Composting of solid and sludge residues from agricultural and food industries. Bioindicators of monitoring and compost maturity

A study to monitor the composting process, to evaluate the effec tiveness of bioindicators for the quality and maturity of cured compost obtained by a mixture of winery residues, sludges from dairies and solid residues from food processing (grape-stalks, grape-dregs, rice husks), was conducted. Composting process lasting five months was monitored by chemico-physical, spectroscopic (FTIR, DTG and DSC), microbiological and enzymatic analyses. Biological activities (ATP, DHA contents and several enzymatic activities), impedance variations (DT) of mixed cultures during growth and potential pathogens (E. coli and Salmonella sp.), were determined. The phytotoxicity tests gave a germination index higher than 90% and no significant genotoxic differences between controls and the compost samples were evidenced. Pathogens were not found on the cured compost that can therefore be satisfactorily used as amendment for agricultural crops. However, no single measurement of a composting process factor, biological, chemical or physical, gave a comprehensive view of the quality of a specific composting. We proposed a tool of bioindicators of potential activity and markers in combination for integrated evaluation of monitoring of composting process and compost quality. The responses of several enzymatic activities were positive and indicative of their favorable use capable to reveal even very small changes within microbial population and activity in test and monitoring of compost programmes.