Effect of high salinity on the fate of methanol during the start-up of thermophilic (55°C) sulfate reducing reactors

Two 6.5 L lab-scale upflow anaerobic sludge bed (UASB) reactors were operated at 55 degrees C fed with methanol as the sole electron and carbon source and in excess of sulfate (COD/SO4(2-) of 0.5) in order to investigate the effect of high wastewater salinity on the start-up period. The first reactor (UASB I) was operated without NaCl addition, while the second reactor (UASB II) was fed with 25 g x L(-1) of NaCl in the first 13 days of operation. Successful start-up of UASB I was achieved, with full methanol conversion (100% elimination) to methane gas (methane production rate up to 3.66 gCOD.L(-1).day(-1)). Despite the detection of sulfide from day 15 onwards in UASB I, methane was the main mineralization product when operating at an organic loading rate (OLR) of 5 gCOD.L(-1).day(-1) and a hydraulic retention time (HRT) of 10 hours. Sulfide and acetate started to be produced after salt omission from the influent in UASB II at day 13, with no detection of methane. Acetate was the main product when operating at an OLR of 10 gCOD.L(-1).day(-1) and HRT of 6.5 hours in both reactors. Apparently, the methane producing bacteria (MPB) are the trophic group most sensible to the NaCl shock.