Specific Gas Production Rate Research Articles

A kinetic model of a recirculated upflow anaerobic sludge blanket treating phenolic wastewater

ABSTRACT: Sludge taken from a recirculated upflow anaerobic sludge blanket (RUASB) treating phenolic wastewater at organic loadings of 6, 12, 16, and 20 kg COD/m3 day was tested by the biochemical methane potential (BMP) method at intervals over a three‐year period for an accurate determination of the specific gas production rate. A modified version of the Haldane equation was used in the selection of a statistically significant model describing this process. Statistical diagnosis was carried out with student t‐test, Durbin‐Watson test for two‐tail distribution and Kalmogorov‐Smirmov statistical approach. The estimated ranges of the maximum specific reaction rate, K; saturation constant, Ks inhibitor constant, Ki; and the order of inhibition, n were as follows: 280–764 mL biogas/gVSS‐day, 202–398 mg phenol/L, 516–880 mg phenol/L, and 1.47–2.51, respectively. The physical meaning of these parameters is explained. BMP tests with sludge taken from the recirculating upflow anaerobic sludge blanket (RUASB) bioreactor running at a loading of 14 kg COD/m3 day validated the effectiveness of the selected model through comparisons of experimental data and predictions. The results indicate that model predictions accurately reflect experimental data within one standard deviation.

Determining specific biomass activity in anaerobic wastewater treatment processes

An experimental method for the measurement of specific gas production rate was developed and tested with biomass samples taken from anaerobic fluidized bed reactors, operating with a variety of carriers with molasses, condensate from cellulose production and brewery wastewater as feeds. The method is based on reactor sampling and offline gas volume measurement during a known time interval. Important factors are biomass and liquid sampling under oxygen-free conditions, using the liquid from the reactor as substrate, providing sufficient mixing and maintaining the physical integrity of the biomass. The method was developed in such a way that small samples (20 ml) were taken under anaerobic conditions (poising agent) for short-term (2–3 min.) gas rate measurements in a small fluidized bed (25 ml) batch reactor with U-tube. Biomass content was measured by an instrumental nitrogen method (Dumas), followed by weight determination of the carrier. The gas rates measured with the test system, and their dependence on substrate concentration, were in good agreement with those directly measured from the continuous fluidized bed reactor. Additions of molasses and acetate to the sample proved that the influence of concentration on the biomass activity can be obtained only by operating the continuous reactor at the concentration levels of interest. Comparison between the reactors showed large differences in the specific activity and the total reactor activity. It was found when comparing two reactors, that the values of the specific and the total activities permitted the calculation of the relative biomass quantities. In this way the influence of the carrier-type could be evaluated.

Comparison of the kinetics of acetate biomethanation by raw and granular sludges

The specific gas production rate for various anaerobic sludges was determined as a function of acetate concentration at 35°C and pH 7.0. Three substrate inhibition kinetic equations were fitted to experimental data by a non-linear regression method. The best description was reached with modified Haldane-type kinetics. Comparison of raw and granular sludges of different origin showed reduced sensitivity of granular sludges to substrate inhibition. A continuous experiment with molasses waste-water in an upflow anaerobic sludge blanket reactor gave similar results: substrate inhibition continuously decreased as granule development proceeded. by modification of the model real physical meaning was attributed to calculated kinetic parameters. This allowed more adequate comparison with data reported previously based on the equations of Monod and Andrews. Our results are of the same magnitude as previously reported data.