Reclaimed water for landscape water replenishment: Threshold nitrogen and phosphorus concentrations values for bloom control

Abstract

Considering the high risk of algal blooms caused by nitrogen and phosphorus in reclaimed water during the utilization of reclaimed water in the landscape, an association model for the nitrogen and phosphorus concentrations in reclaimed water for algal blooms control was derived, which considers the local climatic conditions (temperature and light intensity), hydraulic retention time (HRT), and non-point source pollution. Based on the association model, the effects of different non-point source pollution and HRT on the threshold nitrogen and phosphorus concentration values for bloom control were studied by conducting some numerical simulations for three single species and one mixed algae. At HRT = 30 d, the threshold nitrogen and phosphorus concentrations were obtained for different non-point resource pollution coefficients. The numerical results for different non-point source pollution loads show that, with an increase in non-point source pollution, the control curve of nitrogen and phosphorus concentrations gradually approached the coordinate axis, indicating that the threshold nitrogen and phosphorus concentration values in reclaimed water also be gradually reduced. There have been similar conclusions regarding the effect of HRT on the threshold values of nitrogen and phosphorus concentrations in reclaimed water. This study provides a theoretical scientific basis for determining reasonable water quality control levels in the replenishment of landscape water with reclaimed water.