Reduction of excess sludge and characterization of microbial community in biopolymer-using biological wastewater treatment processes

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Effects of the addition of biodegradable plastics (PHBV, PCL, and PIA)on microbial growth and denitrifying activity in activated sludge process were investigated. A multi-phase activated sludge system consisting a standard aeration process and a sold-phase denitrification proems with PHBV produced 20-30% reduced excess sludge compared to the normal activated sludge process. Also, this multi-system had a high denitirication activity. Most of the predominant denitrifiers isolated quantitatively by the plate-counting method using non-selective agar medium were unable to degrade PHBV and were identified as members of genera of the class Betaproteobacteria by studying 16S rRNA gene sequence information nirS and nosZ gene clone library-based analyses of the microbial community from the reactor showed that most of the nirS and nosZ clones proved to be derived from members of the family Comamonadaceae and other phylogenetic groups of the Betaproteobacteria.Effects of the addition of a chemical uncoupler; 3,5-dichlorophenol (DCP), on microbial growth in activated sludge were also investigated. The addition of 3,5-DCP in an activated sludge reactor resulted in the significant reduction of excess sludge without a great decrease in BOD removal. However, this effect was eliminated during the prolonged operation of the reactor with 3,5-DCP. Population shifts from Betaproteobacteria to Alphaproteobacteria and Actinobacteria took place during this operation. The inhibition of microbial growth by 3,5-DCP was eliminated by the addition of biodegradable plastic such as PHBV.When activated sludge was gown with mineral medium at pH 4, acidophilic nitrification took place In this process, the biomass decreased gradually with operation time.