The four issues relating to improve the efficiency of up-grading and operation of urban sewage systems in China
Combining the practices and experiences learned in the recent years in China and the relevant international practices this paper raises and discusses the four topics,which are related to improve the efficiencies of urban sewage systems up-grading and operation in China,including:ex-traneous water intrusion and overflow of separate sewer system,sewage concentration,the neces-sity to expand sewage treatment capacity,self-clean flow velocity in sewers.A summary and some suggestions are presented at the end of the paper.