Comparative Biosorption of Hexavalent Chromium from Aqueous Solution Using Minimally Processed Nypa fruticans and Orange Peels: An Approach towards Sustainable Remediation

Abstract

Soil contamination has emerged as a significant threat to agricultural sustainability, with chromium toxicity representing a major concern. The presence of chromium in soils disrupts microbial communities and diminishes enzymatic activity, thereby adversely affecting essential soil biochemical processes. These alterations directly compromise soil health and fertility, ultimately impairing crop productivity and ecosystem stability. Chromium is a heavy metal with dual oxidation states; trivalent chromium [Cr(III)] and hexavalent chromium [Cr(VI)]. Hexavalent chromium is a highly toxic and mobile heavy metal pollutant that poses serious threats to ecosystems and human health. This study investigated the comparative biosorption efficiency of minimally processed Nypa fruticans and orange peel (in chunky and pulverized forms) for the removal of Cr(VI) from aqueous solutions. Nypa fruticans was harvested from a mangrove in Kono, Rivers State, while fresh orange peels were collected locally. Nypa fruticans foam was obtained from its petiole. The biosorbents were sun-dried, with orange peels prepared as chunky (≈0.2 cm) and pulverized (≤100 μm) forms. A stock Cr(VI) solution (2849.2 mg/L) was prepared from potassium dichromate and diluted to concentrations ranging from 284.92 to 1424.60 mg/L. Batch biosorption experiments were conducted using 2g of each biosorbent in 100mL solution, agitated at 150 rpm for 30 minutes, followed by filtration and analysis using Atomic Absorption Spectrophotometry (AAS). All three biosorbents achieved exceptionally high Cr(VI) removal efficiencies ranging from 99.66% to 99.995%. Orange peel (both chunky and pulverized forms) slightly outperformed nipa foam, with residual Cr concentrations in all cases approaching or meeting the EPA (0.1 mg/L) and WHO (0.05 mg/L) drinking water guidelines for total chromium. The chunky form of orange peel performed more compared to the pulverized form, indicating its practical advantage for low-cost applications. The results demonstrated that locally available, minimally processed agricultural and invasive plant wastes are highly effective eco-friendly biosorbents for Cr(VI) remediation. This approach supports circular economy principles, valorizes invasive Nypa fruticans and agricultural wastes offering a sustainable, affordable solution for chromium contaminated water treatment in the Niger Delta. The approach aligns with sustainable development goals and addresses the urgent need for affordable remediation technologies in Nigeria’s Niger Delta, where industrial effluents continue to elevate chromium levels. Further optimization and real wastewater testing are recommended.