The purification of crude glycerol derived from biodiesel manufacture and its use as a substrate by Rhodopseudomonas palustris to produce hydrogen

Crude glycerol (CG) from biodiesel production is often contaminated with several compounds, including saponified fatty acids (SFAs). Photofermentative growth of Rhodopseudomonas palustris on glycerol leads to hydrogen production; however, R. palustris is inhibited by SFAs. This study examines inhibition of R. palustris by SFAs, finding that, with increasing concentration of SFA, growth rate falls, reaching zero at an SFA concentration of 0.2 mM. Methods for purifying CG were examined, namely (i) treatment with ethanol and activated carbon, (ii) pH adjustment, (iii) solvent extraction, and (iv) precipitation of the fatty acids with calcium. The rates of growth and production of hydrogen were investigated using CG treated by these methods. It was found that treatment with activated carbon, pH reduction, and calcium precipitation reduced inhibition, while solvent extraction was effective only when used in conjunction with pH adjustment. These treatments allow crude glycerol to be used for hydrogen production by R. palustris.