Department of Civil Engineering, W348 NH, University of Nebraska-Lincoln, Lincoln, NE, 68588-0531, 402-472-3431
This research was undertaken to simplify the selection of the least-cost treatment option for treating waters contaminated with synthetic organic chemicals (SOCs). Five aqueous treatment processes were considered: air stripping, liquid-phase adsorption, steam stripping, biofilm reactor, and combined biodegradation and adsorption (bio-adsorption). Because off gases from air stripping towers are frequently regulated, four off-gas treatment processes also were considered: gas-phase adsorption (both on- and off-site regeneration), thermal incineration and catalytic oxidation. Mathematical process performance and cost models were developed for each process. The least-cost design for each process was identified for a set of typical contaminated waters, and the results were synthesized to create generalizations concerning process selection based on fundamental process variables.
For example, the cost of treating air stripper off gases was found to be primarily a function of a compound's adsorbability, volatility, flow rate and influent concentration. A set of diagrams was created to identify the least-cost off-gas treatment for a given set of conditions.
For aqueous processes, the least-cost air stripping tower design changed when off-gas treatment was added. A methodology for comparing the costs of air stripping with off-gas treatment and liquid-phase adsorption was created in the form of a process selection diagram. The comparison methodology is based upon physical parameters of the target chemical.
In considering bio-adsorption, it offered longer bed lives than adsorption alone in nearly every case, though the degree of improvement varies. Diagrams were created to identify cases where bio-adsorption is particularly economical. Situations were identified where a biofilm reactor and where steam stripping may be economically viable. Heuristics concerning when processes-in-series are valuable were also developed. As discussed, tools and generalizations were created to aid engineers in making intelligent decisions concerning preliminary treatment process selection, with the overall goal of better, cost-effective designs and more rapid selection.
organic chemicals, treatment, remediation, heuristics
This paper is from the Proceedings of the 10th Annual Conference on Hazardous Waste Research 1995, published in hard copy and on the Web by the Great Plains/Rocky Mountain Hazardous Substance Research Center.