Destruction of Pathogens in Sewage Sludge by Composting

EPIDEMIOLOGICAL literature indicates that disease outbreaks have been clearly correlated with the land application of night soil and raw sewage wastes. On the other hand, the limited literature available on disease among sewage workers appears to show no strikingly elevated disease incidence above that in the general population. The demonstrated presence of pathogens in wastewater sludges and the increasing application of sludges to land dictate, however, that treatments to further reduce or eliminate pathogens from sludges should play a role in land application practice. Of all treatments, composting is the only one that greatly reduces pathogen levels and also stabilizes sludges sufficiently so that they can be utilized with essentially no generation of malodors. Recent work has shown that digested sludges can be windrow-composted on a production scale through the action of thermophilic microorganisms, although inclement weather can inhibit composting and pathogen destruction. However, raw sludges (mixtures of primary, secondary, and advanced wastewater treatment sludges) can be composted suc-cessfully by the forced aeration pile method without generating malodors and with excellent destruction of pathogens.