The emission of volatile compounds during the aerobic and the combined anaerobic/aerobic composting of biowaste

Two different biowaste composting techniques were compared with regard to t heir overall emission of volatile compounds during the active composting pe riod. In the aerobic composting process, the biowaste was aerated during a 12-week period, while the combined anaerobic/aerobic composting process con sisted of a sequence of a 3-week anaerobic digestion (phase I) and a 2-week aeration period (phase II). While the emission of volatiles during phase I of the combined anaerobic/aerobic composting process was measured in a ful l-scale composting plant, the aerobic stages of both composting techniques were performed in pilot-scale composting bins. Similar groups of volatile c ompounds were analysed in the biogas and the aerobic composting waste gases , being alcohols, carbonyl compounds, terpenes, esters, sulphur compounds a nd ethers. Predominance of alcohols (38% wt/wt of the cumulative emission) was observed in the exhaust air of the aerobic composting process, while pr edominance of terpenes (87%) and ammonia (93%) was observed in phases I and II of the combined anaerobic/aerobic composting process, respectively. In the aerobic composting process, 2-propanol, ethanol, acetone, limonene and ethyl acetate made up about 82% of the total volatile organic compounds (VO C)-emission. Next to this, the gas analysis during the aerobic composting p rocess revealed a strong difference in emission profile as a function of ti me between different groups of volatiles. The total emission of VOC, NH3 an d H2S during the aerobic composting process was 742 g ton(-1) biowaste, whi le the total emission during phases I and II of the combined anaerobic/aero bic composting process was 236 and 44 g ton(-1) biowaste, respectively. Tak ing into consideration the 99% removal efficiency of volatiles upon combust ion of the biogas of phase I in the electricity generator, the combined ana erobic/aerobic composting process can be considered as an attractive altern ative for aerobic biowaste composting because of its 17 times lower overall emission of the volatiles mentioned. (C) 1999 Elsevier Science Ltd. All ri ghts reserved.