Sewage industry has potential to reduce emissions

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The concept of modern sewage treatment did not arrive in China until the early 20th century. The Shanghai North Sewage Treatment Plant established in 1923 was the first such facility in the country, covering an area of 0.84 hectares with a daily processing capacity of 3,500 cubic meters.

At the time, China suffered from a lack of infrastructure, and its water pipeline network seriously limited its capacity to make wastewater safe. In 1949 the country had just 6,034 kilometers of pipes serving a population of 400 million.

In the 1950s, a number of large-scale sewage treatment facilities were built, including the Beijing Gaobeidian First-class Sewage Treatment Plant established in 1956.

After the reform and opening up, China started to pay increasing attention to environmental protection issues, including the development of its sewage treatment industry.

Relevant regulations and incentives have since been provided, such as the Environmental Law in 1979, Water Pollution Prevention and Control Law in 1984, and the Urban Sewage Treatment Plant Pollutant Discharge Standard in 2002.

By 2020, a total of 4,140 sewage treatment plants had been built and put into operation nationwide.

Among them, 2,471 are located in urban areas, with an annual processing capacity of over 52 billion cubic meters and a treatment rate of 96.81 percent; 1,669 are located in rural areas, with an annual processing capacity of over 9.5 billion cubic meters and a treatment rate of 93.55 percent.

Reducing carbon

The sewage treatment industry has always considered itself as a protector of the environment, and is proud of the progress it has made over the past half century.

However, when the importance of reducing carbon emissions started to be gradually recognized by the public, the industry was quickly identified as a major cause of emissions.

On the one hand, it emits large amounts of nitrogen oxide, sulfides, and other greenhouse gases in the process of sewage detoxification. On the other, it is an energy-intensive industry and consumes a lot of electricity, thus indirectly causing more carbon emissions.

Potential solutions

In order to solve the problem of high energy consumption, it is necessary to adopt a high-efficiency electromechanical system, and optimize the process in each link.

Electromechanical equipment used in the sewage treatment process mainly includes three categories of devices: hydraulic conveying, mixing and stirring, and blast aeration.

The application of high-efficiency equipment in all these processes is expected to reduce energy consumption by 5 to 10 percent.

Another reason for the high energy consumption is that the design scale and equipment operating power at many plants greatly exceeds the actual requirements.

The designs of many of the devices are also unreasonable, resulting in unnecessary transportation distances and energy consumption.

Such energy waste accounts for nearly 70 percent of the industry’s total consumption.

Solutions to greenhouse gas emissions

In recent years, breakthroughs have been made in harmful gas capture and recycling technologies.

Technically, it is possible to produce ethanol, hydrogen and methane by anaerobic fermentation of related nitrogen oxides emitted during sewage detoxification.

Anaerobic treatment technology can play an important role in the inorganic treatment of high-concentration organic sewage, such as the treatment of industrial wastewater.

However, the anaerobic treatment equipment requires a huge amount of investment and covers a large area, so it is not suitable for treating urban domestic sewage with low organic concentration.

Besides, new technologies such as denitrogenation, carbon nitrogen separation, and ultra-high pressure are also expected to help the industry reduce carbon emissions.