Conference Dates

March 8-13, 2009


Two types of anaerobic digesters - a filter (AF) and a hybrid (H) - are tested in the treatment of original olive mill wastewater (OMW), without any pre-treatment or chemical correction of this substrate. The anaerobic filter is equipped with a packed bed material that fills the entire column of digestion; the hybrid digester results from the combination of anaerobic filter with the up-flow anaerobic sludge blanket and the packed bed only occupies the top section of the column.

OMW is the effluent generated from olive oil industries, which activity has a great economic and social importance in the olive growing countries of the Mediterranean area. Outside this area, olives are also cultivated in the USA, Argentina, Australia and South Africa. Carrying a high chemical oxygen demand (COD) content (up to 200 kg m-3), OMW is one of the most polluting agro-industrial effluents but on the other hand it holds a great energetic potential. Anaerobic digestion is a promising technology since it allows the conversion of a considerable fraction of the chemical energy of effluent into a renewable energy source (biogas).

A packed bed material was developed and tested in our laboratory in order to avoid working troubles related to the operation of the fixed bed units. Both anaerobic digesters are packed with the same material and compared on their advantages and drawbacks in terms of star-up, conversion efficiency and running problems. The volumetric amount of raw OMW was gradually increased in the feed mixture from 8 to 18 % v/v under HRT of around 6 days, by using a complementary effluent. Similar concentrations and organic loads of OMW (0.6 – 1.5 kg m-3 d-1) are provided to the units. Good behaviors are observed in both and an identical COD removal of influent (49-70%) and a high biogas quality (70-81% of CH4) are registered along an experiment of 200 days. The characterization of biomass evolution concerning biodegradation capacity and its adaptation process to the influent is also examined.

The results obtained indicate that the hybrid digester can replace the AF for the treatment and valorization of OMW. The hybrid reactor is an interesting choice because it provides lower costs related to the amount of packing material.