VOC and SVOC Emissions from Slurry and Solid Phase Bioremediation Processes

Gaseous emissions of volatile organic compounds (VOCs) and semi-VOCs (SVOCs) from slurry and solid phase bioremediation processes were evaluated. The specific processes considered were those used for the bioremediation of concentrated industrial wastes and of contaminated soils and sediments. The purpose of the evaluation was to document the extent to which such processes emit VOCs and SVOCs. Such information is needed to answer questions such as (1) what are the VOC and SVOC emissions that occur during the operation of these processes?; (2) should emission controls be considered for such processes?; and (3) to what extent does volatilization contribute to the loss of organic compounds in what is considered a bioremediation process? These questions are relevant to understanding the performance of aerobic processes treating concentrated hydrocarbons. The results of this evaluation indicated that, although volatile losses of VOCs and SVOCs can occur from slurry and solid phase bioremediation units, in such units, biodegradation is the primary method of SVOC loss. In well-acclimated bioremediation units, biodegradation of xylene/somers also can be a primary chemical loss mechanism. In situations where mass balances of SVOCs could be determined, volatile losses of SVOCs such as polycyclic aromatic hydrocarbons and polychlorinated biphenyls were <0.1% and frequently <0.01% of the mass of such chemicals in the bioremediation units. Greater volatile losses occurred in the initial phase of units operated as batch bioreactors. This is likely due to higher concentration driving forces from the liquid phase to the air phase coupled with biomass that is not fully acclimated to degrading the added VOCs and SVOCs. To minimize volatilization losses from bioreactors, the bioreactors should be designed and operated as well-acclimated continuously fed units rather than as intermittent batch units. There are many fundamental and operational factors that can affect gaseous emissions from bioremediation units. The more important factors are the partitioning of organic chemicals to solids in the unit, rate of microbial activity, volatility of the chemicals, and manner in which the unit is operated.