Analysis of total amount, types and utilization status of low-polluted water in the Nine Plateau Lake Basins of Yunnan Province

In order to effectively promote the utilization of low-polluted water in the Nine Plateau Lake Basins in Yunnan Province, based on the data of urban sewage treatment plants, meteorology, and agricultural irrigation in the lake basins in 2021, the total amount of low-polluted water in the lake basins in 2021 was calculated from two aspects, i.e. the tail water of urban sewage treatment plants and the drainage volume of farmland runoff. The current utilization situation was analyzed based on actual investigations. The results showed that: 1) In 2021, the total amount of low-polluted water generated in the Nine Plateau Lake Basins was 1 507.360 7 million m³, of which the tail water from urban sewage treatment plants was 825.441 4 million m³, and the drainage volume of farmland runoff was 681.91 93 million m³. 2) The total amount of low-polluted water reused in the Nine Plateau Lake Basins was 462.794 4 million m³, with a reuse rate of 30.70%. The water reuse rate of urban sewage treatment plants was 54.46%, with the highest reuse rate in Dianchi Lake Basin, mainly used for landscape water, followed by agricultural irrigation and urban miscellaneous use. The reuse rate of farmland runoff drainage was 1.94%, mainly achieved through the construction of regulation and storage belts in basins such as Erhai Lake, Fuxian Lake, Qilu Lake, and Xingyun Lake. Among them, Xingyun Lake Basin had the highest amount of farmland runoff drainage reuse. 3) There was still a lot of utilized space for the reuse of low-polluted water in the lake basins. Different goals for low-polluted water reuse could be set based on industrial structure and development positioning in different lake basins, and water quality monitoring of farmland runoff drainage should be strengthened. According to the water quality concentration of farmland runoff drainage in different periods, the purpose and destination of farmland runoff drainage should be determined scientifically and reasonably, the storage and purification function of the regulation and storage belts be fully utilized, and the comprehensive utilization among the tail water of sewage treatment plant, farmland retreat water and initial rainwater be strengthened. It was recommended to select typical areas within the Nine Plateau Lake Basins to carry out pilot projects for the allocation of low-polluted water. Through pilot demonstrations, successful experiences could be summarized, and a replicable and promotable low-polluted water utilization model be formed to promote the reuse of low-polluted water in the basin.