High-Difficulty Fine Chemical Wastewater Treatment Project

I. Project Overview

This project is a wastewater treatment renovation and expansion project for fine chemical and pharmaceutical intermediate production. The company mainly produces benzene-ring and heterocyclic chemical intermediates, synthetic resins, and fine chemicals. The production process generates large amounts of reaction mother liquor, distillation residue, and equipment cleaning wastewater, which is typical high-salinity, high-COD, highly toxic, low B/C, and poorly biodegradable chemical wastewater that is difficult to treat.

The wastewater contains large amounts of benzene series, heterocyclic organics, residual catalysts, high concentrations of chloride ions and sulfates. It has biological inhibitory effects, so ordinary biochemical systems cannot be started directly, and conventional coagulation-sedimentation processes are completely ineffective.

Design treatment capacity: 800 m³/d (24-hour continuous operation)

Water quality characteristics: toxic, extremely poor biodegradability, high salinity, large COD fluctuations, high color

Treatment objectives: pretreatment to break toxicity and improve biodegradability; anaerobic + biochemical advanced degradation; advanced oxidation as a safeguard; membrane advanced reuse; MVR evaporation of concentrated water for near-zero discharge

Applicable standards: Emission Standard of Pollutants for Petroleum Chemistry Industry (GB 31571-2015); reused pure water meets the workshop production cleaning water standard; solid waste is disposed of in compliance with regulations.

II. Raw Water Quality and Classification (Core of Quality-Based Flow Separation)

This project strictly implements quality-based separation of concentrated and dilute wastewater to prevent high-salinity mother liquor from mixing into cleaning water, which is key to system stability and reducing evaporation costs.

1. High-Concentration Mother Liquor Wastewater (Refractory Toxic Wastewater)

Source: reactor residue, rectification wastewater, process mother liquor, off-spec waste liquid

Water quality indicators: COD: 15000-22000mg/L; salinity: 8000-15000mg/L; B/C < 0.15; contains benzene rings, heterocyclic toxic organics, strong biological inhibition.

2. Low-concentration cleaning wastewater

Source: equipment water washing, floor flushing, tail gas absorption water washing, general workshop drainage

Water quality indicators: COD: 800-1500mg/L; salinity: 1000-3000mg/L; no strong toxicity, generally biodegradable.

III. Complete Process Flow

Workshop drainage collected by quality-based segregation

├─High-concentration mother liquor wastewater → High-concentration wastewater equalization tank → Iron-carbon micro-electrolysis tank → Fenton advanced oxidation tank → Coagulation sedimentation tank

└─Low-concentration cleaning wastewater → Low-concentration wastewater equalization tank

Both wastewater streams homogenized and mixed → Comprehensive equalization tank → Hydrolysis acidification tank → UASB high-efficiency anaerobic reactor → A/O anoxic-aerobic biochemical tank → Secondary sedimentation tank

Ozone Catalytic Oxidation Tank, BAF (Biological Aerated Filter), Multi-Media Filtration, Activated Carbon Filtration, Ultrafiltration (UF), DT-RO Anti-Fouling Reverse Osmosis

RO Permeate Reuse Water Tank (Workshop Reuse)

RO Concentrate, Concentrate Collection Tank, Softening Pretreatment, MVR Evaporative Crystallization System

Condensate Return, Integrated Adjustment Tank; Crystallized Salt Entrusted for Compliant Off-Site Disposal

Sludge from All Systems, Sludge Thickening Tank, Plate-and-Frame Filter Press, Hazardous Waste Sludge Off-Site Disposal

IV. Process Principles and Operating Parameters of Each Unit (Core Technologies for High-Difficulty Wastewater)

1. Segregated Quality and Flow Adjustment System

Independent concentrated wastewater and dilute wastewater adjustment tanks are provided to effectively balance water quality and quantity, preventing high-salinity and highly toxic wastewater from impacting the downstream biological treatment system. Concentrated wastewater undergoes separate pretreatment for toxicity destruction, greatly reducing the risk of biological inhibition.

2. Iron-Carbon Micro-Electrolysis Pretreatment (Ring Opening, Toxicity Destruction, B/C Improvement)

Under acidic conditions, iron-carbon galvanic cell reactions are utilized to open rings and break chains of benzene rings, heterocyclic rings, and long-chain macromolecular organic compounds, destroying toxic functional groups, eliminating biological toxicity, and raising the wastewater B/C ratio from 0.1~0.15 to above 0.3, making it biologically treatable.

Operation control: pH=2.5~3.5, retention time 2h.

3. Fenton advanced oxidation for deep breakdown of refractory COD

Dosing ferrous iron + hydrogen peroxide generates hydroxyl radicals, strongly oxidizing and decomposing inert organic matter remaining from micro-electrolysis, greatly reducing high-concentration COD, thoroughly eliminating residual toxicity, and ensuring the biochemical system remains stable without collapse.

Operation control: pH=3~4, reaction time 2h, ORP controlled at 450~550mv.

4. Coagulation and sedimentation unit

After oxidation, the wastewater is adjusted to alkaline and flocculated, dosing NaOH, PAC, and PAM to remove oxidation intermediates, suspended solids, colloids, and partial color, producing clear water quality and protecting the subsequent biochemical and membrane systems.

5. Hydrolysis and acidification tank

Further hydrolyzes macromolecular organic matter, acidifies and decomposes small-molecule acids, stabilizes water quality, provides high-quality influent for the anaerobic system, and buffers against water quality fluctuation shocks.

6. UASB high-efficiency anaerobic reactor (main COD reduction unit)

For high-concentration organic wastewater, anaerobic bacteria efficiently degrade most organic COD, greatly reducing the subsequent aerobic load, while producing biogas to achieve energy recovery. It is the core consumption-reduction unit for high-concentration chemical wastewater.

7. A/O Denitrification Biochemical System

In the anoxic zone, denitrification removes total nitrogen; in the aerobic zone, nitrification degrades ammonia nitrogen and residual COD. The system has strong shock resistance, solving the problems of excessive ammonia nitrogen and total nitrogen in chemical wastewater.

8. Secondary Clarifier Sludge-Water Separation

Precipitates biochemical sludge; sludge is returned to the front end of the A/O process, and excess sludge is discharged into the sludge system, ensuring clear effluent.

9. Ozone Catalytic Oxidation + BAF Advanced Treatment

Targeting residual refractory inert COD and residual color in the biochemical effluent, ozone provides strong oxidation to break molecular chains, combined with an aerated biological filter for further fine treatment, ensuring ultra-low contamination of the membrane system influent and preventing membrane fouling and blockage.

10. UF + DTRO Membrane Reuse System

Ultrafiltration pretreatment intercepts fine suspended solids, and the anti-fouling DT reverse osmosis performs deep retention of salts and organic matter. The produced water is of excellent quality and is reused in production cleaning processes, greatly reducing the enterprise's tap water consumption.

11. MVR Evaporation Crystallization Zero Discharge System

The high-salinity concentrated water produced by DTRO, after softening and hardness removal, enters the MVR evaporator for low-temperature evaporation and crystallization. The condensate is returned to the system for reprocessing and reuse, and the solid crystalline salt is disposed of compliantly as hazardous waste. The entire system achieves near-zero wastewater discharge, fully meeting the strictest environmental protection requirements of chemical industrial parks.

12. Sludge Treatment System

Pretreatment, biochemical, and sedimentation sludge are uniformly collected and thickened, dewatered by plate-and-frame filter press, and the dried sludge is entrusted to a qualified third-party unit for disposal, with complete records and full regulatory compliance.

V. Actual Operating Effluent Indicators of the Project (Acceptance Data)

VI. Key Project Challenges and Solutions (Core Advantages for High-Difficulty Wastewater)

• Solving toxicity inhibition: Iron-carbon micro-electrolysis + Fenton dual detoxification thoroughly resolves the industry pain point where chemical wastewater biochemical systems cannot start up and are prone to collapse.

• Solving refractory COD: Multi-stage coupling of pretreatment + anaerobic + biochemical + ozone degrades inert organic matter step by step, ensuring effluent COD consistently meets standards.

• Solving high salinity: Membrane concentration + MVR evaporative crystallization truly achieves zero discharge, adapting to restricted and prohibited discharge policies in chemical industrial parks.

• Significant water saving and consumption reduction: produced water reuse rate of ≥75%, greatly reducing enterprise water fees and sewage discharge fees.

• Strong system impact resistance: quality-based diversion + multi-stage regulation + advanced oxidation as a fallback, with extremely strong adaptability to water quality fluctuations.

VII. Project Acceptance and Operation Status

After completion, this project was successfully commissioned in one go, with stable system operation, no biochemical collapse, no severe membrane fouling, and no exceedance incidents.