Enhanced Enzymatic Hydrolysis Of Excess Sludge By Surfactant

With the increase of amount of municipal wastewater and sewer-laid rates and expansionof active sludge system, it brings about large amount of sludge and generates a newinternational tendency of sludge minimization and resource utilization. Hydrolysis is the ratelimiting step of sludge digestion. Therefore, enhancing sludge hydrolysis is important baseand premise to reduce sludge. Compared with other sludge solubilization technology such asozone oxidation, chlorine oxidation, thermal hydrolysis, acid, alkali, mechanical andultrasonic, hydrolysis by additional enzyme can not only cut down digesting time, improvesludge digestibility, and reduce energy, but also can be easily controlled, and its products areharmless to environment. In order to enhance the efficiency of enzymatic hydrolysis of excesssludge, the article mainly aims at explaining the influence of sodium dodecyl sulfate (SDS) toexocellular enzyme hydrolysis sludge by preliminary studied and discussed.Through the analysis of sludge pH value and enzyme activity, we were furtherunderstanding the mechanism of SDS strengthening enzyme hydrolyze the excess sludge. AtSDS dosage of0.1g/g, the protease activity of SDS+protease showed a2.3-time increase andthe amylase activity of SDS+amylase showed a1.2-time increase compared with enzymatictreatment. When SDS treatment, sludge pH value slightly increased with the increase ofdosing quantity of SDS at50℃, but the pH changed in7.13~7.38, which still accorded withthe optimal pH requirements of protease and amylase. It explained that SDS didn’t influencethe enzymatic reaction rate by changing the pH of sludge system. SDS can damage sludgenetwork structure, reduce the embedding probability of enzyme and sludge which indirectreduce losses of enzyme activity, and improve the efficiency of the sludge hydrolysis.In this investigation, the effects of SDS and enzyme on the promotion of excess sludgehydrolysis were investigated, and the influences of temperature, the quantity of SDS and themixture of two enzymes were each studied in this paper. The results showed that SDS canstrengthen the enzyme hydrolyze sludge through the contrast analysis of sludge SCOD/TCODand SCOD releasing increased linearly with the increase of SDS dosage. When thetemperature was50℃, SCOD/TCOD increased from1.3%to54.3%and VSS reductionachieved to43.2%at the SDS dosage of0.20g/g. When the dosing quantity of enzyme was60mg/g, the effect of SDS and enzyme (amylase, neutral protease, and the mixture of twoenzymes) on hydrolysis of excess sludge showed that the efficiency of sludge hydrolysiscould be greatly improved by composite enzyme(amylase: neutral protease=3:1), andconfirmed that the best dosing quantity of SDS is0.10g/g, the best of reaction temperature was50℃. The improvement of sludge protein and carbohydrate solubilization by surfactanthad also been observed in our previous studies. We could conclude that after four-hourhydrolysis, the concentration of protein, NH4+-N and soluble sugar in SDS+mixed enzymessystem were improved by85.4%,92.5%and64.0%, respectively. Correspondingly, sludgehydrolysis within prior4h was consistent with first-order reaction dynamics. The reaction rateconstant(K) of soluble sugar increased from0.23to0.41, which indicated that the reactionrate of hydrolysis increased significantly. It is well known sludge protein and carbohydrate areabsorbed onto sludge surface, but they can be solubilized by surfactant and then dissolve intoaqueous phase because surfactant has the feature of solubilization. Also, the enhancedsolubilization of sludge EPS by SDS caused the break-up of sludge matrix, which resulted inmore sludge inner protein and carbohydrate released.