Population dynamics during composting of fecal automated pig slurry

Microorganisms present in pig manure can contaminate the environment. Although composting is recommended as an efficient method to reduce the pollution potential of waste, there is little research information on this process. This study aimed to evaluate the efficiency of automated composting of pig slurry (PS) in reducing the population of coliforms, used as fecal pollution indicators. The PS was added periodically during 106 days in substrate, with a mixture, in equal parts, of wood shavings and sawdust. There were 14 additions of PS and at each addition the compost windrows were revolved through a machine especially developed for this purpose. Two treatments with three replications were evaluated, one with and one without the addition of phosphoric acid to the slurry up to pH 6.0. The acid addition aimed to reduce N losses through the volatilization of ammonia (NH3) during composting. Coliforms were evaluated by the technique of most probable number (MPN) using the Fluorocult broth, incubated at 37 degrees C for 24 h and subsequent reading in ultra violet light. The population of fecal coliforms was not affected by the addition of phosphoric acid. The automated composting process was effective in reducing faecal coliforms, whose original population decreased from 4.2 x 10(10) to 1.2 x 10(5) at the end of composting (156 days) without addition of acid and from 3.8 x 10(10) to 2,3 x 10(4) in compost with added acid. This removal of faecal coliforms, promoted by automated composting of pig slurry, corresponds to 99.99%.