Defined bacterial culture development for methane generation from lactose

The defined microbial cultures for methane generation from lactose were investigated. A mixed culture consisting of homolactic (Streptococcus lactis), homoacetic (Clostridium formicoaceticum), and acetate-utilizing methanogenic (Methanococcus mazei) bacteria was used to convert lactose and whey permeate to methane at mesophilic temperatures (35-37 degrees C) and a pH around 7.0. Lactose was first converted to lactic acid by S. lactis, then to acetic acid by C. formicoaceticum, and finally to methane and CO(2) by M. mazei. About 5.3 mol methane were obtained from each mole of lactose consumed, and the conversion of acetate to methane was the rate-limiting step for this mixed-culture fermentation.