Iron and manganese removal from borehole water using carbonised orange peels as a biosorbent

Abstract

This study addresses two significant civil engineering challenges: solid waste management and heavy metal water pollution. It proposes using carbonised orange peels, a domestic waste by-product, as a biosorbent for the removal of iron and manganese from borehole water. This approach aims to reduce landfill waste while providing a sustainable method for water treatment. The orange peels were collected from a local juice shop and the biosorbent was then prepared by drying, grinding, and then carbonising the material at 600°C in an argon atmosphere. Batch experiments were then completed which demonstrated that carbonised orange peels could effectively reduce iron and manganese concentrations. Various experiments were conducted to assess concentration effects (100 ppm diluted to lower concentrations), biosorbent mass (ranging from 0.05 g to 1 g), pH levels (adjusted) and contact time (1 to 90 minutes). Subsequently, column studies were done where water was passed through a packed column containing the biosorbent, with samples collected at different time intervals for analysis. The experimental data was then applied to various adsorption models to assess the performance of the biosorbent. Various characterization techniques were performed such as Scanning Electron Microscopy (SEM), Electron Dispersive Spectroscopy (EDS), Fourier Transform Infrared (FTIR) Spectroscopy and Brunauer Emmet Teller (BET). The study found experimental biosorption capacities of 11 mg/g for iron (Fe) and 5 mg/g for manganese (Mn). The results showed Fe and Mn removal efficiencies of up to 100% and 75%, respectively. There was a constant percentage removal for iron and the iron concentrations were significantly reduced after treatment while the manganese concentrations varied with initial concentration. The iron performed well in both the model fluid and the borehole water adsorption experiments when compared to manganese. The iron removal was constant even in a binary system. The optimal conditions for maximum biosorption were identified as a biosorbent mass of 0.3 g and a pH of 4. Biosorption was rapid, reaching equilibrium in 40 minutes for manganese. In batch studies, the adsorption of iron and manganese from borehole water by carbonised orange peel followed the Langmuir model. In the kinetic modelling, it was observed that the pseudo second order predicted Qe as 10 mg/g and the experimental Qe was calculated as 11.3 mg/g for Fe. For Mn the predicted Qe is 4.9 mg/g while the experimental Qe was calculated to be 5.3 mg/g. Therefore, the experimental data was best described by the pseudo second order kinetic model. Column studies revealed that the breakpoint and saturation point were directly proportional to the column mass while not limited by the flow rate. The highest saturation capacity for COP in column experiments was 1.465 mg/g, achieved under conditions of 11 mg/L manganese inlet concentration, a flow rate of 20 mL/min, and a 0.3 g adsorbent bed. The column biosorption data was best described by the Yoon Nelson model. The biosorbent demonstrated effective performance on borehole water, achieving removal from an initial concentration of 91 mg/L to 0.05 mg/L for iron while the initial concentration for manganese was reduced from 7 mg/L to 2 mg/L. Although, the removal of both iron and manganese was statically significant, only iron was successfully reduced to below the drinking water standards required by the World Health Organisation. SEM images of the raw orange peels (ROP) and carbonised orange peels (COP) revealed varying degrees of porosity and particle distribution. EDS confirmed the presence of Fe and Mn on the surfaces of both ROP and COP after biosorption. The EDS findings shows that carbonisation of the raw sample can improve biosorption by nearly 3-fold. There were no significant differences in the FTIR spectrum of ROP and COP before and after application for the sorption of Fe and Mn. This indicates that the adsorption of Mn and Fe ions were non-chemical in nature. The BET surface areas of both ROP and COP were found to be very low, which is typical for carbonaceous materials. The surface area of the ROP is seen to increase with carbonisation. This study concludes that carbonised orange peel is an effective biosorbent for removing iron and manganese from borehole water. This approach not only utilises agricultural waste but also offers a sustainable and eco-friendly solution to water contamination problems. The research advocates for the adoption of this method in water treatment practices, particularly in regions facing similar heavy metal pollution issues.