Use of plant-derived sorbents for wicking oil and stimulating biodegradation in wetlands

Remediation of wetlands impacted by oil spills is complicated, because the highly sensitive nature of that environment often limits the remediation technology that can be applied. The use of sorbent technique combined with biodegradation offers an environmentally-friendly option for in-situ remediation of oil-contaminated wetlands. The key concept of this technique is to wick spilled oil from anaerobic subsurface to aerobic surface where indigenous microorganisms degrade oil rapidly. Sugarcane bagasse, the most abundant agricultural byproduct, and its derivatives can be used as a plant-derived sorbent for this application. They are attractive alternatives to synthetic sorbents due to low cost, biodegradability, and diverse derivatives.;Ammoniated bagasse is a sorbent designed to supply slow-releasing nutrients to oil degrading microorganisms. Oil-wicking test results showed that the effectiveness of this sorbent increased with increasing oil-contamination level, increasing sand particle size, and decreasing water coverage. Significantly, water coverage was a primary factor limiting effectiveness, and higher water sorption at higher water coverage was found responsible for limiting effectiveness. To overcome this limitation, research was directed to the modification of sorbent properties to enhance oil-wicking ability in saturated conditions.;A hydrophobic derivative was prepared by acetylating raw bagasse. The changes before and after treatment were investigated by several characterization techniques. The substitution of acetyl group for hydroxyl group was evidenced by FT-IR analysis. SEM analysis and surface area measurement showed the improvement of accessible surface area by perforation of surface and/or swelling of lumens during treatment. The XRD analysis and water sorption tests showed that treatment resulted in structural changes associated with hydrophobic properties and reduced water sorption. Oil-wicking tests results indicated that treated bagasse was more efficient in wicking oil from saturated environments than raw bagasse.;Oil-wicking tests under simulated inter-tidal wetlands resulted in considerable effectiveness over the limitations observed in the previous oil-wicking tests at high water coverage, because oil-wicking mainly occurred at low tide. In this case, the main factors limiting effectiveness were oil penetration depth and tidal amplitude. In cost-effective point of view, the use of raw bagasse immediately after oil spill occurred is suggested for remediation of low energy inter-tidal wetlands even though acetylated bagasse showed higher oil-wicking potential in saturated environments.;The effectiveness of this method depends on the field conditions and sorbent properties. Use of acetylated bagasse is recommended for environments with a strong interaction between oil and sediment, and with a high degree of water saturation, due to its hydrophobic nature and high oil-wicking ability. Use of ammoniated bagasse is recommended for environments with nitrogen-nutrient deficiency, with large grain size of sediment, and with high oil contamination, due to its nutrient availability, and relatively low hydrophobicity and wicking ability in saturated conditions. Reduced oil-wicking ability in ammoniated bagasse possibly resulted from natural wax removal during ammonia treatment, which should be considered in the modification of plant-derived sorbent for oil wicking. The proper use of this technique with high oil-wicking effectiveness will lead to a successful remediation of contaminated wetlands without severe impact on ecosystems.