To dump, or not to dump? That's the question!
Landfill dumping has been a main approach for municipal solid wastes disposal and will be continued in the near future. However, gaseous emission from municipal waste may causes offensive odors and disturbs the neighbors around landfill sites. Usually there are not enough buffer zones between landfill sites and the nearest sensitive neighbor's nose!
Minimization of odor emission from landfill operation
As landfills become more sophisticated and take on the role of massive waste to energy bioreactors (methanogenic digesters), the demand for odor management will become more critical. The principles which need to be adopted are to minimize the number of sources of odor generation which exist on site;undertake direct management of those sources which can give rise to problems; ensure natural attenuation is available for those emanations which cannot be directly managed.
The mitigation of odor can be achieved by the followings:
- Appropriate Daily Cover: Daily cover is best comprised of mulched woody material (MWM) and earth mixtures in 50% by weight mixture. This material has been shown to be permeable but with some capacity to retain water; to be adequately traffic bearing, to be non combustible, heavy and abbrasive enough to prevent litter problems and to behave as a highly effective biofilter with respect to odour (50-70% reduction). This material is also readily available at landfill sites and 300mm thick layers adds to the gas generation potential and energy recovery value of the site long term. Some low permeability interim cover does need to be used to make gas harvesting close to the active face more efficient.
- Minimizing Fresh Waste Exposure: Current practices involve cover removal, followed by waste unloading, spreading and compaction using the smallest area possible. Inevitably, “trash odors” are released in this process and odor flushing occurs due to gas release. These odor releases can be mitigated by progressively spreading mulched woody material/earth mixture and compacting it along with the waste, with a final top up at day end. In this way, a biofilter is established rapidly which does not impede compaction on the face or spreading, but odor is mitigated.
Other Opportunities
Most other odor mitigation measures are common sense. They include:
- avoiding parking full waste vehicles on site overnight;
- providing vacuum venting on leachate sumps and drains;
- direct recycling leachate from sumps to sub cover reinfiltration in bioreactor landfills or to sewer;
- providing close monitoring and maintenance of gas harvesting systems and flares;
- avoiding excessively clayey final cap material or other material prone to dessication or settlement cracking, or provide for a moist biologically active attenuation capacity in the vegetation layer;
- washout of vehicles and their substructure to reduce on road vehicle odor;
- avoidance of odor masking agents which merely reinforce noticeable odor occurrence.
Conclusions
It is clear that any progress in odor control policy from a "no nuisance" approach to a quantitative regulation needs a sound odor monitoring procedure with an acceptable compatibility between the local regulatory agencies, citizens and local government. Decisions should not be based on short term "knee-jerk" reactions, and it should be recognized that every choice comes with a measurable cost. No one wants to live near a landfill. Nature has hard wired us that way to insure our preservation.
If you doubt that, just try to feed your cat in its litter box. As a community and a society, we must find a better way, and we should be prepared to pay for it as well.