Question 1 of 16: 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 Pyrolysis — thermal decomposition of organic material in the substantial absence of oxygen, converting waste into a combustible gas (syngas), a liquid (bio-oil/tar) and a solid char; because no oxidation occurs, the products retain chemical energy for later recovery.

1.2 Btu — British thermal unit, the quantity of heat needed to raise the temperature of one pound of water by one degree Fahrenheit (≈1,055 J); used in North American practice to express the heating value of refuse or recovered fuel.

1.3 Pathogens — disease-causing microorganisms (bacteria, viruses, protozoa, helminths) present in waste, sludge or leachate that pose a public-health risk and must be controlled or destroyed (e.g., by composting temperature, disinfection) before land application or discharge.

1.4 Vadose zone — the unsaturated zone of soil/rock between the ground surface and the water table, where pore spaces contain both air and water; leachate percolating from a landfill travels through this zone before (if at all) reaching the saturated groundwater below.

1.5 Soil porosity — the fraction of a soil's total volume that is void (pore) space, $n = V_v/V_t$, available to hold air and water; it governs how much moisture a cover or liner soil can store and how readily fluid moves through it.

1.6 Henry's Law — for a dilute solution at equilibrium, the partial pressure of a volatile compound in the gas phase is proportional to its concentration in the liquid phase, $p = H\,C$; used to predict volatilization of organic contaminants from leachate or landfill gas migration into groundwater.

1.7 Wet oxidation — oxidation of organic material suspended or dissolved in water at elevated temperature and pressure using injected air/oxygen, used to destroy organics in sludges or strong liquid wastes (e.g., leachate) without first dewatering the feed.

1.8 Darcy's Law — the empirical relation for laminar flow through a porous medium, $q = -K\dfrac{dh}{dl}$, stating the specific discharge $q$ is proportional to the hydraulic gradient $dh/dl$ through the hydraulic conductivity $K$; it governs leachate seepage through liners, cover soil and native subgrade.

1.9 Breakthrough time — the time required for a contaminant (e.g., leachate) to migrate through a barrier layer of given thickness and hydraulic properties and first appear at the far (downgradient) face; used to check that a liner will outlast the facility's operating/post-closure period.

1.10 Life-cycle analysis — a systematic accounting of the environmental burdens (energy use, emissions, resource consumption) of a product or waste-management option across its full life cycle — raw-material extraction, manufacture, use and end-of-life management — used to compare alternatives (e.g., recycling vs. landfilling a given material) on a common, cradle-to-grave basis.