In the case of sewers that release water polluted by viruses and bacteria in places where contact with humans can be created, diseases such as viral hepatitis, salmonellosis or typhoid fever can be determined. Furthermore, the discharge into the water of non-biodegradable detergents or those containing phosphates, determine the covering of a thick layer with their complex chemical structure with branched chains and are hardly attacked and degraded by bacteria into simpler or less harmful compounds.
These substances alter the physical characteristics of the water, modifying its surface tension and causing the disappearance, among other things, of the aquatic flora, of the plankton and, with them, of the components of the entire trophic pyramid.
A very serious consequence, in addition to the extension of large surface layers of decomposing materials, with relative miasmas and various colors, is the diffusion in both fresh and marine waters of bacteria and viruses and the absorption of these pathogenic microorganisms by molluscs destined for feed and reared near drainage outlets with the consequent danger of serious epidemics.
Twenty years of China's water pollution control: Experiences and challenges, a study published on the Chemosphere, analyzes the trend of the situation in its retrospective: "Water pollution is a major environmental problem worldwide, especially in developing countries.
China's environmental protection strategies have been pushed to the highest priority in history, driving remarkable achievements in water pollution control, but were also coupled with new challenges. In this study, we analyzed diverse long-term data (i.e.
water quality, WWTPs, pollutant discharge etc.) to systematically understand the process of water pollution control in China in the last twenty years. developed country level, with the treatment rates exceeding 90% both in urban and country areas.
The environmental quality of surface water was continuously improved, but water pollution problems remained in the river basins of eastern China, with remarkable economic progress. Rapid economic growth rather than population growth was the limiting factor for water pollution control in China.
Therefore, more efforts should be made to further improve wastewater collection and treatment capacity and address the gap between effluent discharge limits for wastewater treatment plants and environmental quality standards for surface water.
China's progress toward water pollution control provided important insights for other developing countries."