Raw cheese whey hybrid treatment by a combined process of bio-coagulation, advanced oxidation, and an anaerobic reactor

Abstract

In this paper, a couple of pretreatments were applied to raw cheese whey to increase its biodegradability in an anaerobic reactor. The first stage consisted of coagulation/flocculation using Carica papaya seeds as a biocoagulant, and the second stage was a study of Fenton and photo-Fenton processes. The cheese whey was collected from a dairy industry plant and characterized according to physicochemical parameters to check the pollution potential (chemical oxygen demand — COD of 55.96 g L⁻¹ and biochemical oxygen demand — BOD of 21.51 g L⁻¹). The coagulation/flocculation process provided high turbidity removal (94–96%). After preliminary experiments with Fenton reactions in coagulated whey, a central composite design, a desirability function and a response surface were applied to obtain the optimal operating conditions (reaction time: 90 min, H₂O₂: 1.95 M; H₂O₂/Fe²⁺ ratio: 55) resulting in 66.4 and 62.6% of COD and TOC removals, respectively. The kinetic evaluation of photo-Fenton reaction under optimal conditions revealed the potential minimization of iron (H₂O₂/Fe²⁺ ratio: 65) and reaction time (60 min) to achieve 70.1% of COD removal under visible ultraviolet light irradiation (UV/vis). After applying the coagulation/flocculation and photo-Fenton processes, an increase in biodegradability was achieved (BOD₅/COD > 0.4), allowing the application of the biological process. The batch treatment in a UASB reactor achieved 86–88% COD removal from the 24^th day of operation. The proposed hybrid process eliminated between 96–98% of total COD.

Keywords:
Carica papaya ; coagulation/flocculatio; photo-Fento; UASB reacto; cheese whey