Appl Biochem Biotechnol (2011) 165:270–278 273 gases, gas was drawn through the stopper by means of a needle guidance sampler and separated on an SRI 31C GC analyzer equipped with thermal conductivity detector. VOAs, alcohols, and ketones were analyzed using a Shimadzu GC-2010 equipped with a splitter (50:1 setting) and flame ionization detector, and using the following temperature profile setup: injector at 240 °C, iso 60 °C for 10 min., ramp 10 °C per min to 240 °C, and detector at 260 °C. For field experiments, urban food scrap was obtained by New Earth Farm, (Hillsboro, OR) from restaurant kitchens and serving delis. This food scrap was made up mostly of discarded produce, restaurant leftovers, coffee grounds, and paper filters. These materials were premixed with a small amount of wheat bran inoculum (~0.015 w/w ratio), blended through a wood chipper, and processed in 210-L capacity MC-fermentors (airtight plastic containers equipped with a spigot for draining the compost tea). Fermentors also had a one- way gas vent for CO2 release. Following ~1–1.5-week incubation at ambient temperatures ranging on day/night cycles of ~10–18 °C, the fermentors were drained. Residue remaining in the fermentors was amended by shovel and tractor spreaders into swaths of soil to a depth of not more than ~20 cm at varying loads (kg m−2) as shown in “Results” section. Soil samples (~100 g per site) taken from the top ~10 cm layer for analysis were dried in an oven for 48 h at 65 °C, and then ground to uniformity using a mortar and pestle before analysis. Control soil (soil not having received processed food scrap) was retained to obtain baseline polysaccharide levels, EPF index values, and organic volatile content. WIAS polysaccharides and the aldehyde reactive group content of soil samples were expressed in gram glucose per gram DW soil. The soil"s pH was measured using a pH meter calibrated to the nearest 0.01 pH unit between pH 4.00 and 10.00 on aqueous slurries of soil made up in 1:25 (w/w) ratios with deionized H2O (dH2O). Results Microbial isolation and then characterization based on staining, optical microscopy, production of extracellular cellulases, and formation of butyrate during fermentation of glucose and screening of isolates by PCR amplification with 16S rDNA Clostridium- specific primers showed that the wheat bran slurries used to inoculate the MC fermentors are dominated (~60%) by cells from the genus Clostridium. During laboratory MC experiments using oak leaves inoculated with these wheat bran slurries, the EPF index dropped sharply through about the 10th day, reaching an end point at ~0.5 EPF (Fig. 2). After amending the MC leaves into soil, the EPF index fell slowly with an estimated polysaccharide half-life of about 100 days. While leaves were in MC fermentors, O2 in the headspace fell sharply, bottoming out between ~0.4% and 2% by the third day. CO2 rose steadily peaking by the 10th day at 740 ± 42 μmol (1SD), (=25 ± 1% CO2) gas content in the headspace. The amount of C given up as CO2 in the headspace during 2 weeks of MC fermentation was ~1% of the initial biomass. In MC experiments occurring for longer time intervals (up to 5 weeks; results not shown), CO2 production was much larger, up to 92% in the gas phase per week. The ratio of O2 respiration to CO2 production ranged between 1.25:1 and 4.6:1. Assuming that sugars were the main energy source, the total CO2 produced during MC exceeded that expected based on aerobic respiration alone, therefore indicating that fermentation is the dominant CO2-releasing process during MC. No CH4 was detected; this is likely because of (1) the acidic pH caused by accumulation of VOAs; and (2)