Emulsion-enabled direct removal and biodegradation of phthalates in river sediment

• Main Authors: Hong-Wei Chen, 陳鴻偉
• Other Authors: Shu-Chi Chang
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/98976091972512827027

碩士 === 國立中興大學 === 環境工程學系所 === 103 === River sediments play a vital role in an ecosystem, such as self-purification, habitats for benthic organisms and planktons, fish reproduction and feeding place, and feeding ground for wading birds. However, due to human activities, sediments are polluted. Thus, human health in turn is under threats. Phthalate esters (PAEs) are one of the endocrine disrupting compounds in the so-called emerging contaminants and are usually used as industrial plasticizers to increase the flexibility and softness of plastics. Commonly used poly vinyl chloride (PVC) plastics have high level of PAEs. The concentrations of PAEs on the dusts of indoor air in Taiwan are the highest in the world. The concentration of one type of PAEs, di(2-ethylhexyl)phthalate (DEHP) in soil and sediment Taiwan is also ranked at the front of all countries in the world. Due to their hydrophobicity, they tend to accumulate in sediments. However, most treatment methods for PAEs are aimed at wastewater treatment instead of sediment contamination. These methods include physicochemical and biological methods and cannot be directly applied to sediment remediation. Moreover, currently widely applied technologies on sediment remediation cannot be employed in Taiwan because the steep landscape of Taiwan resulting high flow velocity of river water in Taiwan. In this study, an instable soy bean oil emulsion is used to recover PAEs from contaminated sediment through frequent high speed collision between oil droplets and sediment granules resulting re-partitioning of PAEs between sediments and soybean oil. Afterwards, the emulsion is broken by increasing ionic strength and the extracted PAEs are removed with separated soybean oil. The residual soybean oil and surfactants elevated the biodegradation rates of PAEs. In this pilot study, both weathered and fresh PAEs in sediment were tested and several different biological treatment schemes were tested, i.e., natural attenuation, anaerobic remediation, aerobic remediation, and sequential aerobic-anaerobic remediation. The optimum emulsion removal parameters are as follows: the ratio of emulsion to sediment (dry weight) at 1:0.84, the final concentration of sodium carbonate as emulsion breaker at 0.78 M, aeration rate at 4.0 L/min, aeration time at 30 min, and left-undisturbed period at 12 hours. Emulsion removal of fresh PAEs ranged from 60% to 70% while that of weathered PAEs ranged from 3% to 25% with an exception of benzyl-butyl phthalate at 77%. For the biological treatment, emulsion did enhance the biodegradation of PAEs.