SUBJECTS:
LAST WEEK
Last week we looked at some of properties of wastes including their physical, chemical and biological properties. In today's lecture we will use some of that information because the properties of wastes also govern collection and transfer of wastes. We will also look at collection methods for recyclable materials.
The collection of garbage, especially MSW has been through some major changes over the years. Some of you may remember the TV programme Steptoe and Sons, the 'rag and bone' men who used to go around the streets with their horsedrawn cart and collect rag and bones, as well as anything else worthwhile. While modern methods involving single person trucks have been introduced in many places, there are still many places where the truck with a team of 1 or more people to pick up and empty the bins is still an important system.
Why should we consider the idea of collection and transport systems? Because it's the most expensive part of municipal waste management systems. Despite all the changes that have taken place, the collection and transfer of wastes accounts for about two-thirds to three-quarters of the costs of waste management systems. In part, this stems from the high cost of equipment, and the high labour costs. The advent of single person trucks has reduced the labour costs, but the trucks cost more.
In the USA, collection costs in 1986 were $10.4billion dollars out of $13.8billion spent on municipal waste costs. (Rhyner et al. 1995). In Lismore the costs are
Waste collection used to be regarded as just a part of the larger collection and disposal system. It meant choosing the most appropriate trucks, designing collection routes, and then administering the collection. With present day emphasis on recycling and composting the need to segregate materials has become most important. It can mean different vehicles collecting different material and taking it to different locations. As a result, the collection of wastes has become more complex and more expensive.
To meet current needs there is a call for the development of an 'integrated collection strategy' which incorporates the following:
(Rhyner et al, 1995)
This requires the following to be addressed.
Frequency of collection
In Lismore we have a weekly collection, but twice weekly collections still are carried out in some centres (eg parts of Sydney). Collection frequency may have to be altered because of weather conditions which can pose health and odour problems. Increasing collection frequency has considerable cost implications and could lead to doubling of labour costs.
Setout locations
This refers to the actual location of the bin to be collected. In Lismore wheelie bins are placed near the kerbside thus allowing the use of one-person vehicles with extending arms to collect the bins. In some locations, eg older Sydney suburbs, there is not off-street parking, so the cars are parked on the roadside, limiting access and hence not allowing the use of automatic arms. This means extra crew are required with extra labour costs. In some locations the crew actually come into the house yard (often around the back) to collect the bin. This obviously slows collection times and increases costs. The use of centralised systems, such as in apartment blocks, will accelerate collection times by reducing travelling distances and times.
Container type
The types of containers used are usually plastic or metals cans (55L), wheelie bins (120 - 240L), bags (plastic and/or paper), and special containers such as recycling boxes. Each type has advantages and disadvantages and must also be related to the setout location. For instance, large wheelie bins will be impractical in narrow urban areas with on-street parking. Bags are susceptible to breakage, and to animal attack, but they are very convenient for collection as they can be picked up and thrown readily. In New Zealand there is another advantage with bags in that in some districts a special sticker is required to be placed on the bag for costing purposes. Stickers can be easily seen by collection crews. The use of paper bags can provide advantages in composting in that they are easily shredded. The disadvantages of wheelie bins is one of size - most people put out more rubbish to fill the bin. They also require mechanical lifting arms for health and safety reasons, and cost more initially. Interestingly, most wheelie bins are made out of recycled plastic.
Collection vehicles
The slides shown in this lecture give an idea as to the different types of vehicles. The setout location, size of area to be served, method of collection and costs of vehicles and operators are the major concerns.
These notes have been adapted from the Introduction to Solid Waste Landfills Course by Philip O'Leary and Patrick Walsh, Co-Directors, Solid and Hazardous Waste Education Center, University of Wisconsin-Madison.
How can solid waste professionals make an intelligent choice among the many technological options for collecting, processing, and storing recycled materials?
One key is the community's commitment to recycling. The resources that are committed to the program will determine the technological mix appropriate for the community's needs. In any case, the object is always the same: to move the material from the point of generation to the market in the least costly and most efficient fashion.
INITIAL PLANNING CONSIDERATIONS
No community or waste hauling company should begin recycling without giving thought to how the program will be structured. This caution applies equally well to selection of recycling equipment.
Planning for purchases can save time and resources. Necessary equipment will be purchased only when needed; equipment that will be seldom or never used can be avoided. Other potential constraints on a piece of equipment's suitability and feasibility for your effort - such as space limitations or the need to install expensive additional electrical service capacity - can be accounted for up-front.
A great variety of materials can be recycled, if a community is willing to support the program. Along with the common short list of newspaper, aluminium, and glass, many communities now recycle other materials: plastics, ferrous, wood products, office paper, concrete, waste oil, and even dirt. It may be best to start off by reclaiming only a few items, with the intention to expand into other types (and larger volumes) of materials at a later date, the system is running smoothly.
Some new recycling centers have had problems because the volume of material to be processed has been seriously underestimated. This may sound like a problem everyone would like to have, and high participation rates are certainly satisfying, but the ensuing problems may permanently damage the program. Very quickly after the beginning of operation, the program may be overwhelmed with the quantity of material and unable to cope with the continuing stream of material coming in from the community.
So, before beginning a program, it is important to:
It is best to assume that the material will not immediately be transferred to a buyer, especially in times of low demand.
Seeking advice from recycling operations already existing in the area may be the best method of helping to accurately predict space needs.
COLLECTION TECHNOLOGIES AND STRATEGIES
Most communities have found that the only way to ensure high participation rates for recycling programs is to provide each participant the most convenient method of participating. In most instances, kerbside pickup is the most convenient, and the trend in recycling is towards some form of kerbside pickup. Drop-off and buy-back centers are not as convenient. Typically, a program using such centers will have lower participation rates.
Most communities and hauling companies face a dilemma in deciding how best to collect recycled materials, especially those with fleets of refuse vehicles. The prospect of replacing a fleet of refuse trucks with an equally expensive fleet of vehicles designed for recycling is normally not economically feasible, at least at first. As a result, most recycling programs try to use existing refuse equipment to collect recycled materials.
Many innovative ideas have been used to convert refuse trucks to all-purpose refuse collection and recycling vehicles. For example, the city of Madison, Wisconsin, designed a newspaper rack welded to the frame of refuse trucks for the purpose of collecting bundled newspaper. This low cost adaptation was first designed by city engineers in 1971 and is still in use today. The split-bin system in use in Byron Bay is a high-cost method, necessitation new bins and new collection vehicles. In the UK in Luton, a system using cuphooks attached to bins was trialed (unsuccessfully)
Some companies which haul waste from commercial accounts generating high volumes of office paper or cardboard make no attempt to separate the material. Instead, they substitute back- end sorting and processing for separation before collection, separating recyclables out of the waste stream at a processing center in what is known as "dump and pick" operation. Some of these operations have proved successful, although contamination of recycled materials from mixing with other waste can be a problem.
Other communities use refuse trucks in concert with pickup trucks. The pickup follows the large vehicle and collects recycled materials on the same day as normal refuse pick-up. By requiring the use of clear plastic bags for recycled materials - and perhaps supplying them - the mixing of recycled materials with other refuse can be minimised.
In still other communities, recyclables are collected on a different day. As long as public education is continuous, and the pick-up schedule is highly reliable, the public seems willing to follow whatever schedule is established for collecting recyclables. One option being considered in Lismore is to duplicate the run by collecting green wastes the day after the garbage collection.
Kerbside Collection
The main options available for kerbside collection of recyclables include:
Source Separation/Multibin Truck
This relies on the public separating the materials into the correct containers prior to pickup. The vehicle use for collection will generally have as many compartments as are required for the different types, usually 3 or 4.
Commingled Recyclables/Multibin Truck
This is similar the recycle box ('blue box' or 'black box' systems) in which all recyclable materials are put into the one container. These are sorted by the crew at collection and obviously this involves more labour costs. This system can be varied, eg a collection system limited to say three types of material.
Commingled Recyclables/Central Processing
This system involves the separate collection of recyclables and then taking them for sorting at a materials recovery facility. Sometimes this can also involve a preliminary sorting, eg paper and plastics in one container, glass and metal in another.
Co-Collection System
In this system recyclables and wastes are collected in the same truck - sometimes in the same compartment - sometimes different compartments. A disadvantage is the problem of contamination, especially in a single compartment system. A further disadvantage is that compaction cannot be carried out as well with a loss in efficiency.
Post-Collection Separation
With this method, solid wastes and recyclable are collected without any separation, taken to a materials recovery facility and then sorted. This is obviously a labour intensive operation, though some materials, eg ferrous metals can be separated by magnets.
Specialised collections
As more communities establish aggressive recycling programs, vehicles specially designed to transport source-separated materials are becoming common. Already, many communities and waste-service companies use compartmentalised trucks or trailers on collection routes. There are a variety of vehicle designs on the market, all of which provide efficient and easy loading and unloading of both recovered materials and solid waste.
Some communities using special recycling vehicles have enhanced participation rates and collecting efficiency by supplying recycling boxes to homeowners. In Kitchener, Ontario, public participation rates of up to 80% have been achieved with the use of highly visible "blue boxes." The blue boxes, distributed free to residents, are believed to create high participation because their absence is noticed by neighbours on collection day. Similar programs exist in cities such as Santa Rosa, California, and St. Louis Park, Minnesota, where residents have received stacking plastic containers for paper, glass, and cans from the city or contractor.
Mobile buy-back operations are also increasing in number, especially for service of rural areas - which may not produce enough volume to support a private recycling operation. In these operations, a compartmentalised vehicle will visit a community on a periodic and well-publicised schedule to purchase recycled materials. Mobile buy-back units often pay for some materials and accept for free other materials.
PROCESSING AND STORAGE APPROACHES
Collected material is usually brought to a processing center. Here it is separated, processed, and stored until enough material has been collected to create a full load for transport to a market. Material usually must be processed to meet the specifications of buyers. The center must be designed to efficiently move the material from the tipping floor or drop-off point through the system to the storage area.
Many technologies are available for efficient processing, materials handling, and storage. The choice of equipment and systems must take into account:
One approach is simple, requiring only a designated space. Glass, which is impervious to weather, can be stored outside; this would require the construction of revetments or concrete storage containers, which is relatively cheap. Collected glass can be dumped into the revetment compartment or removed by a small tractor. A barrier is often placed at the front of the revetment to ensure that injuries to employees or others do not occur from accidental spillage.
Some materials, such as newsprint, cannot be stored outside in the weather indefinitely; to achieve a competitive price for newsprint, one must prevent decomposition. Storage indoors of newspaper and other items can create problems for a poorly designed center, as there can be a constant struggle between space needed for processing and operations and space requirements for materials storage.
What's more, storage problems can result when either the volume of recycled materials expected is significantly underestimated or the demand for materials already on hand is significantly overestimated.
HOW MUCH PROCESSING IS NEEDED?
The amount of processing which will be necessary at the recycling center will depend to a large degree on how the material is collected.
So-called "dump and pick" operations require significant manual labor for extraction of recycled materials from the bulk of the refuse. While some of these operations have workers hand-sort material, hand-sorting can be dangerous for workers, exposing them to hazardous materials and sharp objects contained in the waste.
Some operations utilise sophisticated sorting technology, including trommels, air classifiers, and conveyers to mechanically separate the waste. Where waste volumes collected are large, mechanical separation systems may be economic. Even with these systems, some hand-separation is usually needed to ensure recovered materials are free of contamination.
Material that enters the recycling center already separated is much easier to handle. Processing is generally performed for one of two reasons: to place the material in the most economical form for transport, or to meet buyer specifications. Equipment is normally needed only to move material from one processing station to another or from processing to storage.
BALERS AND SHREDDERS
A standard feature of most recycling centers is a baler. It can be used to place recovered materials (newsprint, cardboard, plastic, and aluminium) in large agglomerations which can be easily moved and are stackable. Since paper, cardboard, and plastic bottles can comprise a high percentage of a municipal waste stream, most recycling operations will need a baler to process this material.
Baler types should be carefully investigated. Operations providing bulk newsprint to paper recycling markets may choose a baler which makes bales of approximately 1,000 pounds each. On the other hand, a center selling shredded newsprint for animal bedding to local farmers will need a hay baler, which makes small 70-pound bales. For maximum flexibility, perhaps both types of balers should be utilised, if sufficient space is available. The question of what type of baler will be best for an operation is just one example of the need to do some homework before getting started.
Other processing equipment may be needed to satisfy buyer specifications and provide sufficient compaction to allow for cost-effective transport. A center may use shredders, shears, grinders, and crushers. Each piece performs a different function but all have the objective of reducing waste volume. For example, there are a variety of shredders available, which will shred paper, cans and even automobiles. Glass crushers reduce bottles into a mixture called cullet, which is the form most attractive to glass recycling markets.
Solid waste is an abrasive and caustic material, which makes proper maintenance of waste processing equipment very important. Moreover, operating this equipment can be dangerous; special training and safety precautions may be required. Power needs can also be high. Consequently, processing's potential benefits must be carefully weighed against its cost and operational considerations.
OTHER EQUIPMENT REQUIREMENTS
Other equipment that may be useful in a recycling center includes:
- Weighing Devices: a scale is a good idea for most operations. Recycling centers may not require drive-on scales, if volumes received are small or the need to move and process material quickly is not great. Note that a recycling center operated in conjunction with a landfill or transfer station might be able to use the disposal facility's scale.
- Magnets & Conveyors: Where manual sorting is used, a conveyer system, often coupled with a magnet to collect ferrous, provides a good way to move material from the tipping floor to other processing stations.
- Storage Boxes: After processing, material is often stored in large cardboard boxes, known as "gaylords," or in other similar containers.
Forklifts, etc. - Freight moving equipment, including hand trucks, dollies, and fork lift trucks may be needed to move material.
ADDITIONAL CONSIDERATIONS
Equipment should be chosen with care: 55-gallon drums full of crushed glass and large bales of newsprint are heavy, and could cause injury or damage if the equipment expected to carry the material is not strong enough.
Purchase of backup transport equipment should also be seriously considered. The inability to move material from processing to storage caused by a lack of backups could create a serious disruption in the recycling operation.
In designing a recycling center, sufficient aisle room is a must. Designers must allow for easy and efficient movement of transport devices. A convenient loading dock, readily accessible to large trucks, is important; it should provide protection from inclement weather. Material storage areas must be located close to the loading dock.
Employee facilities and an office for record keeping and center operations should also be carefully planned. Local building codes likely will mandate these and other features of the recycling center.
For any integrated waste management system the method and type of collection system to be used in extremely important, not just for efficiency but for financial reasons. The different types of systems mentioned, not only for waste collection but also for the collection of recyclable materials is varied and governed by many factors - some of which have nothing to do with waste management.
Further Information
Collection systems are described more fully in Rhyner et al. (1995) and Tchobanogolous (1993) in the Library.
Next Week
The Lab Session this week looks at waste audit techniques. In Next weeks Lecture we will look at Waste Minimisation, and there will be a recycling tutorial as well as discussion on public involvement and education.