October 17, 2016

Remediation of dioxin-contaminated soil in southern VietnamCleanup results of Shimizu’s technologies confirmed

Shimizu Corporation (President: Kazuyuki Inoue) has completed soil washing tests that confirm the efficacy of its soil washing technologies. Shimizu examined samples of soil contaminated with dioxin (introduced to the soil during the Vietnam War through the defoliant Agent Orange) brought from Vietnam to Japan. The results showed a dioxin removal efficiency of 95% for soil. with contamination levels of 20,000 pg-TEQ /g, which appears to account for the majority of contaminated soil in Vietnam. The recovery rate of clean products (sand plus gravel) is expected to be about 71% of the original soil volume. The clean products will meet the dioxin criteria (1,000 pg-TEQ /g) and be suitable for reuse.

Areas of soil in Vietnam remain contaminated with Agent Orange (defoliant) dispersed by the United States military during the Vietnam War. The 28 confirmed contamination hot spots, primarily in southern Vietnam, include former US bases at Da Nang, Bien Hoa, and Phu Cat. To address this toxic legacy, the US Agency for International Development launched activities in 2012 to clean up contaminated soil in the Da Nan area.

In April 2014, Shimizu began studying the feasibility of applying its soil washing technologies to soil contaminated by spraying, handling, and spillage, mainly of Agent Orange. Used in Japan to process a cumulative total of 3 million tons of contaminated soil, these soil washing technologies have established a proven track record in soil remediation projects targeting dioxins. Studies of cleanup potential began with simplified experiments in Vietnam in May 2015. In November 2015, in response to a request from the Vietnamese government, Shimizu gave a presentation on its cleanup technologies at an international symposium on dioxins organized by a Vietnamese public agency in Hanoi. The technologies were warmly received by Vietnam’s Ministry of Natural Resources and Environment, Ministry of Science and Technology, and Ministry of Defense. Shimizu was asked to explore the feasibility of a full-fledged cleanup of Vietnam’s dioxin-contaminated soil. Samples of contaminated soil collected in the Bien Hoa area were eventually brought to Japan, where soil washing tests began in February 2016.

The contaminated soil brought to Japan consisted of five samples, each weighing 20-25 kg, representing dioxin concentrations of 6,600, 12,000, 24,000, 32,000, and 57,000 pg-TEQ /g. The soil washing tests showed that dioxin tends to concentrate in silt/clay fractions (< 63 µm). The sum of sand and coarse (gravel) fractions ranged from 65% to 75% (avg 70%).

Shimizu’s soil washing technologies include classification (screening and hydrocycloning) of contaminated soil, rinsing and scrubbing of soil by particle size, and a flotation process that removes contaminants by causing them to adhere to air bubble surfaces. This particular flotation process is a proprietary Shimizu method. The experiments conducted by Shimizu have successfully identified chemicals that facilitate the adherence of defoliant dioxins to air bubble surfaces, with results showing an increase in the rate of dioxin removal to 95%.

An existing method for rendering dioxin-contaminated soil harmless involves heat treatment at 1,000°C or above. This method entails high treatment costs and strict emissions controls. Shimizu’s soil cleanup treatment is inexpensive and free of concerns related to wastewater or atmospheric emissions. Projections indicate the treatment would make it possible to remediate nearly 70% of soil contaminated at concentrations of 20,000 pg-TEQ /g or less—the majority of the contaminated soil—and to make this soil reusable. Applying heat treatment to render the remaining soil harmless would remediate all of the soil at about half the cost of using heat treatment alone.

Shimizu is currently working to gain the understanding of the government of Vietnam and other related parties regarding the efficacy of its soil washing technologies. Shimizu also plans to pursue pilot plant testing and studies of a wide range of related efforts, including large-scale cleanup projects. This will be exhibited at “Exhibition for Geo-Environmental Restoration 2016” that will be held at Tokyo Big Site from Oct 19th to 21st .

Information provided in this news release is current as of the date of publication. Please note that all such information is subject to change. Please feel free to contact us with any questions.

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