DNA-Based Methods Reveal Complex Kinetics of MSW Leachate Anaerobic Digestion

Abstract

Anaerobic biodegradation is one of the most important natural attenuation mechanisms for contaminants in the vadose zone. It is responsible for preventing many organic pollutants from reaching the aquifer. It has usually been modeled by a first-order decay term (constant first-order growth rate for microorganisms). However, actual degradation may involve many microbial guilds, which may thrive and die one after another. Hence, modeling through a constant decay rate might not be scientifically accurate. First-order growth rate predicts an exponentially increasing biomass concentration. However, temporal oscillations in biomass concentration were experimentally observed through different methods of biomass estimation. Total proteins in the samples were estimated as an indication of the biomass. This method cannot distinguish between material derived from dead and living bacteria (protein). DNA-based methods, both spectrophotometric and fluorometric, have been also used as an indication of biomass growth. Total DNA from the digester samples was extracted and estimated in a spectrophotometer and in a fluorometer. Normalized growth data have been presented. Results show that the kinetics is oscillatory and complex. The fluorometric method was more sensitive and revealed more intricate oscillations in biomass growth. A regression equation for biomass growth has been presented, which can be used in lieu of a first-order growth rate, and for simulating transport of municipal solid waste (MSW) leachate contaminant through the vadose zone.