December 26, 2019
Shimizu Corporation (President: Kazuyuki Inoue) completed the soil washing pilot test on remediating soil contaminated with dioxins from ‘Agent Orange’ (herbicide and defoliant) at the Bien Hoa Airport in southern Vietnam. The pilot test was performed in cooperation with the government agency, NACCET (National Action Center for Chemical and Environmental Treatment), which oversees environmental problems throughout Vietnam. Shimizu has submitted a report to government authorities confirming the effectiveness of remediation as initially expected. This verification experiment was planned by Shimizu and NACCET in accordance with the technology selection process for soil decontamination at the airport, which the Vietnamese and U.S. governments are pursuing. Both governments will consider whether use this technology in the full-scale decontamination project that will begin in June 2020.
Some areas in southern Vietnam are still contaminated by dioxins from Agent Orange sprayed by the U.S. military during the US-Vietnam war. The amount of dioxin-contaminated soil at Bien Hoa Airport is estimated at 850,000 tons, the largest amount in the country. In light of these circumstances, Shimizu began investigating the potential for application of our soil washing technology, in which we have an extensive processing record in Japan, to soil contaminated with organic and inorganic pollutants. In June 2018, we concluded an MOU concerning joint implementation of a pilot plant test with CTET (Center for Technology of Environmental Treatment), a research institution in the Vietnamese Ministry of National Defense which is the predecessor organization of NACCET.
After concluding the MOU, Shimizu shipped a mobile-type soil washing plant by sea from Japan to Vietnam. Installation of the plant at Bien Hoa Airport began in November 2018 and was completed at the end of January 2019. The plant began operation in the pilot plant test from late March, after a commissioning period of approximately two months. We carried out the soil washing pilot test on multiple soil samples (roughly 900 tons in total) in different dioxin concentrations and were successful in removing 95% of the dioxins in feed soil. This was the same highly effective removal rate that Shimizu had verified in the laboratory treatability testing. We consequently expect that the recovery/reusable rate of feed soil is approximately 70%.
We have been performing an additional thermal treatment test with a U.S. firm since the end of November 2019. Thermal treatment is being applied to process the sludge cake (residue) from soil washing to achieve decontamination of all soil.
‘Soil washing’ is a remediation and waste minimization technology that is low-cost and imposes little environmental burden compared to thermal treatment. The use of both makes it possible to minimize the environmental burden and the remediation cost. We will complete the additional thermal treatment test to verify the effectiveness of a decontamination method using a combination of soil washing and thermal treatment by March 2020, and compile a report that summarizes the full results of the experiments in soil washing and thermal treatment.
After demonstrating the effectiveness of its soil decontamination technology through these verification experiments, we intend to contribute to the economic development of Vietnam by rolling this technology out to environmental improvement projects nationwide in Vietnam, including the processing of soil contaminated with dioxins, heavy metals, agrochemicals, and other contaminants.
≪For Reference≫
On-site soil washing plant set up at Bien Hoa Airport
Past Initiatives Involving Soil Contaminated with Dioxins from Exfoliants in Vietnam
| April 2014 | Began investigating feasibility of applying Shimizu’s soil washing technology to soil contaminated with dioxins from exfoliants. |
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| March 2015 | Participated in a seminar held by the Vietnamese Ministry of National Defense and made a presentation on Shimizu’s soil washing technology and facility for removing dioxins. |
| September 2015 | Received contaminated soil sample from Bien Hoa Airport and began in-lab soil decontamination experiments. |
| June 2016 | Discovered an effective chemical agent to combine with dioxins from exfoliants through in-lab experimentation and verified that soil decontamination with Shimizu’s washing technology was applicable. Reported to the relevant Vietnamese authorities (Ministry of National Defense and Ministry of Natural Resources and Environment) and the United States Agency for International Development (USAID) that the technology could remove 95% of the dioxins in soil with a medium level of contamination of 20,000pg-TEQ/g or lower, which is considered to encompass the majority of contaminated soil in Vietnam. |
| November 2016 | Relevant personnel from the Vietnamese Ministry of National Defense came to Japan and visited Shimizu’s washing plant. |
| February 2017 | Shimizu met with the Vietnamese Ministry of National Defense in Vietnam about the soil washing verification experiment. |
| October 2017 | Shimizu installed an actual plant at Bien Hoa Airport and reached a basic consensus on joint research with the Ministry of National Defense. |
| June 2018 | Concluded an MOU concerning joint implementation of a soil washing pilot test at Bien Hoa Airport with CTET, the research arm of the Ministry of National Defense. |
Shimizu’s Soil Washing Technology and Record
- Shimizu has used this soil washing process on soil containing various contaminants in Japan and have washed a cumulative total of 3 million tons.
- While dioxin-contaminated soil can be rendered harmless by incineration (at 850℃ or higher), such processing is expensive and requires strict management of gas emissions. Using Shimizu’s technology for washing is low-cost and does not generate wastewater and gas emissions.
- Shimizu built the first soil washing plant for dioxin-contaminated soil in Japan in 2009. It is located in Kawasaki, Kanagawa Prefecture and operated through 2012.
Shimizu’s soil washing is a water-based process utilizing “physical separation” based on mining and mineral processing principles for removing a broad range of organic and inorganic contaminants from soils. The typical throughput range of commercial operation is 30-50 tons/hour. The operation units involved are: wet screen, hydrocyclone, attrition scrubber, froth flotation, up-flow column, spiral classifier, log washer, and so on.
Hydrocyclone and flotation are the most important separation methods used in soil washing process. Hydrocyclone separates the fine soil from larger sand particles by the centrifugal force. Larger sand particles end up in the underflow; fine/light particles (silt, clay, organic) and water end up in the overflow.
In flotation, contaminant-bearing particles are conditioned such that they become selectively hydrophobic and non-contaminated particles hydrophilic. Adding a frothing agent and passing air bubbles through a slurry material removes the hydrophobic contaminated particles which attach themselves to the air bubbles and concentrate in a discharging surface froth. Flotation has been successfully used to remove contaminants like heavy metals, herbicides, and dioxins from soils.
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