Current state and future perspectives of sewer networks in urban China

Chinese authorities and the public have largely ignored sewer networks; however, various problems are emerging nationwide with the increase construction of new sewers. The current state of sewer network construction, administration, and maintenance in China is comprehensively reviewed in this study. Serving about 444 million people, 511,200 km of sewer lines are located in urban areas. In 2014,$7 billion was invested in sewer network construction. However, both the sewer pervasion rate and the per capita sewer length were significantly lower than those in developed countries. Sewer administrative agencies in local governments are uncoordinated. Laws, regulations, and standards are incomplete, and some practices are unscientific. The future situation of sewer maintenance is extremely grim because sewer corrosion control measures have not been launched. Moreover, inspection and rehabilitation chiefly rely on traditional approaches. In contrast, the overall market share of innovative technologies is very low owing to high cost, funds shortage, and technical limitations. Approaches such-as liner inversion cured-in-place pipe, pull-in ultraviolet light cured liners, and spiral wound lining are applied mostly in economically developed regions. According to status and problem analyses, China＇s top priority will be to conduct aggressive maintenance work in sewer networks in the future. New technical route, corrosion control - periodic visualized inspection - trenchless rehabilitation, could be the best option for future sewer maintenance in China. Instmctions and opportunities for applying this technical route are discussed in detail in this study. Finally.additional factors in the development of sewer networks in China are suggested.

New method for efficient control of hydrogen sulfide and methane in gravity sewers:Combination of NaOH and nitrite

An innovative treatment method by the combination of NaOH and nitrite is proposed for controlling hydrogen sulfide and methane in gravity sewers and overcome the drawbacks of the conventional single chemical treatment.Four reactors simulating gravity sewers were set up to assess the effectiveness of the proposed method.Findings demonstrated hydrogen sulfide and methane reductions of about 96.01%and 91.49%,respectively,by the combined addition of NaOH and nitrite.The consumption of NaNO_(2) decreased by 42.90%,and the consumption rate of NaOH also showed a downward trend.Compared with a single application of NaNO_(2),the C/N ratio of wastewater was increased to about 0.61 mg COD/mg N.The greenhouse effect of intermediate N2O and residual methane was about 48.80 gCO_(2)/m^(3),which is far lower than that of methane without control(260 gCO_(2)/m^(3)).Biofilm was destroyed to prevent it from entering the sewage by the chemical additives,which reduced the biomass and inhibited the recovery of biofilm activity to prolong the control time.The sulfide production rate and sulfate reduction rate were reduced by 92.32%and 85.28%,respectively.Compared with conventional control methods,the cost of this new method was only 3.92×10^(−3)$/m^(3),which is potentially a cost-effective strategy for sulfide and methane control in gravity sewers.