INSIGHTS

1 Buffer zones reconsidered
Kenneth Cameron, director of [MacRobert Incorporated]*, believes that the traditional method of creating buffer zones around a landfill site should be re-examined. The old method of authorising landfill sites involved the requirement to establish a buffer zone of 500 m to 800 m around a new site where residential or other developments were restricted.
Cameron, however, believes that this methodology has little merit, with the result being the excessive sterilisation of land. He argues that the random imposition of buffer zones may pose an excessive financial burden on the landfill developer. Instead, he has devised a system in which the individual environmental aspects of the landfill are assessed separately to enable the creation of a more accurate buffer zone. Effective legal management tools are then used to establish and maintain the buffer zone. The potential for groundwater contamination can be assessed, for example. It may be found that groundwater on one side of the landfill is affected but not on the other sides. The buffer zone should then be moulded accordingly.
“Land within this groundwater buffer zone can be used for any purpose that does not require the use of groundwater within that zone,” Cameron explains. Similarly, a buffer zone may be created to account for contaminants in the air around the landfill.  This buffer zone will take the shape of the air-dispersion modelling results. “There is no logical, legal or scientific reason for a buffer zone to be concentric,” he remarks.

2 Sterile land reduced
Cameron’s system also takes the nominal nuisance and visual impacts on the landfill’s existing or future neighbours into account. Where the sum of the impacts clearly has no potential for adverse health effects, it is perfectly feasible to negotiate suitable monetary compensation without imposing a setback over such areas. Title-deed nuisance endorsements, impact-specific servitude registrations and written compensation agreements form the central mode of control and regulation of all the elements of the buffer zone. Importantly, he claims, this system also ensures the survival of the buffer zone beyond change in property ownership.
Cameron points out that, if someone buys the affected land after the fact, the newcomer is generally not entitled to further compensation as the title restrictions and initial compensation are offset against a concomitant land-value reduction. Assuming proper monitoring practices are followed, the landfill developer can, therefore, establish a self-sustaining buffer zone. “Of course the science behind this method must be accurate and conservative. Using this method, we have found that the buffer zone around a landfill can become significantly smaller and we have a lot less sterile land. An enforceable and scientifically based buffer zone is established that not only protects current and future neighbours but also the landfill developer.”

3 Consistent compaction required
Effective use of landfill space comes down to compaction and four factors determine its success: layer thickness, the number of passes by the compactor, the slope and moisture content.
 The most important of these factors, according to Walton, is the thickness of the waste layer being compacted. Ideally, this should be about 0,6 m to 1 m thick and spread loose prior to compaction. Once the waste has been spread out, the compactor makes several passes over the loose layer. Usually, three to five passes are more than enough. More passes are unlikely to increase the compaction ratio, Walton claims.
Waste also has high moisture content. This is either from the waste itself or from moisture due to rainfall. Walton points out that, even after compaction, waste can store up to 65% moisture. After a major downpour, this moisture content can be as high as 80%. Higher moisture content results in higher compaction densities as the moisture weakens the bridging strength of the waste. If too much moisture is present, however, the extra water ends up at the bottom of the landfill in the form of leachate.
To aid compaction, Walton states that a rapid in-place decay process, as at Perdido Landfill in Escambia County, Florida, US, might be an option. Adding the right amount of water or other chemicals to the waste could increase the rate of decomposition significantly; freeing up airspace more rapidly. “As a result of the waste-mining and recovery project, the Escambia County landfill increased operation by an additional 26 years,” Walton says. 
Van Niekerk says that, at The Waste Group’s Mooiplaats landfill in Tshwane, one of the biggest frustrations in the compaction of waste is the presence of plastic bottles which can withstand a lot of pressure and are nearly impossible to compact. “The solution is simple: the cap must be left off a bottle when it is thrown away. However, almost invariably, they put the cap back on. I have made it a rule in my house to separate the bottles from the caps.”
Apart from compaction, not much else can be done to save landfill space, Van Niekerk claims. He points out that the key to getting the most out of available space is to minimise the amount of waste reaching the landfill in the first place.

4 Waste minimisation is key
Walton states that compaction efforts on site reduce the volume of waste deposited on the working face by 50%. Every tonne diverted from a landfill by recycling or other waste-reduction methods, therefore, results in a significant amount of airspace being preserved. According to Walton, the amount of waste generated per person per day in South Africa ranges from 0,2 kg to 1,2 kg and in excess of 60% of waste generated in households is recyclable.
Van Niekerk states that recycling needs to take place before waste reaches the landfill. “It all comes down to the available space. If the waste reaches our site and we still need to process it for recyclables, we will need to store it temporarily. On a typical landfill site, there is simply not enough space available to do that.”
The Waste Act of 2008, which requires municipalities to approach waste management differently by moving away from traditional end-of-pipe solutions to a holistic integrated approach, is adding impetus to the reduction of waste.
The Waste Act places emphasis on reusing, recovering and recycling. However, the recovery or recycling of the waste must use fewer natural resources than disposal. The Act also stipulates that the minister or MEC may require a person, category of persons, industry or organ of state which produces waste to prepare and submit an industry waste-management plan.
The penalties for non-compliance are substantial. A person convicted of certain offences for example, failure to conduct a site assessment could face a fine not exceeding R10-million, imprisonment for a period not exceeding 10 years or both.

5 Methane-gas extraction opportunity
Another way to minimise waste is to convert it into some form of energy. “Waste-to-energy operations bring significant benefits of reducing waste volumes ultimately going to landfill by up to 95%,” Walton says.
The first and simplest method of converting waste to energy involves methane-gas extraction. Stan Jewaskiewitz, president of the Institute of Waste Management in Southern Africa, explains how gas extraction works: “It is a simple process. An existing landfill is covered with a capping and allowed to decay for a length of time. Once enough methane has built up in the waste pile, gas wells are constructed to extract the gas. The methane is then either burnt in a flare or fed to a gas engine in order to generate electricity.”
Virtually any conventional landfill generates methane gas and is, therefore, a viable option for methane extraction, Van Niekerk adds. However, the process is costly and the funds required for the construction of infrastructure, extraction of gas and generation of electricity are simply not available to every municipality. The eThekwini gas-to-energy project at the Mariannhill and Bisasar landfills has a total project cost of approximately R150-million, for example.

6 Bioethanol alternative
A recently launched company, Stellenbosch Biomass Technologies (SBMT), is researching ways to convert waste organic materials into bioethanol. One of the company founders, Prof Johann Görgens, notes that the key lies in the process of breaking down the ligno-cellulose contained in fibrous plant biomass. More cellulose can be extracted from plant materials and fermented to create ethanol.
Another of the company’s founders, Professor WH van Zyl, says that, once the process has been perfected, SBMT can start looking towards waste products, such as recycled paper, pulp from paper mills and garden refuse, as possible sources of bioethanol. Van Zyl points out, however, that this technology is limited to mediums containing very few contaminants so mixed waste will not be a viable source. SBMT aims to have a demonstration plant up and running in 2011.
Once again, the human element plays a role in how effective this technology will be in South Africa; keeping in mind that waste flows are constant. One snag or delay in the system can have major ramifications for a multi-million-rand operation.

7 Pyrolysis possibility
Another option Jewaskiewitz puts forward is pyrolysis and gasification. Effectively, this involves  the thermal treatment of waste without burning it directly. Even though the incineration process has gained a bad reputation over the years, owing to the emissions involved, he says that the various thermal treatment technologies have advanced and the secret to making this technology more environment-friendly is in the pre-treatment of waste.
Jewaskiewitz provides the ArrowBio process, developed in Israel, as an example. This process integrates liquid-based separation technology and a high-rate anaerobic digestion process which effectively eliminate the need for prior separation or classification of mixed waste streams. During the first stage, water is added under high pressure. The organic material in the waste is disintegrated down to fibre size to form a thin slurry. Heavy components, such as broken glass, batteries, stones and metal parts, sink to the bottom and are separated from the slurry via a discharge chamber.
In the second stage, the organic slurry is pumped into a bioreactor or fermentation tank for anaerobic digestion of the organic phase. Naturally occurring microorganisms start the fermentation process and transform the complex organic material into simpler compounds, such as organic and fatty acids. Finally, the liquids leaving the first-stage reactor are heated to 40°C and pumped into the second bioreactor for anaerobic degradation of the organic materials. Biogas is formed which can, in turn, be used as a source of fuel with a relatively small carbon footprint. While this technology seems particularly suited to South Africa, Jewaskiewitz wonders whether or not it will be considered seriously.


*At the time of publiction of the editorial, Kenneth Cameron was a director at Cameron Cross Incorporated.