Degradation of Solid Waste in a Bioreactor Landfill
Introduction
In many industrialized nations, including the United States, MSW landfills have been planned, authorized, and used as bioreactors for nearly three decades since the notion of improved degradation of Municipal Solid Waste (MSW) using liquid addition was first proposed. Bioreactor landfills are permitted in around 75% of the states in the US, with the remaining states only approving them on a case-by-case basis. Among the advantages of bioreactor landfills are:
Airspace will be gained as a result of the following factors:
(1) Quicker trash settlement
(2) Lower leachate treatment costs
(3) Increased landfill gas output and
(4) Improved gas to energy production. Unknown long-term advantages of bioreactor landfills include improving the mechanical characteristics of MSW and the leachate quality after closure. Three categories can be used to group the main difficulties with bioreactor landfills:
Mechanical property changes, physical and chemical parameter targeting and monitoring, and fluid management are the first three.
This special issue includes coupled hydro-mechanical behavior and settlement, coupled hydro-mechanical behaviors and seepage control, enhanced degradation of waste using septage and air, seismic imaging to monitor moisture content and to capture spatial changes in the dynamic properties of the waste, dual-phase flow, and slope stability implications, and seepage control.
Faster waste stabilization, higher landfill gas generation for efficient energy recovery, increased landfill space, improved leachate treatment, and a shorter post-closure maintenance period are all goals of operating bioreactor landfills. Recirculating created leachate back into the landfills, which produces a conducive environment for quick microbial degradation of the biodegradable solid waste, is the primary process of waste stabilization in bioreactor landfills.
Special considerations of bioreactor landfill
Due to their low beginning costs and lack of knowledge and resources, open dump methods are the most archaic means of disposing of trash in most underdeveloped nations. The fundamental issue with this strategy is that it poses serious threats to both human health and the environment, particularly as MSW in industrializing nations becomes increasingly sophisticated. Other environmental effects could take decades to improve, and contaminated groundwater might never be made useful again. These haphazard piles of uncovered trash, which are frequently burning, are accompanied by stagnant puddles of dirty water, rodents, and fly infestations, as well as families of scavengers who are rummaging through the trash and roaming domestic animals. The bioreactor landfill concept can still play a significant role in providing solutions to all of these issues in this regard. Recirculating leachate also has a few drawbacks. The drawbacks comprise:
(1) A decline in MSW's shear strength, potentially lowering the factor of safety for the landfill's slope stability;
(2) Possible leachate breakouts from the landfill's sidewalls; and
(3) Increased liquid pressure head on the liner, perhaps raising the risk of contaminated groundwater. Thus, before a leachate recirculation system is put in place, designers and landfill owners are expected to assess the benefits and drawbacks on a site-specific basis.
Bioreactor technology - Its significance
The environment at the landfill will have a big influence on how quickly MSW decomposes. It is widely acknowledged that refuse buried in arid climates decomposes more slowly than refuse buried in places that receive more than 50 to 100 cm of annual precipitation because moisture content and pH have been found to consistently affect the rate of refuse decomposition.
Bioreactor landfills are ones that are run to speed up decomposition. A bioreactor landfill is described as "any approved Subtitle D landfill or landfill cell where liquid or air is pumped in a controlled manner into the waste mass to accelerate or promote stabilization of the trash" by the Solid Waste Association of North America (SWANA).
In order to recover bioenergy in the form of landfill gas and residue as manure, bioreactor technology uses physical, chemical, and biological processes with adequate leachate control.
Physical process- The physical process entails uniformly sized waste shredding, waste mixing, and other steps.
Chemical process- Leachate recirculation, pH modification, the addition of buffers and nutrients, etc. are chemical processes used to promote microbial growth.
Biological process- The bio-degradation process in a bioreactor landfill is enhanced by operating in an anaerobic atmosphere.
In comparison to a conventional "dry tomb" landfill, the decomposition and biological stabilization of the waste in a bioreactor landfill can take place much more quickly, potentially lowering long-term environmental hazards as well as operational and post-closure costs. The following are possible benefits of bioreactors:
Lower waste toxicity and movement due to anaerobic conditions. Decomposition and biological stabilization occur in years as opposed to decades in "dry tombs."
Significantly enhanced landfill gas generation that, when captured, can be used for onsite energy usage or sold
Decreased leachate disposal costs
An increase in landfill area of 15 to 30 percent as a result of a greater density of waste matter;
Lessening of post-closure care
Types of Bioreactor Landfills
Aerobic- Leachate from the lowest layer of an aerobic bioreactor landfill is extracted, piped to liquid storage tanks, and then carefully recirculated into the landfill.
Utilizing vertical or horizontal wells, the air is injected into the waste pile to encourage aerobic activity and quicken waste stabilization.
Anaerobic- To achieve the ideal moisture levels, moisture is provided to the waste material in an anaerobic bioreactor landfill in the form of recirculated leachate and other sources. Landfill gas is produced during anaerobic (without oxygen) biodegradation. Methane, which dominates landfill gas, can be recovered and used for energy projects while reducing greenhouse gas emissions.
Hybrid (Aerobic-Anaerobic)- By using a progressive aerobic-anaerobic treatment to quickly decompose organics in the top areas of the landfill and collect gas from lower sections, the hybrid bioreactor dump accelerates trash decomposition. Compared to aerobic landfills, operation as a hybrid causes methanogenesis to begin sooner.
How a bioreactor landfill differs from a conventional landfill?
Within 5-8 years of implementing the bioreactor process, a bioreactor dump is a clean landfill site that leverages increased microbial activities to transform and stabilize the easily and moderately decomposable organic waste elements. In comparison to what would normally happen in standard landfill sites, the bioreactor landfill considerably enhances the extent of organic waste composition, conversion rates of complex organic compounds, and process effectiveness. In the event of any partial containment system failures that last through the lifespan of the bioreactor process, the environmental performance measurement parameters (LFG composition and generation rate, and leachate constituent concentrations) shall remain at constant levels and not change.
For the bioreactor landfill to improve microbial decomposition processes, particular management strategies, and operational changes are needed. The addition of liquids and their control is the single most crucial element for a successful operation. The bioreactor process may also be improved by using additional techniques such as waste shredding, pH modification, nutrient addition, and balance, waste pre- and post-disposal conditioning, and temperature control. The creation and execution of targeted operating and development strategies are also necessary for the successful operation of a bioreactor landfill in order to guarantee the existence of ideal conditions for bioprocesses and to enable the system to operate as intended.
Leachate recirculation in landfilling is extended in the bioreactor landfill; however, the bioreactor process necessitates large liquid addition to achieve and sustain ideal conditions. Usually, there isn't enough leachate to meet all of the bioreactor's needs by itself. Leachate can be supplemented with water or other non-toxic or non-hazardous liquids and semi-liquids (depending on regulatory approvals).
Methods of leachate recirculation in a bioreactor landfill
Leachate recirculation methods employed on a full-scale include:
• Prewetting
• Vertical injection wells
• Horizontal infiltration systems
• Surface ponds
• Spraying
Conclusion
Leachate or other liquid amendments are generally added to the bioreactor landfill to control and optimize the process. There is now enough expertise to determine the best design and operating procedures. Sustainability, liquid addition, leachate hydrodynamics, leachate quality, the addition of air, and cost analysis continue to present technical difficulties and research gaps. It makes sense to use landfill bioreactor technology in conjunction with liquid treatment procedures. Large-scale research programs must continue to be funded in order to overcome technical challenges. Results must be presented in a way that enables data to be applied globally. This method of waste management will become standard practice and the sustainable landfill a reality in the not-too-distant future.
Reference:
https://sci-hub.ru/10.3109/07388551.2010.492206
https://www.tandfonline.com/doi/abs/10.3109/07388551.2010.492206