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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 °C min−1 and 30 °C min−1 and peak temperature between 300 °C and 600 °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 °C and 10 °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. © 2021 Society of Industrial Chemistry and John Wiley & Sons Ltd.

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An experimental study was conducted at field conditions in order to evaluate the effect of application of ash from biomass combustion on some soil fertility characteristics and plant growth. Application of 7.5 Mg ha industrial fly ash (IA), domestic ash (DA), and a 50:50 mix of domestic ash (DA) and spent coffee grounds (SCG) was made in different soil parcels. Lolium perenne seeds were sown and the grown biomass was harvested and quantified after 60 days. Soil samples from each parcel were also collected after that period and characterized. Both soil and grown biomass samples were analyzed for Ca, Mg, Na, K, P, Fe, Mn, Zn, and Al contents. Soil pH was determined before and after amendment. All applications rose significantly soil pH. Domestic ash, whether combined with coffee grounds or not, proved to be efficient at supplying available macronutrients Ca, Mg, K, and P to the soil and also reducing availability of Al (more than industrial ash). However, it inhibited plant growth, even more when combined with spent coffee grounds. As regards to elemental abundance in plant tissue, both domestic ash treatments reduced Ca and enhanced Al contents, unlike industrial ash, which proved less harmful for the load applied in the soil. Hence, it was possible to conclude that application load should be a limiting factor for this management option for the studied materials.