Food Waste Composting in a High Rate Continuous Feed Drum Reactor: Startup and Carbon Balance Analysis

The objective of this work is to investigate the composting of food waste in a continuous feed pilot scale reactor. Food waste, collected daily from university restaurants and canteens, are fed to the composting unit together with wood pellets. During the continuous process the maximum temperature reaches thermophilic levels. The carbon dioxide emission factor is 216 g C kg−1 total solids (TS) per day, while the average oxygen uptake rate is 1245 ± 957 g O2 kg−1 TS per day both based on the daily waste input. The average daily cumulative carbon closure is calculated as −12.5% (±35.2%) with ideal closure of 0%. Inoculation of the final product shows no formation of colonies for total coliforms, Escherichia coli, Enterococcus (E. faecalis, E. faecium, E. durans, and E. hirae) and Pseudomonas (P. aeruginosa). The average respiration activity (AT4) was 12.1 ± 2.14 mg O2 g−1 TS, indicating that the end product is not quite stable and some maturation time may be required, prior to its application as an organic fertilizer. Drum composting has been developed in agreement with the proximity principle of the EU to offer improved rates and simplified housekeeping. During drum composting of canteen waste, more than 50% of the carbon content is lost in the form of carbon dioxide, and the presence of indicator species, including Coliforms and Enterococcus, is minimized while no methane or leachates are formed.