16.12. Anaerobic digestion of organic by-products from meat-processing industry - The effect of pre-treatments and co-digestion

Public examination of a doctoral dissertation in the field of environmental technology

 Doctoral candidate: M.Sc. Sami Luste 

Date and venue: 16.12.2011, 13.00, L1, Canthia, Kuopio campus 

ABSTRACT 

Anaerobic digestion is a multi-beneficial biological treatment during which micro-organisms degrade organic material producing biogas (i.e. methane) and stabilised end-product (i.e. digestate). Methane is a versatile renewable energy source and digestate can be used as an organic fertiliser and/or soil improver. Because of the increasing consumption and tightening environment and health legislation, production of organic wastes suitable for anaerobic digestion increases. 

Animal by-products (ABP) from the meat-processing industry are often rendered (contaminated material), used as feedstock (in fur breeding), or composted. However, ABPs studied could not be utilised in fodder or in animal food production and have currently been rendered or directed to composting, despite being mostly considered unsuitable for composting. Many ABPs are energy-rich, wet and pasty materials and suitable for the anaerobic digestion process. Moreover, suitable pre-treatment to hydrolyse solid materials and/or co-digestion of two or several materials may improve the anaerobic digestion with ultimate goal to increase the methane production, stabilisation and reusability of digestate. 

The case chosen for more detailed research was that of a middle-sized Finnish meat–processing industry. The aim of the thesis was to evaluate the feasibility of different ABPs presently available for treatment as raw material for anaerobic digestion. Another objective was to enhance the anaerobic digestion process via specific pre-treatments and co-digestion cases with the ultimate aim to increase the methane production and the quality of the digestate. The general goal was to observe the overall process from the perspective of real-circumstances in Finland to rise to needs in practice and to produce exploitable information for adopting sustainable development locally and case-specifically into practice via versatile anaerobic digestion technology. The ABPs studied were highly bio-degradable and especially suitable for anaerobic co-digestion. The co-digestion of the ABPs with sewage sludge and cattle slurry resulted improved methane production and reusability of the digestate. These enhancements were further improved by the pre-treatments studied. The most suitable (ultrasound and bacterial product addition) and synergistically beneficial (pre-hygienisation) pre-treatments were found to enhance the complex degradation of materials. Pre-treatments effects on the whole process and on the end-products were depended on the hydrolysis values, but especially on the content of the materials and qualities of the solubilised compounds. Economical feasibility of ultrasound and hygienisation pre-treatments is attainable. 

Materials and process methods studied in this thesis offer required new information and aspects about the case- and material-specific factors of process requirements,process optimisation according to the requirements in practice, degradability of the ABP materials, hygienic matters and mechanisms involved in pre-treatments and co-digestion of ABPs. The information produced could be directly utilised in the practical implementations of the anaerobic digestion of studied or corresponding materials and feed mixtures. 

The doctoral dissertation of M.Sc. Sami Luste entitled “Anaerobic digestion of organic by-products from meat-processing industry - The effect of pre-treatments and co-digestion” will be examined at the Faculty of Science and Forestry. The opponent in the public examination is Professor Jaakko Puhakka, Tampere University of Tecnology and the custos is Emeritus Professor Juhani Ruuskanen of the University of Eastern Finland. 

Photo available for download at http://www.uef.fi/vaitoskuvat 

Contact: Sami Luste, tel.+358 40 514 3694, sami.luste@phnet.fi

Publishing year: 2011

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