Excess propagation and disinfection control of Copepod in an ozone-granular activated carbon filter in southern China

The reasons for the excess propagation of Copepod in an ozone-granular activated carbon filter were investigated and batch experiments were conducted to analyze the influences of CT value, pH and organic matter on the efficiency of disinfection of Copepod using chlorine and chloramines. The experimental results revealed that Copepod accounted for 70% of the zooplankton in the sand filter effluent that flowed into the ozone contact tank. Complete inactivation of Copepod was attained when the ozone dosage was 6 mg/l for 15 min contact time. The high bromide concentration in the raw water prevented increasing the ozone dosage due to the formation of bromate during ozone oxidation. Live Copepod entered the GAC filter via the ozone contact tank effluent. The average period of Copepod growth was approximately 8 days when cultured in the GAC filter water at 25°C and the survival ratio of the Copepod nauplii was greater than 80%. The number of Copepod in the GAC filter effluent was three times greater than the survival in the sand filter. Varying the pH from 6 to10 did not influence the disinfection efficiency of chloramines and the organic matter had rather low negative effects on the inactivation rate.