Study On The Disinfection Technology Of Sludge Water Reusing Safely In Waterworks

The shortage of water resources and water quality deterioration problems are now becoming more and more seriously in China. Since a large number of suspended impurities, pathogenic microorganisms and other contaminants from the raw water are enriched in sludge water which discharges from sedimentation tank or filter backwashing process, reusing sludge water may affect the quality of raw water, thereby affecting the finished water quality. Therefore, it is necessary to take measures to remove pollutants of sludge water before its reusing to assure safety.According to the characteristics of sludge water, including filter backwash and clarifier waste water, the safe proportion of reusing water to total water demand is determined by small scale laboratory studies. Through small scale and pilot experiments we studied the effects of sodium hypochlorite, chlorine dioxide, ultraviolet to disinfect sludge water and results are as follows.Firstly, it will not bring quality risks on water when the ratio of sludge water to total water demand is less than 6% in water directly reusing. In the case of emergencies, when the reflux ratio has to be increased, it is necessary to adopt other methods for reducing risks of sludge water reusing.Secondly, sodium hypochlorite one of the main disinfectants, has a certain removal on bacteria and algae. The inactivation rates of algae and bacteria are up to 60% and 90% respectively when the concentration of sodium hypochlorite is 2 mg/L and the reaction time is 30 minutes.Thirdly, when the concentration of chlorine dioxide is between 1 mg/L ~2.5 mg/L and reaction time at 30 minutes, the inactivation rate of algae is 48%~83%. When the concentration is 1mg/L and reaction time is 20 minutes, the inactivation rate of bacteria is up to 85%. It can also remove iron in sludge water, and its inactivation of cyclops is slightly better than that of sodium hypochlorite.Fourthly, UV disinfection technology would not bring new contaminants into water, and it is a relatively safe and effective method of disinfection. It is effective on removal of algae and bacteria. When the UV radiation dose is 50mj/cm~2, the inactivation rates of algae and bacteria are up to 91% and 96% respectively. But the disinfection effect would be influenced greatly by turbidity which should be reduced by pretreatment.Lastly, UV disinfection is more effective than sodium hypochlorite disinfection and chlorine dioxide disinfection. When the water turbidity meets the requirements, it is a convenient and feasible disinfection method during sludge water reusing.