Co-composting of manure with fat, oil, and grease: Microbial fingerprinting and phytotoxicity evaluation

Sole carbon source utilization profiles to characterize compost maturity were evaluated in reference to several other physicochemical and biological maturity indices. The results suggested that the addition of fat, oil, and grease ( FOG) had a significant effect on the biological processes in the sample piles when compared to the control pile. Additionally, principal components analysis of the patterns and the levels of microbial activity indicate that microbial communities differentiate in response to FOG additions from 1 to 20 L/m(3). However, between 10 and 20 L/m(3), no recognizable differences were found between the control and the FOG amendment communities. Biolog data indicates a shift in the structure and function of the microbial community in compost with high FOG additions, which may be a useful indicator of high functional diversity and evenness during composting processes. Finally, the germination index (GI) of lettuce increased from 9% in the control to 100% in the FOG amended compost. However, the addition of high amounts of FOG might in turn inhibit seed germination and root growth because of the high pH and electrical conductivity (EC), and the volatilization of NH3. From the present results, 10 L/m(3) was found to be the optimum FOG amendment rate for manure compost. These amendment rates are empirical and may be regarded as potential guidelines to agricultural practitioners.