Comparison between anaerobic filter and anaerobic contact process for fermented olive mill wastewaters

Abstract

Abstract During the anaerobic digestion of olive mill wastewaters (OMW) prefermented by aerobic growth with Aspergillus niger , a stationary state was reached more quickly with the anaerobic contact process than with an anaerobic filter, but was more stable with the anaerobic filter. The daily methane production and COD removal recorded with the anaerobic filter were greated than those obtained in the anaerobic contact reactor. The anaerobic filter yielded a biogas with a higher percentage of methane, and effluent with a lower volatile fatty acid and volatile solid content than the anaerobic contact. The immobilizing of VS in an anaerobic filter fermenter is a means of reducing the inhibition of methanogenic bacteria by the residual phenolic compounds present in prefermented OMW. A yield of 0·15 and 0·33 litres methane/g COD removed was obtained with the anaerobic contact and anaerobic filter reactors, respectively. Additional advantages of fixed film over contact fermenters include the elimination of mechanical mixing and sludge settling and return.