Questions Linger Over Denver Zoo’s Plan to Convert Trash

Written by journalist Josh Schlossberg and published in the Glendale Cherry Creek Chronicle,  “Questions Linger” examines the soundness of the Denver Zoo’s proposed waste to energy plan.

From the article:

The Denver Zoo is more than halfway through the construction of a first-of-its-kind energy facility to be fueled by elephant manure and trash — including plastic and food scraps — that would provide 20 percent of the Zoo’s electricity, and heat its elephant exhibit.

The self-described “greenest Zoo Poo 3 9-15zoo in the country” is framing its plan to convert millions of pounds of annual waste into an alternative fuel source as an environmental leap forward that will help it achieve its goal of Zero Waste by 2025.

Critics, however, including local residents, the Rocky Mountain Chapter of the Sierra Club, the former director of the American Environmental Health Studies Project, and a U.S. Environmental Protection Agency (EPA) scientist, voice concerns ranging from air pollution, undermining of recycling and composting efforts, and environmental justice issues.

The Denver Zoo declined requests by this reporter for a tour, interview, or statement for this article.

Green Light For Green Energy?

The Zoo’s “biomass gasification system” has been 10 years in the making, developed by Zoo staff in partnership with the City and County of Denver, National Renewable Energy Labs, Colorado Department of Public Health and Environment (CDPHE), Colorado School of Mines, and University of Colorado.

The facility, which is 50 to 75 percent installed, according to minutes from a June 3, 2015, Denver Zoological Foundation meeting, is located in the Toyota Elephant Passage Exhibit on the Zoo’s southern boundary, adjacent to Duck Lake in City Park.

The project has undergone technical review by CDPHE and the City Council, received its construction permit, and is awaiting approval for an air permit. The State also issued water quality and sewer use permits, though a wastewater permit will not be granted until the facility is operational and liquid waste can be analyzed for potential contaminants.

Fuel To The Fire

The Denver Zoo gasifier will source its fuel from 750,000 pounds of elephant dung per year, along with 3 million pounds of waste from the zoo and outside sources, including: wood chips, food waste, waste paper, biodegradable plastic, non-biodegradable plastic, aluminum and other metals, according to a June 20, 2013, email exchange between EPA and CDPHE. Denver Zoological Foundation minutes state that fuel will be “87-89% biomass depending on the season.”

The materials will be shredded, dried, and converted into pellets and exposed to high temperatures in a low-oxygen environment to create a combustible synthetic gas (syngas), that will be mixed with natural gas to power generators, supplying 20% of the Zoo’s electricity. The leftover heat will run through pipes to heat the Toyota Elephant Passage Exhibit.

The facility is permitted as a controlled partial combustion system, with some aspects of the technology kept from the public as trade secrets. Trash and biomass gasifiers are still in the experimental stages and “not yet proven in commercial applications,” according to the National Renewable Energy Labs.

While the Zoo has avoided the use of the term incinerator, the EPA-funded Combustion Portal defines an OSWI (OtherOLYMPUS DIGITAL CAMERA Solid Waste Incinerator) as “incinerators that due to their small size or other characteristics are not covered under other incinerator air emissions regulations.” The Zoo’s Engineering Design and Operations Plan (EDOP) states that the Zoo will follow the OSWI requirements, while referring to the “incineration (thermal conversion) of waste material.”

The construction permit issued by CDPHE explains that the facility will utilize a thermal oxidizer — which the EPA refers to as a thermal incinerator — for start up and shut down, where excess gas will be combusted in a flare.

Zoo staff will remove tars that build up in the scrubber and send them through the gasifier. Up to 60,000 pounds of ash per year will be a byproduct of operations, which will be landfilled.

The article continues here and questions the veracity of claims by the Zoo that its efforts reflect zero waste principles.