Abstract:
As a principle "recycling should be preferred over treatment wherever possible". In line with this, a multipurpose Mechanical Vapor Recompression (MVR) evaporator pilot plant was designed, fabricated and tested at a pilot plant level with the aim of recovering water and valuable components from industrial wastewaters. A cost of 2.5-3.0 US$ was found to be necessary for evaporation of one ton of wastewater. It was found with different wastewaters that generally the distillate was of a quality which is comparable to many raw water sources used today by the industry (200-500 uS/cm), which have a value of about 1.0 US$. The experiments showed distillates are not of required quality in the presence of solvents or foaming detergents. Even if the distillate is marketed the total cost does not allow this technology to compete with classical wastewater treatment except in cases where classical methods fail (high organic, inorganic or toxic load). Experiments with zinc-bath wastewaters showed that MVR technology can easily separate pure ZnSO4 by fractionated crystallization from other constituents, the value of which is in order of magnitude greater than the evaporation costs. It is believed that this feasibility situation should be the rule for chemicals recovered from wastewater.
