Codigestion of olive oil mill wastewaters together with manure, household waste or sewage sludge

Abstract

Large amounts of organic waste are generated from household, agriculture and industry today. The major part of the waste from industry and households is deposited in landfills, an undesirable solution, because landfills fill up landscapes and leach pollutants into the groundwater. Furthermore, special wastes, such as wastewaters from olive oil processing, are produced in large amounts in concentrated areas mainly in Mediterranean countries. Treatment of oil mill effluent (OME) still presents a problem, which has not been solved to date. If not treated, this waste imposes a great environmental hazard, due to the very high organic chemical oxygen demand (COD) loads. Anaerobic treatment of organic wastes is the most optimal treatment system, reducing the organic content, destructing toxicants and, at the same time, yielding energy in the form of biogas which can be used for heating and electricity production. Several investigators have studied anaerobic degradation of OME and obtained COD-reductions up to approx. 80% [4, 5, 6, 13]. However, especially at high feed concentrations, the process proved probably unstable due to the inhibitory effect of phenols, lack of ammonia and due to the low alkalinity of OME. In order to overcome the above problems, the OME was diluted with water, and urea was added as nitrogen supplement [7, 12]. Furthermore, the alkalinity of the reactor content was often adjusted by NaHCO₃, NaOH or Ca(OH)₂ [6, 7]. However, dilution of OME with water results in unnecessary large effluent volumes, and additions of chemicals is not economically and environ-mentally desirable.