Pilot Scale Pyrolysis of Activated Sludge Waste from Milk Processing Factory

  • M. KwapinskaEmail author
  • A. Horvat
  • Y. Liu
  • James J. Leahy
Original Paper


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 offers 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 calorific 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 Certificate 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.


Dairy processing sludge Pilot scale pyrolysis Pyrolysis gas Tar Char Mass balance 



This work was supported by the Irish State through funding from the Technology Centres programme—Grant Number TC/2014/0016, and Science Foundation Ireland (Grant Number 16/SP/3829).


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© Springer Nature B.V. 2019

Authors and Affiliations

  1. 1.Dairy Processing Technology CentreUniversity of LimerickLimerickIreland
  2. 2.Department of Chemical Sciences, Bernal InstituteUniversity of LimerickLimerickIreland
  3. 3.Dublin Institute of TechnologyDublin 8Ireland

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