Carbonizing NYC's wood waste streams
NYC produces many waste streams - mixed municipal waste that Department of Sanitation picks up from homes and institutions, and what commercial haulers pick up from private businesses.
How much waste does NYC generate? NYC Department of Sanitation handles about 12,000 tons of waste a day, about 50% of the City's total waste, from residential and institutional sources. Private haulers take the other half, from commercial waste sources. Altogether, Sanitation reports that NYC generates around 14 million tons of waste per year.
Sewage biosolids, at 1,400 tons per day times 365, adds up to roughly 5,111,000 tons per year. Of the other organic waste streams, the top candidate for carbonization is wood waste.
Some date for wood waste is found in the NYC Department of Sanitation's 2013 Waste Characterization Study, which found that City produces 3.3 million tons of curbside waste annually. (P. 9)
Wood discarded through construction and demolition, which has been chemically treated or contaminated, makes up 1.3% of that total, for 42,000 tons per year. Untreated lumber, such as pallets and crates, makes up 0.8%, for 26,000 tons per year. (Page 24.)
Additionally, personal communications with NYC Parks Department staff suggests that it produces about 35,000 - 70,000 cubic yards of wood chips annually. Wood chips weigh about 500 pounds, or 0.25 tons, per cubic yard, so add another 8,750 to 17,500 tons of wood chips. It’s said that Con Edison has its own supply of wood waste from tree trimming.
Biochar made from sewage biosolids alone is reportedly 20% carbon, with the remainder being ash. Mixing high-carbon materials like wood waste to sewage biosolids would yield end products that are higher in carbon, and probably, more commercially valuable.
Paper, Cardboard, Yard Waste, and Food Scraps
Ideally, all these waste streams can be recycled or composted. If they had already been collected, and could not be processed, they could be carbonized. This might be the case at times when paper and cardboard could no longer be sold for a profit, or if there wasn't enough capacity to compost yard waste or food scraps.
18% of the City’s waste stream is clean paper and cardboard. The fractions targeted for composting add up to a whopping 31%. 18% is food scraps, 7% is food soiled paper, and 6% is yard waste.
The biggest obstacle to collecting these waste streams, which depend on millions of individual choices, is cultural. It's normal for people to throw away recyclable wastes, and changing personal habits will be difficult. It will be vastly easier for the City to redirect large centralized waste streams like sewage biosolids and wood waste.
Planned expansion of the City’s voluntary food waste composting has been put on hold. New Yorkers are still putting most organic waste in the trash, and buy-in to the Organics program has been slow. In 2018 only 5% of food waste was composted, quite a way to the 90% composting goal.