Core Roles of Large-Flow Filters in Municipal Sewage Treatment (Compliance Discharge)

The core goal of municipal sewage treatment is to remove pollutants such as suspended solids (SS), organic matter, nitrogen, phosphorus, and microorganisms from sewage, ensuring the effluent meets the requirements of Discharge Standards of Pollutants for Municipal Wastewater Treatment Plants (GB 18918-2002) Grade 1A/1B or stricter local standards before discharge. Municipal sewage is characterized by "large flow rate (10,000-ton to 100,000-ton per day per plant), significant water quality fluctuations (e.g., sudden turbidity increase after heavy rains), and complex pollutants (including domestic sludge, kitchen residues, fiber debris, and colloidal organic matter)." Traditional filtration equipment (such as sand filters) has drawbacks including large floor space, frequent backwashing, and limited filtration precision. With core advantages of "ultra-large throughput, high-precision interception, low pressure drop, and modular design," large-flow filters have become key equipment in the advanced treatment stage of municipal sewage treatment. Their roles focus on three core objectives: "ensuring effluent compliance, optimizing treatment efficiency, and reducing operating costs."

1. Deeply Intercept Suspended Solids (SS) and Colloids to Ensure Compliance of Core Effluent Indicators

After biological treatment (e.g., A/O, MBR processes) of municipal sewage, the effluent from secondary sedimentation tanks still contains residual fine suspended solids (such as microbial flocs, unsettled activated sludge, and fiber impurities) and colloidal organic matter. These pollutants are the main causes of excessive SS and turbidity in the effluent. The core role of large-flow filters is to precisely retain terminal pollutants and ensure compliance of discharge indicators:

1. Efficient Removal of Suspended Solids (SS): Selecting large-flow filters with 5-20μm precision can intercept over 95% of fine suspended solids in the effluent from secondary sedimentation tanks, controlling the SS concentration to ≤5mg/L (meeting Grade 1A standards; Grade 1B standard is ≤20mg/L) and avoiding discharge penalties due to excessive SS.
2. Reduce Effluent Turbidity: By intercepting colloidal organic matter and microbial flocs, the effluent turbidity is reduced from 5-10NTU (after biological treatment) to ≤3NTU (Grade 1A standard requires ≤5NTU), improving the visual effect of the effluent. Meanwhile, it provides clean water quality for subsequent disinfection processes (e.g., ultraviolet, chlorine dioxide disinfection), avoiding suspended solids blocking ultraviolet rays or consuming disinfectants, and increasing disinfection efficiency (disinfectant dosage can be reduced by 15-20%).
3. Auxiliary Removal of Partial Pollutants: Intercept phosphorus, organic matter, and trace heavy metals bound to suspended solids, auxiliary reducing the effluent concentrations of TP (total phosphorus) and COD (chemical oxygen demand). This provides a "buffer guarantee" for sewage treatment plants to cope with water quality fluctuations (e.g., mixing of industrial wastewater) and avoids excessive single indicators.

1. Protect Advanced Treatment Equipment and Extend System Operating Life

To achieve high-standard discharge, municipal sewage treatment plants are often equipped with advanced treatment processes (e.g., ultrafiltration (UF), reverse osmosis (RO), disinfection equipment). As a "front-end security filtration" link, large-flow filters play a key role in protecting downstream core equipment and reducing operation and maintenance costs:

1. Protect Ultrafiltration (UF)/Reverse Osmosis (RO) Membrane Modules: UF/RO membranes have tiny pore sizes (UF membrane pore size 0.01-0.1μm) and require extremely high inlet water quality (SS ≤1mg/L, turbidity ≤1NTU). Large-flow filters can efficiently intercept large particulate impurities and colloids, avoiding membrane surface clogging and scratching, extending the service life of membrane modules by more than 30%, and reducing membrane cleaning frequency (from 1-2 times per week to once per quarter) and replacement costs (a single UF membrane costs tens of thousands of yuan).
2. Protect Disinfection Equipment: Prevent suspended solids from depositing on the surface of ultraviolet lamps to form a fouling layer, which affects ultraviolet transmittance (for every 0.1mm increase in the fouling layer, sterilization efficiency decreases by 10-15%). Meanwhile, reduce the reaction consumption of disinfectants with suspended solids, lowering the operation and maintenance costs of disinfection equipment and chemical agent expenses.
3. Reduce Clogging of Subsequent Pipelines: Intercept fiber debris and large particulate sludge in sewage, avoiding clogging of discharge pipelines and lift pump impellers, and reducing equipment wear and shutdown frequency for dredging (shutdown time of sewage treatment plants caused by pipeline clogging can be reduced by more than 40%).

1. Adapt to Large-Flow Characteristics of Municipal Sewage and Optimize Treatment System Efficiency

Municipal sewage treatment plants typically have a daily treatment capacity of 10,000-500,000 tons, imposing strict requirements on filtration equipment for "flow adaptability, space occupation, and energy consumption control." The structural advantages of large-flow filters can significantly improve system operating efficiency:

1. Ultra-Large Throughput Matches Large-Scale Requirements: A single large-flow filter can handle 50-110m³/h. Adopting a multi-filter parallel modular design can meet the advanced treatment needs of 10,000-ton/day sewage treatment plants (e.g., a 100,000-ton/day treatment capacity only requires 20-40 filters), significantly reducing equipment floor space (saving 60-80% compared to traditional sand filters). It is suitable for compact layouts of new sewage treatment plants or upgrading and reconstruction projects of existing plants.
2. Low Pressure Drop Reduces System Energy Consumption: Large-flow filters adopt a pleated design with a large filtration area (an 40-inch filter has a filtration area of 8-10㎡), with an initial pressure drop ≤0.02MPa, much lower than traditional filters (0.05-0.1MPa) and sand filters (0.1-0.2MPa). This can reduce the operating load of sewage lift pumps, reducing the energy consumption of the advanced treatment system by 10-20% (e.g., a 100,000-ton/day sewage treatment plant can save hundreds of thousands of yuan in electricity costs annually).
3. Long Service Life Reduces Operation and Maintenance Workload: The dirt-holding capacity of large-flow filters is 5-10 times that of traditional filters, with a replacement cycle of 1-2 months (traditional filters only 1-2 weeks), reducing filter procurement costs and manual replacement workload. Meanwhile, the modular design supports single-filter replacement without system shutdown, ensuring continuous sewage treatment.

1. Cope with Water Quality Fluctuations and Enhance System Shock Resistance

The water quality of municipal sewage is greatly affected by residents' living habits, seasonal changes, and heavy rain scouring. For example, a large amount of surface runoff after heavy rains brings sediment and garbage, causing the inlet turbidity to surge from 20-50NTU (daily) to 100-200NTU. If not handled in a timely manner, it is easy to cause paralysis of subsequent processes or excessive effluent. Through high dirt-holding capacity and rapid response characteristics, large-flow filters enhance system shock resistance:

1. Buffer Sudden Water Quality Changes: The high dirt-holding capacity of large-flow filters can quickly intercept a large amount of sediment and suspended garbage brought by heavy rains, avoiding "shock loads" of pollutants on subsequent biological tanks and advanced treatment equipment, and preventing problems such as sludge loss from secondary sedimentation tanks and membrane module clogging.
2. Flexibly Adjust Filtration Precision: Flexibly switch filter precision according to water quality changes (e.g., 20μm filters for daily use, 10μm filters for heavy rain periods), ensuring stable compliance of effluent quality under different operating conditions without large-scale adjustment of process parameters.
3. Rapid Emergency Treatment: When the effluent SS and turbidity suddenly exceed standards, the treatment effect can be quickly restored by increasing the number of filters or replacing with high-precision filters, avoiding the risk of non-compliant discharge and providing a flexible solution for emergency treatment of sewage treatment plants.

1. Assist in Sludge Treatment and Reduce Secondary Pollution

Sludge generated during municipal sewage treatment (such as secondary sedimentation tank sludge and biological sludge) needs to be dewatered (e.g., plate and frame filter press, centrifugal dewaterer) before transportation and disposal. The sludge dewatering filtrate (containing high-concentration suspended solids and organic matter) needs to be refluxed to the sewage treatment system for reprocessing. Large-flow filters can filter the dewatering filtrate:

1. Purify Sludge Dewatering Filtrate: Intercept sludge particles and fiber impurities in the filtrate, avoiding increased treatment load on biological tanks and secondary sedimentation tanks after reflux and preventing secondary pollution.
2. Protect Sludge Treatment Equipment: Prevent large particulate impurities in the filtrate from wearing the dewaterer drum and pump impeller, extending the service life of sludge treatment equipment and reducing maintenance costs.

1. Summary of Core Value

In the compliance discharge of municipal sewage treatment, large-flow filters take "compliance guarantee, equipment protection, efficiency optimization, shock resistance, and cost reduction" as their core values, specifically reflected in:

1. Ensure Discharge Compliance: Precisely remove terminal suspended solids and colloids, ensuring core indicators such as SS and turbidity meet GB 18918-2002 Grade 1A/1B standards and avoiding environmental penalties.
2. Extend Equipment Service Life: Protect UF/RO membranes, disinfection equipment, pumps, valves, and pipelines, reducing wear and clogging and lowering equipment replacement and maintenance costs.
3. Improve Treatment Efficiency: Adapt to large-flow requirements, save space, reduce energy consumption, and ensure continuous and stable operation of the system.
4. Enhance Shock Resistance: Cope with water quality fluctuations and heavy rain shocks, avoid process paralysis, and improve the operational stability of sewage treatment plants.
5. Reduce Comprehensive Costs: The characteristics of long service life, low energy consumption, and low maintenance reduce the comprehensive operating cost of the advanced treatment stage of sewage treatment plants by 20-30%.

In short, large-flow filters are key filtration equipment for municipal sewage treatment plants to achieve "high-standard discharge, low-energy consumption operation, and convenient operation and maintenance." They are particularly suitable for compact design of new sewage treatment plants and upgrading and reconstruction projects of old sewage treatment plants, providing reliable technical support for the compliance discharge of municipal sewage.