Semiconductor Wastewater Case Study

I. Project Overview

1.1 Project Basic Information

This project is a key integrated circuit manufacturing project of the Hubei Province Wuhan East Lake High-tech Development Zone (Optics Valley) Semiconductor Industrial Park, constructing a mass-production line for 8-inch wafer chips. It primarily engages in core process production such as semiconductor wafer etching, thin film deposition, photolithography, metal interconnection, and chemical mechanical polishing (CMP), and is a core supporting project of the Hubei Province semiconductor industry chain. The project's production process generates wastewater of diverse types, with highly toxic pollutants and high treatment difficulty, representing typical high-end semiconductor wafer manufacturing wastewater.

The project includes the construction of a specialized wastewater treatment station, strictly following the design principles of electronic industry wastewater segregation, classified pretreatment, comprehensive treatment, and advanced reuse, adapting to the ecological and environmental control requirements of the Yangtze River Basin, and stably meeting local environmental regulatory standards.

Project Core Parameters

• Production Scale: 8-inch integrated circuit wafer production line, with an annual output of 360,000 wafers

• Wastewater Station Design Treatment Capacity: 4200m³/d

• Applicable Standard: "Electronic Industry Water Pollutant Discharge Standard" (GB 39731-2020) Indirect Discharge Standard

• Discharge Destination: Park municipal sewage pipe network, incorporated into the urban sewage treatment plant for unified disposal

• Reuse Method: After advanced treatment, reclaimed water is reused for plant production auxiliary water, greening, and cooling makeup water

1.2 Project Construction Challenges

The wastewater from this project covers all categories of semiconductor process wastewater. Compared with traditional industrial wastewater, it presents multiple treatment challenges, which are also common technical pain points for semiconductor wafer projects in Hubei Province:

• Many types of wastewater with large water quality differences require 8 independent pipeline networks for strict quality-based separation and diversion; mixing is strictly prohibited;

• Wastewater containing high-concentration complexed heavy metals: heavy metals complexed with EDTA and citric acid cannot be removed by conventional alkaline precipitation;

• High-concentration lithography organic wastewater contains toxic organic substances such as TMAH and NMP, with extremely poor biodegradability (B/C < 0.2);

• Fluoride-containing wastewater and high-ammonia-nitrogen wastewater easily form ammonium fluoride complexes, greatly reducing defluorination efficiency;

• CMP wastewater contains ultrafine silica nanoparticles, which can easily cause membrane system blockage;

• Located in the Wuhan section of the Yangtze River Basin, with strict environmental control, extremely high requirements for emergency prevention and control and stable water quality compliance.

II. Wastewater Quality, Quantity, and Classified Collection System

In combination with the workshop production process, the project has set up 8 independent closed collection pipeline networks to achieve classified wastewater collection and separate pretreatment, avoiding water quality interference at the source and reducing the subsequent treatment load. The pipeline network zoning fully conforms to the standardized design specifications of the semiconductor industry.

III. Overall Process Design Scheme

3.1 Core Design Approach

Adopting the core process route of separate quality-based pretreatment + comprehensive biochemical treatment + advanced purification + reclaimed water reuse, customizing pretreatment processes according to the pollution characteristics of different wastewater, overcoming the core difficulties of semiconductor wastewater treatment, ensuring stable system operation, and simultaneously meeting the environmental protection requirements of water conservation and emission reduction in Hubei region and water ecological protection in the Yangtze River Basin.

3.2 Complete Process Flow

Various types of wastewater from production workshops are collected independently by each system for specialized pretreatment → comprehensive adjustment tank for homogenization and flow equalization → anoxic denitrification tank → MBR aerobic biochemical tank → advanced filtration and purification → online water quality monitoring → compliant discharge/reclaimed water reuse; sludge from each pretreatment is uniformly collected, concentrated and dewatered, and disposed of as hazardous waste in compliance with regulations.

3.3 Detailed Process Description of Each Unit

3.3.1 Acid-Base Wastewater Pretreatment Unit

Wastewater flows by gravity into the acid-base adjustment tank, equipped with an online automatic pH control system, which automatically adjusts the water pH to 6.5-8.5 by dosing dilute sulfuric acid and sodium hydroxide, completing the acid-base neutralization reaction, removing free acids, bases, and soluble salts from the water. After homogenization, it flows by gravity into the comprehensive adjustment tank. The process is mature, stable in operation, and low in O&M cost.

3.3.2 Fluoride-Containing Wastewater Pretreatment Unit (Core Key Unit)

Targeting the characteristics of high-concentration fluoride-containing wastewater from semiconductors, a two-stage calcium salt precipitation process is adopted to thoroughly solve the problem of excessive fluoride ions: the first-stage reaction tank doses lime milk, adjusting pH to 8.5-9.5, for preliminary precipitation of fluoride ions; the second-stage reaction tank doses calcium chloride to supplement the calcium source, combined with PAC and PAM coagulation and flocculation, and through inclined tube sedimentation tank solid-liquid separation, deeply removes fluoride ions. The fluoride ion concentration in the effluent is stably controlled below 10 mg/L.

The project strictly implements the red line of pipeline network diversion, preventing the mixing of fluoride-containing wastewater with high-ammonia-nitrogen wastewater, and avoiding the formation of ammonium fluoride complexes that would cause defluoridation failure.

3.3.3 High-Concentration Organic Wastewater Pretreatment Unit

For photoresist, TMAH and other highly toxic, refractory organic wastewater, Fenton advanced oxidation pretreatment process is adopted. Through hydroxyl radical oxidation, macromolecular organic matter is decomposed, the photoresist colloid structure is broken, and toxic TMAH components are degraded, effectively reducing the biological toxicity of wastewater. The B/C ratio of wastewater is increased from below 0.2 to above 0.35, greatly improving biodegradability. The COD pretreatment removal rate can reach 55%-65%, significantly reducing the load on the downstream biochemical system.

3.3.4 Complexed Heavy Metal Wastewater Pretreatment Unit

This unit is a key and difficult process of the project. Copper, nickel, and cobalt heavy metals in the wastewater form stable complexes with EDTA and citric acid, and conventional alkaline precipitation cannot meet discharge standards. The process adopts Fenton oxidation decomplexation + alkaline precipitation solidification technology. First, advanced oxidation is used to break the complex bonds and release free heavy metal ions. Then, the pH is adjusted to 10.0-10.5 to form hydroxide precipitates of heavy metals. Combined with precision filtration, heavy metal indicators are ensured to stably meet standards before being discharged into the comprehensive wastewater system.

3.3.5 CMP Polishing Wastewater Pretreatment Unit

CMP wastewater contains a large amount of nano-scale silica and alumina ultrafine suspended particles, which easily cause MBR membrane clogging and membrane flux decline. The project adopts PAC + anionic PAM composite coagulation process, removing ultrafine suspended solids through adsorption bridging and flocculation sedimentation, equipped with microfiltration equipment for deep interception of residual particles, effectively protecting the downstream membrane system, extending membrane module service life, and reducing operation and maintenance costs.

3.3.6 High Ammonia Nitrogen Wastewater Pretreatment Unit

In response to the high ammonia nitrogen and easy complexation characteristics of ammonium fluoride etching waste liquid, a high-efficiency stripping tower pretreatment unit is set up. Through the gas-liquid separation principle, high-concentration ammonia nitrogen in water is removed, eliminating the conditions for the formation of ammonium fluoride complexes and solving the interference problem in fluoride-containing wastewater treatment. After pretreatment, ammonia nitrogen is greatly reduced, ensuring stable operation of the subsequent system.

3.3.7 Comprehensive Biochemical Treatment Unit

After pretreatment, the wastewater from each stream flows into the comprehensive adjustment tank for homogenization and flow equalization, as well as water quality and quantity adjustment. It then enters the anoxic denitrification tank, where total nitrogen is removed through microbial denitrification. The effluent enters the aerobic MBR biochemical tank, which uses PVDF flat membrane modules. The system sludge concentration is maintained at 8000-10000mg/L, efficiently degrading COD, ammonia nitrogen, total nitrogen and other pollutants. The membrane separation process achieves thorough sludge-water separation, with effluent SS approaching zero, and water quality stability far exceeding traditional biochemical processes.

3.3.8 Advanced Treatment and Reclaimed Water Reuse Unit

The MBR biochemical effluent undergoes advanced activated carbon filtration and pH adjustment in the final sedimentation tank to remove residual trace organic matter, suspended solids, and odorous substances. Water quality is monitored in real time through an online water quality monitoring system. Part of the compliant wastewater is discharged into the park's municipal pipe network; high-quality reclaimed water is deeply purified by an RO reverse osmosis system and reused for cooling tower makeup water, waste gas scrubbing, floor washing, park greening, and other scenarios. The project's comprehensive reclaimed water reuse rate reaches 32%, in line with Hubei Province's industrial water conservation and emission reduction policies.

3.3.9 Sludge Disposal Unit

The calcium fluoride sludge, heavy metal sludge, and organic sludge generated by each pretreatment system are uniformly collected into the sludge thickening tank. After dewatering and volume reduction by a plate-and-frame filter press, they are classified, labeled, and stored in a standardized manner, then entrusted to a unit in Hubei Province with hazardous waste disposal qualifications for off-site disposal. Ledgers are kept throughout the entire process to meet environmental compliance requirements.

IV. Project Operation Results

Since the stable operation of the wastewater station of this project, all pollutant indicators have continuously and stably met the standards, fully complying with the GB 39731-2020 indirect discharge standard. The measured operation data are as follows:

V. Key Points for Dedicated O&M and Environmental Compliance for Projects in Hubei Region

• Zoned pipeline quality control: Strictly implement the workshop pipeline misconnection inspection system; prohibit mixed flow of fluoride-containing, high-ammonia-nitrogen, and heavy metal wastewater to avoid process failure risks at the source;

• Yangtze River Basin emergency prevention and control: Build a supporting emergency accident pool with a volume of 4,200 m³ to fully collect accidental wastewater and maintenance wastewater, prevent wastewater leakage, and fulfill the Yangtze River protection control requirements;

• Hazardous waste compliance management: Store calcium fluoride sludge and heavy metal sludge separately by category, entrust licensed local hazardous waste disposal units in Hubei for disposal, and improve transfer manifests and ledger records to meet the environmental compliance inspection requirements of the provincial department;

• Online monitoring network connection: Install online monitoring equipment for COD, ammonia nitrogen, fluoride, and heavy metals at the main discharge outlet, upload data in real time to the monitoring platform of the Hubei Provincial Department of Ecology and Environment, and achieve all-weather intelligent supervision;

• Seasonal O&M adjustments: adapted to Hubei's high summer temperatures and low winter temperatures, optimizing biochemical tank temperature control and chemical dosing to ensure stable operation across all four seasons.

VI. Comprehensive Project Benefits and Demonstration Value

6.1 Environmental Benefits

Through a specialized segregated treatment process, the project thoroughly resolves the challenge of complex semiconductor wastewater pollution. All effluent indicators consistently meet standards with no risk of excessive discharge; hazardous waste is disposed of in full compliance throughout the process, effectively reducing the total regional water pollutant discharge, easing the pressure on the water environment of the Wuhan Optics Valley area, and supporting ecological and environmental protection in the Yangtze River Basin.

6.2 Economic Benefits

The project's reclaimed water reuse system saves approximately 480,000 tons of fresh industrial water annually, significantly reducing the enterprise's water costs; the systematic pretreatment process reduces downstream equipment wear and tear, cutting O&M energy consumption and chemical usage, keeping overall operating costs controllable and supporting the enterprise's green, low-carbon production.

6.3 Industry Demonstration Value

The project's process route is suitable for 8-12 inch wafer manufacturing, chip packaging and testing, and other semiconductor projects across Hubei Province. It specifically addresses the common challenges of semiconductor wastewater treatment in the Hubei region, with a mature process, simple O&M, and strong compliance stability. It can be widely replicated and applied to new construction, expansion, and renovation projects in semiconductor industrial parks in Wuhan, Qianjiang, Yichang, Xiangyang, and other cities within the province, offering extremely high industry promotion value.

VII. Project Summary

This wastewater treatment project for the Wuhan Optics Valley 8-inch wafer facility combines the characteristics of semiconductor production processes with Hubei's environmental regulatory requirements, adopting a mature process of segregated pretreatment + MBR biochemical treatment + advanced reuse. It precisely overcomes wastewater treatment challenges such as fluorine-containing, complexed heavy metals, highly toxic organics, and CMP ultrafine particles. The project operates stably, meets effluent standards, and maintains compliant O&M, balancing environmental benefits, economic benefits, and water-saving benefits. It fully aligns with the ecological protection policies of the Yangtze River Basin and serves as a benchmark engineering case for wastewater treatment in Hubei Province's semiconductor industry.