18-Env-B5 Industrial & Hazardous Waste Management · May 2018
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Reference texts: LaGrega, Buckingham & Evans, Hazardous Waste Management, 2nd ed.; Nemerow & Dasgupta, Industrial and Hazardous Waste Treatment, 2nd ed.; Metcalf & Eddy, Wastewater Engineering: Treatment and Resource Recovery, 5th ed.; Davis & Cornwell, Introduction to Environmental Engineering, 6th ed.; Cooper & Alley, Air Pollution Control: A Design Approach; CCME, Guidelines for the Management of Biomedical Waste in Canada (1992); Ontario Environmental Protection Act, R.S.O. 1990, c. E.19 and O. Reg. 347 (Waste Management – General); Transportation of Dangerous Goods Act, 1992 (Canada) and Regulations; Canadian Environmental Protection Act (CEPA), 1999.
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
Soil vapor extraction (SVE) is fundamentally a physical mass-transfer process. A vacuum applied at extraction wells draws air through the vadose-zone soil at relatively HIGH flow rates, volatilizing sorbed and dissolved contaminants directly into the moving air stream and removing that contaminant mass from the subsurface as extracted vapor. Because the vapor is collected and typically must be treated (activated carbon, thermal or catalytic oxidation) before atmospheric discharge, off-gas treatment cost and permitting are a central part of SVE system design, and it is most effective on genuinely volatile compounds (high vapor pressure / Henry's constant).
Bioventing instead supplies air at deliberately LOW flow rates — just enough to maintain aerobic conditions — with the explicit goal of stimulating indigenous microorganisms to biodegrade the contaminant in place, rather than to strip it out physically. Because the airflow is low, comparatively little contaminant mass leaves as vapor (minimizing or eliminating the need for off-gas treatment), and the process works on a broader range of compounds, including semi-volatile organics that SVE alone would remove too slowly to be practical, provided they are biodegradable. Bioventing treatment timelines are typically longer than SVE's, since biological degradation kinetics rather than airflow-driven volatilization set the removal rate.
In short: SVE = high airflow, physical removal by volatilization, faster but with an off-gas treatment burden; bioventing = low airflow, biological destruction in place, slower but with a much smaller vapor-phase footprint. The two are often combined or run in sequence — an initial SVE phase to strip the most volatile, easily removed mass, followed by a bioventing phase (at reduced airflow) to biologically finish off the less volatile residual.
