Antibiotics have strong antibacterial activity, even trace antibiotics can greatly inhibit the pollutant degradation efficiency. In order to effectively improve the pollutant degradation efficiency, it was hence of great significance to explore sulfapyridine (SPY) degradation and the mechanism of antibacterial activity. This study selected SPY as the research object, of which the trend of SPY concentration through hydrogen peroxide (H₂O₂), potassium peroxydisulfate (PDS) and sodium percarbonate (SPC) and resultant antibacterial activity at pre-oxidation was examined. The combined antibacterial activity (CAA) of SPY and its transformation products (TPs) was further analyzed. The SPY degradation efficiency reached more than 90 %. However, the degradation efficiency of antibacterial activity was between 40-60 %, and the mixture's antibacterial activity was difficult to be removed. The antibacterial activity of TP3, TP6 and TP7 was higher than that of SPY. TP1, and TP8 and TP10 were more prone to synergistic reaction with other TPs. The antibacterial activity of binary mixture gradually changed from synergism to antagonism as binary mixture concentration increased. The results provided a theoretical basis for the efficient degradation of antibacterial activity of the SPY mixture solution.

Due to population growth and economic development, problems such as uneven distribution of freshwater resources and degradation of water quality are becoming increasingly prominent. Many measures have been adopted to address water resources issues; however, few studies have focused on specific changes in water quality after policy implementation. In this study, Yiwu City, Zhejiang Province, a typical hilly city with a well-developed water system, was selected to analyze the changes in water quality. By analyzing the rainfall series and hydrology characteristics, and water quality characteristics, this paper revealed the water environment characteristics and put forward some suggestions for water management in hilly cities. Results showed that the historical rainfall time distribution is uneven, and the water environment capacity of urban inland rivers exhibits strong variability in Yiwu City. The contents of ammonia nitrogen (NH3-N) and total phosphorus (TP) decreased significantly since the policy implementation of ‘Five water cohabitation’. Urban rivers presented regional pollution and surface source pollution characteristics, and the water quality fluctuated significantly with the increase in rainfall. At the same time, the study confirmed that scientific water replenishment measures can effectively improve water quality, providing reference ideas for the protection and management of China's urban water environment.

Calculation of water pollutant discharge amount is the basis for compiling regional water pollution control plans and water resources protection plans. Although most of the calculation parameters can be obtained from the relevant standards or guidelines, the calculation and value method forsome important parametersare not clear or have different reference standards, such as urban sewage treatment rate, rural domestic pollution discharge coefficient and sewage discharge amount from service industry. Take the calculation of pollutant discharge amount in Hangjiahu plain as an example, the calculation method and value range of the above parametersis discussed in this paper.

The plain river network area is strongly influenced by human activities, with flat terrain, weak hydrodynamics and poor water quality. Previous studies have mostly focused on water quality categories, lacking an overall study of the pollution characteristics of water bodies and their changing trends. In order to comprehensively grasp the water pollution situation of the river network in the northern Yu Plain, this study scientifically analysed the water quality characteristics of the river network in the northern Yu Plain and its correlation with rainfall through regression analysis and MK mutation test based on the long series of water quality and rainfall data of the Dongjin River and Unity River in the northern Yu Plain from 2017-2021. The results show that the correlation between water quality and rainfall in the river network of the northern Yu Plain is not significant, reflecting that the pollution in the watershed is still controlled by point sources, but there is a trend for the Unity River to change to non-point source control; the CODMn, NH3-N and TP of the Dongjin River and Unity River all show a high positive correlation, and the correlation of the Dongjin River is higher than that of the Unity River; the MK mutation test shows that there is no significant mutation point in the Dongjin River in the last five years, and the Unity River has no significant mutation point in the last five years. The MK mutation test shows that there is no significant mutation point in Dongjin River in the past 5 years, and there is a sudden change in water quality in Unity River from 2017 to 2018, and the water quality indexes show a decreasing trend in general, but remain stable in recent years. The study aims to academically reveal the dominant factors, pollutant characteristics and water quality trends of pollutants in rivers in the northern Yu Plain, and to propose scientific references for the pollution prevention and control of other plain river networks.