Chemical and Microbial Aspects of Sludge Compossting and Land Application

A series of six studies was undertaken to study various chemical and microbial aspects of the composting and, land application of sewage sludge. Ammonia, which is generated in sludge by ammonify ing microorganisms, was shown to be virucidal. In the pH range of 7 to 9, NH3, but not OHor NH4+, was effective. Temperature effects were related t o a single NH3 concentration. Sludge and sludge compost wi th high concentrations of heavy metals and chlorinated organic materials appeared to have no inhibitory effect on soil enzyme activity, probably because of the age or the highly stabilized nature of the sludge and sludge compost. Sludges were appl ied once (100 megagrams [Mgllha) or annually (20 Mg lha ) fo r 5 years t o f ie ld p lo ts . N movement down the soil profile occurred in the sludge-amended plots, especially in all of the split plots that received additional fertilizer. Phosphorus movement occurred only down t o the 60-cm depth, or four times the depth of incorporation in the sludge-amended plots. Laboratory studies conducted to test methods for improving the efficiency of composting indicated that the most efficient system was the temperaturedemand aeration system. This method resulted in twice as much drying and yielded 2.5 times as much COz as constant aeration composting. Results of studies have shown that Aspergillus fumigatus (AF) and therm o p h i l i c ac t i nomyce tes (TA) are present in air at very low levels in most non-agricultural sites, even when organic matter is present and temperatures are occasionally higher than ambient. Compost and moldy agricultural substrates are the biggest reservoirs and sources of AF and TA. The tolerance of AF to broad ranges of temperature, COP, and water content l imit the benefits of modifying the composting process by these parameters t o inhibit this microorganism. This Project Summary was developed by EPA's Water Engineering Research Laboratory, Cincinnati, OH, to announce key findings of the research project that is fully documented in a separate report of the same title (see Project Report ordering information at back).