Energy consumption and relative efficiency improvement of Photo-Fenton – Optimization by RSM for landfill leachate treatment, a case study

•Comparative application of Fenton and photo-Fenton for landfill leachate treatment.•Introduction of EEM for evaluation of photo-Fenton energy consumption.•Simultaneous optimization of energy reduction and COD removal in photo-Fenton.•Introduction of mathematical models derived by response surface methodology. The main objective of this study is to investigate the application of Photo-Fenton process to treat landfill leachate with minimum energy consumption and maximum COD removal efficiencies, simultaneously. Accordingly, an operational assessment of Photo-Fenton process was conducted in terms of variables, namely oxidation pH, [H2O2]/[Fe2+] molar ratio, and Fe2+ dosage. The Central Composite Design (CCD) based on Response Surface Methodology (RSM) was applied for statistical analysis and optimization of target parameters. To assess the rate of energy consumption in Photo-Fenton process, the EEM parameter (Electric Energy consumed per organic Mass removed) was introduced, and the same Fenton experiments were performed to compare the results. Applying UV light in the Fenton process (i.e. Photo-Fenton process) increased COD removal efficiencies up to 10%. The results showed that the Photo-Fenton treatment is capable of removing COD by over 80% of the initial COD (i.e. 17,200 mg/L of AradKooh landfill leachate), applying 195–265 mM iron concentration, [H2O2]/[Fe2+] molar ratio of 15.50–20.55, and the oxidation pH value of 3.75–5.55 (other conditions were oxidation time of 30 min, coagulation pH of 8, and coagulation time of 25 min). The regeneration of Fe(II) from Fe(III) by UV light irradiation resulted in a larger degradation of COD than that of conventional Fenton process, and also reduced the amount of iron catalyst consumption (approximately 25% reduction observed). Furthermore, the cost of energy in Photo-Fenton process could be covered considering lower amounts of sludge generated than conventional Fenton treatment (note that the cost evaluations in current paper were based on batch studies and should be confirmed on full-scale system).