Minato and Chiyoda Wards, Tokyo / Sano City, Tochigi Prefecture - Oil Contaminated Soil Remediation (around 2007)

Minato and Chiyoda Wards, Tokyo / Sano City, Tochigi Prefecture - Oil Contaminated Soil Remediation (around 2007)

In the early 2000s, soil contamination associated with former factory sites and urban redevelopment became apparent in Japan, and with the enactment of the Soil Contamination Countermeasures Law in 2003, a nationwide system of investigation, notification, and action began to be established. In many cases, oil contamination from petroleum hydrocarbons did not fall under the substances designated by the law, and more and more cases were corrected under voluntary standards based on local government guidelines and the technical guidelines of the Ministry of the Environment.

In this context, "Solec Tochigi," established by Kajima Road (Hibiya), Nichie (Chiyoda-ku, Tokyo), and Otosaka Quarry Mining (Sano-shi, Tochigi), was a practical model for connecting oil-contaminated soil from urban areas to local resource recycling. The core of the technology is the low-temperature heating method (LTTD). Soil particles are heated to approximately 150-350°C in a rotary furnace or hot-air dryer, and the volatilized and evaporated oil is recovered as off-gas. The off-gas is oxidized at high temperature in an afterburner, and particles, odor, and residual organic matter are removed by fabric filters, washing towers, and activated carbon. After treatment, the residual oil content of the soil is reduced to below a controlled value, and after particle size and water content adjustment, the soil is reused as reclaimed soil and soil preparation material at a quarry in Sano City. This will reduce the amount of soil for final disposal and also lead to a reduction in t
he amount of new soil to be quarried.

On the urban side, contaminated soil generated at redevelopment sites in Minato and Chiyoda wards will be contained and transported by covered dump trucks and containers. On-site primary sorting, moisture content adjustment, and odor countermeasures will be implemented, and on the receiving side, weighing platforms and receiving inspections, mist spraying in loading and unloading yards, and negative pressure tents will be used to reduce the impact on surrounding areas. A system to ensure quality and transparency is built in, with traceability ensured by manifests, rapid analysis (PID, infrared analysis, etc.) at the time of receipt and shipment, and periodic third-party verification.

The advantage of choosing LTTD is that it can process large quantities of excavated soil in a short period of time and has a wider scope for materialization compared to incineration. TPH and BTEX derived from heavy oil, light oil, and lubricating oil are the main targets. Difficult-to-volatile components can be treated by optimizing the temperature range and residence time, or by using activated carbon in combination. Pre-treatment (dewatering and particle size classification) is used to improve thermal efficiency for soils with high water content and fine grain content. On the other hand, if there are contaminants containing a large amount of chlorine, the off-gas treatment load increases, so receiving standards and pre-sorting are important.

Around 2007, the combination of soaring crude oil prices and pressure to reduce emissions under the Kyoto Protocol also drew attention to energy efficiency in transportation and treatment, as well as LCA perspectives. The "Solec Tochigi" siting, which links urban purification needs with local demand for materials, is highly significant as a mechanism that simultaneously satisfies environmental measures, resource recycling, and regional development. The project was significant for its ability to speed up redevelopment in Minato and Chiyoda wards, rehabilitate a quarry in Sano City and secure materials, and optimize costs and environmental impact through wide-area collaboration. The advanced nature of this initiative was in the integration of these efforts.