Using anaerobic digesters for highly contaminated waste streams like municipal solid waste is very problematic, since the resulting product cannot be clean enough to be useful. Using expensive methods like in-vessel composting or digestion to handle municipal solid waste causes the owners to seek to find markets for the resulting "compost." In fact, most municipal solid waste composting projects have a hard time finding a market for their "compost" product and end up giving the "compost" away to farmers, using it on public works projects or as landfill cover.

Below are 2 article from December 2004 about an attempt to use digesters to process municipal solid waste in northcentral Pennsylvania.

Scientists test organic waste technology

Trash may soon become treasure. University researchers are testing several technologies they hope will transform waste into useful byproducts like fertilizer and methane gas.

Associated Press

WILLIAMSPORT, Pa. -- Lycoming County officials and scientists are testing technology they hope will turn organic waste into profitable byproducts.

One of the technologies, a metal tank called a Drygester, is designed to break down organic waste anaerobically -- without oxygen. Manufactured by Young Industries in Muncy, it is one of six systems Bucknell and Vanderbilt University researchers are testing in conjunction with county engineer Michael D. Hnatin.

The tests will determine which system will be used in the landfill's pilot program. The plant would biodegrade up to 30 tons of municipal solid waste per day that previously would have been buried in the landfill.

Byproducts would include methane gas, usable for fuel, and a type of fertilizer.

Hnatin said the process is similar to what occurs naturally in the landfill as organic material decomposes deep within the mounds of garbage. However, the natural process requires 20 to 30 years; a Drygester-type system should take about 20 to 30 days.

The landfill plans to submit a permit application for the pilot plant to the state Department of Environmental Protection by April, Hnatin said. It will cost the landfill roughly $3 million to $5 million to build the pilot plant, he said.

The Drygester prototype processes only 15 pounds of waste daily but the digestion tank planned for the pilot plant could process up to 30 tons a day, Hnatin said.

Officials estimate the county's landfill will be full and will have to close by mid-2011. Anaerobic processing would increase the its life as much as 10 percent by reducing the amount of waste buried there, Hnatin said.

The project is part of the county commissioners' Green Technology Initiatives.

Story produced by Laureen Ricks

Source: http://iml.jou.ufl.edu/newszine/tech/2.htm

Meet the 'Drygester'

Pilot project at landfill uses innovative system to convert raw garbage into energy, fertilizer

Sandra M. Huff

Sun-Gazette Staff

Officials hope a metal tank that sits in one of the county landfill's warehouses will help convert up to 75 percent of the landfill's organic waste into money some day.

The tank is referred to as the "Drygester" and is designed to digest organic waste "anaerobically" ­ without oxygen. Manufactured by Young Industries in Muncy, the Drygester is one of six systems being tested by researchers at Bucknell and Vanderbilt University in conjunction with Lycoming County Resource Management Services engineer Michael D. Hnatin.

The tests will determine which system will be used in the landfill's future pilot plant to provide an alternative way of breaking down waste.

The plant would be the first of its kind in the country and would biodegrade up to 30 tons of municipal solid waste per day, waste that previously would have been buried in the landfill. Among the byproducts will be methane gas, usable for fuel, and "soil conditioners" ­ a sort of fertilizer.

Hnatin said the anaerobic digestion process imitates what occurs naturally in the landfill as organic material decomposes deep within the mounds of garbage. However the natural process requires 20 to 30 years, whereas a Drygester-type system should take about 20 to 30 days. Hnatin said that's because the waste will be digested in an airtight container under controlled conditions.

Hnatin said the landfill plans to submit a permit application for the pilot plant to the Department of Environmental Protection by April 2005. Approval is expected by 2006, and construction of the pilot plant should take about two years. Hnatin said its efficiency will then be monitored for two years to determine whether a larger plant should be built.

The Drygester only processes 15 pounds of waste a day, but the digestion tank planned for the pilot plant will be able to process up to 30 tons a day, Hnatin said.

It will cost the landfill roughly $3 million to $5 million to build the pilot plant, Hnatin said.

Hnatin said several facilities in Europe have been using the process of anaerobic digestion for years, but America has yet to implement what he called a money-saving, energy-efficient method of dealing with its garbage.

"The analogy we like to use is that it's like a waste-water plant," Hnatin said.

He explained that anaerobic digestion can replace landfills just like the outhouses of the past became obsolete when modern sewer systems were introduced.

So far the landfill has received $157,000 in grant money for the project from the state Department of Environmental Protection.

Officials estimate the landfill can operate until mid-way through 2011. At that point it will have reached its limit it will need to close.

Anaerobic processing, however, will increase the longevity of the landfill by up to 10 percent by cutting down on the amount of waste buried there, Hnatin said.

The process will also increase the amount of materials recycled. Hnatin said that one of steps in the process screens out recyclable goods that can then be sent to the landfill's recycling facility.

Increasing the longevity of the landfill eases the burden on taxpayers, who will have to dole out funds to maintain it when it closes.

Hnatin said that municipalities are required to maintain a landfill for 30 years after it closes, at an average cost of about $8,000 a year.

"No one likes a landfill in their back yard, and they're expensive to keep up," Hnatin said. "(Anaerobic digestion) makes it into a process, not a liability for our kids and grandkids."

Hnatin said the methane produced by anaerobic processing can be sold to power plants. Also produced is a substance that Hnatin said looks like potting soil and has an "earthy smell."

The substance is "soil amendment" or "soil conditioners," and can be sold commercially.

Hnatin also said the landfill is working with two corporations within the state on the possibility of producing liquefied natural gas from the process.

He said if the 26,000 other landfills in America followed in the county landfill's footsteps with anaerobic digestion, it would make the nation less dependent on foreign energy providers.

The project is part of the county commissioners' Green Technology Initiatives.

Section: News

Date Posted: 12/5/2004

As appearing in Sunday - December 5, 2004 edition of The Sun-Gazette