Inhibition of volatile fatty acid production in granular sludge from a UASB reactor

Inhibition of volatile fatty acids (VFA), namely acetate, butyrate, and propionate, on the activity of acetoclastic methanogens within a full-scale upflow anaerobic sludge blanket (UASB) reactor was investigated using specific methanogenic activity (SMA) test. SMA tests were carried out at acetate concentrations in a range of 1000-25,000 mg l^-1, butyrate concentrations in a range of 3000-25,000 mg l^-1 and propionate concentrations between 500-10,000 mg l^-1. Maximum potential methane production (PMP) rates were obtained as 389 ml CH₄ gTVS ^-1.d^-1 at 3000 mg l^-1 acetate concentration, 432 ml CH₄gTVS^-1·d^-1 at butyrate concentration of 5000 mg l^-1, and 162 mlCH₄ gTVS ^-1.d^-1 at 1000 mg l^-1 propionate concentration. App. 50% and 100% inhibition occurred at acetate concentrations of 13,000 mg l^-1 and 25,000 mg l^-1, butyrate concentrations of 15,000 mg l^-1 and 25,000 mg l^-1, and propionate concentrations of 3500 mg l^-1 and 5000 mg l^-1, respectively.