Removal of trihalomethanes from activated Napier grass-derived adsorbent using liquefied gas and chemical pretreatment

BACKGROUND AND OBJECTIVES: Disinfection by-products in water treatment result from the reaction of disinfectants with organic and inorganic precursors, mostly dissolved organic matter. Major disinfection byproducts include trihalomethanes, which are probable carcinogens. Public health organizations such as World Health Organization and United States Environmental Protection Agency have set maximum allowed concentrations for trihalomethanes in drinking water. Numerous techniques, such as adsorption, are used to remove trihalomethane precursors, with activated carbon being successful, however expensive. This study investigates the use of low cost materials, namely Napier grass, for the production of adsorbents by pyrolysis, with the objective to enhance efficiency and reduce expenses in the removal of trihalomethanes. The study examined various factors, including chemical pretreatment, particle size, contact time, and concentrations, to assess the efficacy of the adsorbent in relation to trihalomethanes. The purpose of this work is to utilize of low-cost materials, specifically Napier grass, for the production of adsorbents through pyrolysis. Besides, this work aimed at improvement of efficiency and decrease costs associated with the removal of trihalomethanes.METHODS: The application of chemical pretreatments with sodium hydroxide, phosphoric acid, and ferric nitrate resulted in the generation of an adsorbent obtained from Napier grass. The evaluation of the percentage removal of trihalomethanes beside the porous structure of the synthesized adsorbent was carried out to determine the feasibility of utilizing liquefied petroleum gas as a combustion source in the pyrolysis process. The activation duration of 1 hour at 600 degrees Celsius was used to measure the maximum Brunauer–Emmett–Teller surface area and micropore volume of the adsorbent. The nitrogen adsorption-desorption method used for examining pore structure revealed a predominance of micropores compared to mesopores. Adsorbent characterizations were conducted using scanning electron microscopy with energy-dispersive X-ray spectroscopy, and X-ray diffraction. The burn-off percentage, removal effectiveness of trihalomethanes, and the kinetics and isotherm adsorption on the adsorbent generated from Napier grass were analyzed. This study analyzed the trihalomethane species including chloroform, bromodichloromethane, dibromochloromethane, and bromoform.FINDINGS: The maximum removal rate of trihalomethanes reached 94.43 percent for the adsorbent obtained from Napier grass, which underwent phosphoric acid pretreatment at a dosage of 3.0 gram per lite. The pseudo-second order kinetic model (correlation coefficient values=0.982, p-value<0.05) fits with the adsorption kinetics of trihalomethanes on Napier grass-derived adsorbents were pretreatment with phosphoric acid, proving a maximum adsorption capacity of 220.2 micrograms per gram. Furthermore, pore diffusion plays a major part in controlling the adsorption process of trihalomethane species. The main process of absorption is physical absorption, as indicated by the free adsorption energy.CONCLUSION: The use of an adsorbent derived from Napier grass for the removal of THMs demonstrated an environmentally friendly, cost-effective, and efficient approach, indicating its potential application in water treatment processes.