Objective To investigate the disinfection status and efficiency of different disinfection method in central water supply units, to analyze the relevant influencing factors, and to provide a refence for ensuring the safety of drinking water in rural areas of Liaoning Province, China.

Methods From 2018 to 2022, 2-4 monitoring points were set up in each town of 14 cities in Liaoning Province to collect basic information of central water supply units. One finished water sample and 1-2 tap water samples were collected from each water treatment plant for analysis of microbiological indicators (total coliform count, Escherichia coli count, and total bacterial count)in the dry and wet seasons, according to the Standard Examination Method for Drinking Water (GB/T 5750-2006). Water samples with disinfection were tested for the disinfectant indicators (free chlorine or chlorine dioxide). The results were evaluated according to the Standards for Drinking Water Quality (GB 5749-2006) in order to analyze microbial and disinfectant indicators.

Results A total of 5 384 centralized water supply units were investigated. The primary water source was groundwater (94.42%). The water supply was primarily from small-scale centralized systems (96.34%). Water disinfection was performed in 739 (13.72%) water supply units. The disinfection methods included chlorination disinfection (69.68%), chlorine dioxide disinfection (27.60%), and ultraviolet(UV)disinfection (2.72%). Disinfection equipment was used as required in 60.35% of all units. Bleaching powder (81.55%) was mainly used in chlorination disinfection. High-purity chlorine dioxide (67.16%) was the main method in chlorine dioxide disinfection. A total of 23 427 water samples were collected, including 3 389 water samples with disinfection(84 water samples with UV disinfection, and 3 305 water samples with chlorination or chlorine dioxide disinfection). The qualified rate of free chlorine and chlorine dioxide indicators was 91.20%. The qualified rate of water samples with chlorine dioxide disinfection (96.31%) was significantly higher than that with chlorination disinfection (89.22%) (χ²=41.70, P < 0.05). The qualified rate of free chlorine in wet season was higher than that in dry season. The qualified rate of free chlorine in the tap water was higher than that in the finished water. The qualified rate of free chlorine in water samples disinfected using equipment as required was significantly higher than that of water samples disinfected with occasional use of equipment and manual disinfectant addition (P < 0.05). No significant differences in the qualified rates of chlorine dioxide were found between different seasons, different types of water samples, different sources of water, and different methods of adding disinfectant (P>0.05). The qualified rates of total coliform count, E. coli count, and total bacterial count were significantly higher in water samples with disinfection than in water samples without disinfection (P < 0.05). The qualified rates of total coliform count and total bacterial count were significantly higher in water samples with chlorination disinfection than in those with chlorine dioxide disinfection (P < 0.05).

Conclusion The disinfection status of rural drinking water in Liaoning Province needs to be strengthened. The disinfection efficiency of chlorination is higher than that of chlorine dioxide. In the future, we should strengthen the supervision and monitoring of rural drinking water disinfection to ensure the safety of drinking water.