This article discusses the titanium (Ti)-based permanganate advanced catalytic oxidation process (ACOP) for the possible recovery of thousands of tons of dye wastewater. The heterogeneous catalyst TiO₂ in the solid state employed in the liquid phase reaction mixture with dye and potassium permanganate was recovered and reused several times for reproducible results. The kinetics were examined at various operational parameters like the effect of dyes, the effect of oxidants, the amount of catalysts, and the effect of acids, temperature, and various organic and inorganic additives used in the textile industry. The kinetics of advanced oxidation and the mechanism of dye de-coloration and degradation were monitored using the Congo red (CR) dye as a model in an aqueous medium and then applied to other dyes and real dye wastewater samples. The color removal was up to 98%, with the removal efficiency being linear with the dose at a particular time. This method could exhibit the complete color removal of the dye wastewater, leading to mineralization coupled with a change in the oxidation state of Mn from +7 to +2. The method also improved the BOD/COD ratio, followed by an increase in the salinity of the recycled water. This indicated that this method can be used not only for the highly efficient de-colorization of dye wastewater but also as a preliminary step for the utilization of the dye wastewater after its recycling. The newly developed system was proven to be very cost-effective and eco-friendly with low sludge quantity, which contained numerous nitrogenous compounds, and this was validated by FTIR and HPLC analyses; thus, the system may be used in treatment plants for the recovery of wastewater.

The current article reported the investigation of metal toxicity on the oxygen-evolving complex (OEC) in Spinacia oleracea related to depletion in chloride ion concentration, an essential part of the photosystem (II). The greenhouse experiment was conducted where S. oleracea was cultivated in three replicates with control plants (plants “a”) treated with tap water. Moreover, 30 ppm of Cu²⁺ ion solution and Pb²⁺ ion solution was used to irrigate the rest of the plants, labeled as plants “b” and “c”, respectively, on alternative days. Advanced technologies such as Atomic Absorption Spectrophotometry (AAS), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and UV-visible Spectrophotometry were used to monitor the essential nutrients in leaves to validate the function of the photosystem (I and II). Reduced Cl⁻ ions contents showed that both metals (Cu²⁺ and Pb²⁺) altered the essential elements of the oxygen-evolving complex (OEC) of photosystem (II), required to maintain the coordination structure of the Mn₄CaO₅ cluster. SEM analysis revealed the modified leaf structure of the S. oleracea under Cu²⁺ and Pb²⁺ accumulation due to which distorted cellular structure, reduced surface area, and the (shattered) stomatal opening compared to the plants “a” were observed. The EDS analysis of plants “b” and “c” showed high oxygen contents followed by reduced chloride contents over plants “a”, reflecting the infirmity of OEC to push out oxygen, which leads to generating oxidative stress. The lower pigment concentration in leaves of metal-contaminated plants “b” and “c” impacts carbon assimilation, which is linked to the reduced stomatal opening and influences the gaseous exchange rates. Additionally, increased contents of K⁺ and Ca²⁺ may be due to self-defense mechanisms under low chloride contents to speed up oxygen evolution to protect plants against oxidative stress. It was concluded that Cu²⁺ and Pb²⁺ metal toxicity influences essential Cl⁻ and K⁺ contents, which modify the photosystem II system; subsequently, a reduced growth rate was observed.