Landfills are usually required to cover fresh waste with about 15 cm (6 inches) of soil at the end of each operation day in order to control nuisance conditions such as flies, rodents, odors, and windblown litter. Unfortunately the use such daily cover uses up 20 to 25 per cent of the landfill space. In some cases soil has to be transported from other sites for this purpose.
In order to preserve valuable space and minimize costs, a variety of landfill alternative daily covers (ADCs) are currently used in some landfills. ASTM D 6523 classifies these in four categories: (1) foams, (2) geosynthetics, (3) indigenous materials and (4) spray-on slurries.
Foam ADCs: These are applied to the working face of the landfill using special equipment. They don’t occupy any landfill space, but the only last a very short period of time and may be combustible. Foam ADCs also tend to be very expensive.
Geosynthetics: These are sheet-like membranes such as canvas or plastic tarps that are placed over the working face at the end of the operating day. Geotextile covers can be reusable or non-reusable, but have a limited ability to control odours and rodents. They are subject to mechanical damage, such as tears and punctures that require replacement or repair. These covers are combustible, block air/gas movement and are difficult to apply in inclement weather.
Indigenous ADCs: These may include various types of locally-available waste materials such as sludges, ash, shredded tires, shredded green wastes, pulverized construction and demolition debris, automobile recycling fluff, foundry sand, and so on. The characteristics and handling properties of these materials vary from source to source. Suitability and acceptability are dependent on site-specific climatic and operation conditions and regulatory requirements. In most cases, indigenous materials are spread with dozers as with traditional soil daily cover. As with soil, they occupy a lot of landfill space. Also, many unprocessed indigenous materials generate dust.
Spray-on slurries: Special slurry ADCs can be sprayed on with hydroseeding machines. They don’t occupy landfill space and can be used in inclement weather. There are a few products on the market; however, current formulations have problems with adherence to plastics and other slippery constituents in landfilled garbage.
EkoSeal uses waste materials as major ingredients and therefore conserves natural resources. It’s applied as a slurry using conventional hydroseeding technology and forms a thin continuous coating that adheres to the surfaces of landfilled wastes, including glass and plastic film. It minimizes water infiltration, wind blown dust, odour, and vectors such as birds, flies and other insects. EkoSeal has been proven effective in long-term laboratory tests and full-scale field demonstrations. It occupies virtually zero landfill space since it crumbles into the voids in the waste upon compaction, and this extends landfill life up to 25 per cent.
Locally available waste materials are mixed with some proprietary ingredients and water (or landfill leachate) to form a slurry that’s sprayed to a thickness of 3 to 6 mm (approximately 1/8 to 1/4 inches) over the daily operating face using a conventional hydroseeding machine. The slurry sets within several hours into a protective coating.
In addition to adhering well to slippery surfaces such as glass bottles and plastic, it withstands exposure to rainfall and high temperatures. Test samples exposed to the weather for over three months retained their integrity and adherence to the glass, rigid plastic and plastic film.
EkoSeal was demonstrated at the Halton Regional landfill site in Milton, Ontario. The landfill working face was strewn with plastic bags after compaction. The ingredients were loaded into and mixed in a conventional hydroseeding machine. After about five minutes of mixing, the slurry had a thick, viscous “milk shake” consistency and was sprayed onto the compacted landfill face.
During the first demonstration, it took only about seven minutes to cover the 700 m2 (7,534 sq ft) face with an average slurry thickness of 0.65 cm (1/4 inch). The slurry readily adhered onto the plastics and formed a continuous coating. It rained within two hours after application; however no effects on the appearance of the cover were observed. Interestingly, it rained almost every day the following week. An examination at the end of this time period indicated that the integrity and performance characteristics of the material were maintained.
In a second demonstration the slurry was sprayed to a thickness of about 0.4 cm (5/32 inch). It took approximately 10 minutes to spray an area of around 1,500 m2 (1,6145 sq ft). It started to rain about one hour after the application. Visual examination indicated that the cover remained satisfactory for at least one week.
Caijun Shi is president and Robert Booth is senior vice president of Sustainable Landfill Technologies Inc. in Burlington, Ontario. Thanks to Yanzhong Wu in help with preparation of this article.