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Nano-size calcium peroxide (nCaO) is an appropriate oxygen source which can meet the needs of in situ chemical oxidation (ISCO) for contaminant remediation from groundwater. In the present study, an easy to handle procedure for synthesis of CaO nanoparticles has been investigated. Modeling and optimization of synthesis process was performed by application of response surface methodology (RSM) and central composite rotatable design (CCRD) method. Synthesized nanoparticles were characterized by XRD and FESEM techniques. The optimal synthesis conditions were found to be 5:1, 570 rpm and 10 °C for HO:CaSO ratio, mixing rate and reaction temperature, respectively. Predicted values showed to be in good agreement with experimental results (R values were 0.915 and 0.965 for CaO weight and nanoparticle size, respectively). To study the efficiency of synthesized nanoparticles for benzene removal from groundwater, batch experiments were applied in biotic and abiotic (chemical removal) conditions by 100, 200, 400, and 800 mg/L of nanoparticles within 70 days. Results indicated that application of 400 mg/L of CaO in biotic condition was able to remediate benzene completely from groundwater after 60 days. Furthermore, comparison of biotic and abiotic experiments showed a great potential of microbial stimulation using CaO nanoparticles in benzene remediation from groundwater.

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In the present study, magnesium peroxide (MgO) nanoparticles were synthesized by electro-deposition process and characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The batch experiments were conducted to evaluate the MgO half-life (600 mg/L) in groundwater under various temperatures (4, 15, and 30 °C) and initial pH (3, 7, and 12). The effect of Fe ions (enhanced oxidation) on the toluene remediation by MgO was also investigated. Nanoparticles were injected to sand-packed continuous-flow columns, and toluene removal (50 ppm) was studied within 50 days at 15 °C. The results indicated that the half-life of MgO at pH 3 and 12 were 5 and 15 days, respectively, in comparison to 10 days at the initial pH 7 and 15 °C. The nanoparticles showed 20 and 7.5 days half-life at 4 and 30 °C temperatures, respectively. Injection of Fe ions indicated an impressive effect on toluene removal by MgO, and the contaminant was completely removed after 5 and 10 days, in the batch and column experiments, respectively. Confocal laser scanning microscope (CLSM) analysis indicated that the attached biofilm had a significant role in the decontamination of groundwater. Comparison of bioremediation and enhanced oxidation resulted in a considerable insight into the application of magnesium peroxide in groundwater remediation. Graphical abstract ᅟ.