52    ANAEROBIC COMPOSTING OF YARD WASTE WITH
METHANE GAS RECOVERY
Riley N. Kinman, Professor
Department of Civil and Environmental Engineering
University of Cincinnati
Cincinnati, Ohio 45221
David L. Nutini, General Manager
RNK Environmental, Inc.
Covington, Kentucky 41017
INTRODUCTION
Yard waste will be excluded from landfills in Ohio by December, 1993. Many other states have
proposed or have already banned yard waste from landfills. One alternative waste handling method
for treatment of this type of waste is composting. This study took this concept one step further
because of the facilities available at a landfill in Ohio. A pilot anaerobic compost system was set-up at
the landfill with an existing gas recovery plant.
The objectives of this study were to plan, construct and coordinate the operation of an anaerobic
compost pilot plant with methane gas recovery. Gas data were determined. Length of composting
under these conditions was determined. Quality and use of the compost was determined.
METHODS AND MATERIALS
The first task of the project was to develop a work plan incorporating the collection, handling,
preprocessing, composting, curing and final use of the composted material. Other general considerations were for a gas collection and monitoring system, training of staff at the landfill, permitting and
marketing the compost.
The original plan called for the collection of leaves, grass clippings and brush from several communities in the area. A color bag system would be used where the residents would purchase the bag for
a fee ($.50). The bag would be set out at curbside to be picked up by a special truck for compost
collection. The fee charged in the pilot would be evaluated to determine economic feasibility of this
type of collection system full-scale. Residents would be surveyed randomly to determine their attitudes and comments of using such a collection system. (This part of the plan changed and will be
discussed in the Results and Discussion).
Once the trucks reached the landfills the waste was weighed to determine the mix ratios with the
amount of sludge (municipal sewage sludge, paper sludge, etc.) that was added to make up the
compost mixture. 12% sewage sludge was added to the yard waste to seed the compost pile with
microorganisms and increase the gas production process.
Samples of yard waste and sludge were taken and analyzed for moisture content, organic content,
nutrients, heavy metals, pesticides and herbicides.
The compost cell was built before the acceptance of any waste. This consisted of a clay-diked area
designed to handle 1000 tons of material. Subcells were to be built until the complete cell was
constructed (Figure 1 and 2). For this paper, only the construction of the first subcell will be discussed.
This consisted of an 18 ft x 40 ft x 8 deep pile of material placed at one end of the main cell. The
material to be composted consisted of leaves (55 tons) and sewage sludge (10 tons). The leaves were
dumped into the cell. When enough had been accumulated the sludge was brought in to be mixed with
the leaves. Using a large backhoe, the leaves were shaped into a U-shaped bowl. The sludge truck
pulled up to the open end of the bowl and dumped the sludge into it. The backhoe worked the sludge
and leaves until they were thoroughly mixed. Composite samples were taken of each waste type before
mixing and after mixing to determine moisture content of the mix primarily. The pile was shaped to
the dimensions given above. Then the pile was compacted using the shovel head of the backhoe. The
47th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 48118.
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