Reduction of the environmental impact of wastewater from the pretreatment of biodiesel production: A hybrid proposal for decontamination via photo-electro-Fenton/Fered/O3.

Complex wastewater is generated during biodiesel production. We propose a new solution for the treatment of wastewater from enzymatic pretreatment of biodiesel production (WEPBP) by using a hybrid system based on the photo-Fered-Fenton process with O3 assistance (PEF-Fered-O3). We applied response surface methodology (RSM) to determine the suitable conditions for the PEF-Fered-O3 process: a current intensity of 3 A, an initial solution pH controlled at 6.4, an initial H2O2 concentration of 12,000 mg L-1, and an O3 concentration of 50 mg L-1. We performed three new experiments under similar conditions with slight changes to the conditions, namely a longer reaction time (120 min) and single or periodic H2O2 addition (i.e., small H2O2 additions at different reaction times). Periodic H2O2 addition provided the best removal results probably by reducing the occurrence of undesired side reactions that cause hydroxyl radical (•OH) scavenging. With the application of the hybrid system, the chemical oxygen demand (COD) and total organic carbon (TOC) decreased by 91% and 75%, respectively. We also evaluated the presence of metals such as iron, copper, and calcium; electric conductivity; and voltage at 5, 10, 15, 30, 45, 60, 90, and 120 min. We submitted raw and treated WEPBP sludge samples to X-ray diffraction to study the degree of crystallinity. There was a rearrangement of the compounds present in treated WEPBP, possibly caused by oxidation of a large fraction of organic matter. Finally, we evaluated the genotoxicity and cytotoxicity of WEPBP by using Allium cepa meristematic root cells. Treated WEPBP was less toxic to these cells, denoted by improvements in gene regulation and cell morphology. Given the current scenario for the biodiesel industry, applying the proposed hybrid PEF-Fered-O3 system at suitable conditions provides an efficient alternative to treat a complex matrix, namely WEPBP, to reduce its potential to cause abnormalities in the cells of living organisms. Thus, the negative impacts of the discharge of WEPBP in the environment might be reduced.

New hybrid strategy of the photo-Fered-Fenton process assisted by O3 for the degradation of wastewater from the pretreatment of biodiesel production.

The present work aims to fill a scientific gap regarding the treatment of wastewater from the enzymatic pretreatment of biodiesel production (WEPBP), as well as the identification of organic contaminants present in this complex matrix. Different treatment strategies were proposed for the removal of total organic carbon (TOC) and chemical oxygen demand (COD) from WEPBP. The interesting combination of O3/H2O2/UV-Vis and electrocoagulation (EC) process was studied in two setups, with the EC process applied prior to O3/H2O2/UV-Vis and vice versa. Further, the innovative hybrid system based on the photo-Fered-Fenton process with O3 addition (PEF-Fere-O3) was preliminarily studied for WEPBP treatment. The hybrid system provided the best results for the WEPBP treatment when the reactor was operated at pH of 4.5, 65 mg O3 L-1 and 10000 mg H2O2 L-1, UV-Vis was used as the irradiation source, and the current intensity of 3.0 A. Removals of 45% of TOC and 68.7% of COD were reached within 45 min. Oleic acid, linoleic acid, and Diisooctyl phthalate (DIOP) were the main organic contaminants identified in the WEPBP as determined by Gas Chromatography-Mass Spectrometry (GC-MS) analysis. Acute toxicity assays with the bio indicator Artemia salina were carried out in untreated and treated WEPBP samples, indicating that the PEF-Fere-O3 treatment decreased the amount of contaminants present in the WEPBP as well as reduced the toxicity levels and increased biodegradability index, suggesting its great potential for the treatment of complex industrial wastewaters.