Cow, sheep and llama manure at psychrophilic anaerobic co-digestion with low cost tubular digesters in cold climate and high altitude

•Low cost tubular digesters adapted to cold climate are monitored.•Four digesters fed with llama, cow and codigestion of both with sheep manure.•Cow–sheep co-digestion results in 100% more biogas production respect cow manure.•The retention of solids is high and a bottom sludge outlet is strongly recommended.•The increase of OLR leads to an increase in BPR but reduces bioslurry quality.

The aim of this research is to evaluate the co-digestion of cow and llama manure combined with sheep manure, in psychrophilic conditions and real field low cost tubular digesters adapted to cold climate. Four digesters were monitored in cold climate conditions; one fed with cow manure, a second one with llama manure, the third one with co-digestion of cow–sheep manure and the fourth one was fed with llama–sheep manure. The slurry had a mean temperature of 16.6 °C, the organic load rate was 0.44 kgvs m−3 d−1 and the hydraulic retention time was 80 days. After one hundred days biogas production was stable, as was the methane content and the pH of the effluent. The co-digestion of cow–sheep manure results in a biogas production increase of 100% compared to the mono-digestion of cow manure, while co-digestion of llama–sheep manure results in a decrease of 50% in biogas production with respect to mono-digestion of llama manure.