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Cycle 9 (2020 Deadline)
Nanoassisted bioremediation of diffused dioxins in soil and sediment
PI: Nguyen Thi Kim Oanh (kimoanh@ait.asia), Asian Institute of Technology Center in Vietnam (AITVN) and AIT Thailand, with co-PIs Tran Thi My Dieu, Van Lang University (VLU), and Bui Xuan Thanh, Ho Chi Minh City University of Technology (HCMUT)
U.S. Partner: Dana Barr, Emory University
Project Dates: April 2021 - April 2024
Project Overview:
This project aims to reduce residual dioxin contamination in soils and sediments from the past use of Agent Orange during the Vietnam War. Dioxins will be removed from contaminated soils and sediments via anaerobic and aerobic metabolism by microorganisms using a novel stepwise procedure of sequential anaerobic-aerobic biodegradation. In anaerobic conditions, certain anaerobic bacteria can remove chlorine atoms from dioxin molecules and convert them into lower chlorinated congeners through reductive dehalogenation. A stepwise process of anaerobic followed by aerobic biodegradation, can ultimately destroy dioxins in soils and sediments, eliminating the need for any additional steps to handle the pre-concentrated dioxins in plants or other media. Nanoscale Zero Valent Iron particles are reportedly efficient at removing arsenic from environmental matrices as well. While it is not the main focus of this project, the team will also monitor arsenic before and after remediation to determine if there are any secondary benefits from using this remediation approach.
Previous experiments conducted at the Asian Institute of Technology (Binh et al. 2016) showed that sequential anaerobic-aerobic biodegradation could remove 60% of 2,3,7,8-TCDD from contaminated soil after 23 weeks by using the enriched indigenous microorganisms from dioxin-contaminated sediments in Bien Hoa Airbase alone. Building on past experience, this project will first conduct lab-scale experiments to find optimal conditions for dioxin removal and then conduct pilot-scale experiments onsite, at the Bien Hoa Airbase, for the actual contaminated soils and sediments. The aim is to include a range of diffused dioxin levels, from below 1000 ppt to a few ppb. A design for the full-scale treatment will be prepared and proposed for future application for the bioremediation with consideration of the actual pollution situation and local climate.
The contaminated soil with high dioxin concentrations (>1,000 ppt) has been or will be treated to destroy residual dioxins by some attested alternatives (USAID-Vietnam, 2016). However, large volumes of soils and sediments containing dioxins below 1,000 ppt remain at the sites. Current attempts to address these soils and sediments focus on landfill/containment to prevent direct human and ecologic contacts. This project aims to develop technologies to eventually destroy dioxins using enriched indigenous microbes, which have a high potential for application to convert the passive landfills in Phu Cat, Da Nang, and Bien Hoa Airbases into active landfills. It will also consider the effects of any additives used in the treatment on the microbes and the quality of the soils and sediments. The project therefore would supplement USAID’s efforts to remove dioxins from the hotspot airbases in Vietnam and restore the environmental conditions to safeguard ecological and human health in the areas. The project will also build capacity of the local partners in Vietnam by involving research teams from local universities to develop this new treatment approach, hence sustaining the local human resources to deal with the dioxin contamination in soils and sediments in Vietnam in the long term. The US Government-supported (USG) partner from Emory University has extensive experience on bioremediation of heavy metals in soils and sediments and will train the Asian partners on the analysis of dioxins and microbial communities.
Summary of Recent Activities:
The project teams of AITVN, HCMUT, and VLU conducted Work Package (WP) 2 (spiked dioxin experiments) and prepared for WP3 (real soil/sediment experiments) and WP4 (pilot scale) during this period. They completed the anaerobic phase of the WP2 experiments in the first week of April 2023 and in July they received the results of the dioxin analysis. The aerobic phase of the HCMUT team’s soil experiments ended on May 15, while at VLU the aerobic phase was completed on May 22. The researchers prepared and sent dioxin samples from the anaerobic and aerobic phases of both labs to the CENTER-lab in Taiwan for dioxin analysis and to KTEST for microbiome analysis. The researchers at both labs worked closely with AITVN to set up and adjust the experiments to improve the environmental conditions, experimental manipulation, and data analysis. During the WP2 experiments, biogas was also collected and analyzed. HCMUT collected gas under three conditions (bio + enriched microbe, bio + enriched microbe + nanomaterial, and bio + enriched microbe + nanomaterial + Tween80) and received the analytical results on April 1. Both teams also analyzed the microbial community in the soil and sediment experiments. The results of the soil experiments (HCMUT) will be compared with the initial microorganism results (VLU) to see how the enriched microbes grew.
To prepare for the WP3 experiments, the team collected dioxin-contaminated soil and sediment outside the airbase, from locations previously identified as highly contaminated. However, the levels of dioxin in the soil were lower than expected. Given that the permission to collect soil from the airbase is still pending, the team will need to search for appropriate soil in other places to use for the experiment. For the sediment samples, the team is still waiting for the dioxin analysis results. To prepare for WP4 (pilot scale testing), researchers from AITVN, HCMUT, and VLU visited Bien Hoa Airbase on June 4, 2023. The main purpose of this field trip was to identify and survey a feasible location to perform pilot scale testing. On June 5, the project team convene its annual review workshop to discuss progress and plan to complete all proposed activities on schedule.
WP3 will begin in the last week of July 2023 and WP4 in November 2023. The PI Dr. Kim Oanh and three other team members plan to visit their U.S. colleagues at Emory University in September, after which they make presentations on their work at IT3/HWC, the International Conference on Thermal Treatment Technologies and Hazardous Waste Combustors, which is being held in Charlotte, North Carolina, September 13-14. The teams are also working to prepare for manuscripts based on their project findings.
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