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 o f bioindicators for the quality and maturity of cured compost obtained by a mixture of winery residues, sludges from dairies and solid residues from f ood processing (grape-stalks, grape-dregs, rice husks), was conducted. Comp osting process lasting five months was monitored by chemico-physical, spect roscopic (FTIR, DTG and DSC), microbiological and enzymatic analyses. Biolo gical activities (ATP, DHA contents and several enzymatic activities), impe dance variations (DT) of mixed cultures during growth and potential pathoge ns (E. coli and Salmonella sp.), were determined. The phytotoxicity tests g ave a germination index higher than 90% and no significant genotoxic differ ences between controls and the compost samples were evidenced. Pathogens we re not found on the cured compost that can therefore be satisfactorily used as amendment for agricultural crops. However, no single measurement of a c omposting process factor, biological, chemical or physical, gave a comprehe nsive view of the quality of a specific composting. We proposed a tool of bioindicators of potential activity and markers in co mbination for integrated evaluation of monitoring of composting process and compost quality. The responses of several enzymatic activities were positi ve 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.