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18-Env-B5 Industrial & Hazardous Waste Management · December 2017

Question 17 of 28: Handling a Bio-Inhibitory Compound

Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)

Notes on this paper

Reference texts: 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.; LaGrega, Buckingham & Evans, Hazardous Waste Management, 2nd ed.; CCME, Guidelines for the Management of Biomedical Waste in Canada (1992); Canadian Environmental Protection Act (CEPA), 1999; Basel Convention on the Control of Transboundary Movements of Hazardous Wastes (1989); Canadian Nuclear Safety Commission (CNSC) regulations on radioactive waste; provincial hazardous waste regulations (e.g. BC's Environmental Management Act and Hazardous Waste Regulation).

Question 17: Handling a Bio-Inhibitory Compound (4 marks)

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.

  1. Confirm and quantify the inhibition threshold — bench-scale bioassays (respirometry, BOD-inhibition testing) establish the concentration at which the compound impairs the biomass, and whether the effect is reversible or toxic/lethal.
  2. Segregate and pretreat the specific stream at its source, if the inhibitory compound is confined to one process stream, rather than treating the whole combined flow — smaller volume, higher concentration, cheaper to remove.
  3. Select a targeted removal technology for the inhibitor — e.g. activated-carbon adsorption or chemical oxidation for a refractory organic, chemical precipitation for a metal, air/steam stripping for a volatile inhibitor — sized to bring the concentration below the established threshold before the stream rejoins the biological process.
  4. Dilute/equalize as a secondary or interim measure — blending the inhibitory stream with the rest of the flow (or with plant water) can bring concentration below the threshold if the total mass load is small, though this does not reduce the total mass discharged.
  5. Acclimate the biomass — a slow, controlled increase in exposure can, for some compounds, allow a resistant microbial population to develop that tolerates a moderate concentration, reducing (but not eliminating) the need for pretreatment.
  6. Confirm with a pilot/bench trial before full-scale implementation that the pretreated stream, once recombined, no longer inhibits the biological process under realistic loading.