Comparison Experiment Study On The Arsenic Removal In Raw Water Between Whirling -Clarifier And Circulation Clarifier

Arsenic contamination in drinking-water has been recognized as a major problem of catastrophic proportions. With the widespread report of arsenic's toxicology and health hazard to human body, the technologies of arsenic removal have been of great increasing concern. In order to provide a technology of arsenic removal with low treatment cost, stable operation and simple skill-required, arsenic removal in raw water was studied and compared between the whirling-clarifier and circulation clarifier.A jar text of coagulation stirring in the simulation of whirling-clarifier's hydraulic conditions was carried out. In this experiment, several factors had impact on arsenic removal were studied, which respectively inluding the oxidant's dosage of sodium hypochlorite (NaClO) and the time of preliminary treatment in oxidizing, the coagulant's dosage of ferric chloride (FeCl₃) and polymeric aluminium (PAC) and coagulant aids's dosage of polyacrylamide(PAM). From the jar text ,the coagulant of FeCl₃ was optimized, and when the concentration of arsenic was changed from 100μg/L down to 10μg/L, the best dosage of NaClO, FeCl₃ were 10mg/L and 15mg/L, while PAM was not required. The results showed that the removal of arsenic with whirling-clarifier was of feasibility.Whirling-clarifier and circulation clarifier were employed in the experiment of arsenic removal. The experiment was compared under three kinds of hydraulic retention time(HRT)in the first and second flocculation zone, which respectively were equal to 5.4minutes, 2.7minutes and 1.8minutes. In the experiment , the arsenic concentration and the turbidity of the raw water were 100μg/L (0.1mg/L) and 100NTU respectively, in which 10mg/L NaClO, 15mg/L FeCl₃ and no PAM were added. The result showed that both two apparatus had the best effect under the condition of HRT equal to 2.7minutes on arsenic removal and turbidity, which could conform to Sanitary standard for drinking water (GB5749-2006) on the limit 10μg/L of arsenic concentrations. The experiment had proved that whirling-clarifier was superior to circulation clarifier on arsenic removal.Whirling-clarifier would be popularized and applied in engineering. Take a water plant of scale of ten thousand ton per day as an example for economic analysis,the construction investment was about 341,000 yuan and the processing cost (chemical consumption and power consumption) was about 0.16 yuan per ton per day.