Sorption Of Hydrophobic Organic Contaminants From Water By Modified Peat And Its Mechanism Study

Hydrophobic organic contaminants (HOCs) such as polycyclic aromatic hydrocarbons (PAHs) and environmental hormone-bisphenol A (BPA) are widely produced and used. Due to strong organophilicity, HOCs can accumulate in sediments, suspension solids and organisms when discharged into water body, which cause harm to both animals and human beings. It is essential to develop an effective and affordable sorbent which can be used in restoration and treatment of HOCs polluted water.Peat is a biomaterial of natural origin with potential sorption capability and low cost. The application of peat in removal of contaminants from water can archieve both satisfactory treatment performance and cost effectiveness. In this study, a noval biosorbent for sorption of HOCs was prepared through modification of peat by quaternary ammonium cationic surfactant. The nonionic HOCs-PAHs and ionic HOC-BPA were selected as the target contaminants. And the sorption behavior of PAHs and BPA on modified peat as well as the sorption mechanism was investigated.The modification process of peat was optimized through investigation of the effects of modification time, modifier concentration and different modifiers on the content of surfactant grafted into peat. Results show that the content of grafted surfactant increased with increase of modification time and modifier concentration. HTAB is more effective in modification of peat when compared with HPB and TBAB.The modified peat was prepared from raw fibric peat and sulfonated fibric peat. The results of FTIR and element analysis show that the surfactant was grafted into peat effectively through ion-exchange and the organic carbon content of peat increased after modification. SEM results indicate that the fibric structure of peat remained after modification, which suggests that modified peat had same mechanical strength as the raw peat. The zeta potential measurement shows that raw peat and sulfonated peat are negative-charged. The surface negative charge was reduced after modification. In addition, it was also found that the hydrophobicity of modified peat was significantly enhanced.The effect of contact time, initial concentration, PAHs properties on PAHs sorption capacity of modified peat were investigated to show the sorption characteristics and sorption mechanism of PAHs on modified peat. It is suggested that the uptake rate of PAHs by peat increased after modification; the sorption experimental data followed pseudo-second-order kinetic model and the sorption isotherms fitted well to linear partitioning equation. After modification, the sorption rate constant of naphthalene, phenanthrene and pyrene by peat increased from 675,12870,88590 mL-g"1 to 979,26074,178388 mL·g-1. The partitioning coefficients were positively correlated with octane-water partitioning coefficients of PAHs.The sorption characterisitics and sorption mechanism of BPA were explored by investigating the effects of contact time, initial concentration, pH etc. on BPA sorption capacity of modified peat. Results show that the sorption experimental data followed the pseudo-second-order kinetic model. The sorption isotherms and followed both BET model and Freundlich model. The BPA sorption capacity of modified fibric peat and modified sulphonated peat increased by more than 322%and 33%, respectively. It was also found that sorption of BPA by modified fibric peat and modified sulfonated peat were exothermic processes which haveΔH of 8.926 kJ-mol"1 and 19.393 kJ·mol-1, respectively. The results also verified that the sorption of BPA on modified peat were predominated by both partitioning and surface adsorption. The sorption capacity of peat increased with the enhancement of hydrophobicity and the reduction of surface negative charge.To achieve easy separation of peat sorbent from water as well as improve the chemical stability of the sorbent, the modified peat was embedded by sodium alginate for preparation of granular modified peat. The batch sorption characteristics of granular modified peat as well as the feasibility of using granular peat sorbent as filter packer were investigated. Results show that BPA sorption experimental data of granular modified peat followed both pseudo-second-order kinetic model and intraparticle diffusion model. The sorption isotherm followed both BET model and Freundlich model. The optimum pH range for BPA sorption by granular modified peat is 4.0-9.0 and the dynamic sorption performance was found to be affected by intial BPA concentration. In addition, the granular modified peat can be regenerated by bleaching with warm water.