Process evaluation of urban river replenished with reclaimed water from a wastewater treatment plant based on the risk of algal bloom and comprehensive acute toxicity

Municipal wastewater reuse has an important role to play with scarce water resources and serious water pollution. However, the impact of reclaimed water on the aquatic ecology and organisms of the receiving water needs to be assessed. This study investigated one ecological restoration project of an urban river replenished with reclaimed water, and evaluated the risk of algal bloom and acute biological toxicity in the river. Results showed that the concentrations of permanganate index and ammonia nitrogen in the river could stably remain below the standard values, the concentrations of total phosphorus were high and most of the monitoring values were between 0.42 and 0.86 mg/L. The content of chlorophyll a was relatively lower, ranging from 0.06 to 0.10 mg/m3. The maximum value of Fv/Fm was 0.42, which was lower than the algal bloom prediction threshold of 0.63. Moreover, the results of luminescence inhibition rate on luminescent bacteria showed that the reclaimed water did not cause significant biological toxicity to the aquatic ecology. The study suggested that implementing urban reclaimed water reuse projects requires a series of ecological purification and restoration technologies in the receiving water, which can effectively guarantee the stability of water quality and the safety of water ecological environment.