Study On Using Hydrolase To Reduce Excess Sludge In The Activated Sludge Process

The excess sludge has become one of the most serious burdens of urban sewage treatment plant, because of their huge production, high processing costs and the serious pollution to the ambient environment. In this work, aiming to reduce the production of excess sludge, we choose the hydrolases, which have excellent catalytic hydrolysis and can efficiently hydrolyze of bacterial cells, to lyse the sludge from the activated sludge system during the operational process. This research can broaden the reduction of sludge field, deepen the mechanism of the reduction technology, and develop a reliable method to apply in the reduction of sludge engineering.First, several typical hydrolases has been analyzed the effect of lysing the sludge from the activated sludge system. The results showed that compared to а-amylase and protease, lysozyme showed the most hydrolysis effect for the hydrolysis of the sludge in the same dosage of enzyme. Subsequently, the selected lysozyme was added in the sludge from the SBR system by static test reactor. And the most suitable hydrolysis conditions were obtained at the 0.072~0.250 g lysozyme/ g MLSS, 30~60 min, 30~40 ℃.The results about the reduction of sludge in the SBR system showed that(1) the sludge, which was treated by lysozyme before being returned back to the reactor, showed the least amount of sludge yield;(2) the hydrolyzed sludge was reached to 10% of the total amount of the activated sludge in the SBR system, it could ensure that both the best reduction of the excess sludge and degradation efficiency of the organic pollutants;(3) the sludge, which was operated by lysozyme 3 cycles per a day, showed the best sludge reduction effect. The results about the efficient of effluent in the SBR system showed that in the different operating cycles, the COD and TN with and without lysozyme addition were almost the same. The in-depth research found that compared with the reference system without lysozyme, the higher value of both the protease activity, the TTC-ETS and the ATP of the activated sludge with lysozyme indicated a better ability to digest organic pollutants. The reasons of sludge reduction under the SBR system may be ascribe to following points:(1) decomposition of the dissolved sludge nutritional media is the predominant reason;(2) enhanced endogenous metabolism of activated sludge especially in the anaerobic period(i.e. a stronger oxidizability), can result in a better ability of self-consumption. The DGGE fingerprints revealed that no significant differences of the microorganisms could be observed between the activated sludge system with and without lysozyme.The research of sludge yield with lysozyme in the continuous running activated sludge system showed that compared with traditional activated sludge method, the excess sludge production with the assistance of lysozyme could be reduced to 37.33%. The degradation ability of COD and TN were improved in the activated sludge system because of the lysozyme addition. Sludge characteristics, such as the protease activity, the TTC-ETS and the ATP were declared that both the metabolism ability of the sludge and the decompose rate of organic matter in the testing system with lysozyme was improved. The main reasons of the sludge reduction in the continuous running activated sludge system with lysozyme may be that the returned sludge can be hydrolyzed by lysozymes in the mud pool before further decomposed as the substrate in the aerobic pond. Another reason is the better self-consumption of activated sludge with lysozyme during the continuous running system. The DGGE fingerprints showed no significant differences in the microbial community and microbial species between the activated sludge system with and without lysozyme addition, whcih were in good consistence with the SBR system.