Studies On Algae Removal In Micro-polluted Resource Water

Algae has great impact on the production of drinking water. Excessive amount of algae would produce stinking odor, also some algae release toxins in waters, such as microcystin and nodularins; algae and its extracellular polymeric substances were trihalomethane (THM) precursors, which could be transferred into toxic byproducts during disinfection, then made the water unsafe. Algae in the raw water may bring on bad influence:consume more coagulants; clog filter; increase backwashing water and affect water quality. Various research and actual operation indicate that using traditional process to get rid of algae is not effective. Therefore, enhanced coagulation is an important research for removing algae from raw water.The effect of using enhanced coagulation,traditional coagulation and pre-chlorination to remove chlorella vulgaris as represent of algae in NanPing reservoir was compared in this research. New ideas that "modified zeolites+polyaluminum ferric chloride" and "PDMDAAC-PAFC (P-PAFC) " to remove algae and turbidity was brought in this paper. According to the experimental results:â‘ the removal efficiency of the algae and turbidity with the method of "modified zeolites+polyaluminum ferric chloride" was superior to the individual dosing polyaluminum ferric chloride(PAFC). With 3.0 mg/L PAFC and 60 mg/L modified zeolites, the removal efficiency of the algae and turbidity was 85.78% and 90.07% respectively, when modification zeolites was mixed in resource water before PAFC.â‘¡P-PAFC present better coagulation performance when compared with simple PAFC and pre-chlorination-PAFC, including increased algal-removal, turbidity removal and zeta-potential reduction. With 1.0mg/L P-PAFC dosage, the residual turbidity reduced to 1.02NTU, and removal efficiency of algae and turbidity went up to 93.5% and 71.3% respectively.Coagulant tests were also performed using different actual surface water samples, and the effectiveness of P-PAFC was compared with PAFC. The results show that enhanced coagulation is more successful to remove Melosira and Chlorella than Cylindrosperm in reservoir water treatment; and the flocs were tight and uniform after Cylindrosperm (dominant algae in Phoenix and Mirror Reservoir) removal. This could be confirmed that algae characteristics would influence the performance of a water treatment works. The performance of algae removal by P-PAFC depends on the type and characteristic of algae.Meanwhile, Jinshazhou raw water was prepared on jar stirring tests by using enhanced coagulation and pre-oxidation processes for a further study. The effectiveness of algae and turbidity removal were investigated. Residue algae cells were analyzed by scanning electron microscope (SEM). Microscopic examination showed that, P-PAFC/PAFC treated with no damage to algal cells; pre-oxidation of algal cells after injury is more serious. Research shows that "modified zeolites-PAFC" and "P-PAFC" can not only enhance the efficiency of algae and turbidity removal, but also will not destroy algae cells or produce disinfection by-products.This enhanced coagulation process would be of reference and guiding significance to the purification of algae in drinking water.