Question 1 of 18: Definitions

Question 1: Definitions (10 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.

1.1 K_La — the overall oxygen (or volumetric mass-transfer) coefficient. In an aeration system, oxygen crosses a thin liquid film at the gas–liquid interface; K_L is the liquid-film mass-transfer coefficient (length/time) and a is the specific interfacial area available for transfer per unit volume of tank (area/volume), so their product K_La has units of reciprocal time (e.g. h⁻¹) and governs the rate law $dC/dt = K_La\,(C_s - C)$, where C_s is the saturation dissolved-oxygen concentration and C is the actual concentration. K_La is the single most important design parameter for sizing an activated-sludge aeration basin or a diffuser system, because it is measured directly (via a clean-water unsteady-state re-aeration test) and then corrected to field conditions with the α and β factors.

1.2 Biomedical waste. Biomedical (or medical/health-care) waste is waste generated during the diagnosis, treatment or immunization of humans or animals, or during related research, that is contaminated with blood, body fluids or infectious agents, or that is otherwise capable of producing disease. It includes categories such as human anatomical waste, animal waste, microbiology and biotechnology laboratory waste, blood and body-fluid waste, and sharps, and is managed separately from general municipal solid waste because of its infection and injury potential.

1.3 E-waste. Electronic waste (e-waste) is discarded electrical or electronic equipment — computers, monitors, printed circuit boards, cell phones, televisions and similar devices — that has reached the end of its useful life. It is of particular environmental concern because it contains both recoverable valuable materials (gold, copper, rare-earth elements) and hazardous constituents (lead and cadmium in solder and CRTs, mercury in switches and backlights, brominated flame retardants in plastics), so uncontrolled disposal or informal recycling can release these substances to the environment.

1.4 Hazardous waste. A hazardous waste is a waste (solid, liquid or contained gas) that, because of its quantity, concentration or physical, chemical or infectious characteristics, may cause or significantly contribute to an increase in mortality or serious illness, or pose a substantial present or potential hazard to human health or the environment when improperly managed. Regulatory definitions (e.g. under provincial Hazardous Waste Regulations implementing the Canadian Environmental Protection Act) identify a waste as hazardous if it is ignitable, corrosive, reactive or toxic (the "ICRT" characteristics), or if it is specifically listed by source or process.

1.5 β (beta). In the same oxygen-transfer context as K_La above, β is the ratio of the oxygen saturation concentration in the actual wastewater to the oxygen saturation concentration in clean tap water, both measured at the same temperature and pressure: $\beta = C_{s,\text{wastewater}}/C_{s,\text{water}}$. Dissolved solids, surfactants and other constituents in wastewater reduce oxygen solubility, so β is normally less than 1.0 (typically 0.90–0.98) and is applied, alongside the companion α factor (which corrects the transfer rate rather than the saturation concentration), when scaling a clean-water K_La test up to field aeration-system design.