Short communicationCodigestion of cow and guinea pig manure in low-cost tubular digesters at high altitude
Introduction
Low-cost household digesters are considered an appropriate technology which helps expanding modern energy services in developing countries. During the last decades they have spread successfully in rural zones of Asia and Latin America. Previous experiences have shown that low-cost household digesters improve the living quality of rural families by providing biogas, a clean fuel for cooking and lighting (Bhattacharya and Salam, 2002, Chen, 1997, Qi et al., 2005, Garfí et al., in press-b).
In rural zones of India and China brick masonry digesters with a floating drum or a fixed dome have been implemented since the 1970s (Chen et al., 2010). On the other hand, in rural areas of Tropical countries like Taiwan, Colombia and Costa Rica tubular polyethylene and PVC digesters have been spreading successfully due to their low-cost and ease of implementation and handling. Biogas production in such digesters () (Lansing et al., 2008) can be compared to that of traditional digesters in India () (Singh and Anand, 1994).
During the last years low-cost tubular digesters have been adapted to Andean countries. Lab-scale studies simulating the anaerobic digestion of llama, cow and sheep manure in unheated digesters at high altitude (3800 m.a.s.l) have shown that temperature is the most limiting factor, followed by the hydraulic residence time (HRT) and organic loading rate (OLR) (Alvarez et al., 2006); and that the methane production increases with temperature from psychrophilic to mesophilic conditions (Alvarez and Lidén, 2008a). Full-scale studies have confirmed that, under the extreme conditions of the Andes, the relatively low biogas production () covers around 60% of households fuel needs for cooking (Ferrer et al., 2011). For this reason, alternatives to improve the effectiveness of the process should be addressed.
The anaerobic codigestion of a mixture of substrates can outperform the anaerobic digestion of a sole substrate, by providing a feedstock with an equilibrated composition, enhancing bacterial growth. The codigestion of mixtures of manure, fruit and vegetable waste, slaughterhouse waste or cooking grease has been effective in optimizing biogas production (Alvarez and Lidén, 2008b, Alvarez and Lidén, 2008c, Alvarez and Lidén, 2009, Chanakya et al., 1999, Kavacik and Topaloglu, 2010, Lansing et al., 2010). At high altitude, promising results have been obtained in lab-scale psychrophilic anaerobic digesters (Alvarez and Lidén, 2008b, Alvarez and Lidén, 2008c, Alvarez and Lidén, 2009), but full-scale studies are still missing.
Therefore, the aim of this research was to improve the anaerobic digestion of cow and guinea pig manure in low-cost unheated tubular digesters implemented at high altitude, by comparing different operating conditions and codigesting both manures. Additionally, the effect of the greenhouse on process temperature was investigated.
Section snippets
Experimental set-up
The experiments were carried out in a full-scale pilot plant located at an altitude of 2800 m.a.s.l. in Baños del Inca (Cajamarca, Peru). It consists of three unheated low-cost tubular digesters (D1, D2 and D3) covered with a greenhouse. The main design and operational parameters of the digesters are summarised in Table 1. Other aspects of low-cost tubular digesters implemented at high altitude may be found in Ferrer et al. (2011).
Experimental procedures
Peruvian Andes are characterized by two seasons: a dry sunny
Feedstocks and effluents characterization
Average characteristics of the feedstocks and effluents are shown in Table 2. Notice that the concentration of TS in cow manure (17–18%) was significantly lower than in guinea pig manure (28%); whereas the concentration of organic matter was significantly higher in cow manure (80–82% VS/TS) compared to guinea pig manure (68.5% VS/TS), as a consequence of the pre-composting process. The organic content was reduced from 68–82% VS/TS in the influent to 42–64% VS/TS in the resulting effluent.
Conclusions
This study aimed at improving the anaerobic digestion of cow and guinea pig manure in low-cost unheated tubular digesters implemented at high altitude. Additionally, the effect of the greenhouse on process temperature was investigated. In terms of biogas production, the codigestion () outperformed guinea pig manure digestion (), but did not improve cow manure digestion (); which may be due to the
Acknowledgements
This work was carried out in collaboration with the NGOs Intermediate Technology Development Group-Practical Action (ITDG-Peru), Engineers without Borders (ISF-Spain) and Green Empowerment (GE-USA), and the National Institute for Agricultural Innovation (INIA); with financial support of the Centre for Development Cooperation (CCD-UPC) and the Catalan Agency for Development Cooperation (ACCD-U2008-PRIADER). Pau Gelman from the Universitat Politècnica de Catalunya (UPC); Robert Cotrina from
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