Use of hydrophobic membranes to supply hydrogen to sulphate reducing bioreactors

This paper reports on the application of hydrophobic membranes to supply the gaseous substrates hydrogen/carbon dioxide (H₂/CO₂)to a sulphate reducing bioreactor. For this, two flat 0.016m² sheets of flouroplast microporous (0.45m) membranes were inserted in a 3.6 dm016m³ bioreactor for the supply of H H₂/CO₂ gas as small gas bubbles. Thebioreactor was operated at 30 °C 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 SO₄^2- dm^-3 day^-1 and a hydraulic retention time (HRT) of 61 h, a sulphate reduction rate (SRR) of 0.90 g SO₄^2- dm^-3 day^-1 was achieved. When the influent sulphate concentration was reduced from 3.36 to 0.75 g SO₄^2- dm^-3 by lowering the HRT to 10.3 h (SLR of 1.75 g SO₄^2- dm^-3 day ^-1), the SRR dropped to 0.22 g SO₄^2- dm^-3 day ^-1. The lower sulphate reduction efficiency was most probably caused by a too short biomass-substrate contact time or by irreversible sulphide inhibition. Mass transfer limitation of H₂ and improper mixing of the reactor liquid were shown not to contribute to the lowsulphate reduction efficiency.