Enhanced syntrophic propionate degradation and methane production by granular activated carbon in AnSBR

Syntrophic degradation of propionate has been regarded as a limiting factor for methane formation in anaerobic digestion (AD) processes, due to its easier production but harder degradation than other volatile fatty acids. In the present study, 20 g/L granular activated carbon (GAC) was introduced into an anaerobic sequence batch reactor (AnSBR) and the enhancement of propionate degradation and methane production was evaluated with another AnSBR without GAC as a control. Inoculated with the same excess activated sludge, both AnSBRs were synchronously started up at 35 °C with the fed propionate increased gradually from the initial 340 mg/L to the final 1700 mg/L. The results showed that the introduction of GAC made the AnSBR get steady state 6 days earlier. With the fed propionate of about 1700 mg/L in the steady state, the average specific methane production and biomass was enhanced from 0.20 to 0.25 L/L·d, and 7.72 to7.96 g/L, respectively, by the introduced GAC. The results suggested that the GAC had functioned in stimulating microbial growth and enhancing direct interspecies electron transfer between hydrogen-producing acetogens and methanogens, which had resulted in the enhanced propionate degradation and methane production.

Effects of High Sludge Cycle Frequency on Performance and Syntrophic Metabolism of Anaerobic Membrane Bioreactor for Treating High-Lipid Kitchen Waste Slurry

The performance and syntrophic metabolism of the Anaerobic Membrane Bio-reactor (AnMBR) treating high-lipid kitchen waste slurry under different sludge cycle frequencies were investigated in this study. When the sludge cycle frequencies were 3.6 cycles/h, 9.0 cycles/h and 14.4 cycles/h, the obtained Organic Loading Rates (OLRs) were 10.3 kg-COD/m3d, 12.4 kg-COD/m3d and 18.1 kg-COD/m3d, while the corresponding biogas productions were 190 L/d, 310 L/d and 520 L/d. Moreover, with an increase of sludge cycle frequency, the Chemical Oxygen Demand (COD) removal efficiency improved from 86.2% to 90.4% and 96.3%. Additionally, the higher sludge cycle frequency did not break up the sludge flocs and further affect the syntrophic degradation of the toxic Long-Chain Fatty Acids (LCFAs). Conversely, the higher sludge cycle frequency enhanced LCFA degradation and decreased LCFA accumulation. Meanwhile, under higher sludge cycle frequencies, the abundance of syntrophic Methanobacterium, Syntrophomonas and Clostridium increased and favored the syntrophic metabolism of LCFAs.