in china's extensive development in the past few decades, water resources have been seriously polluted, water bodies have gradually lost their capacity to absorb and purify pollutants, and the accumulation of pollutants in water has become a major environmental safety hazard. under the background that ecological civilization construction is highly valued, water pollution control has been promoted rapidly, but the effect is unsatisfactory mainly by building urban sewage treatment plants. according to the 2016 urban and rural statistical yearbook, by the end of 2015, more than 5,000 municipal sewage treatment plants (excluding some plants built by themselves according to national requirements) had been put into operation in china, with a daily capacity of over 200 million tons and a sewage treatment rate of over 85% (93.4% in cities and 87.4% in counties), and had become operational. the largest sewage disposal country in the world.
however, some assessment studies have pointed out that although the construction of urban sewage treatment plants can help alleviate the eutrophication of lakes, algae outbreaks still occur from time to time, which means that the eutrophication problem has not been completely solved and the water quality has not yet reached a clean state. in addition, sewage treatment plants have been built in almost all densely populated cities/towns, so there is very limited space for further control of water pollution through expansion or construction of new sewage plants.
tong, y.d.et al.2017.decline in chinese lake phosphorus concentration accompanied by shift in sources since 2006.nature geoscience, vol.10:507-512.
in this regard, some experts suggest that pollution control and control should be strengthened by further improving the sewage discharge standards of sewage treatment plants. but can it really control water pollution more effectively? first look at what the sewage standard is. china's environmental standards can be divided into two categories: environmental quality standards and pollutant discharge standards, and the two levels refer to the state and the local. environmental quality standards refer to the maximum amount of harmful substances or factors contained in environmental factors which are formulated to protect people's health, social material wealth and maintain ecological balance. pollutant discharge standards refer to the restrictive regulations on pollutants discharged into the environment by man-made sources and their concentrations or quantities in order to achieve environmental quality standards, combined with technical and economic conditions or environmental characteristics.
for water pollution, there are two points to note in the above description of pollutant discharge standards. first, the pollution standards need to consider the technical and economic conditions and environmental characteristics. china is a vast country with vast geographical differences. on the one hand, the key factors affecting pollutant emissions, such as geography, climate, population and industry, are quite different. on the other hand, the natural capacity and economic and technological conditions for pollutant treatment are quite different. however, all kinds of sewage discharge standards, including pollutant discharge standards for urban sewage treatment plants, are "one-size-fits-all" and do not reflect the actual regional differences. improving the standard of sewage discharge is to tighten the unified standard, and it will not be more suitable for the actual situation of various regions. although divided into national and regional levels, due to the limited technical capacity of local standards, only beijing, shanghai, jiangsu and other minority areas have formulated local standards. local standards in these minority areas can only be more stringent than national standards, which also shows that national standards are universal and basic standards.
second, although sewage treatment plants can be regarded as the "end" of the pollutant transport chain, a potential man-made source of pollution, they are not the only source of pollution. therefore, china has also formulated corresponding standards for pollutant discharge for various industries and industries at the source of pollutant manufacture. however, the focus of pollution control and control is still concentrated. at the "end", we do not pay enough attention to the emission control of "front-end" pollution sources. if the source is not effectively controlled and managed, the direct discharge into the environment will directly increase environmental pollution, and the improvement of sewage discharge standards of sewage treatment plants has no effect on this; if the discharge into municipal sewage pipe network into urban sewage treatment plants, because the treatment technology and indicators of sewage treatment plants are mainly for the composition of pollutants in domestic sewage. increasing sewage discharge standards designed for sewage treatment plants does not represent a fundamental change in the existing indicator system (an increase in pollutant indicators from other sources), nor does it represent a fundamental change in existing treatment technologies (in addition to effectively removing pollutants from domestic sewage, but also effectively removing pollution from other sources of pollution). therefore, the improvement of sewage discharge standards can not solve the problem.
such as petroleum refining industry emissions standards (gb31570-2015), inorganic chemical industry pollutants emissions standards (gb31573-2015), traditional chinese medicine pharmaceutical industry water pollutants emissions standards (gb21906-2008), livestock and poultry industry pollutants emissions standards (gb18596-2001), and so on. to sum up, the sewage treatment plant discharge standard itself is not suitable for the actual situation of the region, and the focus of water pollution control on the sewage treatment plant discharge standard is a "terminal treatment" idea, the lack of a systematic ecological view, the effect is bound to be limited. that being the case, it may be able to achieve better results.
first of all, trace the source, find the main source of pollutants, from the source of governance, and gradually achieve clean production, green manufacturing. in cities, water pollution is mainly caused by point source pollution such as domestic sewage and industrial waste water. as mentioned earlier, the sewage treatment technology of urban sewage treatment plants is mainly designed for the pollutants in domestic sewage, and the pollutants in industrial wastewater may not be effectively removed.
