coagulation technology which regard PAC as coagulant had high feasibility and reliability and could apply to dispose the abrupt cadmium pollution incident successful.