Formatted Title
Sub-Boiling Thermal Remediation: Efficient Removal of Organo-Thiophosphorus Pesticides and Innovative Vapor Treatment
Background/Objectives
In situ thermal remediation (ISTR) is gaining traction as an efficacious approach, particularly for treating sites contaminated with specific chemicals, such as organo-thiophosphorus pesticides. These compounds, having intricate removal mechanisms, do not necessarily require heating to boiling points for effective remediation. The objective of this study was to explore the efficacy of ISTR at sub-boiling temperatures for two specific sites contaminated with organo-thiophosphorus pesticides and other compounds, and to derive insights regarding the temperature targets needed for optimal remediation.
Approach/Activities
At the heart of our exploration was the realization that many sulfite compounds can undergo various reactions like hydrolysis well before their boiling point, facilitated by the steam sweeping. To corroborate this, we carried out a dual-zone experiment on a site in North China. Two areas were delineated with target temperatures set at 200°C and 100°C respectively. Our team focused on the latter, utilizing gas thermal remediation (GTR) with thermal conductivity heating (TCH). Preliminary lab batch tests validated our hypothesis on the decomposition of phorate under 100°C, showing a half-life of less than an hour. Field operations involved deploying approximately 1,000 TCH wells, ensuring a steady boiling point during the designated 120 days of heating.
Simultaneously, we introduced the innovative thermal oxidization unit, GTRO, into our test protocol. We compared the GTRO with the conventionally used RTO (Regenerative Thermal Oxidizer). While RTO has been a traditional choice, early evaluations in our pilot project hinted at potential complications, especially in high sulfite concentrations. We hypothesized that GTRO, being a more versatile system, might offer better efficiency and durability.
Results/Lessons Learned
The findings were enlightening. Our approach achieved the desired remedial goal, achieving more than a 98% removal rate for target pesticides, underscoring that a 100°C threshold was adequate for the in situ treatment of organo-thiophosphorus pesticides. Significantly, soil temperatures hitting the groundwater boiling point in approximately 80 days became a pivotal point for pesticide decomposition.
Alongside, the GTRO consistently outperformed the RTO. While the RTO faced issues like corrosion due to the acidic nature of sulfites and operational hiccups, the GTRO ran with a remarkable uptime of over 95%. It showcased not just greater flexibility, but also minimized explosive risks in environments with high sulfite concentrations. Our findings accentuate the need to re-evaluate traditional remediation tools in favor of more adaptive and efficient technologies. The GTRO, with its impressive performance, underscores the future potential of tailored vapor treatment technologies in thermal remediation projects.