PREPARATION OF MARINE NITRIFYING SLUDGE

Activated sludge taken from night soil treatment plants which employ a sea-water dilution system to decrease the temperature elevation caused by fermentative heat during operation was proved to be a good seed source for the preparation of acclimated marine nitrifying sludge (AMNS). The preparation of AMNS with high nitrifying activity was successful from seed activated sludge obtained from a night soil treatment plant which uses a sea-water dilution system throughout the year, within only a two-month acclimatizing period, by applying the fill and draw cultivation method. The nitrifying activity of our newly prepared AMNS was 13.1 mg-NH4-N/g-MLSS/h, which is comparable to that of fresh water nitrifying sludge. The AMNS was composed of 50 to 100 mum bacterial flocs and showed an excellent settling property. The AMNS exhibited high nitrifying activity, even at a low sodium concentration, but its activity decreased at sodium concentrations above 10 g/l. The optimum pH for nitrification by the AMNS was 8.5 and its nitrifying activity did not greatly change within the pH range of 7.0 to 9.0. The optimum temperature for nitrification by the AMNS was 35-degrees-C. The nitrifying reaction of the AMNS was proved to be less sensitive to temperature change.