In-depth investigation of Sodium percarbonate as oxidant of PAHs from soil contaminated with diesel oil.

Sodium percarbonate (SPC, 2Na2CO3∙3H2O2), is a compound that can be used under multiple environmental applications. In this work, SPC was employed as oxidant in the treatment of soil contaminated with diesel oil. The soil samples were collected during the earthmoving stage of RNEST Oil Refinery (Petrobras), Brazil. Then, the samples were air-dried, mixed and characterized. Subsequently, raw soil was contaminated with diesel and treated by photo-Fenton reaction (H2O2/Fe2+/UV). SPC played a significant role in the generation of hydroxyl radicals under the catalytic effect of ferrous ions (Fe2+), hydrogen peroxide (H2O2) and radiation. These radicals provoked the photodegradation of polycyclic aromatic hydrocarbons (PAHs), in the soil remediation. A factorial design 33 was carried out to assess the variables which most influenced the decrease in total organic carbon (TOC). The study was performed with the following variables: initial concentration of [H2O2] and [Fe2+], between 190.0 and 950.0 mmol L-1 and 0.0-14.4 mmol L-1, respectively. UV radiation was supplied from sunlight, blacklight lamps, and system without radiation. All experiments were performed with 5.0 g of contaminated soil in 50.0 mL of solution. The initial concentration of Fe2+ showed the statistically most significant effect. The oxidation efficiency evaluated in the best condition showed a decrease from 34,765 mg kg-1 to 15,801 mg kg-1 in TOC and from 85.750 mg kg-1 to 20.770 mg kg-1 in PAHs content. Moreover, the sums of low and high molecular weight polycyclic aromatic hydrocarbons (LMW-PAHs and HMW-PAHs) were 19.537 mg kg-1 and 1.233 mg kg-1, respectively. Both values are within the limits recommended by the United Sates Environmental Protection Agency (USEPA) and evidenced the satisfactory removal of PAHs from contaminated soil, being an alternative to classic oxidation protocols.

Treatment of biodigested coffee processing wastewater using Fenton's oxidation and coagulation/flocculation.

Biodigested coffee processing wastewater (CPW) presents a high organic load and does not meet the limits imposed by legislation (namely in Brazil) for discharge into water bodies. Anaerobic digestion generally cannot provide a satisfactory organic matter reduction in CPW as a significant fraction of recalcitrant compounds still persists in the treated effluent. So, this study aims to find alternative ways to remove refractory organic compounds from this wastewater in order to improve the biodegradability and reduce the toxicity, which will allow its recirculation back into the anaerobic digester. Three treatment approaches (Fenton's oxidation - Approach 1, Coagulation/flocculation (C/F) - Approach 2, and the combination of C/F with Fenton's process - Approach 3) were selected to be applied to the biodigested CPW in order to achieve that objective. The application of the Fenton process under the optimal operating conditions (initial pH = 5.0; T = 55 °C, [Fe3+] = 1.8 g L-1 and [H2O2] = 9.0 g L-1) increased the biodegradability (the BOD5:COD ratio raised from 0.34 ± 0.02 in biodigested CPW to 0.44 ± 0.01 after treatment) and eliminated the toxicity (0.0% of Vibrio fischeri inhibition) along with moderate removals of organic matter (51.3%, 55.7% and 39.7% for total organic carbon - TOC, chemical oxygen demand - COD and biochemical oxygen demand - BOD5, respectively). The implementation of a coagulation/flocculation process upstream from Fenton's oxidation, under the best operating conditions (pH 10-11 and [Fe3+] = 250 mg L-1), also allowed to slightly increase the biodegradability (from 0.34 to 0.47) and reduce the toxicity, whereas providing a higher removal of organic matter (TOC = 76.2%, COD = 76.5 and BOD5 = 66.3% for both processes together). Approach 1 and Approach 3 showed to be the best ones, implying similar operating costs (∼74 R$ m-3/∼17 € m-3) and constitute an attractive option for managing biodigested CPW.