The present system of using landfills to treat and dispose the mountains of municipal solid wastes generated is not proving to be comprehensive and efficient. These landfills function more as tombs for our wastes rather than as waste treatment centres. The landfills are designed more as engineering mega structures to hold the waste rather than optimizing microbial processes that degrade the solid wastes efficiently. As a waste treatment centre, landfills fare poorly, exhibiting ‘passive’ biological treatment process with very poor biodegradation rates. A recent documentary on a local cable television showed newspapers dumped decades ago in a landfill are not degraded.
Once the landfills reached their maximum capacity to store the solid wastes, it will become a permanent tomb and could not be regenerated as future landfills. Newer landfills have to be found to replace the retired landfills, and this process goes on and on. It will be a matter of few decades before we will be running out of sites to be transformed into new landfills. This is especially so with the rapid increase in population, urbanizations and existing social habits we are practicing.
PRESENT STEPS TO EXTENDING LAND FILL LIFE
At present the approach to solving the shortage of landfills is more from the reduction of the volume of solid wastes that will end up at the landfill. This is achieved by waste reduction, recycling and reusing the wastes. Such activities will only prolong the lifespan of the landfills. While such activities will help it still does not solve the crucial problem of the landfill as it merely reduces the amount of wastes ending in the landfills and not treating the wastes in the landfill. Until such times we can find ways to enhance biodegradation processes in the landfills, the number and volume of landfills in the country will exhibit the cumulative effect!
The poor biodegradation rates that are synonymous with landfills operations occur because no efforts are made to understand the biodegradation processes and how to enhance these processes in the design and operation of landfills.
Efforts must be made now in the planning and building of landfills to include the enhancement of the various biodegradation processes. Now it is not that it is not possible but more due to the unwillingness to incorporate such biotechnology.
BIOPROCESSES IN LANDFILLS
We have to have a change in attitude towards how landfills should be run and operated. All this while we have regarded landfills more as tombs to store our solid wastes rather than as a waste treatment plant. At present the landfills are not designed or operated to maximize microbial degradations. Existing landfills show very slow rate of biodegradation than anticipated. We need to make landfills more efficient in treating the solid wastes by converting the landfills as landfill bioreactors. The failure to optimize the biological decomposition of solid wastes stemmed from the design and operation of landfills that retard biodegradation processes.
The two basic biodegradation processes occurring in landfills are composting and anaerobic digestion processes. Composting process depends on a good supply of air or oxygen and high moisture content. In landfills, composting could not occur efficiently due to compactions of solid wastes which prevent sufficient supply of air in the compacted wastes. Composting process is important in helping breaking down the large organic particles into smaller fragments which will be easily broken down by further microbial actions.
Anaerobic digestion process is the breakdown of organic matter by various types of microorganisms in the absence of oxygen. This process will occur deep within the layers of the landfills. It is however a very slow and sensitive process and easily destabilized.
These two biological processes do occur in the landfills but are not efficiently carried out due to lack of interest in the landfill operators to monitor, control and optimize the processes.
PARADIGM SHIFT IN LANDFILL OPERATION
What we really need now is a paradigm shift and to regard the landfills more as a waste treatment plant and not as a waste storage centre. To achieve this we need to treat the landfill as a ‘landfill bioreactor’ where the microbial processes in the landfill is enhanced by applying the knowledge of Industrial microbiology and Fermentation technology.
In this aspect the engineers that design and operate the landfills must be amenable to inputs by environmental and industrial microbiologists and fermentation technologists to convert the ‘storage landfills’ to become ‘bioreactor landfills’
THE CONCEPT OF LANDFILL BIOREACTOR
The operation of the landfills as an industrial process is not difficult to envisage. As it is now there are a lot of biotechnology industries which utilizes fermentation technology to produce products by using large scale fermentors or bioreactors. Even now, most biological wastewater treatment plants utilize microorganisms grown in large bioreactors such as activated sludge systems and anaerobic digesters to treat various effluents.
A bioreactor is not any ordinary vessel but a specially designed vessel that is designed to cultivate high concentration of microorganisms and bioconversions. In most high rate bioreactors or fermentors, this is achieved by providing a stirrer to ensure good mixing and mass transfers between the substrate and the microorganisms. There are also physical and chemical sensors to monitor and control the bioreactor
The difference between landfill bioreactors compared to other conventional biological wastewater treatment bioreactor is that the landfills bioreactors are larger and uses solid substrate fermentation instead of liquid substrate. The landfill bioreactor is more complex in operating than the conventional biological wastewater treatment reactors due to the volume and complexity of wastes that it is receiving and treating
A landfill bioreactor is a logical extension in attempts to treat solid wastes more efficiently. In the last decade there are attempts to using landfills bioreactors in Unites States as well as the European countries and the results have been more than encouraging.
ADVANTAGES OF LANDFILL BIOREACTOR
There are several distinct advantages that the bioreactor landfills have over conventional landfills. A landfill bioreactor is more effective in treating solid wastes as there is a more complete and faster rate of biodegradation compared to those occurring in typical landfills. This will result in additional capacity for the landfills and the extension of the lifetime of the landfills. There will be a deferment in the need for new and additional landfills and more profit for the operators.
Lesser leachate will be released by the bioreactor landfills to the environment as the leachate will be recycled back into the landfills to promote faster biodegradation. Less cost will be incurred in treating lower volume of leachate from landfills
More methane gas will be generated within shorter time from the landfill bioreactors which can be exploited as alternative energy resources.
The shorter treatment time and higher stability of wastes achieved through landfill bioreactor will ensure shorter periods of care after the landfills are closed. The stabilized wastes of the landfills will be lesser risks to the environment compared to conventional landfills.
OPERATING A LANDFILL BIOREACTOR
The design and operation of the bioreactor landfills will be different from the ‘hands off’ operation of existing landfills. In traditionally operated landfills used as storage facilities there are attempts to fill as much wastes that can be filled and compacted into the existing landfill before a new cell is opened up. Usually each landfill that has received its total daily load is covered with a layer of soil before the next loading is due. New landfill cells are only opened up and used after existing cells have reached their capacity.
In the operation of bioreactor landfills, the design and operation of the landfills will differ significantly and may even appear as opposing the trends of running conventional landfills.
A bioreactor should be operated as a waste processing facility. The bioreactor landfill should be designed and built to promote the growth of the various microbes involved. Proper understanding of the biodegradation process, the involvement of various physiological groups off microorganism and how to provide the optimum environment for these various groups of microorganisms need to be understood. Close monitoring and control of the bioprocess of the landfill is involved
COMBINATION OF BIOREACTORS NEEDED
The biodegradation process in a landfill bioreactor is made complex by the involvement of various types of microorganisms, complexity of wastes to be treated. The complete biodegradation of the solid wastes require a succession of different organisms of different physiological requirements. A single landfill bioreactor could not possibly provide conditions that are optimal for all the organisms.
There is the need to create a series of landfill cells to optimize the conditions at all the major steps of the bioconversion process in a rotating sequence.
Unless the existing operators of landfills are not willing to implement the technology of landfill bioreactors instead of the conventional landfills, solid wastes will continue to accumulate and more landfills will be needed. At the end of the day when the lease of operating the landfills is over, it will be poor taxpayers who will be footing the bill to repair the environmental damages caused by the derelict landfills! And the bill will not be cheap….!
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