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Organic Wastes Are Energy-Rich Resources: Towards A New Era of Productive Alchemy

By: Kendall Christiansen

June 30, 2014

Prediction: by 2020, New York City's wastewater treatment facilities could produce biogas to heat and power their own operations, power some of the agency's fleet, and provide biogas to Con Ed and National Grid pipelines. In addition to the economic benefits, less trash shipped to distant landfills and waste-to-energy facilities reduces truck miles, greenhouse gas emissions from landfills, and creates carbon-positive benefits — all of which are goals of PlaNYC/2030.

How will that prediction be achieved? It's not crystal ball-gazing to see a combination of upgraded and expanded facilities, capable of accepting new sources of materials, or "feedstock" for their anaerobic digesters, complementing the energy potential already present in the city's sewage sludge. Kathryn Garcia, the new Commissioner of Sanitation, notes that digesters love "diner food" — clean, energy-rich, and maybe a little too much fat. But what is anaerobic digestion?[1])

Yes, there are lots of moving parts, but the pieces are lining up to make the City's bio-energy future a reality, and attract partnerships with private-sector companies are expert in managing digesters.

Case in point:

The New York City Department of Environmental Protection (DEP) is investing $175 million in construction of a new cogeneration plan at the North River Wastewater Treatment Plant to produce renewable biogas from its anaerobic digesters, providing on-site energy for equipment power and heat, greatly reducing grid-based energy use and greenhouse gas emissions.

Case in point:

Ohio-based Quasar Energy is both developing "merchant" anaerobic digesters and partnering with cities like Wooster Ohio to expand, upgrade and operate their digesters, taking in additional feedstocks to complement energy-rich sewage sludge; it recently opened two digesters near Buffalo, NY.

In New York, those new feedstocks will likely come as a result of Local Law 146 of 2013 — which targets the largest generators of organic waste to be the first to divert organic wastes to beneficial use — either composting or anaerobic digestion instead of sending it to distant landfills; this NYC statute parallels similar laws and regulations taking effect in Connecticut, Vermont and Massachusetts, with more to follow. This means as much as one-third of the City's commercial and industrial waste stream is organics — principally food waste — amounting to thousands of tons per day, could be re-directed to make compost and biogas, if properly managed and if infrastructure is made available locally, rather than outside of the region.

Today, the systems to make all of that work are not yet in place, but elements of it are being tested.

Case in point:

At DEP's flagship Newtown Creek plant — which just completed a $5 billion expansion/upgrade — small amounts of contaminant-free food waste (such as collected at the city's green markets) are delivered to its digesters after it is processed into a slurry by Waste Management in East Williamsburg; plans are to bring that slurry-making capacity on-site to the plant, and expand its capacity beyond the pilot phase to as much as 500 tons per day.

Other means of converting food scraps into digester-ready slurry also are possible; InSinkErator (for which I am a consultant) — the world's leading manufacturer of food waste processing systems — developed Grind2Energy, an on-site system for installation at hotels, campuses, arenas, and food markets to produce clean, contaminant-free digester-ready feedstock as efficiently as possible. [As a general rule, organics collected at curbside from residences will not be suitable for "wet" anaerobic digesters because of the presence of yard waste, and non-organic contaminants. Instead those resources will be directed to conventional compost facilities capable of working with that mix, and screening contaminants out of finished compost.]

What New York City is doing mirrors larger trends in the newly-emerging field of organics management. What used to be the "pollution control" and "sewage treatment" industry is rapidly morphing into the "water resource recovery" field, with new-found focus on the energy potential and nutrient processing opportunities of organics conveyed via sewers and trucks.

The operative theme is clear; there is a transformational shift from disposal to production and it's happening now. Embrace it.

"About 15 wastewater treatment facilities in the U.S. are engaged in this practice — a small number, but that's up from one or two about a decade ago, according to the American Biogas Council," notes Rachel Cernansky in her recent Yale Environment 360 article. Most comes from commercial and industrial sources, including fats, oils and greases, and airport de-icing liquids.

Case in point:

The Massachusetts Water Resource Authority commissioned a partnership of Waste Management and Save That Stuff (a Boston recycler) to prepare and deliver slurried commercial food scraps by barge from Boston to its Deer Island resource recovery plant.

MWRA Deer Island
Photo: MWRA Deer Island Digester Eggs

Other approaches are being tested: so-called "dry" digesters capable of handling a mix of yard wastes and food scraps recently began operations in San Jose, and Monterey, California and Vancouver, British Columbia. In these cases, the goal is to produce some biogas as an initial step in the production of compost products.

In Europe this resource-not-waste approach to processing all wastes at least once before disposing of residuals is known as "mechanical biological treatment" or MBT; the goal is to recover as much recyclable material as possible, and create energy and soil products from the organics fraction.

But back to New York City: one result of this new collaboration between DEP, the Sanitation Department and commercial waste management companies will be that more of the city's wastes can be processed locally into resources — with both the energy produced used locally, and potentially some portion of what's left composted afterwards. Redirecting collection trucks from existing transfer stations to new locations, including to some of DEP's operations, may create some related impact concerns.

And all of this takes us back to the future: in London in the 1800's, sewage gas lit the city's streetlights — one still exists, behind the Savoy Hotel on Carting Lane (sometimes known as "Farting Lane"); Paris' infamous sewers replaced the "night soil" industry that transported human waste by horse-drawn carts to farms in the surrounding region, to grow vegetables for Parisians to enjoy.

A very dynamic period of handling organic wastes as a resource is approaching at warp-speed; stay tuned for more.

Anaerobic digestion is a series of biological processes in which microorganisms break down biodegradable material in the absence of oxygen. One product is biogas, which is combusted to generate electricity and heat, or can be processed into renewable natural gas and transportation fuels. Remaining solids can be composted, utilized for dairy bedding, directly applied to cropland or converted into other products. Nutrients in the liquid stream are used in agriculture as fertilizer.

Kendall Christiansen is the principal of Gaia Strategies, and senior consultant to InSinkErator, leading its public affairs work across the US and Canada; he was founding Assistant Director of NYC's recycling system, chaired the Citywide Recycling Advisory Board, and worked in/around NYC's waste/recycling sector for many years.

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