Dyeing and printing wastewater is the most difficult industrial wastewater I've ever encountered, bar none. COD levels often exceed 1000. color can be hundreds of times higher, and the water quality changes three times a day. I've been a wastewater treatment equipment manufacturer for over a decade, handling no fewer than a hundred dyeing and printing projects, and only a handful consistently meet standards. Many owners think that buying equipment, placing it in the system, and that's it; if the effluent isn't good, they add chemicals; if that doesn't work, they replace the equipment. This approach is simply a money pit in the dyeing and printing industry.
DIEN Water Treatment: Wastewater Treatment Equipment
Three Core Challenges of Dyeing and Printing Wastewater
Color, high COD, and fluctuating water quality—these three combined are simply too much for ordinary equipment to handle. Color is the most troublesome issue; it's not just simple suspended solids, but also contains many dissolved dyes, which biological treatment is largely ineffective against. High COD is manageable, but dyeing and printing wastewater typically has a very low B/C ratio, resulting in poor biodegradability. Trying to reduce COD through a biological system is several times more difficult than with municipal wastewater.
The most critical issue is water quality fluctuation. The dyeing process might involve dyeing blue in the morning, red in the afternoon, and possibly a different dye type in the evening, resulting in influent concentrations that can vary by three to four times. Equipment designed for peak flow is wasteful during normal times; equipment designed for average flow collapses during peak periods.
Technical Path to Achieving Discharge Standards
Having handled numerous similar projects, a common pattern emerges: achieving standards using only one process is virtually impossible. A combination of physicochemical, biological, and advanced treatment is indispensable. The initial stage must remove large-molecule dyes and suspended solids; the middle stage relies on biological degradation of biodegradable organic matter; and the final stage uses ozone or activated carbon to suppress color and residual COD. Many wastewater treatment equipment manufacturers push integrated systems, claiming one unit solves everything. Let me tell you, I've rarely seen a dyeing and printing project achieve standards using integrated systems.
Customized solutions are the only way out for dyeing and printing projects.
In March 2024. a medium-sized dyeing and printing factory in Shaoxing, Zhejiang Province, contacted us. They had been using standard equipment from a certain brand for eight months, but the COD of their effluent consistently hovered around 150 mg/L, three times lower than the Class A standard requirement of below 50 mg/L. The environmental protection bureau had already issued two rectification notices, threatening to shut down production if they didn't meet the standards. When they contacted us, they were almost ready to give up. Last year, another dyeing and printing factory in Zhejiang Province had excessively high COD in its effluent, severely failing to meet wastewater discharge standards. They learned about our company online and inquired about our equipment. Our team visited the site and found that the problem wasn't with the equipment itself, but with a flawed process design from the beginning. The influent water quality fluctuated greatly; their equalization tank volume was insufficient, and the retention time in the biological treatment tank was inadequate, rendering the subsequent advanced treatment unit practically useless. We redesigned the process, adding Fenton oxidation pretreatment, adjusting the structure of the biological treatment section, and implementing ozone catalytic oxidation in the later stages. After two weeks of testing and modification, the effluent COD stabilized below 40 mg/L, and the color was reduced to within 30 times the standard limit.
DIEN Water Treatment: Wastewater Treatment Equipment
This principle is the same as the advantage of customized wastewater treatment equipment manufacturers in low-temperature areas of Northwest China. The environment and difficulties differ, but the core logic remains the same—you must design for the actual working conditions. Simply copying someone else's solution is like planting seeds of problems. What process is your factory currently using? Is the effluent stable? Let's discuss in the comments section, and I'll help you identify the problem.
