The influence of chemical structure on the anaerobic catabolism of refractory compounds: a case study of instant coffee wastes

Abstract

Due to concerns about meeting the strict legislation currently in force, anaerobic treatment is being investigated for the treatment of a variety of waste streams. Instant coffee wastes are one type of industrial effluent that appears to be amenable to anaerobic digestion, and this paper presents some results on the biodegradation of this effluent. The method used was a batch bioassay technique known as the Biochemical Methane Potential assay (BMP), which gave 84% degradation of a composite coffee waste sample. Various fractions of the coffee waste revealed mixed degradation results mostly attributed to structural differences, with the liquid fractions being almost 60% degradable, and the solids filter cake fraction, containing most of the lignocellulosic material being only 9% degradable. Volatile fatty acid (VFA) analysis revealed high concentrations of formate being formed and subsequently degraded in the bioconversion process, and a possible role for formate production was postulated. Variations in structure did not appear to affect the route by which VFAs were produced. Bioconversion of 5-6 major classes of pure organic compounds thought to be potentially recalcitrant in coffee effluent was investigated to determine possible mechanisms of degradation, and the extent to which structural variation affected degradability. The phenolics and chlorogenic acids gave the highest degradation of 70% and 60% respectively, and the cyclic volatiles the least degradation at 40%.