Impact of reduced straw content on the sewage sludge composting process

The main objective of presented research work was the assessment of the impact of reduced straw content, as organic carbon source, on the course of sewage sludge composting process. During the research work performed in industrial conditions, the composting process going in periodically overturned windrows differing in proportion of dehydrated sludge, straw and structural material being 4:1:1 and 8:1:2 respectively, was observed. The consequence of increase of sludge concentration with relation to straw was decrease of C:N ratio in the input material from 11.5 to 8.5. The following parameters were analyzed as indicators for the assessment of the composting process: contents of fulvic acids (FA), humic acids (HA), lignin, cellulose and hemicellulose as well as absorbance in UV/VIS (λ=280, 465 and 665 nm) range. The results obtained have indicated that the increase of sludge content extends the elevated temperature (T>50°C) period from 42 days to approximately 65 days. Our tests did not confirm that limitation of straw content added to sewage sludge had any adverse effect on the course of composting. PI index (HA/FA), which qualifies the compost as mature in the first case – No 1, exceeds limit value of 3.6 on the 83rd day whereas, in the second case No 2, on the 48th day