Effect of temperature on the number of selected microorganism groups and enzymatic activityof sewage sludge composted with different additions in cybernetic bioreactors

Microbiological characteristics of sewage sludge from a mechanical-and-biological sewage treatment plant composted in controlled conditions with straw and sawdust are presented. Prepared composts were placed in four bioreactors with differentiated oxygen flow (2L and 4L air·min -1 ). In bioreactor K3 and K4, the composted mass consisted of 70% sewage sludge + 25% sawdust + 5% straw, while in bioreactor K1 and K2, the proportion was 50% sludge + 45% sawdust + 5% straw. Compost samples were taken from all chambers at the same time depending on the actual temperature. Microbiological analyses consisted in the determination by plate method on selective medium the numbers of mesophilic and thermophilic bacteria, actinomycetes, molds and pathogenic bacteria from Salmonella genus Clostridium perfringens and from Enterobacteriaceae family. Furthermore, in the experiment, the activity levels of dehydrogenases were determined using 1% triphenyltetrazole chloride as substratum. Studies have shown that the composting process had caused a total elimination of Enterobacteriaceae in all composted masses and a reduction of the remaining microorganism groups. During the experiment, a drop in the level of dehydrogenases activity was observed which was negatively correlated with temperature increase in the studied composts.