Landfill operators tread a fine line. They have to maximize operation efficiency with the least cost while also ensuring worker safety and promoting a positive public perception of the site. Understanding the importance of compaction, properly managing site operation, and choosing the right equipment are all indispensable for the job.
The period from 1960 to the current day has been an era of unprecedented change in how we think about, manage and regulate solid waste. Significant drivers behind these changes - including more rigorous environmental legislation - range from a better understanding of the environmental ramifications of waste to negative public opinion on certain treatment options. Let’s face it, who wants to live next to a landfill? Not me, right? But why is this?
Is there a fundamental belief that we are putting our health at risk, or is there a basic misunderstanding of how a landfill works and how a well managed landfill can be both environmentally and financially viable? My instinct would tell me it’s the latter.
A multitude of elements contribute to successful landfill management: the geological make-up of a site, landfill design, liner technology, type of waste, water content, etc. But one of the more common misperceptions is the general idea that solid waste management is a simple, low-tech, unskilled industry. In reality nothing could be further from the truth.Modern landfill management
There are three significant issues that should be considered:
• the importance of achieving high waste compaction densities
• the vital role management plays in running a modern sanitary landfill
• choosing the best equipment to accomplish the task.High waste compaction densities
Achieving high waste compaction densities is fundamental to managing a modern sanitary landfill. High compaction density is the means by which owners maximize the return on their infrastructure investment. The infrastructure investment is fixed and the incremental operating costs of achieving high densities are small relative to the additional volume and revenue the site can accommodate. Good compaction improves safety by providing a stable surface upon which the machinery and people work. A dense waste mass also reduces the major nuisance factors of vectors (rodents), odour, blowing paper and surface-water contamination. Luckily the ‘how to’ of achieving high compaction densities are few and straightforward.
Proper landfill compaction maximizes the use of a landfill’s capacities and thereby reduces costs Click here to enlarge image
null‘The onion skin approach’
Thin layers improve the crushing action of the compactor and permit increased machine travel speeds due to reduced rolling resistance. Studies have demonstrated up to an 8% increase in machine coverage (due to increased speed) on a 0.6-metre layer versus a 0.9-metre layer. Thin layers cause less wear and tear on the machine, which translates to less maintenance cost, less downtime, therefore less revenue loss and less fuel consumption.Multiple compactor passes
Waste becomes compacted when a force (the weight and motion of the compactor) moves over it, crushing out the air voids, shredding the material and binding it to other waste. By running over the waste in one direction - one machine pass - and returning along the same tracks - a second pass - waste rebound is minimized as the structure of the waste breaks down. This action degrades the waste, improving compaction. Most operators will move over by one wheel width (right or left) and continue to compact across the new layer. This technique assures total coverage of the new layer with four machine passes. To make sure you are achieving the best possible compaction, adopt an attitude of ‘keep moving’. All waste is different and may require modified compaction and shredding techniques. The utilization of a ‘keep moving’ attitude will lead to more complete compaction at higher density levels. This thought process is especially helpful during peak periods.
A track-type loader handling cover material. Landfill equipment incur large costs, so it is important to choose the right one all photos: caterpillar Click here to enlarge image
If the working face of the landfill is relatively large, it may be difficult to tell where a compactor has made a pass and where it hasn’t. Complete and uniform compaction is important because, in its absence, there will be soft spots under the surface. Soft spots will be hidden by subsequent layers of waste and eventually lead to differential settling of the landfill surface. In addition to the safety hazards of ‘soft spots’, differential settling robs the landfill of air space. There is a theory that, over time, all waste in the landfill becomes completely compacted by the weight of the mass above it. Studies in North America demonstrate that if waste is placed and covered before being completely compacted, air space can be lost and is never recovered. Differential settling, which is the inevitable result of soft spots, will require expensive post-closure repairs in landscaping, involving the hauling of additional cover dirt, and often repairing torn liners. It is particularly egregious to suffer these additional expenses at a time when the site is generating no revenue.
To achieve uniform compaction, operators should operate the machines in a defined ‘pattern’. A pattern is defined as a ‘set sequence of operations’. This set sequence, either individually or as a team, should cover the entire area before adding a new layer. This organized approach helps reduce confusion and cycle times while yielding more complete compaction and the reduced risk of soft spots.
It is worth reiterating that compaction is achieved through compression, binding and shredding of materials. The look of the compacted surface can be deceiving. A ‘well finished’ look (neat and even) on a layer of compacted material may present the appearance of ‘total’ compaction while hiding future problems. Again, thick layers may compact only on top and some materials appear compacted when they are not. Thin layers, proper passes and covering the whole area with a pre-planned pattern before adding more waste, is the only method that will assure complete compaction.
The constituents of the waste will influence compaction. An increasing level of biowaste diversion and increasing percentages of packaging, paper and plastics (even with high rates of recycling) have caused waste streams entering landfills in western Europe to become drier. Dry waste is more difficult to shred and structurally break down unless there is adequate surface or ambient moisture. One way to overcome this obstacle is to blend moist waste loads with the dry material. This blending process is a worldwide management challenge that operators, spotters and supervisors face every day.
As previously mentioned, the general public has a variety of misperceptions about waste management professionals’ importance and the complexity of their work. Most people tend to focus their attention on more pleasant endeavours than waste management, which is often perceived as distasteful. This stance can be instantly changed, however, when plans are announced to site a new landfill or expand an existing landfill somewhere in the region. The notice serves as a trumpet call, rallying otherwise docile and amiable individuals to mortal combat against a supposed evil and deceitful enemy. Thus the ‘B.A.N.A.N.A’ concept (Build Absolutely Nothing, Anywhere Near Nobody) is born.
A great deal of this fear and suspicion comes from a lack of understanding of the sophistication and dedication of today’s waste management professional. A well managed, unobtrusive landfill requires all the management acumen and sophisticated tools of any modern complex business.
Protecting the environment and thereby the local population, assuring the safety and well being of employees, and running an efficient site that complies with all legal and environmental requirements are number-one priorities for the waste management team. If done correctly, the site will generate good returns for the owners (if a private enterprise) or minimize financial burden to the general public (if a public enterprise).The financial landscape
The upfront infrastructure costs of a modern sanitary landfill quickly get to millions of euros. Once the landfill is constructed, the largest single variable cost is the procurement and operation of a sizeable fleet of equipment. The main types of equipment used in landfill management are as follows:
• landfill compactors
• track-type tractors
• track-type loaders
• hauling units (articulated trucks or on-highway trucks)
• hydraulic excavators
• wheel loaders.
Some landfill managers prefer to hold in-house all the peripheral requirements of supporting a modern mobile equipment fleet, such as routine maintenance, oil sampling, scheduled machine rebuilds, warehousing of spare parts, etc. That said, landfill applications have proven to be one of the most destructive and demanding applications for heavy equipment. And the harsh nature of the work plus the worldwide scarcity of qualified diesel mechanics have caused many managers to look to their equipment suppliers to provide these services on a cost-effective, contractual basis. TM&R (total maintenance and repair) contracts with the equipment provider have become common, if not the norm, for the industry. This allows the landfill management team to focus their talents on the primary goal of an environmentally compliant operation. It also means maintenance costs can be managed through negotiation and budgeted well in advance.Filling to the brim
The fill sequence is extremely important and a key management requirement. Occupying available air space in the most efficient manner involves multiple variables. The fill sequence should:
• minimize costs related to hauling distances for cover material
• keep dozing distances short
• construct large areas for use during rainy seasons, while assuring that internal slopes are maintained. This allows surface water to flow away from the waste mass, enabling operations to continue uninterrupted regardless of the weather.
Managers must be constantly vigilant to maintain smooth daily operations while also being mindful of the final profile of the site. Rehandling of waste material or inefficient use of cover material are both expensive propositions that are obviously to be avoided.Click here to enlarge image
One new 21st-century management tool available to the modern landfill manager is the use of GPS (global positioning system) technology in the daily operation of the site. This technology, although new to landfill applications, has been successfully used by large earthmoving contractors and mines for a decade.
GPS technology can help operators determine the extent of compaction in different parts of the site. Shown here are the instrument panel and in-cab screen for one such application Click here to enlarge image
One such technology, the Caterpillar CAES system, is accurate to ±2 cm in altitude. Machine operators have a display screen in the cab that tells them when the machine has achieved maximum compaction because there is no further shrinkage in the waste from additional passes. In a track-type tractor, it assures that the operators know when they’ve spread the cover soil to the exact specification. Methane headers, flare vents, drainage pipes and other obstacles are clearly identified on the screen, eliminating the risk of accidentally running over and destroying them. The software ties into the site-engineering software and enables the management to construct the landfill according to the site design and verify it on a real-time basis. GPS can replace much of the intuition of landfill management with real-time data, providing managers and regulators with facts rather than opinion.Machine selection
Choosing the right machine for the task is extremely important particularly in landfills because of the uniquely harsh conditions. Prime production machines such as compactors and track-type tractors are vital in meeting daily production demands and complying with regulatory requirements. Choosing the wrong type or size of machine is a mistake that will cost the operation year after year.
Considerations in waste equipment design include operator safety, increased heat transfer capability and the special guarding of vulnerable components (such as hydraulic cylinders, fuel tanks and moving parts in the undercarriage and transmission). Modifications to equipment from suppliers such as Caterpillar have evolved over years of close collaboration with large waste management companies. Eventually these modifications became so extensive that specialized waste-handling configurations emerged as a means of standardizing arrangements and saving individual customers the expense of multiple, cumulative, single modifications. Waste-handling configurations are the result of years of ‘hard lessons learned’ and should not be taken lightly by procurement managers.
The multitude of variables involved in making the proper machine choice makes it a very difficult topic for brief discussion, but two key guidelines worth noting are as follows:
•Track-type tractors are for dozing, landfill compactors are for compacting.The more you can apply this principle in daily operations, the better your results will be from both a production and cost standpoint. Working together, tractors and compactors can accomplish more as a system than as independently working units. Track-type loaders are extremely versatile and can be used in many varied waste applications in all kinds of weather. Landfills of 500 tonnes/day or less should seriously consider track loaders, it could be the only machine needed. Versatility and capability of working alone also make track-type loaders an attractive machine for larger operations as well.
• Standard machines will not survive on the landfill for long. Operators will benefit from working with equipment suppliers who have a broad range of waste-specific machines and an in-depth understanding of the customer’s requirements. With this in mind, it makes sense to discuss the relevant waste requirements with potential equipment suppliers and check that they understand your business and offer equipment to meet your needs.
Another good tip is to visit other landfills, observe the equipment being used (and not being used because they’re down) and ask the manager for an honest appraisal of performance. They say learning from our mistakes is a sign of intelligence, learning from others’ mistakes is a sign of wisdom. Be wise - it’s less costly!
Richard A. Bliss is Specialty Markets Segment Manager for Europe, Africa and Middle East at Caterpillar SARL, Geneva, Switzerland.
To comment on this article or to see related features from our archive, go to www.waste-management-world.comLandfill management: in brief
Waste compaction is a primary responsibility of the landfill management team. It’s fundamental for protecting the environment and the surrounding population. Optimum compaction increases the life expectancy of the landfill by maximizing the use of available space. It’s also a clear indicator of a well managed landfill.
Landfill management is a complex and demanding task. It requires all the skills of any sophisticated management function with significant consequences for failure. New high-tech management tools can be applied to reduce risk and increase efficiencies.
Machine selection decisions are vitally important to the financial and operational success of a landfill. Work with a knowledgeable machine supplier with waste specific arrangements and a proven track record.