Anaerobic co-digestion of FOG and sewage sludge: Study of the process by Fourier transform infrared spectroscopy

The digestion of residues with high lipid content was investigated. The experimental work focussed on the assessment of co-digestion of sewage sludge and fat, oil and grease (FOG) residues separated from the grease trap of the pre-treatment system of a wastewater treatment plant. A 0.2% volumetric ratio was set, based on the volumetric production of these streams in the plant. The digestion was carried out under semi-continuous operation at mesophilic temperatures. The operation of reactors at a hydraulic retention time (HRT) of 30 days resulted in no observable modifications of the specific methane production when compared to results obtained from sludge digestion and co-digestion systems. However, a decrease in HRT resulted in the detriment of the co-digesting reactor, which was attributed to an inhibitory process associated with the adsorption of FOG onto active sludge.

► Anaerobic co-digestion of FOG results in no detriment to the methane production.
► A decrease in HRT resulted in the detriment of the co-digesting reactor.
► The results of FTIR analysis suggest the possible adsorption of lipid components of FOG.