Physical and Chemical Properties of Biochar Produced from Sewage Sludge Compost and Plants Biomass, Fertilized with that Compost, Important for Soil Improvement

The aim of the research was to investigate the physical and chemical properties of the biochar made from sewage sludge compost (SSC) and the biomass of energy plants (‘Tora’ willow (Salix sp.) and mugwort (Artemisia dubia Wall.)) fertilized with it, and the biochar derived from unfertilized plant biomass (pyrolysis was performed for 2 h at 450 °C and 700 °C); determine how the feedstock type and temperature during pyrolysis affect biochar properties important for soil improvement. One-way and two-way analyzes of variance were performed using Excel-based ANOVA. Fisher test was used for comparison of data. Comparisons were done using p < 0.05 and p < 0.01 as significance levels. It was found that the yield, ash content and pH of mugwort biochar were higher than those of the willow biochar (p < 0.05). However, the dissolved organic carbon (DOC) concentration in willow biochar (0.235–0.344 g/kg) was lower and N concentration (0.00–0.103%) was higher compared to those in mugwort biochar (0.294–0.926 g/kg and 0.00–0.043% respectively) (p < 0.05). Biochar produced at 700 °C has higher pH, higher ash content, and C concentration than biochar produced at 450 °C. SSC biochar is not recommended to use for incorporation into the soil due to particularly high Ni, Cr, Cu and Zn concentrations in this type of biochar (60.2–92.3 mg/kg, 98.8–109.9 mg/kg, 157–186 mg/kg and 1735–1586 mg/kg respectively). It was found that the biochar produced from mugwort biomass at 700 °C was best suited for incorporation into unfertile soil of light texture with the aim of stopping its degradation and improving its properties. The ‘Tora’ willow biochar produced at 450 °C could also be recommended for soil improvement.