A biochemical model describing volatile fatty acid metabolism in thermophilic aerobic digestion of wastewater sludge Original Research Article

A biochemical model was developed to explain the mechanism of volatile fatty acid (VFA) metabolism in Thermophilic Aerobic Digestion (TAD). The effects of substrate addition on the metabolic behavioral patterns of TAD biomass, from a pilot scale system, were examined. The majority of the substrates examined under batch test conditions, with TAD process biomass, under microaerobic conditions, were oxidized to an acetate intermediate. The model predicts that, under microaerobic conditions (i.e. oxygen demand of the biomass is greater than the oxygen supply of the aeration equipment), the NADH (nicotinamide adenine dinucleotide) produced during oxidation of substrates can be reoxidized by operation of the respiratory chain. Therefore, the carbon flow can be uncoupled from the necessity to maintain redox balance via fermentative means. This uncoupling would allow the organisms in a TAD process, under microaerobic conditions, to simplify metabolism and maximize ATP (adenosine triphosphate) production by increasing the flux of substrates to acetate.