Question 3 of 15: On-Farm Biogas Feedstocks — Four Inputs and Ontario Regulatory Issues

Question 3: On-Farm Biogas Feedstocks — Four Inputs and Ontario Regulatory Issues (8 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.

On-farm anaerobic digesters are almost always fed a blend of feedstocks, because each class of organic input brings a different combination of biogas yield, availability, handling difficulty and regulatory burden. Four distinct inputs, and their Ontario-specific regulatory position, are described below.

1. Livestock manure (dairy/swine slurry, poultry litter). Pros: already collected and handled as a waste stream on the farm, provides continuous year-round supply, and its own microbial population helps seed and buffer the digester. Cons: moderate biogas yield per tonne (much of the readily digestible energy has already passed through the animal), and poultry litter with bedding can be high-solids and ammonia-rich enough to inhibit methanogens if not diluted. Ontario regulatory issues: as an Agricultural Source Material (ASM) generated on the farm's own operation, manure feedstock is governed by the farm's existing Nutrient Management Strategy/Plan under the Nutrient Management Act, 2002 and O. Reg. 267/03 — no additional off-farm approvals are triggered by using it as digester feed.

2. Energy/silage crops and crop residues (corn silage, grass silage, straw). Pros: high volatile-solids content gives a high biogas yield per tonne, and co-digestion with manure balances an otherwise low C:N feedstock. Cons: requires dedicated cropping, harvest and storage (silage pit/bunker), competes with food/feed production for land, and lignified residues such as straw need mechanical or thermal pretreatment to digest effectively. Ontario regulatory issues: generally minimal if grown on the farm's own land (still ASM); purchased silage/residue from another Ontario farm can still be treated as ASM under O. Reg. 267/03 since it remains an agricultural-origin material, but the imported volume should be tracked against the digestate land-application capacity documented in the farm's Nutrient Management Strategy.

3. Off-farm organic wastes (food processing waste, fats/oils/grease, out-of-date food). Pros: very high biogas yield per tonne (especially FOG), and many generators pay a tipping fee to have it accepted, improving digester economics. Cons: variable and unpredictable quality, risk of physical contaminants (packaging, plastics) and inhibitory substances (high salt, antibiotics, disinfectants). Ontario regulatory issues: the largest of the four — receiving off-farm material makes the input a regulated Non-Agricultural Source Material (NASM) under Ontario's Nutrient Management Act, requiring a NASM plan, source characterization/testing, and category-dependent (Category 1–3) approval under O. Reg. 267/03 before receipt and before the resulting digestate can be land-applied.

4. Municipal biosolids / septage. Pros: high, consistent volume from a nearby Ontario municipality, often with a tipping fee, and typically pre-characterized (municipalities routinely test biosolids). Cons: potential for pathogens, heavy metals and emerging contaminants (e.g., PFAS) to concentrate in digestate, requiring careful land-application planning; public perception/odour concerns near receiving farms. Ontario regulatory issues: biosolids/septage are NASM Category 2 or 3 depending on treatment and metal content under O. Reg. 267/03 — the higher categories require more extensive testing, buffer distances and government notification than the lower-risk categories above.