Abstract
We investigated the biofiltration ability of the aquatic fern Azolla to remove polyphenols and chemical oxygen demand (COD) from olive mill wastewater (OMWw) collected from the traditional (TS) and continuous (CS) extraction systems. Azolla biomass was packed into five sequential Imhoff cones and five sequential columns. In both experiments, the filtrates collected from the 5 th biofilter showed a decrease in polyphenol contents: from 7650 mg l –1 to 3610 mg l –1 in TS OMWw and from 3852 mg l –1 to 1351 mg l –1 in CS OMWw. The COD contents decreased from 110200 mg L –1 to 52400 mg L –1 in TS OMWw and from 41600 mg L –1 to 2300 mg L –1 in CS OMWw. A 5:1 OMWw to Azolla -fresh-weight ratio was optimal for both polyphenol and COD removal. The biofiltration ability of alfalfa was compared with that of Azolla , but the treatment with alfalfa did not result in the reduction of COD or polyphenols.
Highlights
The extraction and use of olive oil has been an integral part of Mediterranean culture for over 6000 years (Civantos, 1995; Tardàguila et al, 1996).Olive oil is produced by two methods: the traditional system (TS) and the continuous system (CS)
Olive oil extraction involves an intensive consumption of water and produces large amounts of olive mill wastewater (OMWw), the average volume ranging from 0.5 to 1.5 m3 per ton of processed olives (MonteolivaSanchez et al, 1996; Paredes et al, 1996)
The organic compounds in OMWw, in association with its high C/N ratio and low pH, compromise the biological degradation process of soils (Marques, 2000) and can cause eutrophication when the wastewater is collected in basins with low exchange rates
Summary
The extraction and use of olive oil has been an integral part of Mediterranean culture for over 6000 years (Civantos, 1995; Tardàguila et al, 1996).Olive oil is produced by two methods: the traditional system (TS) and the continuous system (CS). Olive oil extraction involves an intensive consumption of water and produces large amounts of olive mill wastewater (OMWw), the average volume ranging from 0.5 to 1.5 m3 per ton of processed olives (MonteolivaSanchez et al, 1996; Paredes et al, 1996). OMWw contains high amounts of organic matter (30-200 kg COD m–3), with a COD/BOD5 ratio between 2.5 and 5, which is considered poorly degradable (Lopez, 1992). The organic compounds in OMWw (sugars, polyphenols, tannins, polyalcohols, pectins and lipids), in association with its high C/N ratio and low pH, compromise the biological degradation process of soils (Marques, 2000) and can cause eutrophication when the wastewater is collected in basins with low exchange rates (closed gulfs, lakes, etc.)
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