Composting Key to Meeting Landfill Organics Ban
The Halifax Regional Municipality (HRM) in Nova Scotia took a giant leap in 1998 to reaching a 50 percent diversion goal by 2000. Between July and November, 1998, organics collection carts were distributed to almost 100,000 households in the region. In December, two new composting facilities designed to process those materials, as well as feedstocks from the commercial sector, opened their doors.
“The Halifax Regional Municipality’s new integrated solid waste-resource management system is ‘leading edge’ in all of North America,” says Mayor Walter Fitzgerald. “We are successfully converting previously designated waste into a valuable resource.” Eventually, the system is expected to achieve diversion in the 65 percent range.
The composting initiatives are due in large part to the province of Nova Scotia’s ban on disposing of compostable organics in landfills and incinerators. The ban became effective on November 30, 1998. To comply, all municipalities have to develop a composting infrastructure (see “Nova Scotia’s Organics Disposal Ban Takes Effect,” November, 1998).
Both composting facilities utilize in-vessel technologies. Originally, one of the two was designed as an open air windrow operation. But Nova Scotia Ministry of the Environment guidelines that place more stringent requirements on large-scale, open air windrows, combined with community concerns about that type of facility, led the vendor, New Era Farms, to rethink its approach and proceed with an in-vessel system.
Contracts between HRM and the haulers determine the flow of residential organics to the composting sites. There is a minimum throughput guaranteed by a put or pay agreement with HRM. Feedstocks from the institutional/commercial/industrial (ICI) sector are directly solicited from generators by the facility owners. No ICI feedstocks were being received as of January, 1999, because of HRM requirements that the plants had to pass performance tests prior to handling ICI material. Estimates by HRM show that flow to both sites will be roughly 55 percent residential feedstock and 45 percent from the ICI sector.
NEW ERA FARMS
The New Era Farms compost facility in Halifax has a capacity of 27,500 tons/year. It is sized to allow expansion by an additional 11,000 tons. The system prototype was first developed about four years ago in Colchester County, Nova Scotia (see accompanying article).
The new facility, which is located in a business park, has three main areas: A receiving and preprocessing building, composting pad and curing structure. Feedstock is unloaded onto the tipping floor, where workers remove oversized items and evident contaminants. Next, material is loaded in a hopper that feeds a conveyor. On the conveyor, hand sorters remove recyclables and residuals that ended up in the organics stream. A magnet with a manual scrape pulls out ferrous.
The conveyor feeds a slow speed rotary shredder that reduces material to a two-inch size. The residential mix is loaded directly into containers for composting. Once ICI feedstocks are received, it may be necessary to mix in amendments prior to composting.
The New Era facility has 24 Stinnes-Enerco containers (each about 30 feet long by 10 feet wide by 8 feet high). After being loaded, containers are placed in an outdoor area connected to a system of process air and water piping. Six additional containers are open at the top and used as biofilters containing a mix of compost, peat moss and bark. Rolled compacted concrete was used for the pad surface.
Processing in the containers takes about ten days. Given the current mix (residential only that is fairly high in carbon), it takes two to three days to reach 55ƒC. After the initial composting phase, the container is moved to a 440 foot by 72 foot wide building with a domed, fabric roof (made from a polymer manufactured in Nova Scotia) where the material is unloaded, further composted and cured.
The HRM required that the curing areas at both plants be covered, ventilated and the air treated through a biofilter. The floor of the building is poured concrete with built-in aeration channels. Four fans provide aeration. Three additional 40 hp fans maintain a negative pressure in the building and exhaust to three biofilters directly outdoors. A sedimentation pond collects surface runoff from the site area; a biowater (leachate) tank collects runoff from processing areas.
Ownership of the facility is a 50/50 partnership between Stinnes Enerco Ltd. and Hartland Developments, a local heavy equipment and landscaping company owned by Kynock Resources. Hartland Developments has been in the topsoil business for many years.
MILLER COMPOSTING SITE
Miller Composting, owner of the second facility servicing the HRM program, designed and built its first flat-bed composting system in Lunenberg County, Nova Scotia over four years ago.
Both Lunenberg and the new plant utilize the Ebara technology. Like New Era, the Miller site has a capacity of 27,500 tons/year. It was built in Nova Scotia’s largest business park, and except for the office/scale house, is enclosed entirely under one roof. The building footprint is 55,000 sq. ft., set on a 20 acre lot. The property could accommodate a second plant directly beside the original if needed in the future.
The main building has three areas: receiving and preprocessing, composting and curing. Only the first two areas are separated by a wall. Workers remove obvious contaminants from loads on the tipping floor. Feedstock then is put in a hopper and conveyed through a handpicking line to sort recyclables and residuals. A motorized cross-belt magnet removes ferrous materials. The feedstock is processed in a slow speed rotary shredder.
After shredding, material is conveyed to a composting room where it is unloaded. Amendments can be added at this point. A front-end loader is used to put the material into the system. Initial composting takes place on the bed of the main composting vessel (220 feet by 75 feet). Material is placed at a depth of about nine feet. Aeration is provided both by forced negative air flow and agitation from the paddle, which passes through the compost about once a day. It takes 18 to 23 days to move the feedstock from one end of the vessel to the other. One large fan provides aeration for the bed with 13 different zones for control. The fan is sized such that all necessary aeration could be provided without movement of the paddle.
At the end of the bed, the material is emptied onto the floor, then moved to the curing area where aeration is provided utilizing in-floor piping. Air is forced upwards through the material by two fans. Negative air pressure for the entire building is provided by six additional fans. All building and vessel air is treated through two outdoor biofilters (made with compost, wood chips and bark). All biowater (leachate) collected in the processing areas is reinjected into the material in the vessel.
After one month of operation, both facilities report some contamination (roughly five to ten percent) in the materials processed on the sorting line. While there is sufficient moisture content from the incoming residential stream, ranging from 50 to 60 percent, current C:N ratios are high — anywhere from the mid-30s to over 110, even after initial screening. This is due to a number of factors. First, source separated residential organic material generally has a higher amount of fiber in its organic stream. Second, the ICI feedstocks are expected to have C:N ratios far lower than the residential stream, however that material isn’t being composted yet. Third, Halifax has never included boxboard in its dry recyclables. Its program, therefore, requires that residents place all boxboard in their carts for composting.
While there are no convenient markets for boxboard in Atlantic Canada, other municipalities in Nova Scotia have been marketing the material elsewhere for years. Halifax is seeking long-term markets to be able to include boxboard with dry recyclables. In the shorter term, as ICI generators climb on board and source separate their organic material, C:N ratios will become more acceptable.
END USE AND FINAL COSTS
New Era Farms reports that its first year of compost production has been presold. Miller Composting also expects strong sales. Topsoil in Halifax costs $150 to $200/ tandem truck load. Most of the landscaping companies in the area have been producing their own topsoil using compost and other organic feedstock for years. These new facilities will make more material available to landscapers and gardeners. HRM also shares in the proceeds from the sale of the product. This provides an incentive to ensure a clean feedstock from the residential program.
Costs for the system are controlled by HRM. Currently, it costs Halifax about $68/metric ton to process its organic material at the facilities. Original costs were lower during the tendering process. Addressing community issues, however, led the facilities to change location and to include complete enclosure of the curing areas. Still, these costs are substantially lower than landfilling, which is $100/metric ton in Halifax, and expected to rise. Furthermore, the final locations in business parks put the composting sites near to the center of generation in Halifax.
Public acceptance of the program has been positive. Of the 98,000 compost carts delivered to every household of six units or less, only about 700 were returned. Setout rates are very high and contamination is low. A poll early in December showed an overall acceptability rate of 67 percent. However, participation is critical, especially because Halifax’s landfill has a finite daily capacity. Early indications of participation do not point to any problems. “Halifax is showing the country and the world that small steps for householders lead to giant leaps for the environment,” says Michel Samson, Nova Scotia’s Environment Minister. By Barry Friesen.