In 2015, the ethanol industry in the US hit a production milestone of 1 million barrel per day. Ethanol is the major type of biofuel produced and its production is expected to continue to increase1. However, hazardous air pollutants (HAPs) such as acetaldehyde, formaldehyde, and acrolein are emitted from distilled dry grain solubles (DDGS) dryers, fermentation tanks and distillation columns during production2. Acetaldehyde is considered the major HAP of concern. Federal regulations limit HAP emissions to 10 tons per year of any individual HAP and 25 tons per year for total HAPs for an ethanol plant to be classified as an ‘Area Source’3. Air pollution control equipment are essential to keep the facility in compliance. The EPA has identified CO2 scrubbing and regenerative thermal oxidation (RTO) as the Best Available Control Technologies3. RTOs and scrubbers are usually used to control the dryers and fermentation, respectively. Both technologies are utility intensive and require large water and energy inputs. At an average ethanol plant producing annually 55 million gallons of denatured ethanol and 164,491 tons of DDGS, the RTO will be sized at about 18 MMBtu/hr. burning natural gas at about 155 MMSCF/yr. An appealing alternative for the treatment of dilute HAPs is biofiltration4. Traditional biofilters were evaluated for the removal of HAPs generated at an ethanol plant with limited success5. Acetaldehyde and formaldehyde fumes were individually biodegraded in 10 seconds empty bed resident time (EBRT). However, long-term treatment leads to pH decline and deteriorating performance thereafter. In another study, acetaldehyde was successfully degraded in a mixture of toluene and ethanol in a two-stage biofilter and 95% removal was maintained at 15 seconds EBRT6. Ethanol and acetaldehyde had removal yields over 97% at an elimination capacity (EC) of 14.67 g/m~3/h at 100 ppmv and 92-98% (EC 10.3 g/m3/h) at 70 ppmv, respectively6. A study on the biofiltration of a mixture of HAPs found that acetaldehyde had more biodegradation potential than ethanol7.
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