How should this high-quality wastewater be treated?
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We have a new project at our factory, and one of the stages involves wastewater that is extremely problematic: its COD level is 100,000, and it contains 10% salt. The biggest issue is that we’re not allowed to use incinerators for treating this wastewater, and biological treatment isn’t feasible either due to the high salt content. If we were to use multi-effect evaporation, it would not be worth it considering only 2 tons of wastewater per day. The preliminary construction work is almost complete, but we still haven’t decided how to deal with this wastewater – it’s really a headache.
Talk about the types and contents of organic matter in wastewater. There might be a lot of things inside that can be reused. Thus, there are still many techniques that can be used for separation.
The main source of COD is acetonitrile; even after extraction and recovery using carbon tetrachloride, the COD remains at over 1W. I still have a headache.
Since the main source of COD is acetonitrile, it’s easy to deal with. The properties of acetonitrile are similar to those of hexanol, so extraction using a non-polar solvent such as carbon tetrachloride will certainly be ineffective. In the low-concentration region, the volatility of acetonitrile relative to water is very high, and 10% salt content also has a strong salting-out effect on acetonitrile; therefore, the acetonitrile concentration in the gas phase in equilibrium with this waste stream is high. If the acetonitrile concentration in the distillation wastewater can be reduced to very low levels (for example, 100 ppm), then the concentration of the acetonitrile by-product obtained depends on the number of theoretical plates in the distillation section and the reflux ratio. It can reach an azeotropic composition up to 85% acetonitrile. Using the above distillation techniques, propionitrile, acrylonitrile, and other volatile components can be removed.
Such wastewater primarily involves the separation of salts; reducing the salt content to below 1W makes it relatively easier to treat using biochemical methods. Electrophoresis, electrodialysis, or membrane treatment can be considered; of course, evaporation concentration should also work well, with relatively lower costs.