Effect Of ClO₂Pre-treatment On Micro-polluted Algae-laden Water At A Water Treatment Plant In Daqing

Rapid development and urbanization accelerate the pace of industry andagriculture, resulting in a series of environmental problems. Emissions fromagricultural/industrial wastewater and domestic wastewater increases every year,resulting in deterioration of water quality of the lake. The nature of algae is very stable,and density is small, routine coagulation is difficult to remove it, causing greatdifficulties for water treatment, and the situation in the event of eutrophication,governance and recovery becomes extremely difficult.Chlorine dioxide pre-oxidationtechnology can changing the surface morphology of algal cells, Zeta potential, theproportion of cells that can kill algal cells, improving water conditions on thesubsequent coagulation process, the use of chlorine dioxide pre-oxidation treatmentcan be satisfied with the treatment effect.The frequent occurrence of algal blooms in Longhupao reservoirs causesproblems to water plant operation and management.In this paper,we investigated theefficacy of ClO2pre-oxidation treatment on micro algae contaminated water, theinfluence factors on ClO2pre-oxidation treatment process, the application of ClO2pre-oxidation in Daqing Zhongyin water treatment plant.By detecting turbidity, UV254,COD, the density of algal and chlorophyll-a to explore the effectiveness of coagulantand algae removal.Pure chlorine dioxide oxidation tests shows that the turbidity removal effect is notobvious by chlorine dioxide, even though the dosage is4mg/L, the removal rate isonly about20%. After chlorine dioxide pre-oxidation treatment, the UV254and CODvalues are higher than the raw water. Pure chlorine dioxide has a good effect on thekilling effect of the algae, can kill more than90%of the raw water algae by1.5mg/L.The chlorine dioxide pre-oxidation and coagulation treatment experimental showsthat the oxidation of chlorine dioxide can promote coagulation process, when thedosage is maintained at0.8mg/L, while at the same coagulant effect, it can improve theturbidity removal efficiency by5percentage points. By chlorine dioxide pre-oxidation,and then make the coagulation reaction in water will make the UV254and COD declinefurther, lower than only coagulation. This trial for algae removal is very significant,when the dosage of chlorine dioxide is1.0mg/L, coagulant dosage is only1.0mg/L, theremoval rate can reach87.65%.By contrast the strengthen coagulation effect from ClO2and KMnO4pre-oxidation for Daqing Longhupao reservoir draws that the effect of ClO2pre-oxidation treatment is superior than KMnO4, but both of the COD removalefficiency is not particularly pronounced. KMnO4and ClO2pre-oxidation all have a good effect for algae remove,but the effect of ClO2treatment is better than KMnO4,1.0mg/L ClO2removal efficiency can be achieved1.5mg/L of KMnO4.Contact time tests shows that within3~12min ClO2can kill most algae. Thereaction of coagulation followed30min by oxidation reaction can get the best effect,and then extend the oxidation time on the water quality does not change significantly.By changing raw water conditions shows that in the pH range of3to8can play abetter oxidation, but after the pH above9, there will be a significant decrease in celldensity and the removal of organic matter. Concentration of organic matter in rawwater also has some influence on the effect of chlorine dioxide pre-oxidation,with theincrease of the organic content in the raw water, the removal of algae effect will besignificantly decreased.