Foam suppression in overloaded manure-based biogas reactors using antifoaming agents

•Rapeseed oil, oleic and octanoic efficiently suppressed foaming in biogas reactors.•Rapeseed oil was the most suitable antifoam for overloaded reactors.•Rapeseed oil showed synergistic effect on methane yield when digested with manure.•Tributylphosphate inhibited severely the anaerobic digestion process.

Foam control is an imperative need in biogas plants, as foaming is a major operational problem. In the present study, the effect of oils (rapeseed oil, oleic acid, and octanoic acid) and tributylphosphate on foam reduction and process performance in batch and continuous manure-based biogas reactors was investigated. The compounds were tested in dosages of 0.05%, 0.1% and 0.5% v/vfeed. The results showed that rapeseed oil was most efficient to suppress foam at the dosage of 0.05% and 0.1% v/vfeed, while octanoic acid was most efficient to suppress foam at dosage of 0.5% v/vfeed. Moreover, the addition of rapeseed oil also increased methane yield. In contrast, tributylphosphate, which was very efficient antifoam, was found to be inhibitory to the biogas process.