Effect of 5% and 10% coal solids loadings was studied in two types of bench scale bioreactors and in chemostat cultures. The bench scale reactors used were rotating biological contactor (RBC) and upflow bioreactors. In RBC, Texas lignite was loaded at 0% and 5% (w/v), while in the upflow and chemostat reactors at 0%, 5% and 10%. Methane, total gas production, soluble carbon and volatile fatty acid production (VFA), as well as microbial growth (measured as cell protein) were monitored. Gas analysis of the headspace from the above mentioned reactors showed higher CO[sub 2] production in experiments with 5% and 10% coal solids (for example, Figure 1). This indicates that acetate degraded into CO[sub 2] but there was not enough hydrogen to carry out the reaction to convert CO[sub 2] to CH[sub 4]. These data obtained confirmed our previous results from laboratory scale reactors, that at coal solids loadings higher than 1%, methane production does not enhance significantly. This phenomena could be due to the production of higher quantities of inhibitory compounds or depletion of factors necessary for methanogenesis.

Effect of 5% and 10% coal solids loadings was studied in two types of bench scale bioreactors and in chemostat cultures. The bench scale reactors used were rotating biological contactor (RBC) and upflow bioreactors. In RBC, Texas lignite was loaded at 0% and 5% (w/v), while in the upflow and chemostat reactors at 0%, 5% and 10%. Methane, total gas production, soluble carbon and volatile fatty acid production (VFA), as well as microbial growth (measured as cell protein) were monitored. Gas analysis of the headspace from the above mentioned reactors showed higher CO{sub 2} production in experiments with 5% and 10% coal solids (for example, Figure 1). This indicates that acetate degraded into CO{sub 2} but there was not enough hydrogen to carry out the reaction to convert CO{sub 2} to CH{sub 4}. These data obtained confirmed our previous results from laboratory scale reactors, that at coal solids loadings higher than 1%, methane production does not enhance significantly. This phenomena could be due to the production of higher quantities of inhibitory compounds or depletion of factors necessary for methanogenesis.