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.
LIU Xin-chun ZHANG Yu YANG Min WANG Zhen-yu LV Wen-zhou
With high content of the Al13 species and the active chloride, an electrochemically prepared polyaluminum chloride (E-PACl) presents integrated efficiency of coagulation and oxidation. The coagula- tion properties of E-PACl were systemically investi- gated through jar tests in the various water quality conditions. The active chlorine in E-PACl can signifi- cantly influence the coagulation behavior due to the active chlorine preoxidation, which can change the surface charge characteristic of organic matter (OM) in water. The active chlorine preoxidation could im- prove the E-PACl coagulation efficiency if the water possessed the characteristics of relatively low OM content (2 mg/L) and high hardness (278 mg CaCO3/L). In the water with medium content of OM (5 mg/L), dosage would be a crucial factor to decide whether the active chlorine in E-PACl aided coagula- tion process or not. Comparing with alkaline condition, active chlorine would show a more significant influ- ence on the coagulation process in acidic region.
