Paraquat Degradation by Biological Manganese Oxide (BioMnO(x)) Catalyst Generated From Living Microalga Pediastrum duplex AARL G060

Paraquat is a non-selective fast-acting herbicide used to control weeds in agricultural crops. Many years of extensive use has caused environmental pollution and food toxicity. This agrochemical degrades slowly in nature, adsorbs onto clay lattices, and may require environmental remediation. Studies have shown that biosynthesized manganese oxide (BioMnO(x)) successfully degraded toxic synthetic compounds such as bis-phenol A and diclofenac, thus it has potential for paraquat degradation. In this experiment, P. duplex AARL G060 generated low (9.03 mg/L) and high (42.41 mg/L) concentrations of BioMnO(x). The precipitated BioMnO(x) was observed by scanning electron microscopy (SEM), and the elemental composition was identified as Mn and O by energy-dispersive x-ray spectroscopy (EDS). The potential for BioMnO(x) to act as a catalyst in the degradation of paraquat was evaluated under three treatments: (1) a negative control (deionized water), (2) living alga with low BioMnO(x) plus hydrogen peroxide, and (3) living alga with high BioMnO(x) plus hydrogen peroxide. The results indicate that BioMnO(x) served as a catalyst in the Fenton-like reaction that could degrade more than 50% of the paraquat within 72 h. A kinetic study indicated that paraquat degradation by Fenton-like reactions using BioMnO(x) as a catalyst can be described by pseudo-first and pseudo-second order models. The pH level of the BioMnO(x) catalyst was neutral at the end of the experiment. In conclusion, BioMnO(x) is a viable and environmentally friendly catalyst to accelerate degradation of paraquat and other toxic chemicals.