18-Env-B5 Industrial & Hazardous Waste Management · May 2013
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 Nuclear Safety Commission (CNSC) regulatory framework and NWMO Adaptive Phased Management; Canadian Environmental Protection Act (CEPA), 1999.
All nineteen questions are compulsory on this paper and are answered in full below.
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.
(a) Hazardous waste. A waste that, by virtue of its quantity, concentration, or physical, chemical or infectious characteristics, poses a substantial present or potential hazard to human health or the environment when improperly managed. In the Canadian regulatory framework this is given legal effect through the Canadian Environmental Protection Act (CEPA, 1999) and its Export and Import of Hazardous Waste and Hazardous Recyclable Material Regulations, together with provincial hazardous waste regulations (e.g., BC's Hazardous Waste Regulation), which classify a waste as hazardous if it exhibits one or more of the characteristics ignitability, corrosivity, reactivity, or toxicity (including leachate toxicity), or if it is specifically listed by name or process origin.
(b) KLa. The overall volumetric mass-transfer coefficient (units of time−1) governing the rate of gas transfer — most commonly oxygen — across the gas–liquid interface in an aeration system, defined through $dC/dt = K_La(C_s - C)$, where $C_s$ is the saturation dissolved-oxygen concentration and $C$ the actual concentration. A higher KLa means faster oxygen transfer for a given driving-force deficit, and it is the key design parameter for sizing aeration equipment in activated-sludge and other biological systems.
(c) Polymer. A long-chain, high-molecular-weight organic molecule (naturally derived or synthetic; cationic, anionic or non-ionic) used as a coagulant aid or primary flocculant in water and wastewater treatment. A polymer works by bridging and aggregating destabilized colloidal particles (or the smaller flocs formed by a metal coagulant) into larger, denser, more readily settleable or filterable flocs, typically dosed at much lower mass than an inorganic coagulant like alum for an equivalent improvement in settling or filtration performance.
(d) API separator. An American Petroleum Institute gravity oil–water separator: a long, rectangular basin (or set of parallel plates within one) sized so that free, non-emulsified oil droplets have time to rise to the surface (per Stokes' law) faster than the water traverses the basin, while settleable solids sink to a sludge hopper below. It is the standard first-stage pretreatment unit for refinery, petrochemical and other oily-wastewater streams ahead of any downstream biological or physical/chemical treatment.
(e) Buffer. A solution or system containing a weak acid and its conjugate base (or a weak base and its conjugate acid) in appreciable concentration, which resists a change in pH when a limited quantity of acid or base is added, because the added ions are consumed by the conjugate pair rather than freely changing the solution's hydrogen-ion concentration. Alkalinity (the bicarbonate/carbonate system) is the natural buffer relied on in biological wastewater treatment to keep pH within the narrow range tolerated by the microbial population, especially during nitrification, which consumes alkalinity.
