Modified Coconut Copra Residues as a Low Cost Biosorbent for Adsorption of Humic Substances from Peat Swamp Runoff

Abstract

The presence of dissolved organic matter, scientifically known as humic substances, gives an undesirable color and taste to water. In addition, they are the precursors of carcinogenic disinfection by-products upon disinfection treatment. Adsorption provides a potential means of removal of humic substances, and lignocellulosic biomass serves as a promising candidate. In this paper, we report the application of modified coconut copra residues for adsorption of humic substances from peat swamp runoff. The FTIR spectra suggest that coconut copra residues are genuinely rich with carboxyl groups with long alkyl chains; this renders the material a natural biosorbent, attaining an average of 50% removal under the conditions of testing. Upon treatment, dissolution of lignin and hemicellulose with the enhancement of effective carboxyl groups occurs, improving the adsorption efficiency to 96%; the treated water is visibly clear. The relative band abundance and band shifts further confirm the involvement of the surface functional groups in the adsorption process. The modified coconut copra residue is an attractive biosorbent option for removal of humic substances. The operating conditions are mild, involving non-toxic chemicals, and no pH adjustment is necessary to allow adsorption.

Application of central composite design for optimization of the removal of humic substances using coconut copra

“…Coconut copra was then refluxed at 100°C for one hour, washed, oven dried and subsequently agitated with 0.5 M citric acid for one hour at room temperature. The treated coconut copra was washed to pH 3 and oven dried [6].…”

“…Biosorption is an alternative gaining increasing attention for its advantages of low cost and abundant availability. Sim et al [5,6] examined the adsorption ability of a spectrum of agricultural biomass in removing humic substances, and reported coconut copra with promising adsorption capacity. The biomass is relatively richer in carboxyl functional groups.…”

“…The untreated coconut copra was evidenced to remove an average of 50 % of humic substances from peat swamp runoff, higher than other selected biomasses including banana trunk, coconut husk, empty fruit bunch, groundnut shell, rice husk, sago waste, saw dust and sugarcane bagasse with removal efficiency ranging between 11 and 40 %, based on the spectrophotometric approach. Upon treatment with citric acid, the adsorption capability of coconut copra is greatly improved [6]. The heterogeneous nature of biomass and humic substances has allowed various interactions such as electrostatic linkages, cation bridging, hydrophobic interaction and hydrogen bonding to take place [7][8][9].…”

“…According to Sim et al [6], the adsorption performance of coconut copra for humic substances was optimized using the conventional one-factorat-a-time strategy; this involves changing a single factor whilst maintaining other factors at constant. This approach does not demonstrate the combined effect of all factors; in addition, it is tedious and provides insufficient information; often time, the optimization point could have been missed [11].…”

“…Note that this paper focuses on examining the optimum conditions for removal of humic substances when multiple variables are considered simultaneously; the information derived is particularly important for scaling up operation. The characteristics and adsorption isotherm studies of raw and modified coconut copra have been reported in Sim et al [6].…”