A sustainable landfill would be a landfill which is designed to clean itself of all harmful substances which might cause a harmful emission within a generation. That way each generation would deal with its own waste and pass on a clean environment to each successive generation.
A sustainable landfill would be a wonderful achievement, and paradoxically without even trying our ancestors once did achieve this, before the arrival of the industrial revolution. Sadly, life is not so simple for our generation, and it will be much harder for future generations unless we can find a way of achieving sustainability in so much of what we do today, which is far from sustainable.
The first step in designing a sustainable landfill would be to speed up the time needed for full decomposition and then continue to flush the landfill with clean fresh water. What do we mean by flushing in this context? We mean putting enough water through the landfill to remove all the water soluble components of a landfill, including all the soluble organic content, such that we need no longer keep it sealed from the environment to protect the surrounding environment from it.
The first step of flushing would be to pump a lot of water through the landfill, and recirculate it to ensure decomposition is rapid. Then, all of that water being recirculated will eventually have to be treated as leachate.
The leachate treatment may be carried out on-site or off-site but in both cases the residual components must be discharged off-site. If this is not done and the treated leachate continues to be recirculated, then components of the leachate such as chlorides will remain in elevated concentrations, and sustainably goals are not achieved. Compounds like chlorides (as in common table salt) may be polluting if they were to be released suddenly into the environment at concentrations significantly higher that the normal background concentration, and thus the landfill would continue to present a threat to the environment.
A strategy that consists only of recirculation of leachate, therefore, is not sustainable. A lot of landfill operators use Reverse Osmosis to treat leachate, however, that is short sighted and runs completely counter to all philosophy of the sustainable landfill, returning as these sites usually do, all of the residual components and removing only he pure water. (Incidentally, the elevated ammoniacal nitrogen resulting will be expected to have a very negative impact on landfill gas production as well.)
The volume of leachate and certainly the concentration of contaminants in that leachate will vary as the site ages. Of the components of leachate which will require treatment, the ammoniacal nitrogen content is usually the most expensive to deal with. As the refuse in the landfill is flushed, the concentrations of components such as ammoniacal nitrogen will fall.
Ammoniacal nitrogen concentrations may initially be in excess of 2,500mg/l and have to be reduced to less than 10mg/l. As the nitrogen is leached from the site, supplying a constant daily load of ammoniacal nitrogen to a treatment plant would require the daily volume treated to increase as the leachate becomes more dilute.
The degradable materials, ammoniacal nitrogen and the degradable organic compounds measured as BOD, can be successfully reduced in an SBR (sequencing batch reactor) biological leachate treatment plant to an acceptable level for recirculation or for discharge to the environment. Poorly degradable organic compounds and inorganic salts ‘will be residual components that may prove problematical for discharge under some circumstances.
If the discharge is to a relatively small surface watercourse then the size of the treatment plant may be limited by the amounts of chloride and non-degradable Chemical Oxygen Demand (COD) which may be discharged. Any limits on the discharge of non-degradable components may have obvious implications for the size of landfill that can be operated in a sustainable manner in a given location.
If the discharge of leachate is to sewer, then chlorides will pass through the sewage works untreated apart from dilution. Poorly degradable organic compounds will also pass through the sewage treatment works apart from a small degree of treatment and possibly some adsorption onto the sludge. The receiving works’ own discharge limits may restrict the volume or load of leachate that can be accepted to sewer, and hence restrict the opportunities for flushing.
Treatment of the necessary large amounts of leachate, either in a purpose-built plant or in a sewage treatment works will obviously entail higher rates of expenditure than are usually allocated for this currently at many landfills. However, present practices lead to the same pollution load being produced, treated and discharged, entailing similar total costs, but simply over longer time scales. The difference is therefore mainly a function of how accounting practices treat short-term and long-term expenditure.
It is ethically and morally wrong of our generation to subject future generations to continually increasing landfill emissions damaging groundwater quality once the landfill containment systems fail, and fail they will eventually, before they have cleansed themselves. That is inevitable.
So, all governments should seek not only to reduce the waste sent to landfill, and flush their landfills, but also to treat their leachate biologically and start doing that as soon as the first waste is placed in a new landfill. Full sustainability will not be achieved, with current standard containment landfill practices, but at least the flushing process will have been begun.