Slaughterhouse by-products treatment using anaerobic digestion Ioannis Moukazis, Frantseska-Maria Pellera, Evangelos Gidarakos ⇑ School of Environmental Engineering, Technical University of Crete, Politechnioupolis, 73100 Chania, Greece article info Article history: Received 20 March 2017 Revised 3 July 2017 Accepted 7 July 2017 Available online xxxx Keywords: Anaerobic digestion Biogas Slaughterhouse Animal by-products Co-digestion Agroindustrial waste abstract The objective of the present study is to evaluate the use of animal by-products (ABP) as substrates for anaerobic digestion, aiming at methane production. Specifically, four ABP of Category 2 and 3, namely (i) stomach and rumen, (ii) stomach contents, (iii) breasts and reproductive organs and (iv) bladders and intestines with their contents, were selected. The methane potential of each ABP was initially deter- mined, while the feasibility of anaerobic co-digestion of ABP with two agroindustrial waste, i.e. orange peels and olive leaves was also studied. To this purpose, Biochemical Methane Potential (BMP), as well as semi-continuous assays were respectively conducted. In the latter, the effect of the variation in the organic loading rate (OLR) on methane production was investigated. Results obtained from BMP assays showed that the samples containing breasts and reproductive organs, bladders and intestine, and stom- ach and rumen, had higher methane potentials of 815, 787 and 759 mLCH 4,STP /gVS, respectively. Moreover, according to the results of the semi-continuous assays, maximum methane yields between 253 and 727 mLCH 4 /gVS fed were obtained at an OLR of 0.8 gVS/L/d. The only case in which methanogen- esis inhibition phenomena, due to increased ammonia concentrations, were observed, was the assay being fed with a mixture of breasts and reproductive organs and orange peels, at the highest OLR. This inhibition phenomenon was attributed to an inappropriate C/N ratio. Ó 2017 Elsevier Ltd. All rights reserved. 1. Introduction The high nutritional value of meat, i.e. high protein, bioavailable minerals and vitamins content, results in an increasing demand for livestock products and consequently, in increasing animal by- products generation originating in slaughterhouses. The character- istics and composition of slaughterhouse by-products vary consid- erably, depending on both the size of the slaughterhouse and the animal species that are slaughtered (Alvarez and Lidén, 2008). More specifically, the total amount of non-edible parts may vary from 20 to 45% of the live animal total mass (Reale et al., 2009). Most slaughterhouse by-products are contaminated with high numbers of microorganisms (Urlings et al., 1992), thus usually giv- ing rise to significant environmental problems, due to both organic pollution and microbial load (Cuetos et al., 2008). The adoption of practices that will allow the sustainable management of such waste is a challenge for modern slaughterhouses (Franke-Whittle and Insam, 2013), with legislative restrictions and increased pro- cessing and disposal costs often being the cause of their inappro- priate management (Arvanitoyannis and Ladas, 2008). The European Union (EU) legal framework for slaughterhouse by- products management is determined by the European Regulation (EC) No. 1069/2009. According to this regulation, animal by- products (ABP) consist of full bodies or parts of animals, as well as products of animal origin that are not intended for human con- sumption, either because they are improper for consumption, as a result of their nature, or due to lack of commercial demand. More specifically, ABP are classified into three categories, namely Cate- gory 1, 2 and 3, which reflect the degree of risk, on the basis of risk assessments. The same Regulation signalizes that ABP disposal does not represent a sustainable choice, while it also recognizes that it would be in the interest of all citizens if a wide range of such by-products were used for various applications, provided that health risks are minimized. To this regard, the Regulation mentions the utilization of ABP of Category 2 and 3 for various applications, under certain conditions, which ensure public and animal health. Several different methods for ABP management have been pro- posed, including incineration, aerobic treatment, alkaline hydroly- sis and anaerobic digestion (AD). AD is a controlled biological degradation process, in which sta- bilization of organic substrates is achieved through the combined action of different microbial consortia, in the absence of oxygen. The main products of this process are biogas (a mixture of CH 4 , CO 2 and other gases in traces) and digested sludge. The former http://dx.doi.org/10.1016/j.wasman.2017.07.009 0956-053X/Ó 2017 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail addresses: imoukazis@isc.tuc.gr (I. Moukazis), fpellera@isc.tuc.gr (F.-M. Pellera), gidarako@mred.tuc.gr (E. Gidarakos). Waste Management xxx (2017) xxx–xxx Contents lists available at ScienceDirect Waste Management journal homepage: www.elsevier.com/locate/wasman Please cite this article in press as: Moukazis, I., et al. Slaughterhouse by-products treatment using anaerobic digestion. Waste Management (2017), http:// dx.doi.org/10.1016/j.wasman.2017.07.009