Granular activated carbon enhances the anaerobic digestion of solid and liquid fractions of swine effluent at different mesophilic temperatures

Abstract

Objectives: This study evaluated the effect of particle size and dosage of granular activated carbon (GAC) on methane production from the anaerobic digestion of raw effluent (RE) of swine wastewater, and the solid (SF) and liquid (LF) fractions. The effect of temperature using the selected size and dosage of GAC was also evaluated.

Methods: 60 mL of swine wastewater were inoculated with anaerobic granular sludge and GAC at different dosages and particle size. The cultures were incubated at different temperatures at 130 rpm. The kinetic parameters from experimental data were obtained using the Gompertz model.

Results: The cultures with the LF and GAC (75-150 μm, 15 g/L) increased 1.87-fold the methane production compared to the control without GAC. The GAC at 75-150 μm showed lower lag phases and higher R_max than the cultures with GAC at 590-600 μm. The cumulative methane production at 45 °C with the RE + GAC was 7.4-fold higher than the control. Moreover, methane production at 45 °C significantly increased with the cultures LF + GAC (6.0-fold) and SF + GAC (2.0-fold). The highest production of volatile fatty acids and ammonium was obtained at 45 °C regardless of the substrate and the addition of GAC contributed to a higher extent than the cultures lacking GAC. In most cases, the kinetic parameters at 30 °C and 37 °C were also higher with GAC.

Conclusions: GAC contributed to improving the fermentative and methanogenesis stages during the anaerobic digestion of fractions, evidenced by an improvement in the kinetic parameters.

Keywords: Anaerobic digestion; Granular activated carbon; Methane production; Swine effluents.