A universal design approach for in situ bioremediation developed from multiple project sites

Abstract

This article describes a design approach that has been developed for bioremediation of chlorinated volatile organic compound-impacted groundwater that is based upon experience gained during the past 17 years. The projects described in the article generally involve large-scale enhanced anaerobic dechlorination (EAD) and combined aerobic/anaerobic bioremediation techniques. Our design approach is based on three primary objectives: (1) selecting and distributing the proper additives (including bioaugmentation) within the targeted treatment zone; (2) maintaining a neutral pH (and adding alkalinity when needed); and (3) sustaining the desired conditions for a sufficient period of time for the bioremediation process to be fully completed. This design approach can be applied to both anaerobic and aerobic bioremediation systems. Site-specific conditions of hydraulic permeability, groundwater velocity, contaminant type and concentrations, and regulatory constraints will dictate the best remedial approach and design parameters for in situ bioremediation at each site.The biggest challenges to implementing anaerobic bioremediation processes are generally the selection and delivery of a suitable electron donor and the proper distribution of the donor throughout the targeted treatment zone. For aerobic bioremediation processes, complete distribution of adequate concentrations of a suitable electron acceptor, typically oxygen or oxygenyielding compounds such as hydrogen peroxide, is critical. These design approaches were developed based on understanding the biological processes involved and the mechanics of groundwater flow. They have evolved based on actual applications and results from numerous sites. An EAD treatment system, based on our current design approach, typically uses alcohol as a substrate, employs groundwater recirculation to distribute additives, and has an operational period of two to four years.An aerobic in situ treatment system based on our current design approach typically uses pure oxygen or hydrogen peroxide as an electron acceptor, may involve enhancements to groundwater flow for better distribution, and generally has an operational period of one to four years. These design concepts and specific project examples are presented for 17 sites. O