Many business owners in the steel, paper, coating, and printing industries are unsure whether their wastewater is suitable for low-temperature evaporation systems. Today, we’ll clearly explain which types of wastewater are suitable for this process.

First, let’s look at the steel industry. The wastewater types primarily suitable for low-temperature evaporation include desulfurization wastewater, cold-rolling pickling wastewater, emulsified waste liquids, and RO concentrate from recycled water systems. This type of wastewater is high in salt content and contains heavy metals, making it difficult to treat effectively through biological processes. Since the volume is relatively small, using low-temperature evaporation to concentrate and reduce the volume—with the concentrate then sent for off-site disposal—can significantly reduce hazardous waste disposal costs. However, for high-volume, low-concentration wastewater such as blast furnace slag washing water, evaporation is not recommended due to the high cost.

Moving on to the paper industry, concentrate from membrane systems, as well as washwater from cleaning coating tanks and coating machines in the coating section, are highly suitable for low-temperature evaporation. These contain fillers, latex, and starch, resulting in high COD and strong color, making them difficult to biodegrade. For large volumes of white water from paper machines, sedimentation, dissolved air flotation, and biological treatment should remain the priority; there is no need to use evaporation.

In the coating industry—whether paper coating or film coating—the key waste streams are color-change washwater and water used to clean coating pipes and tanks. These effluents have high pollutant concentrations and are discharged intermittently; evaporation can reduce their volume by 90%, directly lowering hazardous waste disposal costs.

In the printing industry, the most common wastewater streams are CTP plate-making wastewater and ink cleaning effluents. These contain photosensitive materials, resins, and pigments that inhibit biological treatment systems; low-temperature evaporation is most suitable for small-batch, high-concentration effluents. For large volumes of mixed cleaning wastewater, physical-chemical and biological treatment should be performed first, with evaporation considered only for the concentrated effluent at the end of the process.

Here’s a simple rule of thumb: wastewater with high salt content that is difficult to treat biologically, small volumes discharged intermittently, membrane concentrate, or high-concentration hazardous waste from the workshop is suitable for low-temperature evaporation. Large volumes of low-concentration wastewater containing a large amount of coarse suspended solids are not suitable. Furthermore, wastewater must undergo pretreatment—including filtration, degreasing, and pH adjustment—before entering the equipment to prevent scaling and blockage of the heat exchange surfaces.