Rainwater utilization and storm pollution control based on urban runoff characterization

The characteristics of urban runoffs and their impact on rainwater utilization and storm pollution control were investigated in three different functional areas of Zhengzhou City, China. The results showed that in the same rain event the pollutant loads （chemical oxygen demand （COD） and total suspended solids （TSS）） in the sampling areas were in the order of industrial area 〉 commercial area 〉 residential area, and within the same area the COD and TSS concentrations of road runoffs were higher than those of roof runoffs. The first flush effects in roof and road runoffs were observed, hence the initial rainwater should be treated separately to reduce rainwater utilization cost and control storm pollution. The initial roof rainfall of 2 mm in residential area, 5 mm in commercial area and 10 mm in industrial area, and the initial road rainfall of 4 mm in residential area and all the road rainfall in commercial and industrial areas should be collected and treated accordingly before direct discharge or utilization. Based on the strong correlation between COD and TSS （R2, 0.87-0.95） and the low biodegradation capacity （biochemical oxygen demand BOD5/COD 〈 0.3）, a sedimentation process and an effective filtration system composed of soil and slag were designed to treat the initial rainwater, which could remove over 90% of the pollutant loads. The above results may help to develop better rainwater utilization and pollution control strategies for cities with water shortages.

A multi-objective optimization approach for harnessing rainwater in changing climate

As the world grapples with the profound impacts of climate change,water scarcity has become a pressing issue.However,there is a shortage of in-depth research on the trade-offs between water resource dependence and the economic,ecological,and social needs of arid and semi-arid regions like Lanzhou,China.Flower cultivation in Lanzhou relies heavily on the Yellow River,often overlooking the potential of natural rainfall.Here we first calibrated a water balance model through artificial precipitation experiments in a Soil and Water Conservation Demonstration Park in Lanzhou.We then developed a multi-objective optimization model to balance the cost-benefit considerations of various plausible measures across economic,ecological,and social dimensions in the searching for solutions that are more adaptable to climate change and local devel-opment needs.Model simulations show that the solutions we designed can effectively manage water-shortage days,significantly reduce Yellow River water extraction,and improve cost-effectiveness,meeting 66%-80%of water needs for flower cultivation in the studied park.The findings highlight the potential of rainwater collection and utilization solutions to mitigate water scarcity in arid and semi-arid cities,thereby enriching water resource management.