Recently, undergraduate students from the University of North Texas (UNT) surveyed the commercial-municipal component of Denton’s wastestream. UNT is one of two state-supported universities in Denton, a city of approximately 75,000 people located at the northern edge of the Dallas-Fort Worth Metroplex in north central Texas. The City of Denton and Institute of Applied Sciences at UNT provided funding for this study.
The waste characterization project demonstrated the use of a community resource to accomplish a valuable community task. Characterizing the incoming wastestream was necessary to understand the potential benefits of a materials recovery facility (MRF) in Denton.
Using a combination of handsorting and mechanization, the MRF would separate recyclable materials from all incoming municipal waste, and recovered products would be marketed. Diverting and reusing MSW would save space in the Denton’s landfill, preserve natural resources, and mitigate environmental problems with mining those resources. A MRF could intercept the relatively large commercial-municipal component of Denton’s wastestream, whereas other waste management alternatives largely bypass that component.
|Students sort through waste|
MSW includes durable goods, nondurable goods, containers and packaging, food scraps, yard trimmings, and miscellaneous inorganic wastes from residential, commercial, institutional, and industrial sources. In 1997, the US Environmental Protection Agency (EPA) reported that 217 million tons of MSW were generated in the United States, or an average of 4.4 lb./person/day (Franklin Associates, 1999). Disposal rates for Texas, approximately 6.5 lb./person/day, were higher than the national average (McBee, 1997). Even higher rates, approximately 7.5 lb./person/day, were disposed to the Denton Landfill in 1999.
Texas relies primarily on voluntary measures to reduce municipal waste. Consequently, recycling rates for Texas cities have been lower than the national average. Denton has a recycling rate of only 13%, compared to a national average of 28%, and a Texas goal of 40% set by the Texas Legislature in 1991. Potentially, a MRF in Denton could intercept large volumes of recyclable material currently being placed in the landfill.
Denton’s commercial sector comprises mainly light-industrial and retail operations, totaling about 1,800 commercial solid waste customers. The city’s Solid Waste Department collects commercial containers and places the waste in a Type I landfill. The landfill covers 152 ac. that will be divided into 9-ac. cells. Preparing each cell is a costly process involving liners and leachate collection systems. Refuse is entombed each evening to control odors and reduce interaction with precipitation. At current waste disposal rates, the landfill will last approximately 39 years.
Presently the city encourages voluntary source reduction and recycling through public education programs, recovering recyclable material through locally distributed drop boxes. The city collects yardwaste separately, mixes it with dried biosolids from its wastewater treatment plant, and sells the compost. It also recycles discarded appliances and bulky items and separately collects and disposes of household hazardous waste.
Commercial customers were placed in a database containing business addresses, numbers and volume of Dumpsters, and collection frequency. Businesses were categorized into residential, office, industrial, retail, restaurant, and grocery (Table 1).
|Table 1. Waste-Generator Categories|
|Residential||Mobile home parks, apartment complexes, individual residences on rural roads with commercial containers, multifamily dwellings with commercial containers, university dormitories|
|Office||Financial institutions, office buildings, real estate offices, most university buildings (excluding dormitories and cafeterias), schools, preschools, wholesale establishments|
|Restaurant||Dine-in restaurants, fast-food establishments, bowling alleys, movie theaters, skating rinks|
|Industrial||Auto repair shops, plant nurseries, junk/salvage yards, sheet-metal shops, paint stores, chemistry buildings and physical plants at universities, tire shops, repair shops|
|Grocery||Grocery stores, convenience stores (excluding those attached to auto repair shops)|
|Retail||Businesses receiving merchandise for resale, storage facilities, mall businesses, thrift stores|
(The survey considered residential waste from apartments and complexes using commercial containers, but not garbage cans from single-family dwellings.) The percentage contribution of each business category to the total commercial-municipal wastestream was determined. Business categories were randomly sampled at those percentages. Forty-two locations were sampled, including 13 residential, 11 office, three industrial, seven retail, five restaurant, and three grocery.
The city transported commercial containers to a parking lot behind the Environmental Education, Science and Technology Building at UNT. Commercial waste was delivered in 2-, 3-, 4-, 6-, and 8-yd.3 containers, which arrived periodically over a five-day period. Waste was dumped into piles on a large vinyl tarp. Each pile was covered with a smaller tarp until it was surveyed. Working in one-and-a-half-hour shifts, 14 groups of 20 environmental science students sorted the waste into 18-gal. bins. Each of the 20 bins contained a different waste-material category (Table 2). Intermittently, the bins were weighed, empty-container weights were subtracted, and measurements were recorded. Surveyed waste was discarded into a large Dumpster.
|Table 2. Waste-Material Categories|
|Newspaper||Printed ground-wood newsprint and other minimally bleached ground wood, glossy paper inserts|
|High-Grade Paper||Printing and writing papers including ground wood and thermochemical pulps|
|Corrugated||Cartons and boxes, waxed and unwaxed cardboard|
|Magazines||Glossy papers in catalogs, magazines, and mailings|
|Other Paper||Paper not included above or that is not easily recycled, including carbon paper, tissue, napkins, paper towels, foil-lined paper, and container board|
|Plastic Bottles #1||PET|
|Plastic Bottles #2||HDPE|
|Film and Bags||LDPE plastic such as dry cleaning bags, bread bags, plastic shopping bags, and plastic wrap|
|Other Plastics||All other plastics, including polyvinyl chloride, polypropylene, and polystyrene|
|Food||Vegetative matter, animal byproducts|
|Textiles/Rubber/Leather||Clothing, rubber mats, shoes, cushions, curtains, rubber tubing, carpet|
|Wood||Dimension lumber used in construction, plywood, stumps, wooden furniture, large prunings|
|Yard||Leaves, grass clippings, garden waste, brush|
|Glass||Bottles and jars|
|Other Glass||Window glass, mirrors, light bulbs, ceramics|
|Ferrous Metals||Tin cans, steel cans, metals to which a magnet adheres|
|Nonferrous Metals||Aluminum cans, house siding, cookware, metals to which a magnet does not adhere|
|Other Waste||Disposal diapers|
|Other Organics||Animal carcasses, hair, wax|
|Miscellaneous||Nondistinct material, mattresses, computers, items made of mixed materials|
Assigning an alternative writing project to those not wanting to participate encouraged further student involvement. Article co-author Patricia Brady and two landfill employees supervised the project in the field. All participants wore Tyvek suits; vinyl (inner), Kevlar (middle), and rubber (outer) gloves; safety goggles; and dust masks. They also read and signed a liability waiver.
The students went through 42 samples, totaling 9,981 lb. of waste. There were no injuries, and it did not rain during the five-day survey. Participation rates were high, around 90%, and few problems occurred. Students wanted to keep some of the discards (which could not legally be removed), and there was some unpleasant refuse: One load contained five dead fish and another a dead armadillo.
By waste-material category, the Denton profile is quite similar to a recent national study, commissioned by EPA (Franklin Associates, 1999, see Figure 1).
|Figure 1. Percentage of Total Waste in Each Material Category Compared to EPA Study|
(Franklin Associates, 1999)
The paper, plastics, food, glass, and metals categories contributed very similar percentages to the total wastestream in each study. The largest differences between the two studies were in the Yard and Other categories. Denton had a smaller Yard and a larger Other percentage. The smaller Yard percentage reflects separate hauling of that waste category. Percentage differences also reflect different survey methods: The EPA study considered all municipal waste, whereas the present study considered only commercial-municipal waste.
Paper accounted for the highest percentage (37.9%) of Denton’s commercial-municipal waste. Food, Plastics, and Other each contributed at least 10% to the total. There were significant differences in waste composition among generator categories. Figure 2 shows the percentage of paper in each generator category. Grocery waste was 75.8% paper, including a large amount of cardboard. Office and restaurant waste also contained large paper fractions.
|Percentage of Paper in Each Waste-Generator Category|
The total recyclable component was 58.4%. Thus, a large fraction of Denton’s commercial-municipal waste could be diverted from its landfill. Commercial-municipal waste accounted for 39.4% of the waste coming into the landfill during the survey week. It was the single largest category of incoming waste. Future studies will evaluate the recyclable components of other incoming waste categories.
The waste characterization study was a successful and mutually beneficial collaboration between the City of Denton and UNT. It provided the city with data for planning a MRF. Students learned about Denton’s waste composition, to which they contribute, and opportunities for improving recycling rates. Though limited by a short sampling period, the study yielded useful results. More than half of Denton’s commercial-municipal wastestream is recyclable. A MRF could effectively intercept this waste, becoming a vital component of integrated waste management in Denton. Similar waste characterization projects, combining local university and public works personnel, should be viable in many small to medium-size cities.