The development and future prospect of urban sewage treatment

1.1 Practice history of urban sewage treatment in China

1.1 Late development

Water pollution control is now one of the most pressing challenges facing China. In the fight against environmental pollution, wastewater treatment plays a vital role. Although China has the world's largest wastewater treatment capacity and market, its development history is actually very short. Compared with industrialized countries that had widely implemented wastewater management a century ago, China's wastewater management was almost blank 40 years ago.

1.2 Rapid development in the past 40 years

Since the reform and development in 1979, China has entered a period of rapid development. With the rapid economic development and urbanization, the amount of urban sewage has increased sharply, and because more and more industrial wastewater enters the sewer, the composition of wastewater has become more and more complex. As the discharge of wastewater into the environment increases. Increased environmental pollution directly threatens urban water and food security, so water pollution control is urgently needed. To address this challenge, China has begun to build more centralized wastewater treatment plants and supplementary facilities.

However, the development rate and treatment capacity of wastewater treatment plants and auxiliary facilities (especially sewers and sludge treatment systems) still lag behind China's economic growth and industrial development. Overall water quality continues to decline, forcing the Chinese government to implement stricter pollution control strategies.

In 2007, a massive algae bloom occurred in Taihu Lake due to severe eutrophication of the water body, which seriously threatened the drinking water safety of nearby cities. Since then, local governments have begun to enforce stricter discharge standards for wastewater from sewage treatment plants. A year later, the first wastewater treatment plant to implement the Grade A wastewater discharge standard (GB 18918-2002) was put into use in Wuxi.

The pollution of China's water environment has also exacerbated water shortages, especially in northern China, which has created an urgent need for wastewater recycling and reuse. Beijing has pioneered this and has made great strides in building water recycling infrastructure.

In 2016, Beijing Gaobeidian Sewage Treatment Plant was upgraded to a recycled water plant with a treatment capacity of 1 million m³/d, announcing China's transition from simple treatment to recycled treatment. But China's overall water recovery rate is still low compared to many developed countries, and because of its relatively low quality, reclaimed water is mainly reused as landscape water. At this stage, the price of reclaimed wastewater remains uncompetitive with conventional water supply, and the establishment of reclaimed water infrastructure and programs has been slow.

2. Today's challenges and achievements

2.1 Notable achievements in the field of sewage treatment in China

After nearly 40 years of spectacular development, China now has the largest municipal wastewater infrastructure in the world. By the end of 2018, China had built more than 5,000 municipal sewage treatment plants with a daily treatment capacity of nearly 200 million m3/d. By 2018, the sewage treatment rate had reached more than 90 percent.

The construction of wastewater treatment plants is just one part of the rapid growth of China's wastewater treatment industry. Thanks to its strong national administrative system and the valuable experience of developed countries, China has made great strides in the construction and management of wastewater infrastructure in the past 40 years. The total market value and operational capacity of China's water companies are at the leading level in the world. The wastewater management model has also shifted from a single government-led construction and operation model to multiple systems involving government and business. This transformation has not only reduced the financial burden of the government to a certain extent, but also improved the construction and operation efficiency of wastewater treatment facilities.

China also now has the world's largest research team in water management, thanks to a steady increase in funding that far exceeds that of any other region in the world. China's innovation capacity and international competitiveness can be seen from the publications, and China's total number of SCI papers in the field of water research is second only to the United States. Such excellent innovation ability has laid a solid foundation for the future revolution of China's wastewater management model and treatment technology.

2.2 Remaining gaps and challenges

(1) The design and operation of the water plant is inconsistent with the requirements of sustainable development. At present, improving the pollutant removal rate is still the core objective of wastewater treatment plant operation, and the Grade A wastewater standard is increasingly adopted in wastewater treatment plants nationwide. To this end, most plants have eliminated primary sedimentation tanks, implemented delayed aeration processes, and added some biological filters to improve nitrogen removal rates. This increases energy chemical consumption and therefore makes wastewater treatment plants indirectly a non-negligible source of greenhouse gas emissions.