SIMPLE METHOD FOR THE MEASUREMENT OF THE HYDROGENOTROPHIC METHANOGENIC ACTIVITY OF ANAEROBIC SLUDGES

The specific hydrogenotrophic activity of anaerobic sludges is usually assayed by gas chromatographic analysis for methane in the headspace of sealed test vials. Gas is sampled with a pressure lock syringe whic h allows quantification independent of the pressure prevailing in the vials. An alternative method was developed using pressure transducer m onitoring of the decrease in headspace gas pressure as the H2/CO2 subs trate is converted to CH4. Application of a simple formula related the decrease at each sample point to millilitres of CH4 produced and gave values for the specific hydrogenotrophic activity of granular anaerob ic sludge which were in good agreement with the values obtained by the more labor-intensive gas chromatographic method. The simplicity of th e method facilitates multiple replicate analyses and allows more accur ate determination of initial rates than is achievable by the gas chrom atographic method which is prone to analytical error at the very low c oncentrations of CH4 present in the headspace during the early stages of the assay. Mass transfer of H-2 from headspace to liquid was found to be rate-limiting and to result in significant under-estimation of t he specific hydrogenotrophic activity of the granular sludge. A test p rotocol, which used a vial volatile suspended solids concentration bet ween 1.7 and 8 g 1(-1); a 1:5 ratio between liquid and headspace; incu bation of the vials horizontally with vigorous shaking (180 rev./min) and an initial H-2/CO2 (80/20) gas pressure of 100-150 kPa was found t o give reproducible and maximal values for the specific hydrogenotroph ic activity of the test sludge.