Influence of Supplementary Bioavailable Carbon on the Thermal and Biological Kinetic Parameters of the Composting Process of Tomato Plant Trimmings

Three laboratory-scale bioreactors were used to investigate the influence of bioavailable carbon addition on the composting process of tomato remains. Sugar, cheese whey and used cooking oil were used as bioavailable carbon sources. The amounts of materials added to the compost mixture had equal energy contents. The initial moisture contents and C: N ratios of the compost mixtures were maintained at 60 % and 30: 1, respectively. The average bioreactor temperature was strongly influenced by the type of bioavailable carbon. The maximum bioreactor temperature was 50.8, 56.9, 63.4 and 63.3 ºC for the control and the mixtures receiving sugar, cheese whey and used cooking oil, respectively. Strong correlations were observed between the maximum temperature achieved (and its duration) and the reductions in fat and volatile solids contents. The total fat reductions were in the range of 64.6-88.8 %, whereas the total carbohydrates reductions were in the range of 21.5-31.7 %. Reductions of 12.4-25.3 % and 3.5-17.7 % were also achieved in protein content and TKN. Neither the nitrogen nor the moisture contents were limiting factors. The ammonium nitrogen remained unchanged at 0.33-0.35 % and the moisture content remained at 59.7 ±0.61 %.