Abstract

Styrene has been used widely in the manufacture of polystyrene, plastics, resins and copolymers. Styrene is classified in the EPA's Toxic Release Inventory (TRI) as a carcinogen. Batch and column adsorption experiments were performed to study the adsorbability of styrene onto soil. Soil type 1(10.2% silt and clay, 5.3% organic matter content) presented the highest styrene adsorbability 1190 mg/kg and bentonite presented the lowest adsorbability 385 mg/kg in batch adsorption tests. The sorption capacity is found to be strongly dependent on the amount of organic matter and clay ratio present in the soil. Batch and continuous flow washing experiments were used to evaluate the feasibility of using surfactants for the removal of styrene from contaminated soil. Higher styrene removal was achieved from batch experiments compared to column experiments. The highest styrene removal (98.4%) was achieved at 1% rhamnolipid in the batch test. Maximum styrene removal occurred at the highest rhamnolipid concentration in both batch and continuous washing tests. After rhamnolipid adsorption to soil, the two mechanisms of surfactant-aided soil washing are mobilization and solubilisation. The mobilization mechanism occurs at a rhamnolipid concentration below critical micelle concentration (CMC). In this situation, rhamnolipid reduce the surface and interfacial tension between air/water, oil/water, and oil/soil systems. When rhamnolipid concentration is above CMC, the solubility of styrene increased dramatically due to the aggregation of surfactant micelles. Leachate from soil washing experiments was biodegraded in an DASH reactor before release to the environment. The comparison between the results from batch and continuous experiments led to the conclusion that anaerobic biomass could biodegrade styrene and styrene in rhamnolipid under anaerobic conditions. More than 96% of styrene (co-metabolite with acetic acid, styrene initial concentration was 75 mg/L, 150 mg/L and 250 mg/L) was biodegraded with the 16 hour retention time in the DASH reactor with COD removal up to 82%. Rhamnolipid has proven its ability as a washing agent in styrene removal from soil. Anaerobic biodegradation of styrene with rhamnolipid achieved high styrene removal but low biogas production. More research is required to improve the performance of the rhamnolipid and styrene biodegradation before scale-up.