Biochar Microparticles from Pomegranate Peel Waste: Literature Review and Experiments in Isotherm Adsorption of Ammonia

This research aimed to synthesize biochar microparticles from pomegranate peel waste for ammonia adsorption. This research also focused on analyzing adsorption isotherm and kinetics models to understand the mechanism of ammonia adsorption on the biochar. The experiments were conducted by carbonizing pomegranate peel waste. The carbonized material was then milled and sieved to obtain biochar microparticles with a certain size (i.e. 500, 1000, and 2000 μm). The particles were then characterized using microscopy and infrared spectroscopy (FTIR) to identify particle morphology and functional groups. The prepared particles were then used for the ammonium adsorption process, and compared with ten isotherm models (such as Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, Jovanovic, Halsey, Harkin-Jura, Flory-Huggins, Fowler-Guggenheim, and Hill-Deboer) to identify the adsorption mechanism. Adsorption kinetic analysis was also performed to identify the adsorption rate of the prepared particles using first-order and second-order pseudo-kinetic models. The adsorption isotherm model informed that ammonia adsorption on biochar with sizes of 2000 μm (large) and 1000 μm (medium) occurs in a multilayer process with physical interaction accompanied by pore filling. Meanwhile, small biochar (500 μm) indicates that the ammonia adsorption process occurs on homogeneous sites with physical interaction through pore filling. From the results of fitting the isotherm model, information about the maximum adsorption capacity for each size of 2000, 1000, and 500 μm are 65.631, 62.231, and 50.086 mg/g, respectively. Overall, the adsorption mechanism occurring on biochar involves interactions among ammonia molecules that repel each other under endothermic conditions. The largest adsorption capacity was obtained for biochar with sizes of 2000 μm. Analysis of adsorption kinetics showed that the adsorption process follows a first-order pseudo-kinetic model, indicating an adsorption mechanism controlled by intraparticle diffusion. This study concludes that biochar from pomegranate peel is prospective for use as an environmentally friendly adsorbent for ammonia removal applications from wastewater, offering a sustainable and effective alternative adsorbent to existing water treatment technologies and solving current issues in the sustainable development goals (SDGs).