This paper studied the effect of ferric chloride on waste sludge digestion

dewatering and sedimentation under the optimized doses in co-precipitation phosphorus removal process. The experimental results showed that the concentration of mixed liquid suspended solid (MLSS) was 2436 mg稬

-1

and 2385 mg稬

-1

in co-precipitation phosphorus removal process (CPR) and biological phosphorous removal process (BPR)

respectively. The sludge reduction ratio for each process was 22.6% and 24.6% in aerobic digestion

and 27.6% and 29.9% in anaerobic digestion

respectively. Due to the addition of chemical to the end of aeration tank

the sludge content of CPR was slightly higher than that of BPR

but the sludge reduction rate for both processes had no distinct difference. The sludge volume index (SVI) and sludge specific resistance of BPR were 126 ml穏

-1

and 11.7?10

12

m穔g

-1

respectively

while those of CPR were only 98 ml穏

-1

and 7.1?10

12

m穔g

-1

indicating that CPR chemical could improve sludge settling and dewatering.