Variability of nutrients content during co-digestion process of sewage sludge and brewery spent grain

Digestates are often used as an organic soil fertilizers therefore content of nutrients is important from practical point of view. Assessment of the variability of N and P concentrations during co-digestion process of sewage sludge (SS) and brewery spent grain (BSG) was the aim of the study. The study was carried out in the reactors operating at temperature of 35oC in a semi-flow mode. Two experiments for the co-digestion process were performed at different hydraulic retention times (HRT). As a result, a slight decrease (of about 12%) in the concentration of total nitrogen was observed, to the average values measured in digestates ranged from 2765 to 3806 g m−3. An analogous tendency was observed in the case of total phosphorus. The addition of BSG as a co-substrate in the anaerobic digestion of SS and shortening of HRT did not cause changes in the nutrients concentration in digestate and its supernatant.