Printing and dyeing wastewater has long been regarded as the "hard bone" of industrial wastewater due to its high COD, high pH, intense color, and extremely complex composition, posing significant challenges for treatment. For medium-sized printing and dyeing enterprises with a daily treatment volume of 500–2000 m³, the core concerns for managers and engineers are how to strictly meet the "Textile Dyeing and Finishing Industry Water Pollutant Discharge Standard" (GB 4287) while effectively controlling costs and achieving reclaimed water reuse.  

Hongtai Huarui, relying on years of engineering experience, has launched a full-process solution for this scale, comprising “physicochemical pretreatment + enhanced biological treatment + deep decolorization and reuse.” This article systematically analyzes water quality characteristics, process selection, key equipment, and cost reduction strategies.  

1. Sources and Characteristics of Printing and Dyeing Wastewater  

Printing and dyeing wastewater is a mixture of effluents from different processes. Accurately identifying the characteristics of each effluent is a prerequisite for process design. 

2. Core Process Route: Three-Stage Full Process  

For 500–2000 m³/day scale, Hongtai Huarui recommends the following mature process combination:  

2.1Pretreatment — Conditioning and Load Reduction

 Screening and Equalization Tank   

Mechanical screens intercept lint and fiber debris. Recommended hydraulic retention time (HRT) in the equalization tank is 8–12 h, with stirring for uniform water quality and quantity.  

 Cooling and Heat Recovery   

Influent temperature often reaches 40–65℃; it should be cooled to 30–35℃ via plate heat exchangers for optimal biological treatment while recovering heat for production water heating. Heat recovery benefit per ton of water: 0.3–0.8 RMB.  

 Coagulation Flotation (DAF)   

Addition of PAC/PAM flocculates suspended dyes and floating oil, removed by dissolved air flotation. For wastewater dominated by dispersed dyes, this step can remove 40–60% of color, significantly reducing biological load.  

2.2 Enhanced Biological Treatment — The Heart of Organic Removal 

Hydrolysis-Acidification   

For large molecule dyes, the B/C ratio is typically below 0.2. Hydrolytic acidification bacteria under facultative conditions break long-chain molecules, raising the B/C ratio to 0.3–0.4. Recommended HRT ≥ 10 h, sludge concentration 4–6 g/L.  

 Aerobic Biological Treatment (Contact Oxidation / MBR)   

Contact oxidation is easy to operate, suitable for enterprises with limited staff. MBR replaces secondary sedimentation with membrane separation, achieving effluent SS < 5 mg/L, MLSS 6–12 g/L, saving 30–40% space and providing strong shock resistance.  

2.3Deep Treatment — Dual Guarantee of Decolorization and Reuse 

Advanced Oxidation   

Ozone or Fenton generates ·OH radicals that directly destroy azo and anthraquinone chromophores for deep decolorization. To prevent "recoloring," oxidation should be at the final stage with sufficient reaction time.  

 Dual-Membrane (UF + RO)   

For enterprises requiring water reuse, ultrafiltration removes suspended solids, reverse osmosis reduces salinity to <100 μS/cm, with overall recovery rate 70–80%. In water-scarce regions, investment payback is usually 3–5 years.  

3. Recommended Key Equipment Configuration (500–2000 m³/day)    

Based on project data, Hongtai Huarui recommends the following equipment (final specifications should be calculated based on measured water quality):  

4.Three Core Strategies for Reducing Operating Costs  

1. Separate Collection and Targeted Treatment  

High-concentration sizing wastewater (COD > 10,000 mg/L) and low-concentration rinse water (COD < 300 mg/L) are collected separately. The former is pretreated before joining the main process, the latter is treated simply and reused directly, avoiding raising overall concentration and significantly reducing chemical and energy consumption.  

2. Heat Recovery — Turning Waste into Resource  

For 1000 m³/day at 50℃ influent, about 174 GJ/day heat can be recovered, saving 7–8 tons/day of steam and 200,000–300,000 RMB annually. Plate heat exchanger investment payback is usually less than 2 years.  

3. Intelligent Dosing — Reducing Waste  

Online COD and color meters at the equalization tank outlet and biological effluent, controlled via PLC, adjust PAC/PAM and ozone dosing. Coagulant consumption can be reduced by 15–25%, eliminating crude dosing.  

5. Industry Trend: Towards Zero Discharge and Resource Utilization  

With the deepening “dual carbon” policy, wastewater treatment is shifting from simple compliance to resource recycling:  

-  Salt Recovery:  Electrodialysis (EDR) can concentrate NaCl to 60–80 g/L for reuse in dyeing, saving hundreds of thousands of RMB annually.  

-  Deep Heat Utilization:  Organic Rankine Cycle (ORC) generation or heat pumps enhance heat quality for plant heating and process heating.  

-  Sludge Reduction and Resource Recovery:  Thermal hydrolysis + anaerobic digestion reduces sludge volume while producing biogas for power, reducing disposal costs.  

6. Hongtai Huarui Technical service commitment

As a technical service provider specializing in printing and dyeing wastewater treatment, Hongtai Huarui adheres to the principle of “comprehensive water quality analysis first, pilot verification in engineering.”

We provide full-chain services from sampling and testing, process package design, equipment integration, installation, commissioning to operational training, ensuring stable long-term operation and compliance with national and local standards.  

This solution is based on Hongtai Huarui’s internal technical data from numerous printing and dyeing wastewater treatment projects. For detailed customized process design, please contact us.