Organic matter removal from wastewaters of the black olive industry by chemical and biological procedures

Abstract

Chemical treatments of wastewaters from the olive industry are conducted by means of single UV radiation and by the action of hydroxyl radicals, which are generated by the simultaneous presence of UV radiation and hydrogen peroxide, Fe 2+ and hydrogen peroxide (Fenton system) and Fe 2+ and hydrogen peroxide plus UV radiation (photo-Fenton system). The single photochemical process produces a 35% removal of organic matter present measured as COD after 6 h of reaction, while the hydroxyl radicals enhance significantly this reduction with values in the range 41–76%. At the same time, a removal of aromatic compounds in the oxidation by single UV radiation and combined UV+H 2O 2 was obtained in the range 20–52%. In the anaerobic digestion process, an organic matter reduction in the range 0.77–0.65 g of COD degraded per g of COD fed to the reactor was obtained, and a value of 250 ml CH 4 · g COD −1 obtained for the methane yield coefficient. A kinetic study was conducted using the Monod model, and rate constants k o in the range 0.061–0.015 min −1 achieved. This indicates that some inhibition effects by substances present take place. The application of the Levesnpiel model for that inhibitory effect leads to the determination of the rate constant, inhibitory parameter and critical substrate concentration of inhibition, their values being k=0.205 min −1, n=18.8 and S*=20.1 g l −1 respectively. Finally, the anaerobic digestion of the chemically pretreated wastewaters increases the rate constant k o, as well as the methane yield coefficient, its value being 282 ml CH 4 · g COD −1.