Thermoacidic precipitation of darkly coloured polyphenols of olive mill wastewaters

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Abstract
The colour of olive mill wastewaters varies from dark red to black depending on their state of degradation and the olives they come from. The wastewater contains a mixture of polyphenols which can characterized into two groups; one group responsible for the red colour; the other group being responsible for the black colour. An acid phosphoric treatment (5 per cent) applied to this effluent at 148°C for 20 min induced the precipitation of the polyphenols of the latter group and reduced 35 per cent of the Chemical Oxygen Demand and absorption at 280 nm. The residual solution was red coloured and enriched with 14.8 g dm‐3 of acetate, 5.4 g dm‐3 of methanol, and simple phenolic compounds. The gas produced contained 15 per cent CO2, 8per cent hydrogen and 3 per cent methane.