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Cycle 9 (2020 Deadline)

Nanoassisted bioremediation of diffused dioxins in soil and sediment

PI: Nguyen Thi Kim Oanh (, 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:

Activities during the third quarter of 2022 focused on completion of Work Package 1 with the microbial enrichment experiment at Van Lang University (VLU) and the nanoparticle preparation at Ho Chi Minh City University of Technology (HCMUT). The PI Dr. Kim Oanh and other AITVN staff worked closely with both teams to provide input and advice to improve the experiment results. By September 2022, both VLU and HCMUT were working in harmony to ensure that both key components of the experiment—the enriched microbes and the nanoparticles—are ready for the Work Package 2 experiments in the next quarter. The researchers at HCMUT and VLU are collaborating with the CENTER laboratory of Cheng Shiu University in Taiwan to prepare for sending their samples for analysis.

The project team organized a midway dissemination workshop (hybrid, onsite at VLU) on July 13, 2022, with the participation of the project team (AITVN, HCMUT, and VLU), representatives from USAID, the partner from Taiwan, and invited participants from several universities, institutions, and research centers in Vietnam. During the workshop, the participants had a chance to visit the newly set up dioxin lab in VLU where the enrichment experiment was going on. Before the workshop, a progress review and the workshop preparation meeting was held on July 11, followed by a visit of the project team to the laboratory at HCMUT on July 11. After the workshop, the project team visited and surveyed the sampling sites at Bien Hoa airbase on July 14.

The AITVN team provided technical support for VLU and HCMUT in designing the experiment, finalizing the methodology, and conducting the lab experiments. The VLU team finished the first enrichment experiment on July 18, 2022. They perform rRNA metagenomic analysis of the microbial communities in composite sediment samples before and after 30 days of enrichment. They are looking for bacterial species that have potential for biodegradation of dioxin and dioxin-like compounds and studying the impact of their enrichment protocol. Meanwhile, the HCMUT team investigated the experimental conditions to produce nZVI particles with smaller size, and after applying various techniques they produced particles of 100- 1000 nm with the modal value of about 300 nm. Further refinements in the procedures for synthesizing the particles will be pursued in the coming months.

In the last quarter of 2022, the project team plans to complete the preparation of CMC-nZVI particles meeting the necessary size and stability requirements. The abiotic experiments (without enriched microbes) to find the optimum dose of CMC-nZVI will be started immediately thereafter. The researchers will also carry out bio-treatment experiments on dioxin-spiked soil and sediment in using enriched microbes at the optimum CMC-nZVI dose. Plans call for the pilot-scale phase of the project to begin in mid-2023.

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