I. Contamination from the Desorption and Re-entry of Organic Pollutants Due to Heat

Activated carbon adsorbs volatile organic compounds (VOCs) such as alcohols, organic acids, and electroplating complexing agents from exhaust gases; once the carbon bed becomes saturated, its adsorption capacity is exhausted;

Under conditions of continuous negative pressure in the equipment and exhaust gas temperatures of 40–60°C, the adsorption equilibrium is disrupted. Large amounts of organic matter originally adsorbed within the carbon pores desorb and volatilize, traveling through the vacuum piping into the condenser where they liquefy and dissolve into the condensate.

At this point, the levels of COD, organic acids, and foaming substances in the water will be higher than when no activated carbon is installed; reusing this water in the evaporator will exacerbate foaming and cause the foam to overflow the feed material.

II. Activated Carbon Dust Carried by the Gas Stream into the Condensation System

Long-term gas stream erosion causes the saturated, loose activated carbon to pulverize. Ultrafine carbon dust cannot be completely intercepted by the wire mesh and is carried by the negative-pressure gas stream into the condenser:

Carbon dust mixes with the condensate, causing the water to turn black and increasing its solids content;

Reusing carbon-contaminated wastewater clogs spray nozzles and heat exchange channels, forming composite scale consisting of carbon, salts, and silica.

III. Cumulative Factors Exacerbating Secondary Pollution

The saturated carbon bed accumulates large amounts of organic matter, which slowly decomposes within the sealed piping to produce low-molecular-weight foaming agents. When this mixture is recirculated into the evaporation chamber, foaming increases dramatically, causing more salt-containing mother liquor mist to be carried into the condensate;

Desorbed alcohols and acidic vapors enter the vacuum pump, causing the pump oil to emulsify and degrade; vacuum fluctuations further exacerbate the problem of mist-carried material loss;

Resistance in the carbon tank increases, intensifying airflow pulsations in the piping; the separation efficiency of the demister screen decreases, allowing more mother liquor aerosols to penetrate, and the salt content in the condensate rises accordingly.