Development of a Method to Determine Microbiologically Generated Mercury Vapor and Organomercury in CCBs

Methods and protocols for determining the effect of microbes on the release of mercury from coal combustion by-products (CCBs) were developed by the Coal Ash Research Group at the EERC. An initial method used the slurry of fly ash with buffer and microbes to determine the inorganic and organomercury releases to the air (vapor-phase release) and to the buffer solution (microbiologically mediated leaching). This wet system was used to successfully assess the mercury releases from fly ash samples from multiple sources including samples from bituminous, subbituminous, and lignite combustion. A limited number of fly ash samples with activated carbon (fly ash + AC) present as a result of activated carbon injection (ACI) were also evaluated. It was determined that this method had limitations for alkaline fly ash samples because they were difficult to buffer to neutral pH to support microbial growth. The use of extensive washing with acid to achieve neutral pH was successful for some alkaline fly ash samples but was not adequate for all alkaline samples, so an alternate dry system method and protocol was developed to determine the microbiologically mediated vapor-phase release of mercury for any CCB sample type. A complete description of the two methods and protocols is presented, and a discussion of the results for both successful and failed experiments is included.