| Summary: | 碩士 === 國立中興大學 === 環境工程學系所 === 107 === Sediment contamination in Taiwan is a prevailing environmental problem no matter in freshwater or seawater. Concentration levels of some hydrophobic organic compounds (HOCs) are ranked at the front all over the world. For example, the sediments in a seawater lagoon of An-Shun Plant at the China Petrochemical Development Corporation (CPDC) in Tainan is heavily contaminated by dioxins and mercury. Due to their hydrophobic and xenobiotic nature, dioxins are usually very persistent in ecosystems. Historical data showed that their concentration exceeded the regulated levels posing high environmental health risks. Thus, effective sediment remediation technology is in demand.
Coupling in situ phase-inversion emulsification and biological reductive dechlorination (ISPIE/BiRD) has been shown to be a successful application to Aroclor 1254 and HCB. Within 70 days, removal rate was as high as 98 % for both contaminants. Since coplanar PCBs are highly similar to dioxins, their chemical structure is similar, thus, in this study, we applied ISPIE/BiRD to remediate sediment contaminated by dioxins.
The study focused on three tasks. First, to confirm the feasibility of this method, a batch study was conducted. Second, to test the feasible concentration range, this method was applied to both low and high concentrations of dioxins. Third, to test if heat selection can increase the biodegradative capability of an indigenous culture, different heat selection conditions were applied and the biodegradative capability of each one was defined. Last, the application of ISPIE/BiRD to remediate sediment contaminated by dioxins in polit study.
Batch biodegradation tests showed that the best group was H group (sand : fly ash = 1 : 4), and the removal rate was only 11.70 % within 100 days. There was no significantly different from control group. It was speculated that high concentration of heavy metal and high pH caused microorganisms hard to survive; In column study (sand : fly ash : Er-Ren River sediment = 1 : 1 : 2 ), with single operation of ISPIE and follow-up biodegradation, the removal rate achieved 30.80 % within 91 days; In heat screen batch study, the best condition was 30 mins exposure at 95℃, removal rate achieved 23.03 % within 70 days. The results of PCR-DGGE showed that there was no obvious difference in the upper and lower layers of the sediment in the column. Many bacteria were either halophiles or alkalophiles.
Pilot study showed that microorganisms with biostimulation could effectively degrade dioxins(the degradation constant(k)：0.0097(1/day) , half-life ：71 days) within 35 days. The study showed that single phase-inverse emulsification operation and biodegradation could remove 93.6 % and 82.8 % of weathered OCDF and OCDD with 35 days.
The result showed that the application of ISPIE/BiRD to remediate sediment contaminated by dioxins still has high potential. Heat selected microorganisms were more effective than the unheated ones.
|
|---|
