Codigestion of cow and guinea pig manure in low-cost tubular digesters at high altitude

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. The study was carried out in a pilot plant with 3 full-scale digesters located at the Peruvian Andes (2800 m.a.s.l.). In terms of biogas production, the codigestion (0.08mbiogas3mdigester−3 d−1) outperformed guinea pig manure digestion (0.03mbiogas3mdigester−3 d−1), but did not improve cow manure digestion (0.12mbiogas3mdigester−3 d−1), which may be due to the characteristics of guinea pig manure. Therefore, codigestion with other local organic wastes, such as cheese whey, should be explored. The temperature measured inside the digester greenhouse (15-60 °C) was always higher than ambient temperature (10-30 °C); however the liquor temperature remained fairly constant (around 20 °C), suggesting that the greenhouse effect on process temperature was doubtful. Taking into account that the greenhouse increases implementation costs, it would be worth comparing process performance with and without greenhouse in a future study.