Population dynamics in anaerobic wastewater reactors: modelling and in situ characterization

The effects of changing wastewater composition and SRT on an anaerobic mixed population were modelled and compared with the results from continuous degradation studies of a lactic, butyric, propionic and acetic acid containing wastewater. Particular attention was paid to the population dynamics in the membrane-coupled anaerobic pilot-scale reactor, with population data provided by in situ hybridization techniques. The microbial community structure was characterized using fluorescent, ribosomal RNA targeted oligonucleotide probes specific for Bacteria, Archaea and phylogenetically defined groups of methanogens and sulfate-reducing bacteria. Specific cell counts were determined by a combination of in situ hybridization and epifluorescence microscopy. The anaerobic population was dominated by Archaea belonging to the genus Methanosaeta, whereas sulfate-reducing bacteria were monitored to a less extent. The mathematical model was successful in simulating organic substrate degradation, pH in the reactor, liquid–gas transport of gaseous products and the long-term development of the anaerobic consortia. In the model the microbial population was grouped into substrate-specific organisms and compared to the measured amounts of acetogenic and methanogenic cells. At high SRT the hybridization data underestimated the actual number of active cells in the system. With the new technique of in situ hybridization and mathematical simulation promising tools were combined which help to understand the complex interactions in anaerobic mixed populations and the influence of reactor operational modes.