Effect of organic loading rate on anaerobic digestion process of wastewaters from the washing of olives prior to the oil production process in a fluidized bed reactor

Abstract

A study of the anaerobic digestion process of wastewaters from the washing of olives prior to the oil production process was carried out in a fluidized bed reactor with sepiolite immobilised biomass at 35°G. The bioreactor worked satisfactorily using Influent COD concentrations of 4.5,3.5,2.5 and 1.5 g COD/I for a hydraulic retention time (HRT) range of 4.5 to 1,25 days. COD removal efficiencies in the range 50-90% were achieved in the reactor, when evaluated at organic loading rates of between 0.46 and 2.25 g COD/I day using the highest influent substrate concentration (S_o = 4.5 g COD/I). COD and volatile fatty acid (VFA) concentration were Increased In parallel with the increase of organic loading rate in the reactor, VFA concentration showing a maximum value of 1.55 g acetic acid/I at the most unfavourable case studied (S_o = 4,5 g COD/I and HRT = 1.25 days). The increase in effluent VFA concentrations was always counteracted by the high alkalinity values (3440-4670 mg CaCO₃/l) which brought about the high stability of the process and values of the alkalinity/VFA ratio lower than 0.3-0.5, except for the above-mentioned case, limit value over which the anaerobic process is destabilized. The yield coefficient of methane production was 0.281 methane STP/g COD removed.