Question 1 of 5: General

Question 1: General (25 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) Definitions (10 marks)

i) GHG emission factor. A conversion factor that translates a measurable activity quantity (e.g. head-days of animals managed, tonnes of manure stored, kilograms of nitrogen applied) into an equivalent mass of greenhouse gas — typically expressed as kg CO₂-equivalent per unit activity. Livestock and manure-management inventories use IPCC Tier default emission factors (e.g. a CH₄ factor per animal per year for enteric fermentation, or an N₂O factor per kilogram of manure-N applied) so that very different physical processes can be summed onto one common GHG-inventory basis.

ii) Sodium adsorption ratio (SAR). A soil/irrigation-water chemistry index quantifying the sodium hazard of an applied water or effluent relative to its calcium and magnesium content, $$SAR = \frac{[\text{Na}^+]}{\sqrt{([\text{Ca}^{2+}]+[\text{Mg}^{2+}])/2}}$$ with all concentrations in meq/L. Repeated land application of liquid manure or lagoon effluent with a high SAR promotes soil sodicity — sodium displaces calcium/magnesium on clay exchange sites, causing clay dispersion that collapses soil structure and sharply reduces infiltration and permeability.

iii) Aeration correction factors: alpha (α) and beta (β). Used to scale a clean-water oxygen-transfer test into the actual performance expected in process wastewater. Alpha is the ratio of the oxygen mass-transfer coefficient in process water to that in clean water, $\alpha = K_La(\text{process})/K_La(\text{clean})$ — surfactants, oils and suspended solids typically depress bubble/surface transfer, so α is usually less than 1. Beta is the corresponding ratio of oxygen saturation concentrations, $\beta = C_s(\text{process})/C_s(\text{clean})$ — dissolved solids lower the saturation DO slightly, so β is typically 0.90–0.97. Both factors are required to size an aeration system (lagoon or activated-sludge basin) so that the standard clean-water oxygen-transfer rating translates into a real field oxygen-transfer rate.

iv) Vegetated filter strips. A planted buffer of grass or other dense vegetation established between a manure-management area (feedlot, storage structure, or field edge) and a receiving watercourse. As overland flow crosses the strip its velocity drops, promoting sedimentation of solids, infiltration of the liquid fraction, and plant/microbial uptake of nutrients — a widely used non-point-source best-management practice for intercepting sediment, nutrients and pathogens before they reach surface water.

v) Agricultural waste management system for livestock waste. The complete, deliberately integrated set of structures and practices an operation uses to collect, convey, store or treat, and ultimately utilize (typically via land application) the manure and process wastewater it generates, so that water and air quality are protected while nutrient value is recovered. Per the NRCS/MWPS-18 convention it is planned as one system with distinct components — production/collection, storage or treatment, transfer, and land utilization — sized and managed together, rather than as unconnected ad hoc facilities.

2) Composting vs. direct land application (5 marks)

Composting advantages: thermophilic temperatures (>55 °C sustained) destroy most pathogens and weed seed; the process reduces manure mass and volume substantially, giving a drier, denser, easier-to-transport and easier-to-store product; the finished compost is largely odour-stabilized and can be land-applied on a flexible schedule rather than during a narrow raw-manure window; and it lowers the risk of the strong methane/odour emissions associated with prolonged anaerobic raw-manure storage. Composting disadvantages: it requires land, turning/aeration equipment, labour and several weeks to months of processing time; a portion of the nitrogen (mainly as ammonia) volatilizes during the thermophilic phase and is lost rather than retained for crop use; a bulking/carbon amendment is often needed (added cost); and the nitrogen that remains is more slowly plant-available than in raw manure, since much of it is now bound in stabilized organic (humic) forms. Direct land application advantages: no processing infrastructure or delay — manure nutrient value, especially readily available ammonium-N, is applied essentially as generated, at lower handling cost. Disadvantages: stronger odour, survival of pathogens and viable weed seed, higher runoff/leaching risk if application timing or setback is poor, and the need for enough storage and suitable land access to hit an appropriate application window (agronomic rate, frozen/saturated-ground restrictions).

3) Sketch: temperature, pH and NH₃-N through the composting phases (5 marks)

Temperature rises through the mesophilic phase (I) as easily degraded compounds are metabolized, then climbs to a thermophilic peak (II, commonly 55–65 °C) once thermotolerant organisms dominate — this is the pathogen- and weed-seed-kill window. As the readily available substrate is exhausted, biological activity and heat generation slow, the pile cools (III) back toward ambient, and a slower maturation/curing phase (IV) stabilizes what remains into humic material. pH follows an inverse-then-recovering pattern: it dips early (I) as mesophilic organisms produce organic acids faster than they are consumed, then rises through the thermophilic peak (II) as protein and urea breakdown releases ammonia (a base), commonly reaching pH 8–9, before settling to a near-neutral to mildly alkaline value by maturation (IV). NH₃-N tracks the thermophilic peak closely — protein/urea mineralization is fastest exactly when microbial activity and pH are both highest, so ammonia generation (and volatilization loss) peaks in phase II/III and declines through maturation as remaining nitrogen is immobilized into stable organic forms or lost to the atmosphere.

4) Earthen waste storage pond risks and mitigation (5 marks)

Risk 1 — seepage and groundwater contamination. An earthen pond relies entirely on its native soil or compacted liner for containment; excess in-situ permeability or liner damage lets manure liquid migrate to groundwater. Mitigation: (a) construct a compacted clay (or synthetic) liner engineered to a specified maximum hydraulic conductivity (e.g. ≤1×10^-7 cm/s), verified by geotechnical testing before the pond is put into service; (b) install and routinely sample groundwater monitoring wells around the perimeter to detect any seepage early, before it becomes a larger plume.

Risk 2 — embankment failure or overtopping. Slope instability, erosion, or a storm event exceeding the design freeboard can breach the pond and release a large, uncontrolled slug of manure toward surface water. Mitigation: (a) provide adequate design freeboard plus an engineered emergency spillway sized for the local design storm, with a documented inspection and maintenance schedule for the embankment; (b) construct side slopes to a stable, standard design ratio (commonly 3:1, MWPS-18) with vegetative or riprap erosion protection.

Risk 3 — odour and air emissions. An uncovered pond releases ammonia, hydrogen sulfide and other odorous/greenhouse gases continuously, affecting neighbours and worker safety. Mitigation: (a) site the pond with adequate setback distances from residences and sensitive receptors per local siting regulations; (b) consider a natural crust or an engineered cover to reduce the air/liquid interface available for volatilization.