Replenishment of landscape water with reclaimed water: Optimization of supply scheme using transparency as an indicator

With shortages of urban water resources, reclaimed water (RW) has become increasingly important as an alternative water source, especially for replenishing landscape waters. To meet the requirements of landscape quality control when RW is used for partial replacement of the surface water (SW) source to a channel-type urban water in a city in northwest China, scenario analyses were carried out by mathematical modelling. Water transparency (measured by SD) is used as an intuitive indicator to reflect the comprehensive influence of suspended solids (SS) and algae growth on the water’s aesthetic quality. Findings indicate that although the significantly higher nutrient concentrations of RW might bring about higher algae growth potential, in comparison with SW, its much lower SS concentration could offset the adverse effects on SD, to a large extent. By embedding the water quality model, calibrated and validated based on a two-year measurement data into MIKE 3 software for both SD and algae growth calculation, computer simulations were carried out to assist a series of scenario analyses of RW utilization and optimization of the water supply scheme. As a result, to meet the requirement of SD > 80 cm at the control section of the landscape water, the total water inflow required was not increased but decreased with the optimal application of RW. The advantages of lower SS in RW to reduce the demand inflow of total water was more evident with the higher requirement of SD. Replenishment of the channel-type urban water by RW was, thus, proven feasible from the viewpoint of landscape quality control.