Treatment of Sugar Industry Wastewater by Advanced Oxidation Processes in the Presence of Heterojunction Catalysts Supported on Graphene-Graphitic Carbon Nitride
Project no. 1353 · Status: Kapanmış · 2017
Summary
In this study, treatment of simulated sugar industry wastewater by photo-Fentonlike and catalytic wet air oxidation methods was investigated in the presence of heterojunction catalysts. The treatment efficiency was evaluated in terms of sugar, total organic carbon (TOC), and chemical oxygn demand (COD) removals. Initially, catalyst screening experiments for PFO and CWAO processes were carried out and copper doped bismuth oxyhalides (Cu-BiOX) and lanthanum containing perovskite catalysts (LaBO3) were selected as the most promising catalysts for PFO and CWAO processes, respectively. The sugar and TOC removals at optimum conditions reached up to 56% and 30% for PFO in the presence of selected catalyst Cu-BiOI whereas they reached up to 100% and 55% and for CWAO in the presence of selected catalyst LaCoO3, respectively. The BiOI/g-C3N4 heterojunction catalysts were tested for PFO method and the effect of synthesis procedure was evaluated in terms of catalytic activity. The synthesis method based on in-situ growth at high pH favored the formation of desired heterojunction structure, so the BiOI/g-C3N4 catalyst with the optimum nominal weight ratio synthesized by this method (75BI-25CN) provided compatible sugar and TOC removal efficiencies with the efficiencies obtained by Cu-BiOI at optimum conditions. Similarly, the hybrid catalysts were tested for CWAO and the role of biomass-based material as catalytic support or co-catalyst was investigated. The LaCoO3 catalyst supported on biochar (LC/BC) was determined as the most active catalyst since TOC, and COD removal efficiencies were increased to 90% by supplying 100% of theoretical air prior to reaction. Additional study on the product distribution in liquid and gas effluents for CWAO process demonstrated that the product distributions were consistent with the removal efficiencies. Main oxidation end products CO and CO2 as well as as a valuable by-product, H2 were observed in the gas effluent along with nitrogen as inert gas from supplied air. Simultaneous mineralization and hydrogen production with promising amounts were accomplished which was the secondary goal of this study. The product distribution in liquid effluent included acidic intermediates i.e. organic acids such as formic acid, acetic acid, and levulinic acid. The kinetic studies for PFO and CWAO processes depicted that both pseudo-homogeneous and heterogeneous models represented the reaction rates accurately. The reaction order for pseudohomogeneous rate model was determined as second order with respect to sucrose or TOC concentrations both for PFO and CWAO reactions. For heterogeneous rate models, Langmuir-Hinshelwood model with dual-site mechanism involving two different catalytic sites fitted the rate data best for PFO process without significant mass transfer limitiations for the reactants. For CWAO on the other hand, Langmuir Hinshelwood again was the most appropriate rate model but the reaction mechanism was different and dual site mechanism that involved only one catalytic site was the most accurate one. Another rate model Eley-Rideal model involving only pollutant adsorption (referred as Adsorbed A) also represented the CWAO reactions since mass transfer limitations were signficant for the gas reactant, oxygen, so concentration of pollutant i.e. sucrose or TOC dominated the rate model. The catalyst characterization studies including SEM-EDX, XRD, XPS, BET and TGA analyses showed that the catalytic activites of the catalysts were directly related to their morphological and physico-chemical properties and the selected catalysts used in the parametric studies as well as heterojunction/hybrid catalysts possessed unique structures that enhanced their performances.