Decision analysis: physical/chemical technologies for aqueous organic hazardous wastes

Two treatment technologies for removing volatile organics from water are stripping and carbon adsorption. Since stripping causes air pollution, three treatment schemes were considered in this research: stripping, stripping with gas phase adsorption, and liquid phase adsorption. The research was undertaken to simplify choices among these options. The specific eight compounds chosen for study included: benzene, chloroform, trichloroethylene, dibromochloropropane, phenol, 1,1-dichloroethane, 1,2-dichloroethane, and methyl tertiary-butyl ether. Mixtures also were considered. Mathematical models describing the technical behavior of each option were combined with captial and operating costs. A stripping model was written to run on the Macintosh computer. Gas adsorbers to treat stripping tower off-gases were designeds in the assumption that equilibrium is achieved (since gas adsorption is rapid). Stripper off-gases were considered to be heated to reduce the humidity. For liquid phase adsorption, a multicomponent plug flow homogeneous surface diffusion model was used to predict the effluent concentration profile. The results show that, when feasible, stripping alone is always the cheapest option, stripping was found to be feasible when the Henry constant exceeded 0.013 m³ liquid/m³ air. An exciting result is the development of a simple guideline for determining when stripping with gas phase adsorption is preferable to liquid phase adsorption. The guideline is based on the ratio of the carbon loading from gas phase adsorptions to that from liquid phase adsorption and reflects all the critical design parameters for both options; the stripping factor, Henry's constant, liquid phase influent concentration, adsorption capacities in both phases, and costs.