DRC Food Waste Compost Plan

Gustavus Disposal & Recycling Center

Food Waste Composting
Operational Plan

Paul Berry, Gustavus DRC Manager/ Operator
May, 2005

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Sections:
Purpose and need
Facility
Process description
Composting challenges and solutions
Site diagram

 

Purpose and need

Since 1996 the DRC has operated a food waste composting program for the community’s waste stream. The purposes are to conserve landfill space, promote recycling, reduce bear and people conflicts, provide a low cost soil amendment to Gustavus residents, and improve the working conditions for the DRC's waste baling program. The food waste composting program is not without its challenges and has required much effort on the part of the DRC staff and the DRC Committee.

The organic, liquid nature of food waste presents a challenge to landfill operators. Food waste cannot be compressed and baled like other wastes because the liquid is squeezed out of the bales during compression and the natural decaying process makes it very unpleasant. Direct burial of food waste is extremely wasteful of landfill space and would significantly reduce the lifespan of our facility. Future odor problems could also occur from the presence of many tons of putrefied food waste buried within the landfill. A more optimum treatment method is aerobic composting. Aerobic composting produces temperatures over 140 degrees Fahrenheit, which helps to sanitize the food waste as well as reduce its volume. A further advantage of aerobic composting is the production of a marketable garden compost. Sale of compost is used to help offset the program’s cost.

Food waste composted by the DRC in the previous two years (pounds).
 

Compost produced during the past 2 years is approximately 15 - 20 yards per year. Assuming a value of $72 per yard, this represents a marketable value of $1,080 - $1,440 annually.

Funding of the operational costs associated with the food waste composting program are through user fees and the sale of compost. Funding of the capital costs associated with the food waste composting program are through Federal, local and private grants.

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Facility

The composting yard is a raised and leveled 110' x 60' (6600 sq ft) area adjacent to the original landfill. It is enclosed within an eight foot high chain link fence. There are 4 runs of high voltage (~10,000 volt) electric wire fastened to the outside of the fence. The horizontal runs of this wire are spaced from eight inches to six feet above grade. Access to the yard is through a 12' wide gate. When the DRC is unattended the gate is locked and fence is electrified. There are warning signs along the fence to warn the public. The original landfill enclosure is electrified as well.

Inside the composting area is the mixing station, a Quonset for indoor windrow composting, an outdoor windrow composting area as well as areas for wood chip and finished compost storage.

Mixing station:
 

The mixing station is a 16' x 16' 4” uncovered concrete pad with two inch thick reinforced back wood wall 40” high attached to 6” x 6” vertical supports.

Quonset:
 

The Quonset is 48' long x 30' wide x 16' high with 4' 2” pony walls anchored every 8' with 6” x 6” treated spruce wood posts set four feet in the gravel pad. The four corner posts are set in concrete. The cover is a 10 mil woven poly fabric over a 14 guage galvanized tubular frame. Wooden end walls with bird mesh over any openings. It is naturally ventilated. The ends are open at this time though doors may be added later.

Compost screener:
 

Screen USA Trom 406 trommel screener with 1/2” mesh screen. When possible screener is located within compost yard. If additional outdoor windrow space is required during the peak season, the screener is moved to an alternate area, outside the compost yard.

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Process description

Customer delivery:
 

Gustavus residents and businesses deliver their food waste to the DRC, typically in 5 gallon buckets or larger containers. Food waste is weighed and placed into the Bobcat dumping hopper (model 25, 2.5 yard capacity). If the food waste is not to be processed that day, the food waste is covered by 1/3rd to 2/3rd yard of wood chips to keep flies and odors controlled. The dumping hopper is covered by a lid to keep birds, rain and snow out of the hopper. The DRC operator moves the hopper into the fenced composting yard where actual compost operations take place.

Mixing with bulking agents and other amendments:
 

Food waste is mixed with bulking agents and other amendments every two or three weeks in winter, but three times a week during the peak summer season. Mixing is done at our mixing station. Our primary bulking agent is wood chips and our common amendments are grass clippings and/ or horse manure depending upon availability. The amendments are included to increase the amount of nitrogen available to the bacteria during composting process, which improves the compost’s value as a garden additive.

The Bobcat operator mixes the food waste with wood chips and amendments, in a ratio of one part food waste to two parts wood chips and amendments. When it is thoroughly mixed the operator transports the mix in the bucket to the windrow area for composting.

Outdoor windrow composting method:
 

The food waste and wood chip mixture is composted using the windrow method. At present all windrowing is done outdoors in the composting area. Windrows are approximately 20' long and 8' wide at the base and 4' – 4 ½' tall. Each windrow is built upon a 2” - 4” thick base of wood chips. One or two lengths of 20' perforated pipe four inch SDR 11 HPDE pipe are set on top of the base for passive aeration. Once all the food waste and wood chip mixture is placed on the windrow, the windrow is capped with 2” - 4” of wood chips to control odor and flies. Then the windrow is covered with Compostex covers, which allow carbon dioxide to escape oxygen to enter, and which shed rain. These covers assure the windrow will remain aerobic. Finally a bird barrier is placed around the base and atop the windrow to keep ravens, crows and other birds from scavenging and disturbing the windrow.

Planned indoor windrow method:
 

We intend to begin using the new Quonset structure this summer to allow the compost windrows to be constructed under cover throughout the year, but expect some overflow to uncovered areas during the heavy summer season. The windrows will be 10' – 15' wide at the base, 20' long and 5' – 8' high. There will be two runs of aeration pipe under each windrow. The windrows will be actively ventilated using a Green Mt Technologies Modular Aeration Control System (MACS 100S-P). Windrows will have negative aeration where air is drawn into the windrow, through the MACS blower assembly and exhausted through a bio-filter. The aeration blower has a temperature probe placed in the windrow. The blower is programmable, typically the blower turns on once the windrows exceed 140 degrees Fahrenheit and run for a minimum amount of time. The Bio-filter assembly consists of a 20' section of 4” perforated pipe similar to windrows along the base of a 20' long x 5' wide pile of wood chips, finished compost and lime.

Compost windrows typically sit for 3 – 4 weeks before they are turned or screened. Determination of compost maturity is through temperature measurements. Temperatures below 80 degrees Fahrenheit indicate the compost is ready for final screening. After final screening the compost matures for an additional month or more before sale.

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Composting challenges and solutions

Birds
 

Birds are naturally attracted to food waste. Presently the mixing activity is the only activity where food waste is exposed and birds can scavenge. The solution is to minimize the exposure time and get the mixture into the windrow and covered as soon as possible. We also use mesh screening on outdoor windrows and composting within the Quonset whenever possible to minimize scavenging by birds during windrowing. We intend to control bird scavenging during the mixing process by enclosing the mixing station, in FY 2007.

Rain and snow
 

Excess moisture contributes to anaerobic conditions and resulting smells. Snow and freezing temperatures make working with the windrow covers almost impossible. The Quonset structure should provide ample room for fall and wintertime composting and provide shelter for the Trom 406 screener during the winter.

Bears
 

Bears were historically attracted to the smells associated with the landfill and composting at this site. However, since the installation of an electrified chain link fence, bear intrusion has not been a problem. The DRC operator checks the electrification system daily, and periodically cuts vegetation around the wires to ensure the proper operation of the electric fence at all times.

Odor
 

Aerobic composting typically has a mild odor that is effectively dissipated by natural ventilation. Nuisance odors are generated if anaerobic conditions develop within the compost windrows. Eliminating excess water, careful construction and adequate ventilation of the windrows are essential to keeping the windrows aerobic and nuisance odor free. Construction of a covered shed for the storage of wood chips to ensure they are kept dry during wet weather is in the DRC 06-07 budget plan.

To monitor any composting odors, the DRC has established a numerical odor index. This information is recorded in the DRC's daily log: 0 = background levels to 4 = serious problems. Normal operation is in the range of 1 to 2. The DRC operator performs a nasal appraisal of the compost operation daily to detect any anaerobic activity. The DRC has asked Gustavus residents to notify the DRC manager or operator immediately should nuisance odors become apparent. Immediate reporting is essential to identifying and correcting odor problems. Complaints of odors submitted weeks or months after their occurrence are of little use in identifying their source.

For complaints regarding odor the DRC has established the following procedure:
 

For a complaint to be considered valid, it must be first made to the DRC operator, in person or by telephone, in a timely manner (24 or at most 48 hours). If the DRC operator receives more than one complaint within a five day period the DRC Manager will ask for members of the city council to come to the place where the alleged complaint is present and give an objective assessment of the level of the problem. All complaints will be recorded and kept on file at the DRC.

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Site diagram