In recent years, the green chemistry based-approach for the synthesis of nanoparticles has shown tremendous promise as an alternative to the costly and environmentally unfriendly chemically synthesized nanoparticles. In this study, copper oxide nanoparticles (CuO NPs) were synthesized through a green approach using the water extract of papaya (Carica papaya L.) peel biowaste as reducing as well as stabilizing agents, and copper (II) nitrate trihydrate salt as a precursor. The structural properties, crystallinity, purity, morphology, and the chemical composition of as-synthesized CuO NPs were analyzed using different analytical methods. The analytical results revealed that the synthesized CuO was observed as spherical-like in particles with measured sizes ranging from 85–140 nm and has monoclinic crystalline phase with good purity. The Fourier transform infrared (FTIR) spectroscopic results confirmed the formation of the Cu-O bond through the involvement of the potential functional groups of biomolecules in papaya peel extract. Regarding photocatalytic activity, the green-synthesized CuO NPs were employed as a photocatalyst for the degradation of palm oil mill effluent (POME) beneath the ultraviolet (UV) light and results showed 66% degradation of the POME was achieved after 3 h exposure to UV irradiation. The phytotoxicity experiment using mung bean (Vigna radiata L.) seed also showed a reduction of toxicity after photodegradation.
The application of microalgae in wastewater treatment has attracted the attention of researchers since a few decades ago. Palm oil industry is one of the lucrative main exporting industry in Malaysia which has drawn the attention of researchers in mitigating the polluting impacts caused by the palm oil mill effluent (POME) released from the oil palm processing. In this study, the growth of the green algae Chlorella vulgaris and Chlamydomonas reinhardtii in the pre-treated POME was studied for 7 continuous days. The number of microalgae cells, chlorophylls and carotenoids contents were monitored throughout the cultivation period. The potential of both strains of microalgae as the water polisher for post-treatment of POME was investigated as well. The findings revealed that both microalgae showed lag phase at the beginning of cultivation and grew exponentially later. When monitoring the chlorophyll content, chlorophyll a and chlorophyll b played a role in photosynthesis when the microalgae detected environmental changes. The carotenoids in the microalgae acted as the accessory pigments which assisted in light harvesting under poor light condition and as the antioxidant protecting the cells when there was excess light. C. vulgaris was able to remove 98.1 % of phosphate and 53.1 % of ammoniacal nitrogen while C. reinhardtii removed 90.1 % and 37.3 %, respectively. This study indicated that two microalgae species have a high potential to be integrated in the post-treatment for POME.
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