The EPA of U.S. has identified Countercurrent Plow Packed Tower Air Stripping (AST) and Liquid Phase Granular Activated Carbon Adsorption (LPGAC) as the Best Available Technologies for remediating water contaminated with SOCs and VOCs. Traditional methods for assessing the feasibility of these processes consist of bench scale, pilot and field scale studies. A drawback of this approach is that, one does not have a prior estimate of what operating conditions should be employed during the study so as to get optimum performance and correct results. Also, one does not know beforehand whether it is feasible and economical to remove the target VOCs/SOCs on a full-scale. A tool that would evaluate the performance and cost of these processes for a large domain of operating conditions would thus...[ Read more ]

The EPA of U.S. has identified Countercurrent Plow Packed Tower Air Stripping (AST) and Liquid Phase Granular Activated Carbon Adsorption (LPGAC) as the Best Available Technologies for remediating water contaminated with SOCs and VOCs. Traditional methods for assessing the feasibility of these processes consist of bench scale, pilot and field scale studies. A drawback of this approach is that, one does not have a prior estimate of what operating conditions should be employed during the study so as to get optimum performance and correct results. Also, one does not know beforehand whether it is feasible and economical to remove the target VOCs/SOCs on a full-scale. A tool that would evaluate the performance and cost of these processes for a large domain of operating conditions would thus be valuable.

A novel protocol is proposed in this study for evaluating the techno-economic feasibility of air stripping, gas phase and liquid phase carbon adsorption and their combinations based on mathematical models. A computer based system consisting of numerical models, cost estimation models, databases and a prototype expert system is developed. The models simulate the preliminary process design. An algorithm for the use of models to predict the process design parameters is proposed and compared to the conventional approach. The cost estimating modules give detail design component costs and also the least cost design. A prototype rule based backward chaining expert system is also developed to comment on the feasibility of the processes and their combinations based on raw water characteristics, physico-chemical properties of the VOCs/SOCs, treatment goal and design specific heuristics. The system sports a character user interface (CUI) for easy access to different modules.

Simulations on the system show that optimum stripping factor and pressure drop for packed towers without off-gas control is in the range of 3-5 and 50-150 Pa/m respectively. The off-gas adsorber performance is more sensitive to changes in the stripping factor than the pressure drop. With the off-gas adsorber, the packed tower gives optimum results when operated at lower stripping factors (i.e, l-3). In general, AST is more economical than LPGAC (single contactors) even with off-gas control. For LPGAC (single contactors) a l0-15 min EBCT gives minimum usage rate. But the study found that a parallel-series configuration of the contactors gives the least cost and is comparable to AST with off-gas control.