Prevention of volatile fatty acids production and limitation of odours from winery wastewaters by denitrification

The effect of the addition of nitrate to winery wastewaters to control the formation of VIA in order to prevent odours during storage and treatment was studied in batch bioreactors at different NO3/chemical oxygen demand (COD) ratios and at full scale in natural evaporation ponds (2 x 7000 m(2)) by measuring olfactory intensity. In the absence of nitrate, butyric acid (2304 mgL(-1)), acetic acid (1633 mgL(-1)), propionic acid (1558mgL-1), caproic acid (499 mgL(-1)) and valeric acid (298 mgL(-1)) were produced from reconstituted winery wastewater. For a ratio of NO3/COD = 0.4 gg(-1), caproic and valeric acids were not formed. The production of butyric and propionic acids was reduced by 93.3% and 72.5%, respectively, at a ratio of NO3/COD = 0.8, and by 97.4% and 100% at a ratio of NO3/ COD = 1.2 gg(-1). Nitrate delayed and decreased butyric acid formation in relation to the oxidoreduction potential. Studies in ponds showed that the addition of concentrated calcium nitrate (NITCAL (TM)) to winery wastewaters (3526 m(3)) in a ratio of NO3/COD = 0.8 inhibited VIA production, with COD elimination (94%) and total nitrate degradation, and no final nitrite accumulation. On the contrary, in ponds not treated with nitrate, malodorous VIA (from propionic to heptanoic acids) represented up to 60% of the COD. Olfactory intensity measurements in relation to the butanol scale of VIA solutions and the ponds revealed the pervasive role of VIA in the odour of the untreated pond as well as the clear decrease in the intensity and not unpleasant odour of the winery wastewater pond enriched in nitrates. The results obtained at full scale underscored the feasibility and safety of the calcium nitrate treatment as opposed to concentrated nitric acid. (C) 2007 Elsevier Ltd. All rights reserved.