LAUSR

A trapezoidal constructed ditch (TCD) of 300 m length and 2.2 m width was designed and built in the downstream section of the upper Yangtze River for in situ treatment of primary domestic sewage. The removal efficiencies of TN, NH4-N, NO3-N, TP and PO4-P from the TCD were approximately 61, 63, 48, 58 and 51%, respectively. The concentrations of TN, NH4-N, NO3-N, TP and PO4-P showed a decreasing trend with increasing distance downstream. Plant assimilation and sediment retention were the key mechanisms for N and P removal within the TCD, with subsequent microbial uptake and transformation of the nutrients. The TCD outlet showed significantly higher dissolved oxygen (DO) concentrations and lower values of electrical conductivity and total dissolved solids compared to the influent. Results of this study highlight the potential of TCD to mitigate nutrients from primary domestic sewage transported downstream and could be incorporated into local best management practices.