Evaluation of sewage sludge for further nutrient conservation

Conversion of organic-containing sludge to a high value fertilizer is considered to be a rational solution from a recycling point of view. Aerobic respiration could serve as an indicator of stability and maturity of the treated sewage sludge (SS). The aim of this study was to characterize two SS samples obtained from different wastewater treatment plants („D” and „J”) at the initial stage of treatment, alone and with amendments. Two methods for estimation of microbial respiration as well as dehydrogenase activity were used. The SS-J demonstrated higher microbial biodegradation activity, compared to SS-D. In experiments with OxiTop® device, statistically significant (p < 0.05) differences of the pressure drop between SS-J and SS-D were revealed. Addition of peat to SS resulted in a more intensive pressure drop compared to non-amended SS: −145 hPa vs. −76 hPa for SS-D and −199 hPa vs. −180 hPa for SS-J. The obtained results represent a methodical approach for characterization of raw SS in order to evaluate the amount of aerobically degradable organic substances and intensity of their oxidation. Further research is needed for highlighting the mechanisms responsible for interrelation of respiration intensity, bacterial community activity, and other metabolic changes towards SS stabilization.