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Coagulation–flocculation mechanism and characterisation of Hylocereus undatus foliage as a natural coagulant in industrial wastewater treatment

Aina Afiqah Ramlee, Ayub Md Som, Siti Wahidah Puasa, and Hairul Amani Abdul Hamid

School of Chemical Engineering, College of Engineering, Universiti Teknologi MARA (UiTM), Shah Alam, Malaysia

Received: 28 November 2022 Accepted: 10 June 2023

Abstract:

Considering various drawbacks regarding the application of chemical-based coagulants in industrial wastewater treatments, plant-based coagulants have been receiving the spotlight as an alternative due to their biodegradability and environmentally friendly nature. Coagulation–flocculation mechanism of a natural coagulant is predominantly essential in understanding its coagulation activity; hence, a characterisation study of the sludge being formed after the coagulation–flocculation process is urgently needed. For instance, Hylocereus undatus (H. undatus) foliage has been proven for its potential and efficiency as a plant-based coagulant in treating latex concentrate wastewater, palm oil mill effluent (POME) and paint wastewater as evidenced by previous works. However, the coagulant type for H. undatus foliage still remains unknown due to no research has been done in analysing its coagulation–flocculation mechanism and the characterisation of its sludges. Hence, this study was conducted to analyse its coagulation–flocculation mechanism and characterise the sludge formed when the H. undatus foliage was used as a natural coagulant in treating paint wastewater. The raw paint wastewater, its sludge formed from the coagulation–flocculation process at optimum operating conditions, and H. undatus foliage powder were sent for several instrumental analyses using Zetasizer Nano ZS, FTIR, SEM–EDX, TGA, and BET for the determinations of zeta potential, functional groups, morphology (images) and elemental compositions, thermal degradation and decomposition, and surface area measurement, respectively. A substantial increase in zeta potential from − 21.9 to − 1.33 mV was observed when the H. undatus foliage powder was added to the treatment. It was perceived that the increased zeta potential value on the tested sludge was attributed to the H. undatus foliage which potentially possessed sufficient H⁺ ions, often demonstrated by cationic coagulants, in prompting the charge neutralisation mechanism during the coagulation process. Moreover, the presence of amines, amides, carboxyl, and carbonyl groups from the FTIR spectroscopy corresponded to the contribution from both particle bridging and charge neutralization mechanisms. The rough and porous structures of the H. undatus foliage from the SEM–EDX analysis and its BET surface area of 0.5882 m²/g also indicated the availability of a higher concentration of adsorption sites for the coagulation–flocculation process.

Keywords: Dragon fruit foliage; White dragon fruit; Plant-based coagulant; Paint wastewater; Charge neutralization; Particle bridging; Porous structure

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-023-02923-z

Chemical Papers 77 (10) 6083–6093 (2023)