RECYCLING OF ORANGE PEEL TO NANOBIOCHAR: A SUSTAINABLE STRATEGY FOR WASTEWATER POLLUTANT REMEDIATION

Abstract

The rapid demand in citrus food product, approximately 15 million tonnes of orange peel are created from the citrus industry annually that directly or indirectly impact on environmental pollution. Oranges are extensively grown and consumed across the world. Approximately 10-15% of peel waste is produced after the consumption of oranges. This waste can be valorised to generate a carbon rich product that can be applicable as an adsorbent for wastewater treatment. Conversely, lithium (Li+) pollution from industrial and electronic waste in wastewater is a great concern due to its toxicity to ecosystems. This study explores recycling of orange peel into biochar production through pyrolysis at three temperatures (500, 600 and 700 °C) and to assess microbiochar and nanobiochar impact on the lithium (Li+) adsorption from aqueous solution. This study exhibited nanobiochar at three different temperatures has higher BET surface area, porous in structure, and zeta potential compared to microbiochar. However, the carbon value is almost equivalent. Batch adsorption experiments were conducted under varying conditions, like adsorbent dosage, pH, contact time, and different Li+ concentrations to optimize the removal efficiency. The pyrolysis process from 500 to 700 °C reduced the yield of biochar from 28 to 13.5% with rising temperature, however various properties increased. Compared to micro size, nanobiochar has higher BET surface area and pore volume, zeta potential and carbon content. The nanobiochar generated at 700 °C appears the most efficient adsorbent with the greatest BET surface area of 295.7 m2/g, zeta potential of 44.03±0.5 mV, fixed carbon content of 69.34% and different functional groups of carbon compounds. However, the nanobiochar properties at 600 °C also showed similar characteristics to the biochar at 700 °C and could also be considered as a potential adsorbent. Different adsorption isotherm studies were conducted for Li+ adsorption by microbiochar and nanobiochar. The nanobiochar at 700 °C shows a maximum capacity of 58.51 mg/g (98%) Li+ removal at a solution pH of 6 at a dose of 0.8g for a solution concentration of 1000 mg/L at 120 min. However, at each pyrolysis temperature, the nanobiochar enhanced 20 to 24% of adsorption capacity compared to microbiochar. Additionally, most of the adsorption isotherms tested provide a best model fitting with a good regression coefficient except for the Harkin-Jura isotherm. This finding contributes to the valorisation of orange peel to nanobiochar for a circular economic approach by addressing Li+ removal by supporting sustainable wastewater treatment.

Date of Award	2025
Original language	American English
Awarding Institution	HBKU College of Science and Engineering