Biochar from slow pyrolysis of biological sludge from wastewater treatment: characteristics and effect as soil amendment

摘要

Biological sludge from wastewater treatment is a by-product from the pulp and paper industry, for which several management approaches are being researched to develop added-value applications and to decrease the disposal costs. This work studied biological sludge pyrolysis to produce biochar for further use as soil amendment. The pyrolysis was conducted in a bench-scale fixed-bed reactor using distinct operating conditions, namely heating rate between 2 degrees C min(-1) and 30 degrees C min(-1) and peak temperature between 300 degrees C and 600 degrees C. The results demonstrated that biochar yield was between 0.40 and 0.73 kg kg(-1) dry sludge. A trend for biochar yield to decrease with increasing peak temperature and heating rate was observed. The carbon content of biochar was between 42.8 and 47.0 wt%. The biochar pH was between 6.9 and 11.2. The effect of the biochar produced by pyrolysis as a soil corrective was evaluated in this work. Samples of biochar produced at 450 degrees C and 10 degrees C min(-1) were incubated in a selected soil and its influence on soil properties and plant growth was evaluated. It was observed that the biochar portion 2.5%, 5%, and 10% promoted an increase in soil pH and an increase in water retention. The biochar portion 2.5% and 5% promoted a higher growth of Lepidium sativum plants. The results demonstrated the potential of the pyrolysis of biological sludge from the pulp and paper industry to produce biochar to be further used as a soil amendment. This strategy is of major importance in this industrial sector, thus contributing to the European Union goals on circular economy and industrial sustainability. (c) 2021 Society of Industrial Chemistry and John Wiley & Sons Ltd.