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Animal and dairy science, 4. AGRICULTURAL SCIENCES, 1.5 EARTH AND RELATED ENVIRONMENTAL SCIENCES
The majority of the sludge from the treatment of wastewater in milk processing plants is land spread. The drawbacks of land spreading include local oversupply due to high transport costs, which results in sludge being spread on lands in the vicinity of the dairy factories. Local oversupply can lead to accumulation of certain substances in soil through annual application over many years. Therefore, in the long term, there is a need for alternative methods to recover energy and nutrients from increasing volumes of sludge generated from dairy processing. Pyrolysis ofers a potential alternative to land spreading, which can reduce health and environmental risks, while providing an avenue for the recovery of energy and nutrients. Pyrolysis allows energy recovery in the form of a high calorifc value pyrolysis gas and a char which may be used as a soil amendment. In this study pyrolysis of dried dairy sludge was carried out at pilot scale. The results indicate that a dried biological sludge can be successfully pyrolysed and when mixed with wood the resulting char meets European Biochar Certifcate criteria regarding carbon content. Most of the initial energy content of the feedstock was retained in the pyrolysis gas prior to cleaning, 53%, compared to 34.5% in the char and 1.5% in the tar. For the pyrolysis gas after cleaning (mainly cracking in presence of air) the initial energy content of the feedstock retained in the gas was only slightly higher than that retained in the char, 39.2% versus 34.5%, while the tar accounted for 0.8% of the initial energy content.
Kwapinska, M., Horvat, A., Liu, Y. et al. Pilot Scale Pyrolysis of Activated Sludge Waste from Milk Processing Factory. Waste Biomass Valor 11, 2887–2903 (2020). DOI: 10.1007/s12649-019-00596-y
Irish State; Science Foundation Ireland