In the complex landscape of urban water environment management, overflow pollution—characterized by its sudden onset, high pollutant load, and unpredictability—continues to pose a serious challenge for water management and environmental protection authorities. As policy guidance becomes increasingly clear and governance requirements keep rising, seeking efficient, cost-effective, and sustainable solutions to overflow pollution has become both a consensus within the industry and an urgent need.

 

Nonpoint source pollution has complex causes and significant harmful effects.

Overflow pollution primarily stems from two sources: first, the large volumes of initial stormwater and domestic sewage that enter the sewer system during rainfall; second, the long-term accumulation of pollutant-rich sediment and sewage within pipes on clear days. During the initial stages of rainfall, the pollution intensity of this mixed water body is extremely high. Key eutrophication indicators—such as chemical oxygen demand, total nitrogen, and total phosphorus—often exceed the Class V water quality standards set forth in the "Surface Water Environmental Quality Standards" by a factor of 10 to 50, creating a powerful “pollution pulse” that severely impacts receiving rivers and lakes. Moreover, the volume of this overflow is highly variable, influenced by multiple factors including rainfall intensity, duration, and the capacity of the sewer network to intercept flows. Although some rivers and lakes have implemented measures to control overflow pollution, the phenomenon persists nonetheless.

 

Faced with this systemic challenge, our company has focused on the end-of-pipe stormwater culverts that experience overflow during rainy days and retain water on sunny days. We have adopted a comprehensive approach—from the three core dimensions of rapid ecological response, system integration, and economic feasibility—to develop a complete integrated solution for controlling and rapidly addressing overflow pollution. This solution aims to ensure stable water quality in receiving water bodies and provide robust technical support for the continuous improvement of urban water environments.

Sewer sludge degradation technology along the pipeline, with meticulous control from “source” to “end” on sunny days.

Under clear-sky conditions, the sewage accumulated inside pipelines and the sediment deposited at the bottom represent potential endogenous pollution sources. The pipeline sludge degradation technology adopted by our company is a precise treatment process designed specifically for the sewage and sludge stored within pipelines.

 

The core of this technology lies in the combination of “process control” and “end-of-pipe enhancement.” First, an intelligently controlled interception, storage, and flushing system creates controllable hydraulic forces within the pipeline, gradually scouring and transporting sludge that has been dispersed along the pipeline’s length, and concentrating it in a specific section located between 500 and 800 meters from the end. This process achieves spatial concentration of pollutants, thereby creating favorable conditions for subsequent efficient treatment.

In the end-of-pipe enrichment zone, the system activates a sediment-dragging device to thoroughly mix the sludge and water, thereby fully releasing pollutants. At the same time, the ultra-nano-aerosol reoxygenation system begins operation. This ultra-nano-aerosol reoxygenation system dissolves oxygen into the water in the form of microscopic bubbles—whose particle size is less than 200 nm—making them invisible to the naked eye. By introducing this ultra-saturated oxygen-rich water into the water body, the system significantly enhances the mass transfer efficiency of oxygen and raises the dissolved oxygen levels. The high concentration of dissolved oxygen provides an optimal metabolic environment for aerobic microorganisms in the water body, enabling these microorganisms to rapidly degrade and transform organic pollutants (such as COD and ammonia nitrogen) present in both the aqueous phase and the suspended phase.

The purified “clear water” can be directly discharged into rivers and lakes on sunny days. As for the purified sediment sludge, it undergoes dehydration and volume reduction via an in-situ treatment system, after which it is transported off-site for harmless disposal. This approach effectively reduces the pollutant load entering water bodies at the source.

Rapid treatment technology for overflow pollution, efficiently reducing “pollution pulses” during rainy days.

During rainfall, initial surface runoff carries ground pollutants and mixes them with newly generated sewage from the sewer network, resulting in high-intensity, high-flow overflow pollution. Our company’s rapid treatment technology plays a critical role at this stage.

The system first uses highly efficient debris-control facilities to rapidly intercept floating debris and litter carried along with stormwater runoff, preventing their widespread dispersion and safeguarding the aesthetic appeal of the water surface.

 

The core purification stage still relies on an ultra-nano-aerosol reoxygenation system (which is shared with the end-stage ultra-nano-aerosol reoxygenation system used in the in-line degradation process of sewer sludge). This system leverages its secondary circuit to reoxygenate receiving water bodies near the discharge outlets. During rainy days, this system can rapidly inject large amounts of dissolved oxygen into highly polluted stormwater and sewage mixtures. On the one hand, it reduces the oxygen-consuming organic matter and reductive pollutants in overflow stormwater and sewage, thereby preventing excessive depletion of dissolved oxygen in water bodies and avoiding the formation of hypoxic or even anaerobic conditions that could lead to unpleasant odors and blackening of the water. On the other hand, it enhances the metabolic activity of the naturally occurring aerobic microbial communities in the water body, promoting the efficient purification and control of incoming pollutants such as COD, ammonia nitrogen, and total phosphorus, and significantly mitigating the impact intensity of “pollution pulses.”

In addition, an ecological transformation system for discharge outlets can be integrated to construct or reinforce ecological barriers—such as gravel beds, ecological filter dams, and aquatic plant zones—near drainage outlets. These barriers are equipped with functions of filtration, adsorption, and biodegradation, enabling further deep purification and buffering of the effluent. This multi-layered approach provides enhanced protection, ensuring stable water quality and aquatic ecological safety in receiving waters during periods of heightened water quality sensitivity.

Smart early-warning and control technology enables “precise and intelligent governance.”

Efficient governance requires not only “speed” but also “precision.” Our company has integrated and applied intelligent early-warning and control technologies to build an intelligent management and control system that features “integrated land-and-air monitoring and cloud-based collaboration.”

 

By deploying multi-parameter monitoring instruments at key nodes—such as those measuring water quality five parameters, ammonia nitrogen, COD, and liquid levels—and leveraging the mobility of drone inspection systems, we can achieve all-weather, three-dimensional, real-time sensing of sludge accumulation in pipeline networks and overflow conditions at discharge outlets. Monitoring data and video information are transmitted in real time to a smart cloud platform.

The platform’s built-in algorithmic models can perform intelligent data analysis, accurately identifying abnormal conditions such as water quality exceeding standards, water volume overloading, and outlet overflows, and issuing timely warnings. More importantly, the system enables unified access and remote intelligent scheduling of treatment equipment, monitoring devices, and drones. Based on the warning information, the platform can automatically or with human assistance generate response instructions, remotely starting, stopping, or adjusting relevant treatment equipment (such as activating re-oxygenation systems or adjusting interception, storage, and flushing cycles). This creates a closed-loop management system—“perception-warning-decision-control”—significantly enhancing operational efficiency and emergency response capabilities, and truly achieving the refined control objectives of “being able to see clearly, judge accurately, and control effectively.”

Quantitative indicators testify to improved water quality.

After the implementation of this comprehensive plan, during clear weather, clean water will flow into the river through the culvert without producing any odors inside the pipeline. Moreover, sediment buildup in the pipeline will undergo effective inorganic conversion, volume reduction, and harmless treatment.

In the receiving water bodies surrounding the discharge outlets, there is no perceptible abnormal odor, and transparency has gradually increased to 25 centimeters or more, with no signs of bottom sediment resuspension. Within 48 hours after the treatment system is put into operation, the redox potential (ORP) of the water body can rise to 50 millivolts or higher, and the dissolved oxygen (DO) concentration can recover to 2.0 milligrams per liter or higher. Within 7 days, the removal efficiency of ammonia nitrogen will be significant: the ammonia nitrogen concentration in lake waters can drop below 2.0 milligrams per liter, and the ammonia nitrogen concentration in river waters can fall below 8.0 milligrams per liter.

 

Conclusion

Addressing overflow pollution is by no means a quick fix—it’s a long-term systems engineering endeavor that requires the integration of advanced technologies, intelligent system scheduling, and continuous operational optimization.

Our company closely focuses on three core principles—“separate management of clear and rainy weather, intelligent early warning, and ecological synergy”—and deeply integrates technologies for in-depth degradation of sewer sludge along the pipeline, rapid treatment of overflow pollution, and smart early-warning and control systems. This integration has enabled us to develop an efficient governance approach tailored to the complex water conditions found in Chinese cities, providing reliable technological equipment and solution support to realize the beautiful vision of “clear waters and green banks, with fish swimming freely in shallow waters.”