Use of hydrophobic membranes to supply hydrogen to sulphate reducing bioreactors

This paper reports on the application of hydrophobic membranes to supply th e gaseous substrates hydrogen/carbon dioxide (H-2/CO2)to a sulphate reducin g bioreactor. For this, two flat 0.016 m(2) sheets of flouroplast microporo us (0.45 mum) membranes were inserted in a 3.6 dm(3) bioreactor for the sup ply of H-2/CO2 gas as small gas bubbles. The bioreactor was operated at 30 degreesC and pH 7.0 and was also equipped with an external ultra filtration module for biomass retention. At a sulphate loading rate (SLR) of 1.32 g S O42- dm(-3) day(-1) and a hydraulic retention time (HRT) of 61 h, a sulphat e reduction rate (SRR) of 0.90 g SO42- dm(-3) day(-1) was achieved. When th e influent sulphate concentration was reduced from 3.36 to 0.75 g SO42- dm( -3) by lowering the HRT to 10.3 h (SLR of 1.75 g SO42- dm(-3) day (-1)), th e SRR dropped to 0.22 g SO42- dm(-3) day (-1). The lower sulphate reduction efficiency was most probably caused by a too short biomass-substrate conta ct time or by irreversible sulphide inhibition. Mass transfer limitation of H-2 and improper mixing of the reactor liquid were shown not to contribute to the low sulphate reduction efficiency.