Water pollution characteristics and control strategies in arid areas of Northwest China: a case study of Qingshui River Basin in Ningxia

Taking Qingshui River Basin, the largest first-level tributary of the Yellow River in Ningxia, as an example, the water quality, water environmental capacity and the characteristics of pollution loads of each control unit in key sections were analyzed, and targeted pollution control strategies were proposed. The results showed that the water quality of Sanying national control section of the Qingshui River in 2015-2018 could not stably reach the Class Ⅳ water quality standard of Environmental Quality Standards for Surface Water (GB 3838-2002), and the chemical oxygen demand (COD) of Quanyanshan Section was at risk of exceeding the Class Ⅳ water quality standard. The water environmental capacity of the basin was 592.83-1 238.25 t/a for COD, 51.99-193.60 t/a for ammonia nitrogen (NH₃-N) and 5.02-12.85 t/a for total phosphorus (TP). The pollution load into the Qingshui River of the basin was 15 661.1 t/a for COD, 1 670.2 t/a for NH₃-N and 784.5 t/a for TP in normal water period, which was 16, 14 and 89 times of the water environmental capacity (COD 940.57 t/a, NH₃-N 114.64 t/a, TP 8.81 t/a). The pollution load per unit area in Guyuan City was the highest (COD 3.04 t/a, NH₃-N 0.22 t/a, TP 0.06 t/a), with outstanding problems of industrial pollution load and urban living pollution. The total pollution load in Zhongwei City control unit into the river was the highest (COD 6 738.45 t/a, NH₃-N 868.88 t/a, TP 218.12 t/a), with relatively serious urban living source pollution, while Wuzhong City control unit had relatively heavy poultry-farming pollution. Based on the water quality targets and the pollution characteristics of each unit, it was recommended that the wastewater recycling and utilization of industrial enterprises be strengthened and the urban wastewater treatment capacity be improved in Guyuan City control unit; the construction, transformation and upgrading of sewage collection and treatment facilities be focused on Zhongwei City control unit; and the centralized treatment and reuse of livestock manure in large-scale farms be implemented in Wuzhong City control unit.