EFFECT OF ORGANIC LOADING RATE ON ANAEROBIC-DIGESTION PROCESS OF WASTEWATERS FROM THE WASHING OF OLIVES PRIOR TO THE OIL PRODUCTION PROCESSIN A FLUIDIZED-BED REACTOR

A study of the anaerobic digestion process of wastewaters from the was hing of olives prior to the oil production process was carried out in a fluidized bed reactor with sepiolite immobilised biomass at 35 degre es C. The bioreactor worked satisfactorily using influent COD concentr ations 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 rang e 50-90% were achieved in the reactor, when evaluated at organic loadi ng rates of between 0.46 and 2.25 g COD/I day using the highest influe nt 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 m aximum value of 1.55 g acetic acid/I at the most unfavourable case stu died (So = 4,5 g COD/I and HRT = 1.25 days). The increase in effluent VFA concentrations was always counteracted by the high alkalinity valu es (3440-4670 mg CaCO3/I) which brought about the high stability of th e process and Values of the alkalinity/VFA ratio lower than 0.3-0.5, e xcept for the above-mentioned case, limit value over which the anaerob ic process is destabilized. The yield coefficient of methane productio n was 0.28 I methane STP/g COD removed.