Question 1 of 6: General

Question 1: General (23 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.

i) Available nitrogen is the fraction of the total nitrogen in a manure or fertilizer source that becomes accessible to a crop's roots within the growing season being planned for — the mineral forms (ammonium, $\text{NH}_4^+$, and nitrate, $\text{NO}_3^-$) already present, plus the share of the organic nitrogen pool that mineralizes during that same season. It is distinguished from total nitrogen, most of which is bound in slowly-decomposing organic compounds and is not available to the current crop; nutrient management plans are written against available, not total, nitrogen.

ii) Indicator organisms are non-pathogenic microorganisms — classically fecal coliforms, E. coli, or enterococci — whose concentration in water, soil, or manure is used as a proxy for the likely presence of enteric pathogens. Direct pathogen assays are slow and expensive; indicator organisms are easy and cheap to culture, and their numbers correlate with the degree of fecal contamination, so regulators set water-quality and land-application standards in terms of indicator counts rather than individual pathogen counts.

iii) Eutrophication is the nutrient enrichment (principally nitrogen and phosphorus) of a water body that stimulates excessive algal or aquatic-plant growth. When that biomass dies and is decomposed by aerobic bacteria, dissolved oxygen in the water column is depleted, degrading habitat for fish and other aquatic life and, in severe cases, producing fish kills and harmful algal blooms.

iv) A vegetative filter strip is a vegetated buffer located between a manure or runoff source area and a receiving watercourse. It slows and spreads concentrated overland flow into sheet flow, promoting infiltration, trapping sediment, and allowing plant/soil uptake and adsorption of nutrients before runoff reaches surface water.

v) An engineered wetland is a constructed treatment system that reproduces the settling, filtration, microbial transformation, and plant-uptake processes of a natural wetland inside an engineered basin or series of cells, used to polish agricultural wastewater, milkhouse washwater, or contaminated runoff before it is discharged or reused.

2) Three steps of anaerobic oxidation of agricultural wastes. (i) Hydrolysis: extracellular enzymes secreted by fermentative bacteria break the complex polymers in the waste — carbohydrates, proteins, and lipids — down into soluble monomers and oligomers (sugars, amino acids, fatty acids) that can cross the cell membrane. (ii) Acidogenesis and acetogenesis: fermentative bacteria convert those monomers to volatile fatty acids, alcohols, hydrogen, and carbon dioxide (acidogenesis); acetogenic bacteria then convert the longer-chain VFAs and alcohols to acetate, hydrogen, and carbon dioxide (acetogenesis), the substrates methanogens require. (iii) Methanogenesis: methanogenic archaea convert acetate (aceticlastic pathway) and hydrogen plus carbon dioxide (hydrogenotrophic pathway) to methane, the terminal step that yields biogas and completes the anaerobic digestion sequence.

3) Anaerobic vs. aerobic for high-strength wastes. Aerobic treatment of a high-BOD waste requires continuously replacing dissolved oxygen at the rate the microorganisms consume it; because oxygen's solubility in water is low, this demands very large aeration energy input as the waste strength rises, and the aeration itself strips little of the organic load without that energy. Anaerobic treatment needs no oxygen supply at all, so its energy cost does not scale with waste strength the same way; it also converts a large share of the organic matter directly to biogas (methane) rather than to new bacterial cell mass, so it produces far less excess sludge to handle and dispose of, and the biogas is itself a usable energy product rather than a cost. These combined effects — no aeration energy, an energy co-product, and less sludge — make anaerobic treatment the more economical choice once waste strength is high enough that aerobic aeration costs become prohibitive.

4) Air emissions from land-applied manure. Short-term (during and shortly after application): ammonia ($\text{NH}_3$) volatilization from the freshly exposed manure surface, which is both the dominant nitrogen-loss pathway and the main source of the associated odour, plus some volatile organic compound (VOC) release contributing to the immediate odour plume. Long-term: nitrous oxide ($\text{N}_2\text{O}$), a potent greenhouse gas generated by nitrification/denitrification of the nitrogen that infiltrates the soil, and methane ($\text{CH}_4$) where anaerobic microsites persist in wet or compacted soil; secondary fine-particulate ($\text{PM}_{2.5}$) formation also occurs downwind as atmospheric ammonia reacts with acidic pollutants over the following days.

5) General waste management system, 1,000-cow dairy farm. The system runs production → collection → storage → (treatment) → utilization → crop uptake, shown in the figure below.

Production (the barn) is where manure and urine are generated continuously by the herd; its main concern is in-barn odour and ammonia release affecting worker/animal health. Collection (scraping or flushing to a reception pit) removes the waste from the animal environment on a regular cycle; poor collection frequency lets emissions and pathogen loads build up. Storage (a tank or lagoon sized for the region's land-application timing, typically several months to a year in a cold climate) provides the flexibility to apply manure only when agronomically and environmentally appropriate; its concerns are continued odour/ammonia emission from the exposed surface and the risk of seepage or a structural failure contaminating groundwater if the structure is not lined, covered, or properly maintained. An optional treatment step (solids separation, composting) reduces volume, stabilizes the material, and can produce a marketable soil amendment. Utilization (land application under a nutrient management plan) is where the nutrients are returned to crop uptake; its concern is nutrient loss — runoff to surface water or leaching to groundwater — if application rate, timing, or setback distances are not matched to agronomic need and site conditions.