Biofiltration is a pollution control technique using a bioreactor containing living material to capture and biologically degrade pollutants. Common uses include processing waste water, capturing harmful chemicals or silt from surface runoff, and microbiotic oxidation of contaminants in air. Industrial biofiltration can be classified as the process of utilizing biological oxidation to remove volatile organic compounds, odors, and hydrocarbons.
Examples of biofiltration include:
When applied to air filtration and purification, biofilters use microorganisms to remove air pollution. [1] The air flows through a packed bed and the pollutant transfers into a thin biofilm on the surface of the packing material. Microorganisms, including bacteria and fungi are immobilized in the biofilm and degrade the pollutant. Trickling filters and bioscrubbers rely on a biofilm and the bacterial action in their recirculating waters.
The technology finds the greatest application in treating malodorous compounds and volatile organic compounds (VOCs). Industries employing the technology include food and animal products, off-gas from wastewater treatment facilities, pharmaceuticals, wood products manufacturing, paint and coatings application and manufacturing and resin manufacturing and application, etc. Compounds treated are typically mixed VOCs and various sulfur compounds, including hydrogen sulfide. Very large airflows may be treated and although a large area (footprint) has typically been required—a large biofilter (>200,000 acfm) may occupy as much or more land than a football field—this has been one of the principal drawbacks of the technology. Since the early 1990s, engineered biofilters have provided significant footprint reductions over the conventional flat-bed, organic media type.
One of the main challenges to optimum biofilter operation is maintaining proper moisture throughout the system. The air is normally humidified before it enters the bed with a watering (spray) system, humidification chamber, bio scrubber, or bio trickling filter. Properly maintained, a natural, organic packing media like peat, vegetable mulch, bark or wood chips may last for several years but engineered, combined natural organic, and synthetic component packing materials will generally last much longer, up to 10 years. Several companies offer these types of proprietary packing materials and multi-year guarantees, not usually provided with a conventional compost or wood chip bed biofilter.
Although widely employed, the scientific community is still unsure of the physical phenomena underpinning biofilter operation, and information about the microorganisms involved continues to be developed. [2] A biofilter/bio-oxidation system is a fairly simple device to construct and operate and offers a cost-effective solution provided the pollutant is biodegradable within a moderate time frame (increasing residence time = increased size and capital costs), at reasonable concentrations (and lb/hr loading rates) and that the airstream is at an organism-viable temperature. For large volumes of air, a biofilter may be the only cost-effective solution. There is no secondary pollution (unlike the case of incineration where additional CO2 and NOx are produced from burning fuels) and degradation products form additional biomass, carbon dioxide and water. Media irrigation water, although many systems recycle part of it to reduce operating costs, has a moderately high biochemical oxygen demand (BOD) and may require treatment before disposal. However, this "blowdown water", necessary for proper maintenance of any bio-oxidation system, is generally accepted by municipal publicly owned treatment works without any pretreatment.
Biofilters are being utilized in Columbia Falls, Montana at Plum Creek Timber Company's fiberboard plant. [3] The biofilters decrease the pollution emitted by the manufacturing process and the exhaust emitted is 98% clean. The newest, and largest, biofilter addition to Plum Creek cost $9.5 million, yet even though this new technology is expensive, in the long run it will cost less overtime than the alternative exhaust-cleaning incinerators fueled by natural gas (which are not as environmentally friendly).
Biofiltration was first introduced in England in 1893 as a trickling filter for wastewater treatment and has since been successfully used for the treatment of different types of water. [5] Biological treatment has been used in Europe to filter surface water for drinking purposes since the early 1900s and is now receiving more interest worldwide. Biofiltration is also common in wastewater treatment, aquaculture and greywater recycling, as a way to minimize water replacement while increasing water quality.
A biofilter is a bed of media on which microorganisms attach and grow to form a biological layer called biofilm. Biofiltration is thus usually referred to as a fixed–film process. Generally, the biofilm is formed by a community of different microorganisms (bacteria, fungi, yeast, etc.), macro-organisms (protozoa, worms, insect's larvae, etc.) and extracellular polymeric substances (EPS) (Flemming and Wingender, 2010). Air or water flows through a media bed and any suspended compounds are transferred into a surface biofilm where microorganisms are held to degrade pollutants. The aspect of the biofilm [6] is usually slimy and muddy.
Water to be treated can be applied intermittently or continuously over the media, via upflow or downflow. Typically, a biofilter has two or three phases, depending on the feeding strategy (percolating or submerged biofilter):
Organic matter and other water components diffuse into the biofilm where the treatment occurs, mostly by biodegradation. Biofiltration processes are usually aerobic, which means that microorganisms require oxygen for their metabolism. Oxygen can be supplied to the biofilm, either concurrently or countercurrently with water flow. Aeration occurs passively by the natural flow of air through the process (three phase biofilter) or by forced air supplied by blowers.
Microorganisms' activity is a key-factor of the process performance. The main influencing factors are the water composition, the biofilter hydraulic loading, the type of media, the feeding strategy (percolation or submerged media), the age of the biofilm, temperature, aeration, etc.
The mechanisms by which certain microorganisms can attach and colonize on the surface of filter media of a biofilter can be via transportation, initial adhesion, firm attachment, and colonization [Van Loosdrecht et al., 1990]. The transportation of microorganisms to the surface of the filter media is further controlled by four main processes of diffusion (Brownian motion), convection, sedimentation, and active mobility of the microorganisms. The overall filtration process consists of microorganism attachment, substrate utilization which causes biomass growth, to biomass detachment. [5]
Most biofilters use media such as sand, crushed rock, river gravel, or some form of plastic or ceramic material shaped as small beads and rings. [7]
Although biological filters have simple superficial structures, their internal hydrodynamics and the microorganisms' biology and ecology are complex and variable. [8] These characteristics confer robustness to the process. In other words, the process has the capacity to maintain its performance or rapidly return to initial levels following a period of no flow, of intense use, toxic shocks, media backwash (high rate biofiltration processes), etc.
The structure of the biofilm protects microorganisms from difficult environmental conditions and retains the biomass inside the process, even when conditions are not optimal for its growth. Biofiltration processes offer the following advantages: (Rittmann et al., 1988):
Because filtration and growth of biomass leads to an accumulation of matter in the filtering media, this type of fixed-film process is subject to bioclogging and flow channeling. Depending on the type of application and on the media used for microbial growth, bioclogging can be controlled using physical and/or chemical methods. Backwash steps can be implemented using air and/or water to disrupt the biomat and recover flow whenever possible. Chemicals such as oxidizing (peroxide, ozone) or biocide agents can also be used.
Biofiltration can require a large area for some treatment techniques (suspended growth and attached growth processes) as well as long hydraulic retention times (anaerobic lagoon and anaerobic baffled reactor). [11]
For drinking water, biological water treatment involves the use of naturally occurring microorganisms in the surface water to improve water quality. Under optimum conditions, including relatively low turbidity and high oxygen content, the organisms break down material in the water and thus improve water quality. Slow sand filters or carbon filters are used to provide a support on which these microorganisms grow. These biological treatment systems effectively reduce water-borne diseases, dissolved organic carbon, turbidity and color in surface water, thus improving overall water quality.
Typically in drinking water treatment; granular activated carbon or sand filters are used to prevent re-growth of microorganisms in water distribution pipes by reducing levels of iron and nitrate that act as a microbial nutrient. GAC also reduces chlorine demand and other disinfection by-product accumulation by acting as a first line of disinfection. Bacteria attached to filter media as a biofilm oxidize organic material as both an energy and carbon source, this prevents undesired bacteria from using these sources which can reduce water odors and tastes [Bouwer, 1998]. These biological treatment systems effectively reduce water-borne diseases, dissolved organic carbon, turbidity and color in surface water, thus improving overall water quality.
Biotechnological techniques can be used to improve the biofiltration of drinking water by studying the microbial communities in the water. Such techniques include qPCR (quantitative polymerase chain reaction), ATP assay, metagenomics, and flow cytometry. [12]
Biofiltration is used to treat wastewater from a wide range of sources, with varying organic compositions and concentrations. Many examples of biofiltration applications are described in the literature. Bespoke biofilters have been developed and commercialized for the treatment of animal wastes, [13] landfill leachates, [14] dairy wastewater, [15] domestic wastewater. [16]
This process is versatile as it can be adapted to small flows (< 1 m3/d), such as onsite sewage [17] as well as to flows generated by a municipality (> 240 000 m3/d). [18] For decentralized domestic wastewater production, such as for isolated dwellings, it has been demonstrated that there are important daily, weekly and yearly fluctuations of hydraulic and organic production rates related to modern families' lifestyle. [19] In this context, a biofilter located after a septic tank constitutes a robust process able to sustain the variability observed without compromising the treatment performance.
In anaerobic wastewater treatment facilities, biogas is fed through a bio-scrubber and “scrubbed” with activated sludge liquid from an aeration tank. [20] Most commonly found in wastewater treatment is the trickling filter process (TFs) [Chaudhary, 2003]. Trickling filters are an aerobic treatment that uses microorganisms on attached medium to remove organic matter from wastewater.
In primary wastewater treatment, biofiltration is used to control levels of biochemical oxygen, demand, chemical oxygen demand, and suspended solids. In tertiary treatment processes, biofiltration is used to control levels of organic carbon [ Carlson, 1998].
The use of biofilters is common in closed aquaculture systems, such as recirculating aquaculture systems (RAS). The biofiltration techniques used in aquaculture can be separated into three categories: biological, physical, and chemical. The primary biological method is nitrification; physical methods include mechanical techniques and sedimentation, and chemical methods are usually used in tandem with one of the other methods. [21] Some farms use seaweed, such as those from the genera Ulva, to take excess nutrients out of the water and release oxygen into the ecosystem in a “recirculation system” while also serving as a source of income when they sell the seaweed for safe human consumption. [22]
Many designs are used, with different benefits and drawbacks, however the function is the same: reducing water exchanges by converting ammonia to nitrate. Ammonia (NH4+ and NH3) originates from the brachial excretion from the gills of aquatic animals and from the decomposition of organic matter. As ammonia-N is highly toxic, this is converted to a less toxic form of nitrite (by Nitrosomonas sp.) and then to an even less toxic form of nitrate (by Nitrobacter sp.). This "nitrification" process requires oxygen (aerobic conditions), without which the biofilter can crash. Furthermore, as this nitrification cycle produces H+, the pH can decrease, which necessitates the use of buffers such as lime.
Filtration is a physical separation process that separates solid matter and fluid from a mixture using a filter medium that has a complex structure through which only the fluid can pass. Solid particles that cannot pass through the filter medium are described as oversize and the fluid that passes through is called the filtrate. Oversize particles may form a filter cake on top of the filter and may also block the filter lattice, preventing the fluid phase from crossing the filter, known as blinding. The size of the largest particles that can successfully pass through a filter is called the effective pore size of that filter. The separation of solid and fluid is imperfect; solids will be contaminated with some fluid and filtrate will contain fine particles. Filtration occurs both in nature and in engineered systems; there are biological, geological, and industrial forms. In everyday usage the verb "strain" is more often used; for example, using a colander to drain cooking water from cooked pasta.
Water treatment is any process that improves the quality of water to make it appropriate for a specific end-use. The end use may be drinking, industrial water supply, irrigation, river flow maintenance, water recreation or many other uses, including being safely returned to the environment. Water treatment removes contaminants and undesirable components, or reduces their concentration so that the water becomes fit for its desired end-use. This treatment is crucial to human health and allows humans to benefit from both drinking and irrigation use.
Wastewater treatment is a process which removes and eliminates contaminants from wastewater. It thus converts it into an effluent that can be returned to the water cycle. Once back in the water cycle, the effluent creates an acceptable impact on the environment. It is also possible to reuse it. This process is called water reclamation. The treatment process takes place in a wastewater treatment plant. There are several kinds of wastewater which are treated at the appropriate type of wastewater treatment plant. For domestic wastewater the treatment plant is called a Sewage Treatment. Municipal wastewater or sewage are other names for domestic wastewater. For industrial wastewater, treatment takes place in a separate Industrial wastewater treatment, or in a sewage treatment plant. In the latter case it usually follows pre-treatment. Further types of wastewater treatment plants include Agricultural wastewater treatment and leachate treatment plants.
A constructed wetland is an artificial wetland to treat sewage, greywater, stormwater runoff or industrial wastewater. It may also be designed for land reclamation after mining, or as a mitigation step for natural areas lost to land development. Constructed wetlands are engineered systems that use the natural functions of vegetation, soil, and organisms to provide secondary treatment to wastewater. The design of the constructed wetland has to be adjusted according to the type of wastewater to be treated. Constructed wetlands have been used in both centralized and decentralized wastewater systems. Primary treatment is recommended when there is a large amount of suspended solids or soluble organic matter.
Industrial wastewater treatment describes the processes used for treating wastewater that is produced by industries as an undesirable by-product. After treatment, the treated industrial wastewater may be reused or released to a sanitary sewer or to a surface water in the environment. Some industrial facilities generate wastewater that can be treated in sewage treatment plants. Most industrial processes, such as petroleum refineries, chemical and petrochemical plants have their own specialized facilities to treat their wastewaters so that the pollutant concentrations in the treated wastewater comply with the regulations regarding disposal of wastewaters into sewers or into rivers, lakes or oceans. This applies to industries that generate wastewater with high concentrations of organic matter, toxic pollutants or nutrients such as ammonia. Some industries install a pre-treatment system to remove some pollutants, and then discharge the partially treated wastewater to the municipal sewer system.
An aerated lagoon is a simple wastewater treatment system consisting of a pond with artificial aeration to promote the biological oxidation of wastewaters.
Septic drain fields, also called leach fields or leach drains, are subsurface wastewater disposal facilities used to remove contaminants and impurities from the liquid that emerges after anaerobic digestion in a septic tank. Organic materials in the liquid are catabolized by a microbial ecosystem.
Secondary treatment is the removal of biodegradable organic matter from sewage or similar kinds of wastewater. The aim is to achieve a certain degree of effluent quality in a sewage treatment plant suitable for the intended disposal or reuse option. A "primary treatment" step often precedes secondary treatment, whereby physical phase separation is used to remove settleable solids. During secondary treatment, biological processes are used to remove dissolved and suspended organic matter measured as biochemical oxygen demand (BOD). These processes are performed by microorganisms in a managed aerobic or anaerobic process depending on the treatment technology. Bacteria and protozoa consume biodegradable soluble organic contaminants while reproducing to form cells of biological solids. Secondary treatment is widely used in sewage treatment and is also applicable to many agricultural and industrial wastewaters.
Microbial fuel cell (MFC) is a type of bioelectrochemical fuel cell system also known as micro fuel cell that generates electric current by diverting electrons produced from the microbial oxidation of reduced compounds on the anode to oxidized compounds such as oxygen on the cathode through an external electrical circuit. MFCs produce electricity by using the electrons derived from biochemical reactions catalyzed by bacteria. Comprehensive Biotechnology MFCs can be grouped into two general categories: mediated and unmediated. The first MFCs, demonstrated in the early 20th century, used a mediator: a chemical that transfers electrons from the bacteria in the cell to the anode. Unmediated MFCs emerged in the 1970s; in this type of MFC the bacteria typically have electrochemically active redox proteins such as cytochromes on their outer membrane that can transfer electrons directly to the anode. In the 21st century MFCs have started to find commercial use in wastewater treatment.
Aerobic granular reactors (AGR) or Aerobic granular sludge (AGS) are a community of microbial organisms, typically around 0.5-3mm in diameter, that remove carbon, nitrogen, phosphorus and other pollutants in a single sludge system. It can also be used for wastewater treatments. Aerobic granular sludge is composed of bacteria, protozoa and fungi, which allows oxygen to follow in and biologically oxidize organic pollutants. AGS is a type of wastewater treatment process for sewages and/or industrial waste treatment. AGR was first discovered by UK engineers, Edward Ardern and W.T. Lockett who were researching better ways for sewage disposal. Another scientist by the name of Dr. Gilbert Fowler, who was at the University of Manchester working on an experiment based on aeration of sewage in a bottle coated with algae. Eventually, all three scientists were able to collaborate with one another to discover AGR/AGS.
A trickling filter is a type of wastewater treatment system. It consists of a fixed bed of rocks, coke, gravel, slag, polyurethane foam, sphagnum peat moss, ceramic, or plastic media over which sewage or other wastewater flows downward and causes a layer of microbial slime (biofilm) to grow, covering the bed of media. Aerobic conditions are maintained by splashing, diffusion, and either by forced-air flowing through the bed or natural convection of air if the filter medium is porous. The treatment of sewage or other wastewater with trickling filters is among the oldest and most well characterized treatment technologies.
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 pollution from raw sewage discharges. Sewage contains wastewater from households and businesses and possibly pre-treated industrial wastewater. There are a high number of sewage treatment processes to choose from. These can range from decentralized systems to large centralized systems involving a network of pipes and pump stations which convey the sewage to a treatment plant. For cities that have a combined sewer, the sewers will also carry urban runoff (stormwater) to the sewage treatment plant. Sewage treatment often involves two main stages, called primary and secondary treatment, while advanced treatment also incorporates a tertiary treatment stage with polishing processes and nutrient removal. Secondary treatment can reduce organic matter from sewage, using aerobic or anaerobic biological processes. A so-called quarternary treatment step can also be added for the removal of organic micropollutants, such as pharmaceuticals. This has been implemented in full-scale for example in Sweden.
Membrane bioreactors are combinations of membrane processes like microfiltration or ultrafiltration with a biological wastewater treatment process, the activated sludge process. These technologies are now widely used for municipal and industrial wastewater treatment. The two basic membrane bioreactor configurations are the submerged membrane bioreactor and the side stream membrane bioreactor. In the submerged configuration, the membrane is located inside the biological reactor and submerged in the wastewater, while in a side stream membrane bioreactor, the membrane is located outside the reactor as an additional step after biological treatment.
A rotating biological contactor or RBC is a biological fixed-film treatment process used in the secondary treatment of wastewater following primary treatment. The primary treatment process involves removal of grit, sand and coarse suspended material through a screening process, followed by settling of suspended solids. The RBC process allows the wastewater to come in contact with a biological film in order to remove pollutants in the wastewater before discharge of the treated wastewater to the environment, usually a body of water. A rotating biological contactor is a type of secondary (biological) treatment process. It consists of a series of closely spaced, parallel discs mounted on a rotating shaft which is supported just above the surface of the wastewater. Microorganisms grow on the surface of the discs where biological degradation of the wastewater pollutants takes place.
Recirculating aquaculture systems (RAS) are used in home aquaria and for fish production where water exchange is limited and the use of biofiltration is required to reduce ammonia toxicity. Other types of filtration and environmental control are often also necessary to maintain clean water and provide a suitable habitat for fish. The main benefit of RAS is the ability to reduce the need for fresh, clean water while still maintaining a healthy environment for fish. To be operated economically commercial RAS must have high fish stocking densities, and many researchers are currently conducting studies to determine if RAS is a viable form of intensive aquaculture.
A vermifilter is an aerobic treatment system, consisting of a biological reactor containing media that filters organic material from wastewater. The media also provides a habitat for aerobic bacteria and composting earthworms that purify the wastewater by removing pathogens and oxygen demand. The "trickling action" of the wastewater through the media dissolves oxygen into the wastewater, ensuring the treatment environment is aerobic for rapid decomposition of organic substances.
Moving bed biofilm reactor (MBBR) is a type of wastewater treatment process that was first invented by Professor Hallvard Ødegaard at Norwegian University of Science and Technology in the late 1980s. The process takes place in an aeration tank with plastic carriers that a biofilm can grow on. The compact size and cheap wastewater treatment costs offers many advantages for the system. The main objective of using MBBR being water reuse and nutrient removal or recovery. In theory, wastewater will be no longer considered waste, it can be considered a resource.
Bioclogging or biological clogging refers to the blockage of pore space in soil by microbial biomass, including active cells and their byproducts such as extracellular polymeric substance (EPS). The microbial biomass obstructs pore spaces, creating an impermeable layer in the soil and significantly reducing water infiltration rates.
