Evaluation of watermelon peel, banana peel and bay leaves hydrochars as green catalysts in the degradation of malachite green by thermally activated persulfate oxidation method

Abstract

Water is essential for the continuation of life, moreover, clean water is of great importance on the basis of a healthy life. However, one of the biggest problems of our age is water scarcity and the rapid pollution of existing water resources. Besides, solid food wastes are becoming a growing problem day by day. Therefore, both environmentally friendly, effective and innovative techniques are required in the reuse of solid waste in the treatment of wastewater that is generated at enormous levels. In this study, the thermally activated persulfate (TAP) oxidation method was applied to remove the color and total organic carbon (TOC) of an industrial dye, malachite green (MG). The effects of different levels of experimental variables such as concentration of the oxidising agent, K2S2O8, (0.048 mM–0.55 mM), temperature (336 K–370 K) and treatment time (1.6 min–18.4 min) on the color and TOC removal of MG were investigated. Color removal efficiencies of 97.3% and TOC removal efficiencies of 56.4% were achieved. Evaluation of the effects of the experimental variables on the responses and the optimisation of the TAP method was performed using the response surface method (RSM). The accuracy of the method was assessed by ANOVA. Catalytical efficiencies of hydrochars synthesized in the subcritical water medium (SWM) and obtained from solid food wastes such as banana peel (BP) and watermelon peel (WM) as well as bay leaf (BL) were evaluated. The synthesized hydrochars were characterised by scanning electron microscope (SEM) and (Brunauer–Emmett–Teller) BET analyses. The most effective hydrochar in the catalysis of K2S2O8 was BP hydrochar as 83.6% of color removal was obtained using 0.048 mM K2S2O8 and 2 g/L BP hydrochars at 353 K in 10 min.