Photovoltaic-thermal-assisted electro-fenton wastewater treatment with temperature and heat-transfer optimization

A photovoltaic–thermal (PVT)-assisted electro-Fenton (EF) system (PVT–EF) was developed for temperature-regulated methylene blue (MB) treatment in a 400 mL batch reactor equipped with a foam-nickel cathode and graphite anode. The PVT subsystem supplies electricity to the EF reactor, while recovered low-grade heat regulates wastewater temperature, coupling oxidant generation with the reaction environment. After 20 min, MB decolorization increased from 81.6 ± 1.1 % at 15 °C to 86.8 ± 0.6 % at 30 °C and then decreased to 72.2 ± 1.2 % at 40 °C. At 30 °C, chemical oxygen demand (COD) and total organic carbon (TOC) removals reached 70.6 ± 2.0 % and 62.1 ± 1.7 %, respectively, after 60 min. The bottom exchanger position gave significantly higher 20-min removal than the top position, whereas copper tubing and higher circulation velocity showed the highest observed means without statistically significant overall effects at the α = 0.05 level (material: p = 0.054; velocity: p = 0.288). Computational fluid dynamics (CFD) suggested that a middle exchanger position may provide greater robustness under variable inlet conditions. For the 6.198 MWp engineering scenario, a Global Solar Atlas site-screening yield of 811.5 kWh kWp −1 yr −1 gave an estimated annual AC electricity output of 5.030 × 10 6 kWh yr −1 . This is 1.299 GWh yr −1 below the identified conventional annual loads of 6.329 × 10 6 kWh yr −1 , before additional EF, storage, curtailment, and auxiliary-heating terms are included. Because plant-scale useful-heat delivery and the complete industrial life-cycle and cost inventories were not closed, energy payback time (EPBT), greenhouse-gas payback time (GPBT), net project economics, and annual grid export are not reported numerically for the engineering scenario. Quantitative environmental and cost results are reported only as a laboratory-scale operational screening ( Section 4.4 ), where the operating cost is USD 3.13 m −3 and the operational-screening global-warming potential is 5.44 kg CO 2 -eq m −3 under the stated photovoltaic–thermal electricity scenario. The results support the feasibility of using recovered PVT heat as an active EF temperature-control variable while defining the remaining requirements for real-wastewater and pilot-scale validation. All degradation results reported here were obtained on a synthetic single-pollutant methylene-blue solution (20 mg L −1 ) in a 400 mL batch reactor; no real industrial wastewater was treated, and the bench-scale validation protocol and acceptance criteria required to extend the findings to a real effluent are specified in Section 3.6.