Determination of heat generated by metabolic activities during composting of greenhouse tomato plant residues

Abstract

Heat and mass balances were performed on an insulated laboratory composting bioreactor operating on tomato plant residues. Wood shavings and municipal solid compost were used as a bulking agent and an inoculum, respectively. The moisture content and C:N ratio were adjusted at 60% and 30:1, respectively. Both the thermal and biological parameters were evaluated. The moisture content stayed relatively constant at 59.7 ± 0.61%. The reductions in volatile solids, total carbohydrate, fat and grease, protein, and TKN-N were 29.1, 31.7, 88.8, 17.8, and 11.0%, respectively. The NH4+-N remained unchanged (0.33–0.35%). The temperature peaked after 31 h of operation reaching 63.3 °C and lasted for 9 h. The result of the thermal analysis indicated that the average heat production value was 14.6 kJ/g DM degraded. The conductive heat losses through the cylindrical body and the sidewalls of the bioreactor accounted for 36.53% of the total cumulative heat produced, whereas the heat loss due to aeration accounted for 62.57% and the heat gained by the compost and bioreactor materials accounted for the remaining 0.9%. The addition of a bioavailable carbon source (used cooking oil) at the peak temperature could extend the duration of the maximum temperature to insure that the composting process is effective in destroying pathogens and pesticides. Key words: compost, bioavailable carbon, tomato residues, wood shavings, nitrogen, carbohydrate, protein, fat, temperature.