Abstract: The effect of pH value(4.0-12.0) of soluble chemical oxygen demand (SCOD),volatile fatty acid (VFAs),nitrogen and phosphate production in the activated sludge hydrolysis process was investigated at ambient temperature by batch experiments.The experiment results showed that the sequence for hydrolysis-acidification efficiency of activated sludge was: alkaline station,acidic station and neutral station.When the pH value was between 6.0 and 11.0,the efficiency increased with the increasing of pH,but when the pH was at 12.0,the activated sludge hydrolysis-acidification efficiency decreased because of the browning reaction.It was observed that the SCOD and VFAs production increased as the reaction time prolonged.While pH changed between the ranges of 4.0-11.0,ρ_SCOD and ρ_VFAs reflect a trend of declining first and then rising,with the neutral pH as the division point.When pH=11.0 the concentrations of SCOD and VFAs were the highest,and the data were 2 599 and 749 mg/L,respectively.However,the concentrations of NH₄⁺-N and PO₄^3--P reached the maximum when pH=4.0 with the data of 208.1 and 193.4 mg/L,respectively.Thus,by using pH value as the controlling parameter higher efficiencies of sludge hydrolysis and acidification could be achieved.Especially when pH value was between 10.0 and 11.0,higher fermentation efficiencies and lower rates of nitrogen and phosphate releasing can be realized.This can bring more carbon source for nitrogen and phosphorus removal and reduce the quantity of excessive activated sludge within the wastewater treatment system.