From July 27 to 28, 2023, Typhoon "Dusuri" made landfall in China. Affected by it, wind and rain increased significantly in the southeastern coastal areas, especially the area where the border between Fujian and Guangdong was the strongest. Sewage treatment plants are mostly built in the middle and lower reaches of cities or in relatively low-lying areas. When heavy rains or floods strike, sewage treatment plants face severe challenges. What impact does heavy rain have on sewage treatment plants?

Firstly, the hydraulic load of the sewage plant would increase, the sand content would increase, and the treatment pressure would also increase. During rainstorm, the water level in the plant area reaches or even would exceed the water inflow standard. And the hydraulic load of the sewage treatment facilities would increase causing the water volume operation of the sewage plant to be overloaded. And due to the erosion of water, most of the sediment and suspended matter in the pipe network would be poured into the sewage plant, causing great pressure on the pretreatment facilities of the sewage plant.

 Secondly, due to the increase in water volume, the concentrations of CODcr, BOD₅, NH₃-N, and TP in the incoming water would be diluted and reduced. The biochemical system would be easily inhibited, and pollutant indicators such as NH₃-N and suspended solids in the effluent are easy to fluctuate.

 When these so-called "impacts" occur, how do sewage treatment plants/stations that mainly use rapid biochemical sewage treatment processes respond? Before revealing the secret, let’s first understand what the rapid biochemical sewage treatment process is.

 What is the rapid biochemical sewage treatment process?      

In 2008, Chen Fuming, a professor at Tsinghua University and a foreign academician of the Russian Academy of Engineering, proposed the definition of rapid biochemical sewage treatment process at the Yichang conference, that is: the amount of pollutants digested in the reactor per unit time and unit volume for biochemical treatment is more than 50% higher than that of conventional biochemical processes. In general sewage treatment, increasing the concentration of reactants and strengthening mixing can be used to increase the biochemical reaction rate.


 
RPIR rapid biochemical sewage treatment technology based on the activated sludge method and T-Bic rapid biochemical sewage treatment technology based on the biofilm method are both typical rapid biochemical sewage treatment technologies.
Rapid purification of sewage using sedimentation Integrated rectangular airlift loop Reactor (RPIR), which uses the airlift power of aeration to circulate the mixed liquid, improves the mass transfer effect, and at the same time, couples sedimentation. During the separation process, the activated sludge is trapped in the reactor, allowing the sludge to automatically flow back without power, allowing the microorganisms in the reactor to maintain quantitative and qualitative advantages and achieve biodegradation of pollutants.（https://tsinghuan.world/Technology/index.html）

Three-dimensional Biological Immobilized Curtain (T-Bic) technology integrates multiple technologies such as bio-enhanced functional microorganisms, polymer material-modified immobilized microorganisms, and rapid biochemical reactors to achieve high efficiency and high density. The immobilization of functional bacteria is suitable for rapid biochemical treatment of low-pollution water bodies. （https://tsinghuan.world/technology_3/index.html）

 How is the sewage treatment plant/station with rapid biochemical process?

1. Shenzhen Binhe Water Purification Plant Temporary Treatment Facility Project for Upgrading and Expansion Project

In order to ensure that Shenzhen Binhe Water Purification Plant would not stop production, reduce volume, or meet lower standards during the rainy season ，this project plans to transform the original aeration tank and secondary sedimentation tank in Section A of the plant into a set of secondary biochemical equipment. Temporary treatment facilities with functions of treating and separating mud and water. The main process of this project is the "RPIR+magnetic coagulation precipitation" process. After the renovation, the designed treatment capacity of the facility is 42,000 m³/d (water volume change coefficient is 1.2). When the water inflow increases due to heavy rain or other reasons, the peak treatment capacity is 50,400 m³/d, and the effluent meets the surface quasi-Class IV standard. (TN≤15mg/L).



2、Shenzhen Guanlan Estuary Detention Tank Initial Light Rain Water Treatment Facility Upgrading and Reconstruction Project

This project is located in Longhua District, Shenzhen City. It mainly adopts the "pretreatment + RPIR biochemistry + magnetic mixing precipitation + ultraviolet disinfection" process. It is a well-known "storage + high-standard water treatment facility complex" in China, which has both dry season sewage treatment and rainy season. The maximum treatment scale in the dry season is 150,000 tons/day, and the current treatment capacity is 100,000 tons/day; the maximum treatment scale in the rainy season is 250,000 tons/day, and the current treatment capacity is 130,000 tons/day, and the effluent water quality reaches surface water category IV (except TN) ).

# Shenzhen Guanlan Estuary Detention Tank Initial Light Rain Water Treatment Facility Upgrading and Reconstruction Project

https://tsinghuan.world/overview/16.html


3、Wastewater treatment project in villages and towns in Huaiyang District, Zhoukou City

This project is located in Huaiyang District. The T-Bic biological purification tank is used to treat domestic sewage in Liuzhuang Village. The size of the biochemical tank is 3.95*2.20*1.20 m (L*W*H), the treatment scale is 20m³/d, and the effluent met Henan Landmark Grade II Standard. During rainstorms, the T-Bic biological purification pool has a strong ability to withstand impact loads and keeps the water output relatively stable. After a heavy rain, the regulating pool, fans, photovoltaic storage system, etc. should need to be inspected promptly to ensure that the system is operating normally.



Heavy rain brings considerable pressure to the normal operation of sewage treatment plants/stations. Taking into account the optimal comprehensive benefits, it is recommended that the main sewage treatment process in the factory area should be biochemical processes that can withstand the impact of water quality and quantity as much as possible.
In the long run, it is necessary to improve the diversion of rainwater and sewage, strengthen the collection of rainwater and the treatment of first rainwater pollution, and reduce the intensity of pollution to rivers (such as the "regulating storage + high-standard water treatment facility complex" treatment model of Guanlan River in Shenzhen) .We look forward to regions with conditions and needs to actively explore the systematic management of urban non-point source pollution with us, and look forward to the rapid biochemical sewage treatment process to help sewage treatment.