Engineers Canada Agricultural / Biosystems / Bioresource / Food Engineering examination syllabus Agricultural Waste Management & Environmental Engineering: practice questions

1 · Wastewater characteristics: BOD and COD · hard

Lactose, the main sugar in whey, oxidises as C12H22O11 + 12 O2 → 12 CO2 + 11 H2O. Its theoretical oxygen demand (molar mass 342 g/mol) is:

1. 0.89 g O2 per g lactose
2. 1.12 g O2 per g lactose
3. 1.54 g O2 per g lactose
4. 1.07 g O2 per g lactose

2 · Wastewater characteristics: BOD and COD · medium

A food plant sends 750 kg of BOD5 per day to treatment. Taking the domestic contribution as 60 g BOD5 per person per day (this figure differs between countries and texts), its population equivalent is:

1. 45,000 persons
2. 125,000 persons
3. 1,250 persons
4. 12,500 persons

3 · Basics of wastewater treatment · hard

An activated sludge plant treating sugar-rich food wastewater develops an SVI above 250 mL/g with a cloudy, slow-settling sludge. Which combination is most likely to cause this?

1. Very high dissolved oxygen together with a short sludge age of one day
2. Over-wasting of sludge that lowered the MLSS well below the design value
3. Excess nitrogen and phosphorus added at well above the BOD:N:P need
4. Filamentous growth favoured by low dissolved oxygen and nutrient shortage

4 · Composting · easy

A compost mix of poultry manure and little bedding has a starting C:N of 10:1. The most likely problem is:

1. Loss of nitrogen as ammonia and strong odour
2. Temperatures that never rise above ambient
3. Excess carbon locked up as stable humus
4. Very slow decomposition from nitrogen shortage

5 · Composting · medium

Which observation best indicates that compost has become stable and mature?

1. A C:N ratio that has risen well above that of the starting mix
2. Low respiration rate and no reheating after the pile is turned
3. A core temperature that rises again to 60 °C after turning
4. A strong ammonia smell when the pile is opened and turned

6 · Manure handling systems · easy

In standard methods for manure analysis, total solids and volatile solids are determined by heating the sample at, respectively:

1. 60 °C for one hour, then 900 °C for six hours
2. 550 °C first, then 103–105 °C to constant mass
3. 20 °C for five days, then 150 °C under reflux
4. 103–105 °C to constant mass, then 550 °C

7 · Basics of wastewater treatment · hard

For an activated sludge plant treating dairy wastewater, the operator increases the sludge wasting rate so that SRT falls from 20 days to 3 days. The most likely consequence is:

1. Loss of nitrification, since nitrifiers wash out at short SRT
2. Better nitrification, since nitrifiers grow faster than heterotrophs
3. Lower F/M, since more biomass is kept in the system
4. Less surplus sludge, since shorter SRT reduces cell yield

8 · Composting · hard

In forced-aeration composting, the airflow needed to remove heat and hold temperature is far greater than that needed to supply oxygen for decomposition. The design consequence is that:

1. Moisture is gained as air passes, so the pile needs no water management
2. Aeration fans are sized from the stoichiometric oxygen demand of the feedstock alone
3. Aeration is controlled by temperature feedback rather than oxygen demand alone
4. Aeration should be stopped once the pile reaches 70 °C to save energy

9 · Manure handling systems · hard

A slurry has 8% total solids, 2.0 kg/m³ of P and 4.0 kg/m³ of ammonium-N. A separator captures 60% of solids, 50% of P and 10% of ammonium in the solid fraction. For the liquid fraction, the ratio of ammonium-N to P compared with the raw slurry is:

1. 0.6 times higher
2. 1.0 times higher
3. 1.8 times higher
4. 3.6 times higher

10 · Wastewater characteristics: BOD and COD · hard

A seeded BOD test gives these data: sample bottle DO drop 5.0 mg/L with 10 mL sample and 2 mL seed in 300 mL; seed control DO drop 4.0 mg/L with 10 mL seed in 300 mL. The BOD5 of the sample is:

1. -450 mg/L
2. 150 mg/L
3. 30 mg/L
4. 126 mg/L