|Granulated Activated Carbon Bio-Filtration System
Granulated Activated Carbon Bio-Filtration System (GACBF)
Granulated Activated Carbon Adsorption / Bio-Filtration (GACBF) Systems are becoming the low cost solution for
VOC, BTEX, H2S, SO2, and Odor control from industrial, agricultural, energy and municipal sources of air
emissions. Biofiltration is currently being used to bio-oxidize toxic and other volatiles in industrial effluents present
in higher concentration amounts.
However, the market for abatement technology based solely on biofiltration has been a fraction when compared to
more traditional abatement control technologies such as; thermal oxidizers, regenerative thermal oxidizers,
catalytic thermal oxidizers and granulated carbon filters.
Granulated Activated Carbon Absorption / Biofiltration Introduction
A frequent cited example is the overall emission control efficiencies of 98% percent or slightly above conditions
that exist within the United States, the United States industry has preferred the use of abatement control
technologies such as incinerators i.e. Thermal oxidizers which actively reach destruction efficiencies of 98%+ and
are more conventional in nature. GACBF in the U.S. are competing against these control technologies which have
been widely accepted and used, and whose performance has been well understood for decades.
Currently, second and third generation GACBF systems are capable of achieving much higher destructions 99%+
and are equal to or often surpass many of the more conventional destruction methods, such as thermal oxidizer
systems, these newer systems have adopted a granulated carbon adsorption bed and are currently achieving
documented destruction efficiencies above 98 percent.
The reality that most European countries have odor standards that may help to explain why there are more solely
biofiltration systems that exist in European countries. The objective in the European case is overcoming, the odor
nuisance rather than meeting specific destruction efficiency as adopted by most U.S. State and Federal Agencies.
After analysis you will find that there are no real obstructions that exist preventing the total widespread use
of the combination granulated carbon absorption/bio-filtration system as a very clean and viable pollution
control technology within the United States.
The Clean Air Act (CAA) has an important impact on the United States environmental regulations, and many
regulatory aspects are contained in its provisions. Directed by various provisions dealing with metropolitan air
pollution, the U.S. Environmental Protection Agency has issued regulations and State instruction documents to
control many pollutants to include ground level Ozone, nitrogen oxides (NOx), and sulfur compounds that include
hydrogen sulfide (H2S), sulfur dioxide (SO2), sulfur trioxide (S03) and Siloxanes.
Volatile organic compounds (VOCs) are restricted because they are a significant contributor to the formation of
ozone with many of the compounds contributing hundreds of times that of carbon dioxide (CO2) per pound. To
reduce, VOCs, the EPA and State agencies have developed regulations to minimize levels of emission that have
been identified in their State
Implementation Plans. Most often the level of VOC control is based on those presented in a Control Techniques
Guidelines (CTG) issued by the United States Environmental Protection Agency for a particular source category.
Control Techniques Guidelines provides an overview of the various emission points with industry and the typical
cost of using reasonably available control technology (RACT) to reduce emissions from the relevant emission
points at an existing facility. Emission points differ and may be a stack, collection system, bag house, ventilation
area, boiler or other operational unit.
Often VOCs and Hazardous Air Pollutants (HAP's) are considered toxic. Today there are some 188 listed toxic
pollutants. Listed within the toxic list are chemicals such as benzene, xylene, and toluene. The United States
Environmental Protection Agency is mandated to develop rules based on maximum achievable control technology,
referred to as MACT. The level of MACT for new sources must be based on the best-controlled similar source, for
existing sources with more than 30 facilities. The level of MACT must be based on the average of the best
performing 12 percent of the existing sources.
MACT Standards focus on cancer and irreversible health effects, whereas RACT focuses on reducing ground
level ozone reduction because of its effect on human health and welfare. Hence, it should not be unexpected to
find MACT levels of control for reducing a compound such as benzene, a more restrictive control level.
The Pollution Prevention Act in 1990, United States Environmental Protection Agency has been working to
promote pollution prevention (P2), mainly through source reduction. However, there is little evidence that issuance
of the P2 Act has resulted in regulations that have precluded any use of control technologies for meeting emission
limits. However, P2 is now offered as a competing alternative to control technology.
Accessibility of Control Information
It was a difficult assignment in the past for an owner or operations manager to select a pure biofiltration system to
reduce waste or off-gas emissions as a means of compliance. Unlike in the case of microbial treatment of VOCs in
wastewater, vapor phase GACBF systems have mostly been used in the United States for treating odor and far
less for treating VOCs, H2S, SO2 or toxics in air. This is not because the pollutants in air are more complex than in
waste water. In fact, the off-gas waste streams can be easily analyzed using conventional flame ionization
There are numerous publications describing what granulated carbon adsorption systems offer as a control
technology and the use of biofilters as a digestion system. Most of these articles described only biofiltration units
or granulated carbon adsorption systems, it has been understood that in an aerobic environment, degradation
(bio oxidation) of the pollutants occurred in the bio-film, and the bio-film was attached around the carbon particles,
which make up the granulated carbon bed. The oxidation reacted bi-products are carbon dioxide, water.
The parameters that were needed to characterize the size and estimate the cost of building a GACBF unit are well
understood. If we adopt the presently used representation of the design parameters, they included the empty bed
residence time (EBRT) in seconds, which is calculated as the volume of the space occupied by the packing
material (assuming no void volume) divided by the air-flow rate.
Efforts to model the performance (microbial pollutant removal) of biofiltration system are abundant and very
specific, as most modeling work is. In 1997 OAQPS hosted the 1997 Air Biofiltration or reactor Meeting. The
purpose of the meeting was to bring together the wood furniture industry, academic institutions, and
manufacturers. Thus United States Environmental Protection Agency would have a better understanding of the
state of the technology and would learn more about the information that EPA needs to consider such a technology
as an industrial control option.
GACBF systems were discussed during the later 1997 meeting. Among the latest of designs presented was a
bio-filtration system GACBF system, which used a granulated activated carbon bed and offered a self carbon
cleaning system that produced no bio-mass waste.
In the granulated activated carbon system is housed within a stainless steel carbon bed which is used to capture
(adsorb) the pollutants in the waste or off-gas process stream. During the process the pollutants are trapped
within the granulated carbon and leached into a bath of oxygenated water, it is here that the micro-organisms
reside and destruction of the hazardous pollutants occurs. The hazardous pollutants are leached to the microbial
water bath during the system cycle.
The GACBF system as discussed is able to control the emissions of pollutants from the waste gas process stream,
to a specific designed level absorption level capable of reaching 99% capture and 99+% destruction efficiency.
Various microbial and structural systems may be addressed based on the pollutant type and if they contain
The combination granulated activated carbon/bio-filtration system produces no biomass during the bio-oxidation
reaction, which would have to be disposed of. Particulate matter should be limited within the process stream as this
matter may be released during the submersion of the bio-filter reactor bed and cause the production of biomass to
Water must also periodically be drained from system, but requires no down time as the granulated activated
carbon adsorbs the pollutants until the system is re-filled with water and microbes. The amounts and quantity of
the drain will depend on the type emissions and operation of a system, but are usually every 30 days. The bio
oxidation reaction creates by-products which are carbon dioxide and water vapor. The microbes are natural
occurring and as such periodically need to be replaced. Disposition of the natural occurring microbes may be
completed by normal waste water treatment.
Sizing And Cost Of A Bio-Filtration Systems
The installed cost of a specific type GACBF system depends on the amount and pollutant being degraded. There
are also variations within a type of system. For a medium sized closed bed system where input and output streams
can be readily monitored medium-sized 7,500 CFM, designed for destruction of styrene, Type 4a (activated
carbon), the costs are around $230 per month, and will vary with the microbial cost. The pre-installation cost is
estimated to be approximately ($14-18/cfm). The actual cost of a system and cost of operation may vary with size,
loading capabilities and controls.
Discussions And Conclusions
Biofiltration systems, especially the open bed systems, were widely used in the early 1990s in Europe, because
odor standards were in place, which required controlling nuisance from species in amounts less than less than 50
ppmv. However, in the U.S. the focus was to destroy VOCs and HAPs. The GACBF technology for higher level
VOCs and HAPs has recently proven as a viable system for industrial emission control. This may more accurately
explain why biofiltration technology has gained a much smaller share of the U.S. market than more traditional
To date GACBF systems have been controlling VOC and HAPs emissions. Many of the prior systems have been
designed for odor control, where this technology is said to be both reliable and economic, great advances have
been made using the GACBF systems for emission control. Odor treatment currently remains the largest market
for the pure biofiltration technology which includes odors from waste water treatment, such as sludge treatment,
pulp and paper production, tobacco production, and bakery operations.
The GACBF system is designed to meet performance requirements as required in United States Environmental
Protection Agency Regulations and is presently competing against more traditional control devices, such as
regenerative thermal oxidizers, catalytic thermal oxidizer, direct fired thermal oxidizers.
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