Optimisation of methane fermentation as a valorisation method for food waste products

The aim of the study was to optimize methane fermentation of food waste products based on the composition of substrates mixture and technical parameters of anaerobic digestion to obtain the highest biogas and methane production. The study was conducted in the laboratory scale in the mesophilic (37 degrees C) and thermophilic (55 degrees C) conditions. Also the effects of the organic loading rates (OLRs) on the biogas productivity and composition were analysed. The highest biogas yield was obtained in mesophilic digestion of the substrates mixture containing 50% of meat, 40% dairy products, 10% fruit and vegetables. It amounted to 740.4 +/- 19.9 cm(3).g ODM-1 of biogas with 68.6 +/- 1.8% of methane. Biogas potential in thermophilic digestion was from 2.1 to 2.8 times lower for analogical feedstock. It was caused by high concentration of volatile fatty acids (VFAs) in the reactor chamber. The ratio of VFAs to alkalinity was on the level from 0.5 +/- 0.1 to 0.8 +/- 0.1. In continuous experiments, the average biogas production rate was from 2646.9 +/- 117.3 cm(3).d(-1) for OLR of 2 g ODM.dm(-3).d(-1) to 9893.4 +/- 362.0 cm(3).d(-1) for OLR amounting to 8 g ODM.dm(-3).d(-1). Methane content in biogas was between 65.6 +/- 2.5 and 65.5 +/- 1.9%, respectively. It was confirmed that applying OLR above 6 g ODM.dm(-3).d(-1) causes inhibition of methane fermentation.

Automated summary

The study aimed to optimize methane fermentation of food waste by identifying the best composition of substrates mixture and technical parameters of anaerobic digestion. Mesophilic conditions yielded higher biogas production compared to thermophilic conditions due to the presence of higher VFAs concentration. Above a certain OLR threshold, methane fermentation was inhibited.