Abstract
This paper used the Mann-Kendall method to analyse the water quality changes trend of the municipal sewer network in Beijing North Second Ring Road area from Oct. 2013 to Nov. 2017, which selected chemical oxygen demand (CODcr), ammonia nitrogen (NH3-N) and total phosphorus (TP) as three indicators, used the concentration value divided by the standard values as the pretreatment way, and then calculated the comprehensive index. The analysis result showed that the drainage water quality changes were divided into three phases since the "Decree on Urban Drainage and Sewage Treatment" was issued in this area. The first phase was from Oct. 2013 to Feb. 2014. It continued to decline. The second phase was from Mar. 2014 to May 2014. It rebounded and rose. The third phase was from Jun. 2014 to Nov. 2017, the shocks fell. In the end, the paper predicted that in Dec. 2017 the water quality of the sewer network in this area was still showed a downward trend but not significant. Through actual monitoring, it was found that the predicted results were in good agreement with the actual monitoring results.
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