18-Env-B6 Agricultural Waste Management · May 2018
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams, May 2018 — 04-Env-B6, Agricultural Waste Management (3 hours, open book, all 16 questions to be attempted, 100 marks total).
Reference texts: Rynk et al., On-Farm Composting Handbook (NRAES-54); OMAFRA, Nutrient Management Act, 2002 and O. Reg. 267/03 / Nutrient Management Protocol (NMAN); Metcalf & Eddy, Wastewater Engineering (anaerobic digestion chapter); ASABE Standards (manure storage, land application equipment); Ontario Environmental Protection Act and Ontario Water Resources Act; Canada–Ontario Lake Erie Action Plan / Great Lakes Water Quality Agreement Annex 4.
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.
Drywall's core is calcium sulphate (gypsum, CaSO₄·2H₂O), and while gypsum itself has legitimate agricultural uses (a soil amendment, a bedding additive for moisture absorption), several discussion points are essential before adopting ground drywall specifically as bedding:
Sulphate reduction to hydrogen sulphide. Under the anaerobic conditions that develop in manure storage, sulphate-reducing bacteria convert the gypsum's sulphate to H₂S — adding a bedding material rich in sulphate directly increases the H₂S generation potential of the stored manure, compounding the gas hazards already discussed in Questions 11 and 13. This is the single most important safety discussion point.
Source and contaminant screening. Ground drywall from construction/demolition (C&D) waste can carry paint, adhesives, joint compound, screws/staples, and occasionally older material with contaminants not present in virgin gypsum bedding products — the farmer needs to know the material's provenance and whether it has been screened for physical and chemical contaminants before it goes anywhere near livestock or a manure system that will later be land-applied.
Particle size and dust/absorbency performance. Bedding-grade gypsum is processed to a controlled particle size for good moisture absorption and low airborne dust; construction-waste-derived ground drywall may not meet either specification, risking poor cow comfort/absorbency or a respiratory dust hazard for animals and workers.
Downstream nutrient/sulphur management. Elevated sulphate in land-applied manure affects soil chemistry (can influence micronutrient availability and, at high loading, soil structure) and should be accounted for in the farm's Nutrient Management Strategy alongside N/P/K, not just accepted as an inert bedding material.
Regulatory classification. If the drywall is sourced off-farm as a waste material, it is a Non-Agricultural Source Material (NASM) under Ontario's Nutrient Management Act framework once it enters the manure system, triggering the same testing/approval requirements discussed for off-farm digester feedstocks (Question 3).
