Denim production wastewater is an industrial wastewater with a high organic pollutant content. The aim of this study was to improve a cost-effective method via solar panel integration to the photo Fenton process (PFP) and photo electrochemical Fenton process (PEFP) for removing high chemical oxygen demand (COD) from denim production wastewater. To determine process parameter values, the double criterial optimization option was used. The results that maximized the COD removal efficiency and minimized the operating cost of two oxidation processes were determined by response surface methodology (RSM). Optimum operation conditions for the PFP process were 3.18 initial pH, 2.3 g/L Fe2+ concentration, and 27 g/L H2O2 concentration while they were 3.00 initial pH, 27.06 A/m2 current density, and 28.16 g/L H2O2 concentration for PEFP. At the optimum conditions, COD and the total organic carbon (TOC) removal efficiency of PFP were 85% and 61%, respectively. They were determined as 90% and 73% in PEFP. Carbon oxidation state (COS) and average oxidation state (AOS) parameters were used to obtain the biodegradation capability of organic materials. The biodegradability capability of wastewater was observed as high after the Fenton processes. As a result of the optimization of technical parameters, total operating cost was obtained as USD 14.62/m3 (USD 4.25/kgCODremoved) in PFP and USD 13.79/m3 (USD 3.73/kgCODremoved) in PEFP. After the integration of the photovoltaic solar panel to the processes, the total operating cost of PFP and PEFP decreased in a ratio of 61% and 64%, respectively.