Plastic Bags - Embodied Energy & Carbon

As follow up to my question about the footprint and energetics of plastic bags, here is a crude estimate of embodied energy and carbon for polyethylene bags similar to ones used at produce stands and butcher shops (i.e., about 10 inches by 10 inches). Embodied energy is the total primary energy consumed during the life time of a product. Ideally the boundaries would be set from the extraction of raw materials (inc fuels) to the end of the products lifetime (including energy from; manufacturing, transport, energy to manufacture capital equipment, heating & lighting of factory...etc), this boundary condition is known as Cradle to Grave. The figures here are from the University of Bath (http://www.bath.ac.uk/mech-eng/sert/embodied/) and specify only the embodied energy as Cradle to Gate, which includes all energy (in primary form) until the product leaves the factory gate. The final boundary condition is Cradle to Site (not available), which includes all energy consumed until the product has reached the point of use (i.e. building site).This analysis is based on plastics manufactured in Europe and may differ when similar figures are calculated for Canadian product. Note: this calculation considers the use of these bags a liners for garbage bins in an office building. It assumes that only 75% of the bins are using bag liners, and of that, they are changed 4 days of every 5-day week. Also, due to vacation time, any one bin only operates 48 weeks of a year.  Current number of garbage receptacles: approximately 450 Estimated number of plastic bags used per week/year: 450 * 0.75 = 338 bags; * 4 days (of 5 per week) = 1352 bags/ week; * 48 weeks/year = 64,896 bags per year. One bag represents: approximately 4.3 grams of low density polyethylene (LDPE). There are roughly 233 of these bags in one kilogram. A preliminary analysis from University of Bath in the UK suggests the following for 1Kg of LDPE: * Embodied energy*: 78.1 megajoules (energy in the feedstock alone is about 51.6 MJ/Kg) * 1.7 Kg of carbon dioxide are emitted in the same process To put these bags into perspective consider a comparison with a barrel of diesel fuel (159 litres or 135.2 Kg): * When burnt, 1 Kg of diesel releases 40.9 MJ * Burn a barrel (bbl) of diesel and you release approximately 6,503 MJ of energy * 31, 442 of our little bags weigh roughly 135.2 Kg, or about the same as one barrel of diesel * Cradle to Gate embodied energy of 135.2 Kg of LDPE is approximately 10,559 MJ, or about the same as burning 1.624 barrels of diesel * Estimated Richmond consumption of 64,896 bags per year amounts to about 279 Kg of LDPE annually, which would embody about 21,794 MJ of energy * The embodied energy for our annual consumption of bags is roughly the same as burning 3.35 bbl of diesel * This energy equates with generation of roughly 474.3 Kg of carbon dioxide * Considered over ten years, this would total roughly 4,750 Kg of CO2 and 33 barrels of diesel fuel burned .

Cheers,
Neil