New insights into biodrying mechanism associated with tryptophan and tyrosine degradations during sewage sludge biodrying.

Sewage sludge biodrying is a treatment that uses bio-heat generated from organic degradation to remove water from sewage sludge. Dewatering is still limited during biodrying, due to the presence of extracellular polymeric substances (EPS) in sludge. To study the biodrying mechanism associated with EPS compositions tryptophan and tyrosine degradations, this study investigated the microbial function in sludge biodrying material. This study conducted a taxonomic analysis of biodrying material; determined the most abundant genetic functions; analyzed the functional microorganisms involved in the degradations of tryptophan and tyrosine; and summarized the metabolic pathways. The results indicated efficient degradations of tryptophan and tyrosine were observed during the initial thermophilic phase; functional microorganisms were mainly from the phyla Firmicutes, Actinobacteria, and Proteobacteria, enriched with genes involved in amino acid transport and metabolism. These findings highlight the potentially important microorganisms and typical pathways that may help improve dewaterability during biodegradation.

Analysis of bacterial community structures in two sewage treatment plants with different sludge properties and treatment performance by nested PCR-DGGE method.

The bacterial community structures in two sewage treatment plants with different processes and performance were investigated by denaturing gradient gel electrophoresis (DGGE) of nested polymerase chain reaction (nested PCR) amplified 16S rRNA gene fragments with group-specific primers. Samples of raw sewage and treated effluents were amplified using the whole-cell PCR method, and the activated sludge samples were amplified using the extracted genomic DNA before the PCR products were loaded on the same DGGE gel for bacterial community analysis. Ammonia-oxidizing bacterial and actinomycetic community analysis were also carried out to investigate the relationship between specific population structures and system or sludge performance. The two plants demonstrated a similarity in bacterial community structures of raw sewage and activated sludge, but they had different effluent populations. Many dominant bacterial populations of raw sewage did not appear in the activated sludge samples, suggesting that the dominant bacterial populations in raw sewage might not play an important role during wastewater treatment. Although the two plants had different sludge properties in terms of settleability and foam forming ability, they demonstrated similar actinomycetic community structures. For activated sludge with bad settling performance, the treated water presented a similar DGGE pattern with that of activated sludge, indicating the nonselective washout of bacteria from the system. The plant with better ammonium removal efficiency showed higher ammonia-oxidizing bacteria species richness. Analysis of sequencing results showed that the major populations in raw sewage were uncultured bacterium, while in activated sludge the predominant populations were beta proteobacteria.