Bioreactor landfills are a more sustainable alternative to traditional landfills. Where traditional landfills face long aftercare periods and associated costs due to long-term potential for

environmental contamination Pollution is the introduction of contaminants into the natural environment that cause harm. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the component ...

, bioreactor landfills aim to stimulate breakdown of the waste within the landfill. Costs associated with management of leachate treatment and liner replacement are thereby significantly reduced while gas production (

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...

) is significantly enhanced to stimulate energy generation and amount of land required for landfills is reduced. Waste breakdown is stimulated either through leachate recirculation or aeration.

Traditional landfills and associated problems

Landfills are the oldest known method of

waste disposal Waste management or waste disposal includes the processes and actions required to manage waste from its inception to its final Waste disposal, disposal. This includes the Waste collection, collection, transport, Sewage treatment, treatm ...

. Modern sanitary landfills are typically large dug-out or natural pits surrounded by impermeable artificial liners, filled with waste and subsequently covered to prevent environmental emissions.

Bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

and

archaea Archaea ( ) is a Domain (biology), domain of organisms. Traditionally, Archaea only included its Prokaryote, prokaryotic members, but this has since been found to be paraphyletic, as eukaryotes are known to have evolved from archaea. Even thou ...

decompose the waste over several decades, producing harmful by-products including

greenhouse gases Greenhouse gases (GHGs) are the gases in the atmosphere that raise the surface temperature of planets such as the Earth. Unlike other gases, greenhouse gases absorb the radiations that a planet emits, resulting in the greenhouse effect. T ...

(notably methane),

leachate A leachate is any liquid that, in the course of passing through matter, extracts soluble or suspended solids, or any other component of the material through which it has passed. Leachate is a widely used term in the environmental sciences wh ...

rich in contaminants and particularly

ammonium Ammonium is a modified form of ammonia that has an extra hydrogen atom. It is a positively charged (cationic) polyatomic ion, molecular ion with the chemical formula or . It is formed by the protonation, addition of a proton (a hydrogen nucleu ...

,Kjeldsen, P. M. (2002). Present and Long-Term Composition of MSW Landfill Leachate: A Review. Critical Reviews in Environmental Science and Technology , 297-336. and

volatile organic compounds Volatile organic compounds (VOCs) are organic compounds that have a high vapor pressure at room temperature. They are common and exist in a variety of settings and products, not limited to house mold, upholstered furniture, arts and crafts sup ...

(VOCs) such as

hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is toxic, corrosive, and flammable. Trace amounts in ambient atmosphere have a characteristic foul odor of rotten eggs. Swedish chemist ...

(H₂S) which are associated with causing

smog Smog, or smoke fog, is a type of intense air pollution. The word "smog" was coined in the early 20th century, and is a portmanteau of the words ''smoke'' and ''fog'' to refer to smoky fog due to its opacity, and odour. The word was then inte ...

and

acid rain Acid rain is rain or any other form of Precipitation (meteorology), precipitation that is unusually acidic, meaning that it has elevated levels of hydrogen ions (low pH). Most water, including drinking water, has a neutral pH that exists b ...

.Brosseau, J. H. (1994). Trace gas compound emissions from municipal landfill sanitary sites; Atmospheric-Environment. Atmospheric Environment, pp. 285-293. The placement of liners in sanitary landfills prevent environmental pollution. Build-up of methane can lead to explosive conditions, and hence gas is captured and flared or, when gas is of sufficient quality, used for energy generation. Leachate build-up can reduce the structural stability of the landfill and ultimately enter the

groundwater Groundwater is the water present beneath Earth's surface in rock and Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. About 30 percent of all readily available fresh water in the world is groundwater. A unit ...

and pollute the environment.Christensen, T. H. (1999). Landfilling of waste: Biogas Hence, leachate is captured and treated at

sewage treatment plants Sewage treatment is a type of wastewater treatment which aims to remove contaminants from sewage to produce an effluent that is suitable to discharge to the surrounding environment or an intended reuse application, thereby preventing water ...

. Yet the created anaerobic conditions in the landfill means the “aftercare” period, where the landfill poses a significant environmental threat and thus monitoring and treatment are required, lasts a substantial amount of time and for certain countries, e.g. the Netherlands, is legally considered eternal. Costs of aftercare, such as replacement of liners and treatment of leachate shift to future generations and have an estimated cost of up to 20 million euros per landfill. Additionally, with an increasing amount of waste generation,United Nations Environment Programme (2024). Global Waste Management Outlook 2024: Beyond an age of waste – Turning rubbish into a resource. Nairobi. https://wedocs.unep.org/20.500.11822/44939 appropriate places to safely store waste have become difficult to find.

Working of a bioreactor landfill

Bioreactor landfills are operated in three modes:

aerobic Aerobic means "requiring air," in which "air" usually means oxygen. Aerobic may also refer to * Aerobic exercise, prolonged exercise of moderate intensity * Aerobics, a form of aerobic exercise * Aerobic respiration, the aerobic process of cellu ...

anaerobic Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to: *Adhesive#Anaerobic, Anaerobic ad ...

and a hybrid (combining the aerobic and anaerobic method). All three modes aim to stimulate microbial activity, enhancing

decomposition Decomposition is the process by which dead organic substances are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars and mineral salts. The process is a part of the nutrient cycle and is ess ...

while attempting to minimise harmful emissions.Hinkley Center For Solid and Hazardous Waste Management. (2006). Bioreactor.org - General Info. Retrieved February 3, 2010, from Bioreactor.org

/ref> Contaminants are flushed out during the treatment period, rapidly degraded, or retained within the landfill. In

bioreactors atmospheric air is introduced into the landfill using either Vertical direction, vertical or horizontal system of pipes. Aeration is either passive, where air passively moves into the landfill through the pipes, or active, where energy is used to either actively pump in air or extract landfill gas and introduce air based on overpressure. The created aerobic environment strongly accelerates waste decomposition, which is more efficient in the presence of

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

. Thanks to the aerobic conditions the amount of VOCs, generation of methane, and toxicity of leachate are minimised. Organic contaminants are degraded, inorganic contaminants are removed at a rapid pace during the aeration period, and ammonium is allowed to be transformed to

nitrate Nitrate is a polyatomic ion with the chemical formula . salt (chemistry), Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are solubility, soluble in wa ...

through

nitrification ''Nitrification'' is the biological oxidation of ammonia to nitrate via the intermediary nitrite. Nitrification is an important step in the nitrogen cycle in soil. The process of complete nitrification may occur through separate organisms or ent ...

in aerated pockets, followed by the transformation to

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

gas through

denitrification Denitrification is a microbially facilitated process where nitrate (NO3−) is reduced and ultimately produces molecular nitrogen (N2) through a series of intermediate gaseous nitrogen oxide products. Facultative anaerobic bacteria perform denitr ...

in anaerobic pockets. In anaerobic bioreactors treated leachate is recirculated to optimize landfill moisture levels, recirculate

microbes A microorganism, or microbe, is an organism of microscopic size, which may exist in its single-celled form or as a colony of cells. The possible existence of unseen microbial life was suspected from antiquity, with an early attestation in ...

through the landfill body, and flush previously unreachable sections of the landfill. The stimulated decomposition produces methane at a rate much faster and earlier than traditional landfills, which allows it to be used more efficiently for commercial purposes while reducing the time that the landfill needs to be monitored for methane production. Ammonium remainsa contaminant of primary concern for anaerobic bioreactors, as the nitrification process cannot take place. Furthermore, recirculation efficiency can be low because of the existence of impermeable layers and preferential flow paths in landfills. Hybrid bioreactors subject the landfill through aerobic-anaerobic cycles to combine the increased decomposition rate and ammonium removal of aerobic reactors with the optimal moisture content and flushing capabilities of anaerobic landfills.

Advantages of bioreactor landfills

The main goal of bioreactor landfills is an accelerated decomposition. As decomposition progresses, the mass of biodegradable components in the landfill declines, creating more space for dumping waste, up to an expected increase of 30%. With an increasing global waste production, bioreactor landfills can thus provide a significant way of maximizing landfill space. The operation as a bioreactor landfill furthermore decreases the aftercare period where landfills need te be monitored to an estimated less than a decade, down from several decades to eternity for traditional sanitary landfills. Contaminants are removed from rather than retained in the landfill. Bioreactor landfills are thereby significantly more cost-effective, do not shift costs to future generations, and allow landfills to be used for other purposes such as reforestation or parks at an earlier date.

Disadvantages of bioreactor landfills

Bioreactor landfills are a relatively new technology, hence initial monitoring costs are higher to ensure that everything important is discovered and properly controlled. This includes gases, odours and seepage of leachate into the ground surface. The increased moisture content of bioreactor landfill may reduce the structural stability of the landfill by increasing the pore water pressure within the waste mass. Since the target of bioreactor landfills is to maintain a high moisture content, gas collection systems can be affected by the increased moisture content of the waste.

Implementation of bioreactor landfills

Bioreactor landfills are a novel technology and most studies are on a laboratory scale in landfill simulation reactors. Translation to real life situations is difficult due to the relatively perfect conditions of landfill simulation reactors contrary to the complex and heterogeneous nature of landfills. Pilot projects on landfill scale are showing promise and more are being experimented with in different parts of the world. Despite the potential benefits of bioreactor landfills there are no standardised and approved designs with guidelines and operational procedures. Following is a list of bioreactor landfill projects which are being used to collect data for forming these needed guidelines and procedures:

United States

* California ** Yolo County * Florida ** Alachua County Southeast Landfill ** Highlands County ** New River Regional Landfill, Raiford ** Polk County Landfill, Winter Haven * Kentucky ** Outer Loop Landfill * Michigan ** Saint Clair County * Mississippi ** Plantation Oaks Bioreactor Demonstration Project, Sibley * Missouri ** Columbia * New Jersey ** ACUA's Haneman Environmental Park, Egg Harbor Township * North Carolina ** Buncombe County Landfill Project * Virginia ** Maplewood Landfill and King George County Landfills ** Virginia Landfill Project XL Demonstration Project

Canada

* Sainte-Sophie Bioreactor demonstration Project, Quebec

Australia

* New South Wales ** WoodLawn, Goulburn * Queensland ** Ti Tree Bioenergy, Ipswich

Netherlands

* Project introduction sustainable landfill management, including three landfills ** ''The Kragge'' landfill (leachate recirculated) ** ''Braambergen'' landfill (aerated) ** ''Wieringermeer'' landfill (aerated) * Landgraaf

Austria

* Heferlbach landfill (aerated) * Vienna (aerated)

References

External links

Toward a Twenty-first Century Landfill
- Yolo County's Bioreactor Research Project web page.
Bioreactorlandfill.org
{{DEFAULTSORT:Bioreactor Landfill Landfill Biochemical engineering Bioreactors