Anaerobic digestion of short chain organic acids in an expanded granular sludge bed reactor

Short chain organic acids occur in industrial effluents such as those from advanced oxidation processes. An Expanded Granular Sludge Bed (EGSB) reactor was used to examine the anaerobic treatment of a mixture of maleic, oxalic, fumaric, acetic and formic acids (2500 mg l−1 COD). At a 6-h hydraulic retention time (HRT) and an organic loading rate (Bv) of 10 kgCOD m−3 d−1, 98% COD removal was seen. Influent containing maleic, oxalic, or fumaric acids separately at organic loading rates (Bv) of between 1.8 and 5 kgCOD m−3 d−1 COD was also treated, with 90–98% COD removal at HRTs between 8 and 12 h. A mixture of known products of a wet air oxidation process (acetic, propionic, butyric, maleic, glyoxylic and benzoic acids) was also tested at a 24-h HRT (Bv 3 kgCOD m−3 d−1) giving 90% COD removal.