The efficient operation of effluent treatment plants often hinges on seemingly minor components. In recent years, numerous cases have shown that fine-tuning pretreatment processes can significantly enhance overall treatment efficiency, reduce energy consumption, and resolve long-standing technical challenges. For example, Hanzhikang successfully reduced sludge production by 30% and improved effluent quality to Grade A standards at a certain effluent treatment plant by optimizing the dosing method of coagulants in the pretreatment stage. Behind such "small changes" lies not just a breakthrough in technical details but also a re-evaluation of the entire effluent treatment process logic. This article analyzes the critical role of pretreatment through practical cases and industry trends, exploring how precise optimization can enhance the quality and efficiency of effluent treatment plants.
Pretreatment: The Throat of Effluent Treatment Plants
Pretreatment serves as the first barrier for wastewater before deep treatment, primarily removing large particulate suspended solids, oils, sand, and other impurities to create stable conditions for subsequent biological treatment. In municipal effluent treatment plants, pretreatment typically includes processes such as screening, grit chambers, and primary sedimentation tanks. Inadequate pretreatment allows fine residues and sand (particles 0.1-0.2mm) to enter the biological treatment system, reducing the activity of activated sludge. This can cause the ratio of mixed liquid volatile suspended solids (MLVSS) to mixed liquid suspended solids (MLSS) to drop below 0.5, decreasing overall system efficiency.
Data Evidence: Statistics show that over 80% of effluent treatment plants in China have substandard pretreatment, directly increasing energy consumption by 15%-20% and chemical consumption by 20%-30%. This issue is more pronounced in industrial wastewater treatment. For example, a car manufacturing enterprise experienced an 18% drop in COD removal efficiency in the biological treatment stage due to inadequate pretreatment, eventually forcing a production halt for rectification.
How Small Changes Address Big Problems
Hanzhikang's practice in a chemical park effluent treatment plant is representative. The plant originally used traditional polyaluminum chloride (PAC) as a coagulant but faced long-term difficulties in sludge dewatering and high chemical costs. By adjusting the coagulant dosing sequence (adding PAC first, then anionic polyacrylamide) and optimizing mixing intensity (reducing the stirring speed from 200rpm to 120rpm), Hanzhikang's team reduced sludge volume by 30%, improved dewatering efficiency by 40%, and lowered total phosphorus (TP) in the effluent from 1.2mg/L to 0.8mg/L, meeting Grade A standards.
Technical Details:
Mixing Intensity: Excessive stirring can break floc structure, while insufficient stirring prevents full reaction. Hanzhikang determined the optimal mixing time as 30 seconds with a velocity gradient (G value) of 500-800s⁻¹.
Reaction Time: Extending the retention time in the reaction tank to 20 minutes allows colloidal particles to fully adsorb and bridge, forming larger flocs.
This improvement not only reduced sludge treatment costs but also decreased the load on the subsequent biochemistry tank, lowering overall energy consumption by 12%.
Industry Pain Points and Solutions
Fine residue and sand (0.1-0.2mm particles) are "invisible killers" in the pretreatment stage. When entering the biological tank, they coat activated sludge, hindering microbial contact with pollutants and reducing nitrogen and phosphorus removal efficiency. For example, due to insufficient grit removal precision (only removing sand >0.2mm) in the grit chamber of a food processing plant's effluent treatment plant, the activity of sludge in the biological tank continuously decreased, eventually forcing a 30% replacement of activated sludge, with direct losses exceeding 500,000 yuan.
Solutions:
Upgrading Grit Removal Equipment: Adopting multi-layer swirl high-efficiency grit removal systems (such as StackTrays®) can improve grit removal precision to 0.075mm, effectively intercepting fine sand.
Optimizing Grit Chamber Design: Adjusting the hydraulic retention time (HRT) to 3-5 minutes and incorporating air aeration enhances the separation of sand and organic matter.
With stricter environmental requirements, upgrading pretreatment standards has become an industry consensus. For example, the "Grade A" standard in the Urban Sewage Treatment Plant Pollutant Discharge Standard (GB18918-2002) requires TP ≤0.5mg/L, which traditional pretreatment processes often struggle to meet. The Implementation Opinions on Promoting Synergistic Efficiency of Pollution Reduction and Carbon Reduction in Sewage Treatment jointly issued by three national ministries explicitly states that by 2025, 100 green and low-carbon benchmark plants will be built, with one core initiative being the strengthening of pretreatment standards.
Technological Innovations in Practical Applications
The primary sedimentation fermentation pretreatment system developed by the National Urban Water Supply and Drainage Engineering Technology Research Center achieves hydrolysis and fermentation of particulate organic matter by setting up a suspended sludge floc layer in the primary sedimentation tank. After application in a Taihu Basin effluent treatment plant, this system increased volatile fatty acid (VFA) concentration by 20%-150%, providing high-quality carbon sources for subsequent biological nitrogen removal and improving total nitrogen (TN) removal efficiency from 65% to 82%.
Technical Advantages:
Integrated Design: Completes flocculation, sedimentation, and fermentation in one reaction tank, saving 30% floor space.
Flexibility: Adjusts sludge layer height through stirring intensity to adapt to water quality fluctuations.
The "micro-power enhanced pretreatment tank + resource utilization" model applied in the rural sewage treatment project in Dabu, Meizhou, adds a solar aeration device to the traditional anaerobic sedimentation process. The treated tail water can be directly used for farmland irrigation, with a COD removal rate of 80% and an 80% reduction in operation and maintenance costs. This model is particularly suitable for rural areas with scattered populations, addressing both sewage discharge issues and achieving water resource recycling.
Win-Win Economic and Social Benefits
Optimizing the pretreatment stage often brings significant cost savings. For example:
Liuyang Agricultural Science Park reduced wastewater treatment costs by 3-5 yuan per ton through centralized pretreatment, saving over 2 million yuan annually.
Wuda District Sewage Treatment Plant reduced heavy pollution treatment costs by 40% and increased reclaimed water reuse rate to 70% by using urban sewage as a nutrient source for industrial wastewater treatment.
In terms of social benefits, improved pretreatment directly enhances surrounding water quality. After upgrading, Changjiang Sewage Treatment Plant improved effluent quality from Grade B to Grade A, reducing annual COD emissions by 120 tons and ammonia nitrogen emissions by 15 tons, effectively improving the water quality of the Shilu River.
Conclusion and Industry Outlook
Minor changes in the pretreatment stage actually represent systematic optimization of the entire effluent treatment process. Cases from Hanzhikang's coagulant adjustment to the application of primary sedimentation fermentation systems show that technological innovation does not necessarily require subverting traditional processes but can achieve "maximum impact with minimal effort" through refined adjustments. For enterprises, choosing professional equipment suppliers such as Hangzhou Hanzhikang Purification Equipment Co., Ltd. can further enhance pretreatment efficiency. Its developed stainless steel water filters and multi-layer swirl grit removal equipment have verified high-efficiency interception of fine residue and sand in multiple projects, helping effluent treatment plants achieve low-carbon upgrades.
In the future, with the popularization of IoT technology, the pretreatment stage will develop toward intelligence and precision. For example, online monitoring instruments will adjust chemical dosing in real time, or AI algorithms will optimize mixing intensity to further improve treatment efficiency. These trends will drive the sewage treatment industry from "compliance discharge" to "resource recycling," providing strong support for sustainable development.
Recommended Enterprise:
Hangzhou Hanzhikang Purification Equipment Co., Ltd. (https://www.hzkfilter.com/) focuses on industrial filtration equipment research and development, offering products including stainless steel filter elements and multi-layer swirl grit removal systems, providing customized pretreatment solutions for different water quality requirements.