A Silent Current Running Underground: Obayashi Corporation's Challenge to Clean Up Soil Contaminated by Heavy Metals (1990s)

A Silent Current Running Underground: Obayashi Corporation's Challenge to Clean Up Soil Contaminated by Heavy Metals (1990s)
In the 1990s, Japanese cities were beginning to confront the reality beneath the ground. Heavy metal contamination left behind by industrial activity during Japan's period of rapid economic growth began to appear with every redevelopment and land use change, and in many cases, substances such as cadmium, lead, hexavalent chromium, and arsenic were detected in excess of standard values. While there was still no Soil Contamination Countermeasures Law and the government and companies were still groping their way through the process, the technology itself was at the forefront of society's expectations and concerns. Should the contamination be dug up, contained, or washed away? This was a time when engineers in the field were exploring their options.
The electrochemical remediation technology developed by the Obayashi Corporation was a new light in the midst of this uncertainty. When an anode and cathode are placed at both ends of contaminated soil and a direct current is applied, a quiet electric field spreads through the soil. This electric field slowly attracts metal ions to the cathode side and simultaneously moves soil water. Although nothing seems to be happening on the surface of the earth, the metals gradually change locations underground and begin to precipitate as hydroxides. Without drilling or noise, pollution moves, collects, and separates deep in the ground. The serenity of the process foreshadowed the arrival of an era different from the conventional large-scale purification.
However, establishing the technology required deciphering many conditions. If the distance between the electrodes was too large, efficiency would drop; if they were too close, workability would suffer. The way the electric current passes through the soil and the speed at which metal moves through the soil change depending on whether the soil is cohesive or sandy. Since the soil becomes acidic near the anode and alkaline near the cathode, the position at which metals dissolve or precipitate also changes from moment to moment. A series of tests were conducted to find the optimum conditions while combining these complex phenomena.
However, purification is not completed simply by collecting metals. The question of how to handle the metal precipitated on the cathode side remained. Should it be solidified and buried or recycled? In Japan in the 1990s, final disposal sites for waste were tight, and there was concern that precipitates containing heavy metals might become a new burden. The article's term "research on post-treatment technology" is indicative of the very second stage of the technology's task.
Overseas, the technology has attracted attention as Electrokinetic Remediation, and the U.S. Environmental Protection Agency has evaluated it as particularly effective in low permeability clay soils. In Europe, it has also been taken up as part of site rehabilitation, and Obayashi's efforts were part of the global trend. In Japan, the dissemination of the Basic Environmental Law and ISO 14001 has caused companies to reevaluate environmental impact reduction as a management issue, and the possession of advanced environmental technology by construction companies has become a competitive advantage.
In the 2000s, various developments were seen, including the use of chelating agents and surfactants in combination with surfactants and the introduction of nanomaterials for higher efficiency. The quiet current that moved metals underground was not just a technology, but also a manifestation of the will of the times to balance development with the environment.