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The pyrolysis and gasification of digestate from agricultural biogas plant

Wiśniewski, Dariusz, Gołaszewski, Janusz, Białowiec, Andrzej
Archives of environmental protection 2015 v.41 no.3 pp. 70-75
anaerobic digestion, arable soils, biogas, carbon dioxide, cations, dewatering, drying, energy, eutrophication, gases, gasification, heat treatment, mineral fertilizers, pyrolysis, sewage sludge, soil fertility, surface water, temperature, vegetation, winter
Anaerobic digestion residue represents a nutrient rich resource which, if applied back on land, can reduce the use of mineral fertilizers and improve soil fertility. However, dewatering and further thermal processing of digestate may be recommended in certain situations. Limited applicability of digestate as fertilizer may appear, especially in winter, during the vegetation period or in areas where advanced eutrophication of arable land and water bodies is developing. The use of digestate may be also governed by different laws depending on whether it is treated as fertilizer, sewage sludge or waste. The aim of this paper is to present the effects of thermal treatment of solid fraction of digestate by drying followed by pyrolysis and gasification. Pyrolysis was carried out at the temperature of about 500°C. During this process the composition of flammable gases was checked and their calorific value was assessed. Then, a comparative analysis of energy parameters of the digestate and the carbonizate was performed. Gasification of digestate was carried out at the temperature of about 850°C with use of CO₂ as the gasifi cation agent. Gasification produced gas with higher calorific value than pyrolysis, but carbonizate from pyrolysis had good properties to be used as a solid fuel.