Water quality variation of a typical urban landscape river replenished with reclaimed water

Abstract

Replenishing landscape water with reclaimed water has been an effective way to alleviate urban water shortage. In order to investigate the variation of water quality along the pipeline and flow direction in a typical urban landscape river replenished with reclaimed water, relevant water quality indexes were consecutively monitored for 8 months. Concentrations of chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) all showed a downward trend along the flow direction in reclaimed water effluent pipeline. However, values of turbidity, COD, and chlorophyll a (Chla) were decreased significantly, while concentrations of TN and TP were increased in the mixed area of reclaimed water and river. Furthermore, along Licun River, an upward trend of COD and ammonia-nitrogen (NH₄⁺-N) was observed in summer, while in other seasons, a falling first and then rising trend of COD concentration appeared. The concentration of NH₄⁺-N randomly fluctuated between 0.08 ​mg/L to 2.05 ​mg/L among all seasons, and TN and nitrate-nitrogen (NO₃⁻-N) were below 15 ​mg/L with a downward first and then upward trend in each season. The concentration of TP showed a slightly upward trend (ranging from 0.08 ​mg/L to 0.57 ​mg/L) and Chla was at a relatively low level (0 – 46.32 ​μg/L). The correlation analysis revealed that light intensity, nitrogen and phosphorus were the influential factors of algae growth in river. In addition, the biomass of emergent plants and submerged plants was increased after replenishing with reclaimed water, playing a vital role in the remediation of urban landscape river.