Valorization of organic waste as biosorbents for wastewater treatment

With increasing population and waste generation, organic waste disposal has presented an unprecedented challenge. Valorization of the waste for wastewater treatment emerges as a feasible way to recycle or upcycle the waste. Agricultural and non-agricultural waste has been successfully converted into biosorbents to remove various pollutants. Through reviewing 126 papers, this review aims to provide a comprehensive overview of the effectiveness and mechanisms of biosorbents from organic waste in adsorbing different organic and inorganic waste. Most recent studies have focused on using biosorbents to remove dyes, pharmaceuticals, and heavy metals. The biosorbents were synthesized primarily through drying and pulverization, or pyrolysis. Some biosorbents have been chemically treated with acids, alkalis, or salts to increase their surface functional groups. Furthermore, different biomass materials have also been combined to synthesize biocomposite sorbents. The extraction of lignocellulose and chitin from biomass as biosorbents is also common. Biosorption occurs via chemisorption and physisorption, with the former more prevalent among organic pollutants and the latter among inorganic pollutants. The Langmuir isotherm model, which indicates monolayer sorption, and the pseudo-second-order kinetic model, which implies chemisorption as rate-limiting, best describe most of the biosorption data. Biosorption is governed mainly by pH, temperature, initial pollutant concentrations, dosage and size of biosorbents, and contact time. This review highlights the need to standardize optimization procedures and develop cost-effective and scalable biosorption systems. It highlights the potential of biosorbents, especially biochar, as potential substitutes for activated carbon in the column adsorption process of tertiary wastewater treatment.