MONITORING BIOCHEMICAL-ACTIVITY DURING SEWAGE-SLUDGE COMPOSTING

A sewage sludge with the addition of two woody materials (1:2 ratio), tree-pruning chips and vine shoots, to provide structure were composted under controlled conditions of temperature (28-degrees-C) and humidity (70% ambient humidity). Hydrolytic enzyme activities [urease, phosphatase, N-benzoil L-argininamide (BBA) hydrolysing protease, casein-hydrolysing protease, ATP, hydrosoluble and hydrolysable polysaccharides] were determined during the aerobic incubation. Samples were taken and incubated under the same conditions in an accelerative bioreactor to test potential C mineralisation by measuring the CO2 evolved. A rapid mineralisation phase (2-3 weeks) was followed by a slow maturation (4-14 weeks) period. The slow phase and the dynamics of substrate decomposition were better indicated by the hydrolytic enzyme activities that were measured. The structuring agents slightly retarded the compositing process with tree prunings having the strongest effect. Hydrolysable polysaccharides and Folin-reactive compounds (proteins, polyphenols) released by the structure-providing lignocellulose material appear to have controlled both the intensity and the length of the maturation phase.