Xylanase activity and thermostratification during the thermogenic phase of industrial composting in aerated trenches.

Extracellular xylanase activity and thermostratification were monitored during the thermogenic phase of industrial composting (mainly garden waste) in aerated trenches. Xylanase activity was assayed at different temperatures and pH by incubation of clarified compost extracts with xylan. The highest xylanase activity and temperatures were measured during the summer (when waste was rich in freshly cut grass). Xylanase activity was higher in the peripheral layers of the trenches, at moderately high temperatures (48 to 68°C), than in the hottest central layers (70 to 78°C). Optimal temperature for the xylanases was between 60 and 80°C at pH 6, depending on the temperature of the sampling site. The thermostability of the xylanases from surface samples was high until 60°C, moderate at 70°C and weak at 90°C. Our results show a broad thermostratification of the compost mass. Frequent turnings of the compost stimulate xylan degradation by redistributing the substrates, the free enzymes and the microorganisms.