Agricultural Pea Waste as a Low-Cost Pollutant Biosorbent for Methylene Blue Removal: Adsorption Kinetics, Isotherm And Thermodynamic Studies

Biosorbents are an alternative pollutant adsorbent, usually sourced from waste biomass and requiring little to no treatment. This makes them cheaper than conventional adsorbents. In this paper, green pea ( Pisum sativum) haulm was used as a biosorbent for the adsorption of methylene blue dye. The potential application of pea haulm as a biosorbent has not been investigated before. Characterisation using scanning electron microscopy, infrared spectroscopy and thermal gravitational analysis showed the surface to be coarse, detected functional groups important for adsorption and identified the composition of key biomass components. The effects of particle size, contact time, agitation, dosage, solution pH, temperature and initial dye concentration on the removal of MB by pea haulm were investigated. Using the data from these studies, the best fitting kinetic and isotherm models were found and the thermodynamic properties were identified. The maximum theoretical adsorption capacity was 167 mg/g, which was relatively high compared to other recent biosorbent studies. The pseudo-second-order adsorption kinetic and Freundlich adsorption isotherm models were the best fitting models. The biosorption process was exothermic and spontaneous at low temperatures. It was concluded that pea haulm was an effective adsorbent of methylene blue and could perhaps find application in wastewater treatment.