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Feasibility of anaerobic co-digestion as a treatment option of meat industry wastes
Inmaculada M. Buendía *, Francisco J. Fernández, José Villaseñor, Lourdes Rodríguez
Chemical Engineering Department, ITQUIMA, University ofCastilla-La Mancha, Avda. Camilo José Cela S/N 13071, Ciudad Real, Spain
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The anaerobic biodegradability of meat industry wastes was investigated in mesophilic batch reactors and combined with a mathematical model for describing their biodegradable fractions. The characteristics and methane yield achieved when digesting waste sludge, suggested the use ofthis as co-substrate for enhancing the biodegradability of the other wastes. The co-digestion experiments showed that it would be feasible to co-digest cow manure or ruminal waste with waste sludge, but biodegradability of pig/cow slurries was not improved, being strongly inﬂuenced by the ammonium concentration of co-digestion mixture. By applying the mathematical model, it was observed that whenincreasing the amount of waste sludge in the co-digestion mixtures, the amount of inert and slowly biodegradable fractions decreased leading to an increase in readily biodegradable fractions, volatile solid removal efﬁciencies and methane yields. These results suggest that using readily biodegradable wastes as co-substrate, the anaerobic biodegradability of complex organic wastes can be improved.Ó 2008 Elsevier Ltd. All rights reserved.
Article history: Received 1 July 2008 Received in revised form 9 October 2008 Accepted 12 October 2008 Available online 28 November 2008 Keywords: Ammonia inhibition Anaerobic biodegradability Biodegradable fractions Co-digestion Meat industry wastes
1. Introduction A prolonged storage of organic waste (e.g. disposal in landﬁlls) can cause naturaland uncontrolled decomposition of the organic matter, polluting soils, groundwater, surface waters and releasing gases such as methane and carbon dioxide (Møller et al., 2004; Vedrenne et al., 2008). Due to the increasing regulation on waste disposal and as a result of the global warming effects resulting from the release of greenhouse gases, biological treatments of organic wastes are increasingin importance as an option to reduce the water and soil pollution and greenhouse gas emissions. The treatment of the organic wastes through anaerobic digestion processes has been widely recognized as a way to control greenhouse gas emissions and to use them for energy generation (Lettinga, 1995, 2001; Barton et al., 2008). In that respect, the EU countries have agreed on supporting the productionof biogas as a renewable energy source in combined heat and power plants in order to decrease the greenhouse gas emissions according to the Kyoto protocol (CEC, 2001). Additionally, the use of the anaerobic digestion reduces the volume of waste, which after an aerobic treatment as composting, could be used as soil amendment. Meat industries and farms are important sources of animal wastes includingrumen, stomach and intestinal content from slaughterhouses, slurry (low solid content) and manure (high solid content) from farms. For enhancing yields during the anaerobic digestion when treating animal wastes, some studies show several possibilities, such as modiﬁcations in mechanical pre-treatment,
* Corresponding author. Tel.: +34 902 204 100; fax: +34 926 295 242. E-mail address:firstname.lastname@example.org (I.M. Buendía). 0960-8524/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2008.10.013
temperature and mode of mixing (Karim et al., 2005; Kaparaju et al., 2008). Nevertheless, due to the high organic content, high biological oxygen demand and low carbon/nitrogen ratio compared to domestic or vegetal waste, the enhancement of yields in...