| This paper aimed at enhancing sludge dewaterability and settleability, and screened aluminum sulfate from metal flocculants to combine with lysozyme. The research determined optimum dosage and dosing pattern, and studied the effects of experiment conditions. Reaction mechanisms were discussed by analysing Zeta potential, floc structure and surface feature, EPS contents and EEM and aluminum distribution and forms in sludge.Through single factor experiment and response surface methodology, the optimum dosage of lysozyme and aluminum sulfate were determined at 0.10g/g TS and 0.10g/g TS respectively, and the dosing pattern was treating sludge with lysozyme first followed by aluminum sulfate. Under this condition, the initial settling speed was 2.24 m L/min and the final settling volume was 66.2m L. The cake moisture content and SRF declined to 71.84% and 0.68 ×1012m/kg respectively, which reduced 20.82% and 2.92×1012m/kg respectively comparing to raw sludge. The influences of experiment conditions were evaluated through further tests: the sludge settelability and dewaterability were improved with the increasing of temperature during10~50 ℃. The lower the sludge concentration, the better the sludge settelability and dewaterability during 10000~30000mg/L. Under acid conditi on, degree of dewatering was enhanced with dewatering velocity and settleability worsened comparing to neutral condition; the settelability and dewaterability dramatically deteriorated under alkaline condition. Through comprehensive consideration, it was a ppropriate to treat sludge under common condition, which were sludge concentration of 15000~25000mg/L, temperature of 30℃ and p H=7, since sludge settelability and dewaterability were fairly enhanced under this condition.Research on Zeta potential, floc structure and surface feature, EPS contents and EEM showed that lysozyme presented positive potential in liquor phase due to its high isoelectric point, and could neutralize with sludge which possessed negative charges and reduce zeta potential to a certain extent; aluminum ions and its hydroxyl complex through hydrolysis possessed higher charge density, could remarkably dedu ce zeta potential; after treated by the combination of lysozyme and aluminum sulfate, sludge |ζ| reduced to 0.18, which could promote destabilization and flocculation of sludge particles, and stayed good settleability while achieving better dewaterability. Flocs of sludge treated with aluminum sulfate were large and compact; treating sludge with lysozyme first followed by aluminum exerted little impact on forming flocs, and flocs structure and surface feature stayed well; treating sludge with aluminum first followed by lysozyme would damage flocs structure, and flocs became loose with surface pores increased, which may lead to poor dewaterability. The main components in S-EPS and LB-EPS of raw sludge were tryptophan-like(Ex/Em =280/350,Ex/Em=230/350) and ocean-humus-like(Ex/Em=290/370), and fulvic-acid-like fluorescence peak was detected in TB-EPS. EPS of sludge treated with lysozyme increased due to the hydrolysis of cell wall and substan ces released from cells, and fluorescence intensity augmented as well; EPS of sludge treated with aluminum sulfate markedly inclined, especially the decrease in LB-EPS contents was beneficial for enhancing settleability and dewaterability. When sludege was treated with combination of lysozyme and aluminum sulfate, protein in S-EPS and TB-EPS increased camparing to sludge treated with aluminum alone, but LB-EPS content obviously lowered, which indicated that aluminum sulfate remained good conditioning effect, and dewaterability got further enhanced. When sludge was treated with aluminum sulfate and the combination of lysozyme and aluminum sulfate, most of aluminum distributed in sludge solid while few in liquid phase. Main fraction of aluminum in sludge solid was residual form which was steady and difficult to be released to environment, and exerted little impact on environment. |
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