Catalytical efficiency, mechanism and characterization of hydrolysed waste eggshell in the subcritical water oxidation of pistachio processing wastewater

Sustainable, effective and environmentally friendly methods are needed in wastewater treatment as quality water is necessary for a healthy life. Valorisation of solid food waste is also of great importance. This study examines the effectiveness of hydrolysed waste eggshells (HES), a green catalyst, in pistachio processing wastewater (PPWW) treatment using subcritical water oxidation (SWO). HES was prepared in the subcritical water medium (513 K, 100 bar of N-2, 2 h) with a 92.3% yield. 88.8% of COD, 100% of both TPC and color removals of PPWW were achieved. The effects of independent variables such as temperature (363-403 K), treatment time (20-100 min), the concentration of H2O2 (0.25-1.25 M) and amount of catalyst (0-100 mg/100 mL) on the responses were investigated using response surface methodology (RSM). SEM, EDX and XRD were used to investigate the characterization of the waste eggshells. The percentage of Ca in HES increased with the hydrolysis, thus CaO increased the catalysis of hydrogen peroxide to form hydroxyl radicals.

Automated summary

This study examined the effectiveness of hydrolysed waste eggshells (HES) as a green catalyst in pistachio processing wastewater (PPWW) treatment using subcritical water oxidation (SWO), achieving high removal rates of COD, TPC, and color. Response surface methodology (RSM) was used to investigate the effects of different variables on the treatment responses, while SEM, EDX, and XRD were utilized for characterization of the waste eggshells.