Technological trends in activation and modification of palm oil fuel ash for advanced water and wastewater treatment – A review

Palm oil fuel ash (POFA) is a noxious agricultural waste with considerable disposal challenges. Being a pozzolanic material, the bulk of generated POFA materials is used in the construction industry. Recently, its utilization in wastewater treatment is receiving increased attention. POFA is a silica-rich material with poor surface property. Its value-added utilization in water treatment requires activation of the surface sites and modification of the particle for enhanced and effective pollutant removal. However, there is a shortage of well-structured review articles outlining POFA activation, applicability and associated challenges. This work presents a critical review of the recent literature to highlight the factors and effects of activation and modification of POFA for application in wastewater treatment. Characterization techniques to confirm POFA particle tuning was also extensively discussed. POFA has potential in its natural form as an adsorbent, a catalyst, or a membrane additive. Nonetheless, poor surface and size characteristics limit its performance. Traditional surface modification methods, such as acid/alkaline activation, thermal treatment, and impregnation with metal/metal oxide nanoparticles, are more effective for removing inorganic water contaminants and dyes. As the emerging size and surface modification approaches, nano-sizing and polymer-coating could improve the efficiencies of treating organic pollutants. A considerable catalytic potential of POFA is not yet fully explored. This review opens up the research areas that would accelerate the transformation of palm oil fuel ash from waste to water treatment resource.