18-Env-B5 Industrial & Hazardous Waste Management · May 2015
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
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); provincial hazardous waste regulations (e.g. BC's Environmental Management Act and Hazardous Waste Regulation).
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) Gravity thickening — a circular tank in which dilute sludge settles under gravity, concentrating at the bottom while clarified supernatant overflows, the simplest and lowest-cost thickening option for a readily-settling sludge. (2) Dissolved air flotation (DAF) thickening — fine air bubbles attach to sludge solids and float them to the surface for skimming, effective for lighter, poorly-settling sludges (e.g., waste activated sludge) that gravity thickening handles poorly. (3) Centrifugation (or gravity belt thickening) — mechanical thickening using centrifugal force (a solid-bowl centrifuge) or a moving belt with polymer conditioning to concentrate sludge solids, typically achieving a higher solids concentration than gravity thickening alone, at higher capital and operating cost.
