Study On Promoting Excess Sludge Hydrolysis Under Alkaline Thermal Condition

As a effective pretreatment technology of excess sludge treatment, alkaline thermal hydrolysis method was not only good at cells disintegration, but also enhancing the treatment results of subsequent process (anaerobic digestion, sludge Dewatering,etc.).The infuences of alkaline thermal parameters(such as temperature, pH value,reaction time,sludge concentration,alkaline concentration etc.) on excess sludge hydrolysis effect were investigated. The concentration of SCOD (soluble chemical oxygen demand) was represented the quality of sludge hydrolysis effect. The results showed that the concentration of SCOD increased with the increase of temperature, reaction time, pH value, sludge concentration and alkaline concentration. The concentration of SCOD reached 17 950 mg/L and SCOD/TCOD was 0.65 on the conditions of pH=13, 170℃and 75 min. The concentration of SCOD after alkaline thermal hydrolysis treatment increased with the increase of sludge concentration, in which the nice linear relation was reached and the correlation coefficient(R~2) was above 0.97. The increasing rate of the SCOD was improving with the increase of the pH value and the SCOD of unit sludge reached 672 mg/g at pH13.The addition of alkali can reduce the resistance of the sludge cells to high temperature and enhance the release and the hydrolysis of organic materials from the sludge cells. The affect of alkaline thermal hydrolysis method on excess sludge and its characteristic parameters(such as soluble chemical oxygen demand, volatile fatty acids, ammonianitrogen,pH value, sludge concentration, etc.) were investigated. The maximal dissolving rate of suspended solids(SS) was 67％and 72％for volatile suspended solids(VSS) at pH13 with 60min. No matter for unadjusted pH or adjusted pH, various nitrogen concentration increased, especially the increase was with the increase of temperature and reaction time. After pH adjustment, the alkalinity of the sludge was reduced significantly by the increase of the organic acids and ammonia-nitrogen and the consumption of alkali during reaction.The affect of three factors on the SCOD was investigated through orthogonal experiment at the temperature of 170℃, the importance was sludge concentration, pH value and reation time in turn..