Why China's Wastewater Plants Go Underground?

Globally, the idea of an underground wastewater treatment plant originated in the 1980s. For example, in Northern Europe, an underground wastewater treatment plant was built due to the extremely low temperature. In Asian countries, the reason for going underground was severe land scarcity. In China, underground wastewater treatment plants meet the needs of rapid urbanization while preserving land value.

Recent years have seen an uptick in underground wastewater treatment projects across China. In cities such as Shanghai, Guangzhou, Kunming, Hefei, and Qingdao, more than 50 underground wastewater treatment plants are either in operation or under construction, despite the industry’s conservatism in adopting new technologies. This accelerated development goes hand in hand with the rise of China’s middle class, and rapid urbanization demanding that the use of available land and water resources be maximized to their full potential.

The odor and the ugly appearance of traditional facilities hurt the lives of people living in the surrounding areas. With China's rapid urbanization and stricter environmental requirements, the distance between sewage plants and residential areas has never been shorter. However, urbanization has led to land scarcity. To strike a balance between an undesirable wastewater treatment plant, scarce land resources, and protecting the environment, an underground facility is favored as a temporary solution and a compromise.  Therefore, they are gradually becoming a trend, and recent years have seen an uptick in underground wastewater treatment projects across China.

Compared with traditional “above-ground” wastewater plants, underground wastewater plants have some obvious advantages in the following aspects.

Small footprint and high land utilization: the underground sewage treatment plant greatly reduces the land occupation and improves the surrounding land utilization compared with the ground type. According to the survey data, the land occupation index of above-ground sewage plants is generally 0.8~1 m²/m³, while the land occupation index of underground sewage plants is less than 0.5 m²/m³, and the land use can be saved by more than 37%. For example, the land occupation per unit water volume index of Jingxi Underground Wastewater Treatment Plant is 0.18m²/m³, and the unit land occupation is only 1/5 of the traditional above-ground type.

The environment and noise pollution are almost eliminated: the production structures in the factory area are completely closed and managed, and the main noise-generating equipment is located in the underground closed box. The ground air, noise, and landscape environment are improved, with a reduced impact on the surrounding environment.

Globally, the idea of an underground wastewater treatment plant originated in the 1980s. Finland began to build underground wastewater treatment plants in 1932. Since the 1970s and 1980s, Sweden, Norway, France, the Netherlands, Japan, South Korea, and other developed countries/regions started to build underground wastewater treatment plants one after another.

At present, more than 200 underground wastewater treatment plants are operating stably in more than 10 countries in the world. Among them, the Henrinksdal Sewage Treatment Plant, built in 1941 in Stockholm, Sweden, is built in a cave. It is the world's first modern wastewater treatment plant and the world's largest MBR process wastewater treatment plant; France's underground wastewater plant is built in the center of Marseille, under the famous football factory.

Since 2010, there have been more than 200 underground wastewater treatment plants in China under construction, accounting for about 5.7% of the total number of urban wastewater treatment plants in the country. Guangdong, Sichuan, and Guizhou are the top three provinces when it comes to the number of underground wastewater plants. The first fully underground wastewater treatment plant designed and constructed in China is Shenzhen Buji Wastewater Treatment Plant.

The main construction forms of underground wastewater treatment plants include: In a semi-underground wastewater treatment plant, the pool is buried underground, and the operation layer and landscape layer are exposed to the ground. This form of construction has a smaller digging depth, lower construction cost, and no fire protection problem, but still covers a large area and requires higher deodorization and noise reduction. Some of the examples are Shenzhen Futian Sewage Treatment Plant, Tianjin Dongjiao Sewage Treatment Plant, etc.

From the perspective of the main process route, the underground wastewater treatment plant still uses the AAO process (45%) the most, followed by the MBR process (36%) and the multi-stage AO process (5%), oxidation ditch, SBR, CAST, biological aerated filter, and other processes that account for 14%.

In terms of comprehensive benefits, according to the results of the comprehensive life cycle comprehensive benefit comparison study conducted by Hao Xiaodi's team, the comprehensive environmental, investment and ecological impacts of underground sewage treatment plants are 21% higher than those on the ground.

The downsides of underground wastewater treatment plants are complicated construction, high construction costs, high risks, potential safety hazards, and lack of normative documents. However, in the context of rapid urban development, underground wastewater treatment plants are still favored as a compromise solution to undesirable wastewater treatment plants, scarce land resources, and environmental protection.  

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