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Dioxin removal systems for waste gases |
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AGC Engineering Co. of Japan has developed a dioxin removal
system based on activated carbon. The process basically
involves injecting 0.1-0.2 g/Nm3 activated carbon relative to
the amount of waste gas. AGC Engineering says that the system
guarantees a toxicity equivalent of 0.5 ng/Nm3 or less at
inlet of the bag filter, and less than 0.1 ng/Nm3 after bag
filter process with catalyst device. The system can be
designed to use activated carbon mixed with slaked lime, if
needed. The catalyst employed is plate-type, with opening
widths of 4 mm or 6 mm.
Contact: AGC Engineering Co. Ltd., WBG Marive West, 19th
Floor, 6 Nakase 2-chome, Mihama-ku, Chiba-shi, Chiba 261-7119,
Japan.
Source:
www.agec.co.jp |
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Catalytic removal of nitro-PAHs |
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Siemens Aktiengesellschaft, based in Germany, has been
assigned a United States patent on a process for the catalytic
removal of polycyclic aromatic nitro, nitroso and/or amino
compounds (nitrated polycyclic aromatic hydrocarbons – nitro-PAHs)
from the exhaust gas of a combustion system, in particular a
diesel engine. The exhaust gas is brought into contact with a
catalytic converter at a temperature of from 150º to 600ºC.
The nitro-PAHs are oxidized at the catalytic converter through
the use of oxygen to form nitrogen oxides (NOx), carbon
dioxide (CO2) and water.
The catalytic material contains, by weight, 80 to 95 per cent
titanium dioxide, 2 to 10 per cent tungsten trioxide or
molybdenum trioxide, and 0.05 to 5 per cent vanadium pentoxide.
To oxidize the nitro-PAHs, a certain oxygen content is
required in the exhaust gas. The exhaust gas of a diesel
engine is inherently high in residual oxygen content.
In one of the configurations, a reducing agent containing
nitrogen is added to the exhaust gas before it is brought into
contact with the catalytic converter in the presence of oxygen
to reduce NOx contained in the exhaust gas. In this way, first
the formation of the nitro-PAHs from PAHs and NOx in the
exhaust gas is prevented.
Second, the catalytic converter is used as a deNOx catalytic
converter for the removal of NOx using the SCR process. Also,
nitro-PAHs are converted at the catalytic converter, together
with oxygen and the nitrogen-containing reducing agent, to
form non-hazardous compounds. This is a reaction pathway in
addition to the oxidation of the nitro-PAHs with oxygen to
form CO2 and water.
Source:
www.freepatentsonline.com |
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PAH removal from spiked municipal sewage sludge |
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Researchers from the Institute of Scientific Research,
University of Québec, Canada, studied different processes for
removing polycyclic aromatic hydrocarbons (PAHs) from
municipal sewage sludge and wastewater. PAHs are strongly
adsorbed on to particulate matters of soils, sludge or
sediments owing to their strong hydrophobicity, which makes
them less “bio-available”, thus limiting their bioremediation.
Using sludge doped with 11 PAHs at 5.5 mg of each PAH per kg
of dry matter, the scientists tested different treatment
processes to evaluate the PAH removal performance of each. Two
biological processes – mesophilic aerobic digestion (MAD) and
simultaneous sewage sludge digestion and metal leaching (METIX-BS)
– were tested to evaluate PAH biodegradation in sewage sludge.
In parallel, two quite similar chemical Fenton processes –
chemical metal leaching (METIX-AC) and chemical stabilization
(STABIOX) – and one electrochemical stabilization process (ELECSTAB)
were tested to measure PAH removal by these oxidative
processes. Moreover, PAH solubilization from sludge by the
addition of a non-ionic surfactant Tween 80 (Tw80) was also
tested.
The best PAH removal rates were obtained by MAD and METIX-BS
with more than 95 per cent 3-ring PAH removal after 21 days of
treatment.
Addition of Tw80 during MAD treatment increased removal rate
of 4-ring PAHs. More than 45 per cent of 3-ring PAHs were
removed from sludge by METIX-AC, while about 62 per cent of
3-ring PAHs were removed by ELECSTAB process. However, STABIOX
process showed only <35 per cent removal of 3-ring PAHs. None
of the processes were efficient for the elimination of high
molecular weight PAHs (5-ring or above) from sludge.
Source:
www.ncbi.nlm.nih.gov
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Biodegradation of PAHs in petroleum-contaminated
soil |
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Scientists at the National Research Centre for Environmental
and Hazardous Waste Management, Thailand, investigated
bioremediation of polycyclic aromatic hydrocarbons (PAHs) in
petroleum-contaminated soil using tamarind leaf inoculums.
Leaves of tamarind and other leguminous trees have been
reported to contain several PAH-degrading micro-organisms.
To minimize the amount of leaves added, tamarind leaf
inoculums were prepared by incubating the leaves with a
sub-sample of contaminated soil for 49 days. Then the
efficiency of the inoculums was tested with two soil samples
collected from a navy dockyard and railway station. These soil
samples had different levels of petroleum contamination.
Bioaugmentation treatment was carried out by mixing
contaminated soil with the inoculums at the ratio of 9:1. For
navy dockyard soil, the concentration of phenanthrene in the
inoculated soil was reduced gradually to undetectable level
within 56 days; 70-80 per cent of fluoranthene and pyrene
remained at the end of the treatment. For railway station
soil, which had lower petroleum contamination, PAH degradation
occurred faster: the phenanthrene concentration was below
detection limit after 28 days.
The treatment also succeeded in reducing the quantities of
several hydrocarbons. At the same time, numerous phenanthrene-degrading
bacteria, which were used as representatives of PAH degraders,
could be observed in both inoculated soils. Higher numbers of
bacteria, however, were found in railway station soil, which
corresponded with the lower amount of PAHs and higher amount
of soil nutrients. The results showed that inoculums prepared
from tamarind leaves could be used to degrade PAHs as well as
clean-up petroleum contaminated soil.
Source:
www.psu.ac.th
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Promising discovery for PCB clean-up without
dredging |
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Dr. Donna Bedard at the Rensselaer Polytechnic Institute and
scientists from Georgia Institute of Technology, the United
States, have discovered a bacterium that could remove
polychlorinated biphenyls (PCBs) from the environment without
dredging. The discovery is a first step towards a
bioremediation strategy to naturally detoxify the chemicals
without risky removal of the sediments in which they persist.
Dr. Bedard, describing the potential breakthrough, said the
research will help scientists understand the process by which
PCBs have been known to break down naturally in water.
In microcosm studies in her lab, Dr. Bedard found that Aroclor
1260 was being degraded by native sediment microbes. She
developed sediment-free enrichment cultures, characterized
them in collaboration with Dr. Frank Loeffler and Dr. Kirsti
Ritalahti of GeogiaTech. After a series of experiments, the
team was able to determine that bacteria in the
Dehalococcoides (Dhc) group were responsible for the
dechlorination of Aroclor 1260. These microbes replace the
chlorine atoms in Aroclor 1260 with hydrogen, which fuels
their growth and initiates the PCB degradation process.
Source:
www.gtresearchnews.gatech.edu
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Sorbent to prevent dioxin synthesis |
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DIOX-BLOK® from Beco Engineering Company, the United States,
is a patented sorbent that prevents new dioxin synthesis in
combustion processes. Although modern incineration processes
completely destroy dioxins, they form anew as the flue gas
cools below 400ºC. On cool-down, trace organics adsorb on the
fly-ash and are converted to dioxins by reaction with the
metal chlorides on the surface of the ash.
DIOX-BLOK achieves two things:
- It “starves” the fly-ash of dioxin reactants by removing
organics before they can be adsorbed by the ash; and
- Dioxin-contaminated ash is not created: unlike powdered
activated carbon (PAC), DIOX-BLOK is chemically inert and
adsorbed organics are not converted to dioxins.
DIOX-BLOK is used at rates of from 450-900 g/t of waste
burned. The delivered cost of is generally less than, or equal
to, the cost of PAC.
Besides, as prevents dioxins from forming, its environmental
cost is far less than PAC. Its use with medical / hazardous /
municipal waste inci-nerators in dry / wet scrubber units has
reportedly shown good results, reducing dioxin emissions to
0.001-0.006 ng/dscm, TEQ.
Contact: Beco Engineering Company, P.O. Box 443, 800 3rd
Street, Oakmont, PA 15139, United States of America. Fax: +1
(412) 828 6144
E-mail:
becoengco@aol.com
Source:
www.becoengineering.com
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