Effect Of Enzyme-Chemcal Reagent Co-conditioning On Dewaterability Of Activated Sludge

With the increasing production and its urgent need for reduction of municipal sludge,the study investigated the key operational factors of activated sludge(AS)conditioning with single enzyme or combined enzymes.The relationships between enzymatic degradation and sludge dewatering performance were assessed and the corresponding optimal operating parameters of the combined enzymes/single enzyme-chemical reagent conditioning technology were also determined.Moreover,the physical and chemical properties,moisture distribution and the variation characteristics of organic matter in different EPS layers of typical AS samples were analyzed.The interaction mechanism during enzyme-chemcal reagent co-conditioning AS process was investigated.The results as shown below:Compared with neutral cellulase,acid cellulose and acid protease,medium temperature a-amylase and neutral protease were more efficient under enzyme conditioning.With 0.1 g·g-1 TS a-amylase or 0.15 g·g-1TS protease conditioning respectively,the corresponding polysaccharide(PS)and protein(PN)contents in extracellular polymeric substances(EPS)reached their own minimums of 12.1?170.3 mg·g-1VSS.The optimized combined enzyme technology through response surface methodology(RSM)was after 0.13 g·g-1TS a-amylase for 1hr and 0.16 g·g-1TS protease was added to treat subsequent AS for 4hrs.The corresponding PS and PN contents in EPS reached their own minimums of 17.88 and 218.72 mg·g-1 VSS respectively,but both the Zeta potential and size of AS flocs decreased,thus AS dewaterability deteriorated accordingly.During combined enzymes-chemical reagent conditioning,With the increase of cetyl trimethyl ammonium bromide(CTMAB)and cationic polyacrylamide(WD4960)dosage,the moisture content of vacuum filtrated sludge cake and the capillary suction time(CST)decreased gradually for above-mentioned combined enzyme conditioned AS.The moisture content of vacuum filtrated sludge cake for re-conditioned AS at 0.5 g·g-1TS CTMAB was reduced to 64.66%.It was 5.01%lower than the minimum value of raw sludge control.But the CST was higher than raw sludge control.The CST for re-conditioned AS at 9.46 g·Kg-1TS WD4960 reached its minimum of 16.3s which was close to the minimum value of raw sludge control.The moisture content of sludge cake was slightly lower than raw sludge control.This phenomenon implied that subsequent CTMAB dosing could ameliorate the dewaterability of AS flocs pre-treated with combined enzymes by neutralizing their negative surface charge and changing their hydrophilicity/hydrophobicity,while WD4960 functioned in terms of neutralizing surface charge and adhesion-bridging.The varying degrees of bound water were released from AS treated by different aforementioned conditioning ways,such as:complex enzymes,chemicals(CTMAB/WD4960)and combined complex enzymes-chemicals,WD4960 led to the least bound water release from the others.During single enzyme(a-amylase/protease)-chemical reagent conditioning,with the optimized dosage of 0.1 g·g-1TS a-amylase or 0.12 g·g-11TS protease,the corresponding moisture content of vacuum filtrated sludge cake for AS re-conditioning at 0.4 g·g-1TS CTMAB approached 62.4%and 68.3%.Besides charge neutralization,CTMAB could scatter AS flocs and release AS EPS,thus leading to the reduction of part bound water through its dispersion,solubilization effect.The a-amylase-CTMAB conditioning released the most bound water from AS,followed by neutral protease-CTMAB conditioning.