Biological Stability Analysis And Evaluation Technology Optimization For Drinking Water Distribution System Of A City In The Lower Reaches Of The Yellow River

Bacterial regrowth in drinking water distribution system has impacted severely on the security of urban water supply in our country. This study was carried out for the drinking water distribution system in the lower reaches of the Yellow River, in view of the lack of accurate biological stability evaluation data and the imperfect evaluation indicator system. In this study, the indicators, including assimilable organic carbon (AOC), biodegradable dissolved organic carbon (BDOC), microbially available phosphorus (MAP) and heterotrophic plate counts (HPC) were measured to evaluate the biological stability of drinking water in Jinan, a city in the lower reaches of the Yellow River. Simultaneously, the limiting factor for bacterial regrowth was tested. A biofilm-based method was used to measure the biological regrowth potential of drinking water by a biofim annular reactor. The relationship among various indicators of biological stability was explored. The significance of biofilm biomass as an indicator in the evaluation of biological stability was analysed. The results were shown as follows:(1) In the water distribution system of this city, AOC ranged from8.7to328.7μg/L, and the value below100μg/L covered83.6%of the data detected. The AOC increased with the temperature increased seasonally without a character of on-way change. AOC-P17, the dominant component in AOC concentration, presented a seasonal change in contrast to AOC-NOX.(2) Similarly, AOC/DOC, BDOC/DOC but AOC/BDOC varied with season. The concentration of BDOC fluctuated from0.06to0.63mg/L and was high in summer, which was distinct for water treated by different waterworks.(3) The MAP was low and exhibited no regular change against seasons or pipeline distance. The limiting factor for bacterial regrowth differed along the distribution system with different candidates of AOC, phosphorus and other inorganic nutrients.(4) When the AOC concentration of influent water is stable, the AOC concentration of effluent water decreased with the increase of suspended bacteria and biofilm biomass, and vice versa. The form of biofilm on the wall of pipeline can be impacted greatly by the pipeline material. Cast iron pipe is liable to form biofilm compared with PVC pipe and the corrosion increases the turbidity of water. PVC is better than cast iron in biological stability maintaining. Biofilm index, like biofilm biomass, is necessary as a comprehensive indicator for a biological stability evaluation technology.