[Aerobic treatment of pig slurry: microbial aspects]

During the treatment of raw pig slurry by batch aerobic fermentation, the presence of surfaces for bacterial attachment resulted in a 1,000-fold increase in the microbial population. In the absence of such surfaces, a 65% reduction of the chemical oxygen demand (COD) of the manure was obtained after 168 h of aeration, whereas a value of 90% was observed in their presence. In the early stages of the treatment, during which the redox potential passed from a value characteristic of anaerobic conditions (-305 mV) to a stable value typical of aerobic conditions (+125 mV) some 120 h later, an amylolytic population dominated by Gram-negative bacteria (chiefly Acinetobacter calcoaceticus) developed; this was followed by a phase in which a proteolytic population tended to become dominant. Populations of some potentially pathogenic bacterial strains characteristic of the porcine intestinal flora declined noticeably during the treatment.