Aerobic Biological Treatment of Chestnut Processing Wastewater

Abstract

Chestnut agro-industrial companies consume a high volume of water for washing and processing fruit, generating a large volume of wastewater. This work studied the biodegradation of chestnut processing wastewater through aerobic assays, varying substrate, and biomass concentrations. In general, this wastewater presents a good biodegradability, especially in experiments with relatively low chemical oxygen demand (COD) (0.4 and 0.6 g O2 L−1) allowing a COD removal of 85–90 %. The best results were obtained in the reactor initially loaded with 2 g L−1 of biomass and 0.4 or 0.6 g O2 L−1 of COD. These experiments also showed high COD removal rates: 4.25 and 3.88 g COD g−1 volatile suspended solids (VSS) h−1, respectively. The sedimentation rate, evaluated for different initial values of biomass (1, 2, and 3 g L−1), always presented higher values in the experiments with 2 and 3 g L−1 of biomass, regardless of the initial COD value used. After comparing different kinetic models (Monod, Contois, and Haldane), it was observed that the Haldane inhibition model satisfactorily describes the COD biodegradation. AQUASIM software allowed calculating the kinetic constant ranges: Ks, 1.59–6.99 g COD L−1; νmax, 25–40 g COD g−1 VSS day−1; and Ki values, 0.07–0.11. These kinetic constants corresponds to maximum rates (ν*) between 1.48 and 4.25 g COD g−1 VSS day−1 for substrate concentrations (S*) from 0.38 to 0.88 g COD L−1.