Purification of diazinon pesticide by sequencing batch moving-bed biofilm reactor after ozonation/Mg-Al layered double hydroxides pre-treated effluent

The catalytic ozonation process (COP) using MgAl-layered double hydroxide (MgAl-LDH) nanoparticles was used as a pre-treatment of the sequencing batch moving-bed biofilm reactor (SBMBBR) to degrade diazinon pesticide from aqueous solutions. The structure of the synthesized MgAl-LDH was investigated by X-ray diffraction pattern (XRD), field-emission scanning electron microscope (FESEM), energy dispersive spectroscopy (EDS) mapping, and Fourier-transform infrared spectra (FTIR). The response surface methodology (RSM) was adopted to optimize the COP variables, including LDH dose (0-1000 mg/L), initial diazinon concentration (50-200 mg/L), initial pH (3-10), and reaction time (10-90 min). Under the optimal conditions, COP effluent was introduced to the SBMBBR for further purification. The dispersive liquid-liquid microextraction (DLLME) method was employed to extract diazinon from aqueous samples. The GC-mass analysis was performed to determine by-products during diazinon degradation reactions. To evaluate system performance, the removal efficiency of chemical oxygen demand (COD), total organic carbon (TOC), and diazinon was compared in processes of aeration, single ozonation process (SOP), COP, SBMBBR, and COP/SBMBBR. The formation of the LDH nanoparticles was confirmed by XRD and EDS mapping analysis. In the COP reactor, under optimal conditions (initial diazinon concentration: 120 mg/L, pH: 8.25, LDH dose: 750 mg/L, and reaction time: 70 min), the removal efficiency of diazinon, COD, and TOC equaled 92, 80, and 74%, respectively. The effluent of COP reactor was treated further in the SBMBBR system with the pH of 6.5-7, hydraulic retention time (HRT) of 24 h, mixed liquor suspended solids attached to bio-carriers (MLSSatt.) of 4500 mg/L, mixed liquor volatile suspended solids attached to biocarriers (MLVSSatt.) of 3600 mg/L, MLSS of 950 mg/L, and MLVSS of 830 mg/L. The use of COP/SBMBBR resulted in the complete degradation of diazinon pesticide and COD and TOC removal efficiency of 99.37 and 99%, respectively. Therefore, this method can be used for the purification of non-biodegradable industrial wastewater.