Effects of magnesium chloride on the anaerobic digestion and the implication on forward osmosis membrane bioreactor for sludge anaerobic digestion

This work elucidates the effects of model reversed salt MgCl2 on methane production in an anaerobic digestion bioreactor treating waste sludge. Along with MgCl2 concentration being raised stepwise, the methane production was only slightly less than in the control when MgCl2 was 20 g/L and under, and then suddenly reduced to only about 10 mL/(L·d) at a MgCl2 concentration of 30 g/L, and finally stopped when the MgCl2 concentration reached 50 g/L. However, the total relative abundance of methanogens Methanomicrobia and Methanobacteria still accounted for 84.97% of the archaeal community when MgCl2 was 50 g/L. The high correlation between live/dead cell ratio and methane production suggests that the live/dead cell ratio instead of the inhibition of methanogen might be the major cause for the halt of methane production at a magnesium chloride concentration of 50 g/L.