The higher the degree of urbanization, the tighter the land resources, and accordingly, the higher the land use requirements for infrastructure. As one of the important components of infrastructure, sewage treatment plants are also the role that occupies a large amount of land area. So, how should a sewage treatment plant be built with high population density, land shortage, and difficult demolition?

The biochemical treatment process is the main unit that occupies a sewage treatment plant. Under the requirements of ensuring economy and high-standard water effluent, reducing the land occupancy of the biochemical process is the primary consideration . Generally, biochemical processes often use AAO and its deformations, which include two processes: reaction and precipitation. Reaction makes pollutants harmless; precipitation makes water clear. If the reaction and precipitation processes can be coupled in vertical space, it will be efficient and less land occupancy.

In fact, this model has been developed on a large scale for about 10 years, with a cumulative sewage treatment capacity of nearly 3 million tons per day. The implementation method is to install a special diversion structure (is known as circulation clarifier, also is called RPIR module) on the aerobic tank to realize the four functions of oxygen supply, airlift circulation, biochemical reaction, and sedimentation separation. It could effectively reduce the land occupancy while achieving high standards of water discharge. RPIR technology is commonly used in engineering applications to re-divide the functional areas of the original AAO pool, which is used to replace the secondary sedimentation tank and the traditional aerobic tank (to achieve vertical integration of the reaction and sedimentation processes), followed by a deep treatment process, the effluent could achieve quasi-Class IV surface water standard. Compared with the traditional activated sludge method, it could reduce about 40% of civil construction costs, 40~45% of land area and about 30% of energy consumption.







In order to eliminate black and odorous rivers, a certain place in Dongguan, China required a new sewage treatment plant
with a treatment capacity of 5,000 tons per day and an effluent quality of national first-class A standard on about 1,200 square meters of land along the river in the short term. Engineers started working on the main biochemical process. The RPIR module eliminates the need for a secondary sedimentation tank, and also superimposes functional areas such as anoxic reaction, aerobic reaction, and mud-water separation in the AAO process in the vertical direction. The entire biochemical process occupies only 0.068 m²/ton of water, and there is no external sludge return system. The energy consumption is also extremely low, and the effluent reaches the level of national Class A standard. This project was selected as the "Typical Technologies and Cases for the Construction of the Guangdong-Hong Kong-Macao Green Greater Bay Area" and the "2021 Key Environmental Protection Demonstration Project".

The development of society has given rise to various demands for pollution control. In the future, innovative technologies and governance models that with strength of less land occupancy, more intensive, more ecological, and more cost-effective would continue to emerge. They may leverage the entire industry to produce greater development effects, and also make our cities glow with a greener ecological style.