An overview of options commonly used for disposal of plastic silage bags- from an Australian perspective
Disposal of plastic is a difficult issue facing farmers worldwide
Farmers have little choice at present when considering what to do with used silage wrap plastic. Currently, the only viable options are burial on farm or disposal in landfill at rubbish disposal sites.
The use of stretch wrap polyethylene (polythene) for conserving silage is increasing in Western Australia.
In 1995, an estimated 250 to 280 tonnes of silage wrap plastic was used in Western Australia and approximately 1500 tonnes in Australia. This is a small proportion of all plastic film used.
Controlled landfill sites
Many Western Australian farmers dispose of used wrap plastic at local shire rubbish disposal sites. Most shire tips accept bulk plastic under sufferance but cannot continue to handle increasing quantities under current arrangements. In the future, there are likely to be fewer disposal sites which accept plastics and site fees may be charged to reflect the cost of disposal.
Landfill burial is an environmentally benign form of disposal for polyethylene but the plastic will remain stable in the absence of light and at low temperatures. Burning the tip site will cause problems associated with low temperature incineration.
South West tip site managers report that plastic is being delivered in increasing but manageable volumes. When buried promptly, plastic film does not pose special problems, but it takes up landfill volume and adds to the overall cost of rubbish disposal. Plastic dumped at uncontrolled rubbish disposal sites creates problems by blowing around, and producing smoke and fumes if the tip burns. These problems are minimised if plastic is baled before disposal.
Burial on farm
Burial on farm is a stop gap measure for some farmers, but requires earth moving equipment. Subsequent excavation may exhume un-degraded plastic. There may be problems with burying contaminated plastic near streams or ground water bodies.
The Western Australian Department of Environmental Protection recommends that agricultural plastic film should be disposed of by burial on farm in suitable areas or at controlled council landfill sites.
An increasing amount of plastic is burned on farms, in water heaters or open fires at relatively low temperatures and produces incomplete combustion. The Victorian Environmental Protection Authority regards burning plastic on farm as an 'Environmental Nuisance'. Temperatures need to be over 600°C for relatively safe burning.
High temperature combustion of polyethylene produces water and carbon dioxide. As polyethylene contains no chlorine, dioxin is not a combustion product. Other combustion products may result from burning plastic contaminated with organic or other residues.
Polyethylene is a useful heat source when burned in a high temperature furnace. There has been some investigation of the use of plastic and other combustible wastes in industrial heat generation.
In Western Australia, the cement industry has considered the use of polyethylene, other container plastic, tyres and waste oil for heat. In most cases, the quantities of combustible waste available here do not justify the expense of setting up a combustor to handle each type of product. In addition, cement manufacturers are sensitive to criticism that they are using contaminated fuels which could produce noxious by-products, rather than uncontaminated energy sources such as new oil or gas.
Agricultural plastic has a high relative energy value and would be very suitable as a fuel for high temperature combustion if large quantities were available close to the incinerator.
While polyethylene can be recycled by the plastics industry, there is very little recycling of polyethyl-ene from agricultural uses in this country.
Recycling of agricultural plastics is an energy negative process, that is, more energy is used in collection, cleaning and processing than in producing new plastic. When labour costs for collecting and handling are added, it is cheaper to use new plastic feed stock than to recycle. Recycling plastic film from metropolitan areas is more feasible because of economies of scale, easier collection from closely grouped sites and less contamination.
If plastic is available in large enough sheets, it could be used to wrap intractable waste, such as asbestos, before burial. Large sheets of plastic film can be re-used if not damaged or degraded. There is no prospect of re-using stretch wrap silage plastic for silage wrapping.
Handling used plastic film
Loose plastic film occupies a large volume, making compaction into high density bales desirable for transport, storage or disposal.
Standard hay balers can be used to reduce volume to about one-sixth of the loose volume. Balers need a tine fork feed, not an auger feed, to avoid plastic wrapping around the feed mechanism. Large round balers can be used, but small square balers are preferred because their bales are easier to handle.
Plastic should be as clean as possible, laid out on a clean surface in a windrow about 1 m by 0.6 m and picked up in the normal manner. Tie the bales with plastic twine, not jute.
Hand feeding the baler is dangerous because tangles could pull the operator into the machine.
What's happening overseas?
Canadian recycling pilot schemes have produced pelletised plastic for use in manufacturing film, moulded planking and furniture.
The United Kingdom plastics industry has started a recycling scheme managed by Farm Film Producers Group Ltd. Backed by major agricultural plastic suppliers, the scheme is financed by a levy of one hundred pounds per tonne (environmental protection contribution) on farm plastic products. This adds 10 to 20 pence to the cost of a bale. The plastic recovery scheme complies with the European Unionís Packing Directive.
Contamination of plastic and high handling costs are cited as deterrents to recycling in New Zealand and the United States.
Most plastic is disposed of in landfill in Canada, the United States and New Zealand. Uncontrolled burial on farm is discouraged in Canada because of the risk of polluting ground water.
Energy recovery techniques are being explored in Germany and the United States. There were more than 100 facilities in the United States in 1995, with this number expected to double by the year 2000.
Some plastic has been re-used, mainly for stock bedding in Canada, with minor uses for good quality sheet plastic.
A Victorian group, the Silage and Mulch Film Group, comprising raw material suppliers, the Plastics and Chemical Industries Association and Agriculture Victoria, is investigating strategies for disposal of silage and mulch films.
They aim to develop systems to dispose of or re-use film in an economic and environmentally acceptable way. The group has investigated options and will test processes for recycling unwashed wrap plastic.
Agriculture Victoria suggests that farmers can
- dispose of compacted waste plastic at local tips where permitted;
- bury in on-farm landfill where allowed (beware of problems of water pollution and soil slippage if filling eroded gullies); or
- store compacted plastic on farm for reprocessing by one of the systems to be developed by the Silage and Mulch Film Group (contact Frank Mickan, Agriculture Victoria, RMB 2460, Ellinbank VIC 3820 (056) 242 222.