The Application Of Microbial Flocculants In Sludge Dewatering Of Municipal Sewage Plant

The highly efficient and environmentally friendly microbial flocculants (MBF) produced by Aspergillus sojae to optimize the experiments of flocculation and dewatering of concentrated municipal sewage sludge have been discussed in this paper. The production conditions of MBF, the mixed effect of different flocculants, field experiments of sludge dewatering as well as composting were also investigated.Aspergillus sojae was incubated in a rotary shaker, with initial pH at 5-7, temperature at 32℃and culture time of 60h, MBF showed high flocculating activity, and optimal dosage was 0.65% for Standard kaolin solution. When using fermentor, the best culture time was 36h. The flocculating rate of MBF remained above 80% after 50d when stored under 4℃, showing its good storage stability.The optimal dosage of bioflocculant was 9mL when treating 200mL concentrated sludge. The sludge dewatering rate could reach over 80% after centrifuging at 3000r/min for 5min.With the increasing amount of sludge, the optimal unit consumption of MBF decreases. Compared with PAM and PAC, MBF has a higher efficiency of centrifugal dewatering and better filtration conditioning.With ultrasonic frequency at 28 KHz and ultrasonic time of 20s, the ultrasound could improve the performance of sludge dewatering. MBF adding with 3% (v/v) of 1g/L FeCl₃ could promote dewatering rate more than 80.5%. Using cPAM alone, the lowest water content of sludge after centrifuging was 79.81%; while mixing the cPAM and MBF, the water content of sludge could reduce to 77.9%, the absolute value of Zeta potential of sludge filtrate tended to zero, and flocculant size of sludge was larger as well.Hydrogen bonds test proved that the flocculating function of MBF depended on hydrogen bond strength, while the cPAM depended on ionic bond. Infrared spectra revealed that the structure of MBF was polysaccharide material with linear structure. Ion chromatogram showed that the hydrolysis monomer of MBF contained lots of arabinose and glucose rhamnose, also contained galactose and rhamnose, but no mannose. The organic elemental analysis approved that MBF contained a large quantity of oxygen elements, which were presumed to be carboxyl and hydroxyl of polysaccharide. HNMR spectra also indicated that this MBF were polysaccharide. It could be inferred that MBF was a kind of polysaccharides material with linear structure, also containing the special structure of rhamnose monomer and enol-type as well as protein substances. The SEM with 5000 times amplification exhibited that the surface of pure bioflocculant was membrane structure with villous protrusions, but cPAM was crystalline structured shape.Using belt filter press, when cPAM mixed with MBF, the dosage of cPAM was reduced to 1/4 compared with using alone, while the proportion of MBF was 3/4, and water content of the sludge was 65% after dewatering. Frame filter combined with limestone and FeCl₃ had good ability of dewatering, the water content of sludge was under 60%, however, this treatment could bring serious corrosion and higher yield of sludge. The sludge conditioned by MBF had higher compost value, with a dark brown color.