The Application Of Microbial Flocculant In Sludge Dewatering

This thesis studied in using sugarcane bagasse, as the low-cost raw materials, toproducing the microbial flocculant, discussed the dehydration property of microbialflocculant to municipal sludge and dyeing sludge and, systematically researched onmicrobial flocculant enlarge cultivation, the synergism of microbial flocculant withskeleton builder and other auxiliary means also the heavy metals mobilization beforeand after the treatment, etc.Through inoculating at the optimum inoculum size of0.5%and processing batchfermentation cultivation by fermentation tank for60hours, the fermentation liquorhad the best flocculation effect, especially when the dosage is5.0mg/L, which raisedthe sludge dewatering rate from75.60%to84.2%, decreased the sludge moisturecontent from95.82%to76.21%with the crude bioflocculant yield of1.16g/L. In theevent of cultivation for108hours, the fermentation liquor still had significantflocculation effect, which could keep the sludge moisture content around76.81%. Theexperiment of fed-batch fermentation indicated that, cultivation with constant PHwould inhibit the secretion of microbial flocculant, the best flocculation effecthappened with the cultivation of72hours and the dosage of5.0mg/L, simultaneouslythe sludge moisture content fell to76.47%.The flocculating effect of fermention liquid rose rapidly after feeding newculture medium and stopping pH control. The sludge moisture rates were keptbetween76.22%~75.60%under different bioflocculant dosages. Generally speaking,feeding new culture could both decrease the waste of raw material and improve theflocculating rate of flocculant efficiently.In the event of conditioning the municipal sludge only by microbial flocculantand with the dosage of45mg/L, the sludge dewatering rate was raised to81.33%andthe sludge moisture content could reach79.91%; in case of conditioning the sludgewith the ultrasonic radiation the low-frequency of which could not promote the sludge dewatering ability, in order to improve such ability, the high frequency one wereneeded and the time for ultrasonication shall not exceed60seconds. The sludgemoisture content could be even lower provided that the sludge was conditioned bymicrobial flocculant after the ultrasonication. If the sugarcane bagasse as the skeletonbuilder was compounded with the microbial flocculant to condition the sludge, withthe optimum combination of58.4mg/L microbial flocculant,5g sugarcane bagasse,0.96g/L calcium chloride, the sludge moisture content could be reducedto71.76~71.42%.Microbial flocculant and Fenton reagent both could reduce the moisture contentof dyeing sludge in a certain extent which is about4~5%. The best degradationconditions compounded by microbial flocculant and Fenton reagent were52.4mg/Lof microbial flocculant dosage,88.2mg/L of H2O2dosage,8specific value ofH2O2/Fe2+,3.5of PH. In such case, the sludge moisture content can be decreased from87.32%to79.72%. After co-conditioning, Pb and Cu can be transferred to residualform; Ni and Zn were activated and achieved better bio-availability; at the same time,the corresponding forms of Cd did not show significant difference pre-and post-conditioning.