18-Env-B5 Industrial & Hazardous Waste Management · Undated paper
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — May 2019 — 18-Env-B5: Industrial & Hazardous Waste Management (3 hours, open book). Marks are indicated beside each question for a total of 100 marks; all ten questions are answered in full below as a complete study resource.
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.).
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. Pyrolysis, not gasification. The process described — thermal decomposition of an organic substance into gas, liquid (tar/oil) and solid (char) fractions in the total absence of oxygen — is the definition of pyrolysis. Gasification is a related but distinct thermal process that reacts the feedstock with a strictly controlled, sub-stoichiometric amount of oxygen or steam (partial oxidation), converting most of the feedstock into a combustible syngas (CO, H2, CH4) rather than roughly equal gas/liquid/solid fractions. Corrected statement: "The thermal process that splits organic substances into gaseous, liquid and solid fractions in an oxygen-free atmosphere is called pyrolysis."
2. Composting ceiling is far below 95 °C. Composting is a controlled aerobic biological process, and even thermophilic organisms are inhibited or killed well before 95 °C. A well-managed pile is deliberately kept in the thermophilic range, roughly 55–65 °C (pathogen-kill guidance under most provincial/EGBC-recommended standards calls for ≥55 °C sustained for several days); once the pile drifts much above about 65–70 °C, microbial activity collapses and decomposition slows or stops. Corrected statement: "the temperature in the body of the pile should not exceed about 65 °C."
3. High Kow means hydrophobic and less mobile in water, not hydrophilic and more mobile. The octanol–water partition coefficient measures how strongly a compound favours a non-polar (octanol-like) phase over water. A high Kow (>10, and especially log Kow > 3–4) identifies a hydrophobic/lipophilic compound that partitions out of the aqueous phase onto soil organic carbon or into fatty tissue — it is therefore less mobile in groundwater (though more prone to bioaccumulation and sorption-limited transport). Corrected statement: "chemicals with high Kow tend to be hydrophobic, sorb strongly to organic carbon/lipids, and are generally less mobile in the aqueous environment."
4. The organic waste is the electron donor, not the acceptor. In biological treatment, the organic substrate is oxidized — it donates electrons and is itself the electron donor. The electron acceptor is whatever gets reduced: O2 under aerobic conditions, or NO3−, SO42−, Fe3+/Mn4+, or CO2 under anoxic/anaerobic conditions. Corrected statement: "the organic waste is usually the electron donor; the electron acceptor is O2 (aerobic) or an alternate oxidized species such as nitrate, sulfate or CO2 (anoxic/anaerobic)."
5. The POHC screening threshold is about 100 mg/kg, not 1000 mg/kg. Principal Organic Hazardous Constituents are Appendix-VIII-type constituents selected from the waste feed for trial-burn destruction-and-removal-efficiency (DRE) demonstration; the conventional screening criterion (LaGrega et al.) is presence in the feed at a concentration greater than roughly 100 ppm (100 mg/kg), combined with an incinerability ranking (heat of combustion). The statement overstates the threshold by a factor of 10. Corrected statement: "POHCs are constituents identified in the incoming waste stream at a concentration greater than about 100 mg/kg (100 ppm)."
