Semi‐continuous evaporation model for leachate treatment process evaluation

Abstract

AbstractThe use of evaporation for treatment of landfill leachate may be effective at removing contaminants in one principal unit operation. A semi‐continuous evaporation treatment process model, Reaction EQuilibrium Evaporation Model (REQEM), was developed for engineering assessment to: i) simulate different batch flash vaporization processes, ii) predict the effluent stream compositions and quantities, and iii) compute the energy requirements. The model integrates previously separate features into a composite chemical equilibrium and dynamic process simulation model.Simulations have shown that multi‐stage flash with recirculation and condensation heat recovery maximizes the amount of evaporate produced and minimizes the steam and pumping energy requirements. Leachate with low volatile organic acids may need only acidic evaporation to efficiently treat the leachate. Leachate with high concentrations of both ammonia and volatile organic acids may require a two‐step, pH‐adjustment evaporation process. If nonionic volatile organic compounds are present in leachate, then pretreatment such as air stripping may be necessary to obtain adequate evaporate quality. Adjustments of the initial leachate pH value will have no direct effect on the product‐to‐feed ratio, the performance ratio, or the evaporate quality with respect to nonvolatile compounds such as metals. Landfill gas may provide sufficient energy for leachate vaporization in many instances for modern landfills, and semi‐continuous operations may be the most practical treatment mode.