The "Bulletin on China's Urban Construction Status in 2022" released by the Ministry of Housing and Urban-Rural Development has shown that as of the end of 2022, the treatment capacity of sewage treatment plants in China has reached 216 million cubic meters per day. Generally speaking, if the sewage treatment plant is not upgraded, its service life is range 20 to 30 years. According to statistics in the "2020 Urban and Rural Construction Statistical Yearbook", the sewage treatment volume with a service life of 20 years and above is approximately 43 million tons/day, and the sewage treatment volume with a service life of 10 years and above is approximately 125 million tons/day, accounting for approximately 57.87% . This means that at least nearly 60% of sewage treatment plants would face challenges in the next 10 years.

In recent years, the standards for sewage treatment have become more and more stringent, from the national standard level B to level A, quasi-surface category V, and quasi-surface category IV. In November 2023, Hebei Province issued the "Water Pollutant Discharge in the Chaobai River Basin" Standards" (DB13/5881-2023) even introduced quasi-Class III emission standards.
 
There is also an urgent need to expand the capacity of sewage treatment. Cases reported by the Central Ecological Environment Protection Inspection Group of the Ministry of Ecology and Environment in December 2023 had shown that: There are some urgent sewage treatment problems in many places，such as the Insufficient sewage treatment capacity, Low sewage collection rate，Sewage discharge without  treatment，and serious urban drainage system overflow pollution. 
 
Thus, could these sewage treatment facilities that have made contributions in the past years still meet the new standards and capacity expansion requirements? This article introduces typical concepts and practices in functional enhancement and upgrading of old municipal sewage treatment facilities, with a view to providing reference.

 

Traditional aerobic pool upgraded to reaction-sedimentation integrated pool
 

Reaction makes pollutants harmless, precipitation makes water clear. Generally speaking, as the main position for reducing pollution load, the secondary biochemical treatment unit requires the largest area in sewage treatment, and it is also the unit that needs renovation firstly. Is it possible to couple the reaction process and the sedimentation process together to maximize the reaction efficiency and sedimentation load, and supplement it with in-depth treatment measures such as "filtration, coagulation and sedimentation", so that the effluent could stably reach the national standard Class A or surface water standard?

 
The standard upgrading and renovation project of a sewage treatment plant in Xiangshui County, Jiangsu Province is a typical case. This project directly set up reaction-sedimentation integrated equipments within the aerobic pool for micro-modification. It used the air lift power generated by aerobic aeration to circulate the mixed liquid, which improved the mud-water mass transfer effect, and achieved unpowered full sludge reflux. Moreover, the special structure intercepts activated sludge, whose sludge concentration is maintained at 5-6g/L. After the transformation, the treatment process does not need to go through the secondary sedimentation pool, shortening the sewage treatment process, and the effluent stability reaches National Grade A standard. The original secondary sedimentation pool could be used for long-term in-situ expansion of the water plant without demolition costs.

Standard upgrading and renovation project of a sewage treatment plant in Xiangshui County,
Jiangsu Province 30,000 m³/d, Grade A

 

The sedimentation pool was upgraded to a reaction-sedimentation integrated pool

When there is no available land for expansion in the sewage treatment plant, we should pay our attention to the sedimentation pool, which occupies a huge area. Should some idle sedimentation pools be upgraded in situ plants with biochemical reactions and sedimentation reactions to achieve capacity expansion?
For example, Shenzhen Nanshan Water Purification Plant transformed six primary sedimentation pools into reaction-sedimentation integrated pools, adding a processing capacity of 176,000 tons/day, and the main indicators of the effluent are better than the national Class A standard.

Shenzhen Nanshan Water Purification Plant System Upgrading and Reconstruction Project
176,000 m³/d, Class A

 

Rainwater storage tank is upgraded to storage + rapid sewage treatment plants
 

In many cities the pollution caused by overflows has become one of the important reasons for the deterioration of river water quality. As an important rainwater collection facility rainwater storage tank also plays the role of intercepting mixed rainwater and sewage in the combined flow system. It may be the last line of defense against sewage/stormwater entering surface waters. So, a Rainwater storage tank with only a pretreatment function cannot meet the requirements of high-standard water effluent.、

If it could be given the function of rapid sewage treatment, its effluent can stably reach the surface water level V, or even the surface water level IV standard. It is an effective solution to maintain stable water quality.

 

Guanlan River Estuary Adjustment Tank Early Light Rain Treatment Facilities Upgrading and Renovation Project
150,000 m³/d (dry season); 250,000 m³/d (rainy season)
Quasi-surface Category IV (dry season); Quasi-surface Category V standard (rainy season)

 

Under the new development requirements, by implanting innovative concepts and innovative technologies into sewage treatment plants, new development connotations have been injected into the quality and efficiency improvement of sewage treatment plants. Upgrading of antiquated sewage treatment functions is indeed an economical and efficient choice for standard expansion and capacity expansion of urban sewage treatment plant.