Treatment of concentrated fruit juice wastewater by the combination of biological and chemical processes

Concentrated fruit juice industries use a wide volume of water for washing and fruit processing, generating a large volume of wastewater. This work studied the combination of an aerobic biological process with a chemical coagulation/flocculation step to treat a high concentrated fruit juice wastewater. This wastewater presents a good biodegradability (BOD5/COD = 0.66) allowing a chemical oxygen demand (COD) removal above 90% in most reactors. The best results in aerobic biological treatment were obtained in reactors initially loaded with 2 g VSS L−1 of biomass concentration and 20 g COD L−1 of organic matter concentration. Three different kinetic models were evaluated (Monod, Haldane and Contois). The Haldane-inhibition model was the one that best fitted the COD biodegradation. AQUASIM© software allowed calculate the following kinetic constants ranges for aerobic biodegradation: K s: 6–20 g COD L−1; v max: 2.0–5.1 g COD g−1 VSS day−1 and K i values: 0.10–0.50 g COD L−1. These constants corresponds to maximum removal rates (v*) between 0.11 and 0.26 g COD g−1 VSS day−1 for substrate concentrations (S*) from 0.77 to 3.16 g COD L−1. A tertiary coagulation/flocculation process improved the efficiency of the biological pre-treatment. Ferric chloride was selected as best compromise to treat this wastewater. Optimal conditions were 0.44 g L−1 of coagulant at pH = 5.5, achieving 94.4% and 99.6% on turbidity and COD removal, respectively.