EVE seminar Background Information

 

Speaker: Dr. Baikun Li, Environmental Engineering Professor at the University of Connecticut  

For more on her research see: http://www.engr.uconn.edu/~baikun/

Presentation Title: Hydrogen and Electricity Generation from Anaerobic Wastewater Treatment

Presentation Date: 16 November 2007

  

 

The plant's four egg-shaped anaerobic digesters; the first of their kind in the country, they are of reinforced concrete construction, with external cladding.

Aman digester

fixed film digester

(water-technology.net)

PennState Dept. of Agriculture and Biological Engineering

PennState Dept. of Agriculture and Biological Engineering

 

 

SUMMARY:

 

Anaerobic digestion is a biological process in which organic matter is degraded by bacteria into carbon dioxide and methane (a mixture known as biogas) without the presence of oxygen (California Energy Commission, 2007). A simplified overall chemical reaction to describes anaerobic digestion is shown below:

 

C6H12O6 à 3CO2 + 3CH4

 

The use of anaerobic digestion to treat wastes has dated as far back as the 10th Century BC.  It can be used to treat wastewater sludge, industrial effluents, farm wastes and other wastes high in organic matter (Wikipedia, 2007).  There are a variety of types of anaerobic digesters including completely stirred tank reactors, plug-flow digesters and covered lagoons (California Energy Commission, 2007).  

 

Anaerobic digestion consists of three steps: hydrolysis, volatile acid fermentation and methane formation.   Each step is carried out by a different group of microorganism.  In the first step, hydrolysis, water is used to break down complex cellular organics into smaller molecules. In the next step, volatile acid fermentation, the products of hydrolysis are converted into fatty acids which are then converted into acetic acid, carbon dioxide and hydrogen, through the processes of acidogensis and acetogensis, respectively.  In the last step, methane formation, the organic acids are converted to methane and carbon dioxide (EPA, 2006). 

 

The methane produced in the anaerobic digestion process can be used to generate electricity, cooking, illumination, heating and automobile fuel, while the hydrogen produced can be used to make hydrogen fuel cells which can also be used to generate electricity and power cars (Environmental Encyclopedia, 2006).  According to the California Energy Commission, there is approximately 5300-6300 MW of anaerobic digestion capacity worldwide with Asia accounting for over 95% (California Energy Commission, 2007).  It is estimated that 40 ft3 of methane can be produced from the waste of a single dairy cow per day, with each cubic foot of methane producing about 1,000 BTUs (Anaerobic Digestion Found to Produce Renewable Energy, 2006). 

 

Anaerobic digestion is an environmentally friendly process.  It reduces the potential for global warming by reducing the natural emissions of methane, and it can be used as a renewable energy source, in place of fossil fuels, which produce carbon dioxide when burned (Anaerobic Digestion Found to Produce Renewable Energy, 2006).  In addition, hydrogen-powered fuel cells not only produce no pollutants, but they also are two to three times more efficient then current combustion technologies (DOE Hydrogen Program, 2006).  Anaerobic digestion also produces little sludge and the byproducts can be as liquid fertilizer and compost reducing the need for systematic fertilizers (Anaerobic Digestion Found to Produce Renewable Energy, 2006).

           

See references below as well as Dr. Baikun Li’s research website listed above for more details on the production of electricity from anaerobic wastewater treatment.

 

References:

 

“Anaerobic Digestion Found to Produce Renewable Energy.” (22 Feb. 2006). RenewableEnergyAccess.com, accessed (01 Oct. 2007).

 

“Anaerobic Digestion.” (2006). Environmental Encyclopedia. (accessed: 01 Oct. 2007).

 

“Anaerobic Digestion.” (2007). Wikipedia, The Free Encyclopedia. (accessed: 01 Oct. 2007).

 

Biogas and Anaerobic Digestion. Penn State University, Pennsylvania. (accessed: 01 Oct. 2007).

 

California Energy Commission. Anaerobic Digestion. (10 Apr. 2007).  (accessed: 01 Oct. 2007).

 

“Cars May Get Their Hydrogen From Wastewater Plants.” (2002). Daily University Science News. (accessed: 01 Oct. 2007).

 

Logan, B. E. “Simultaneous Wastewater Treatment and Biological Electricity Generation.” (2005). Penn State University, Pennsylvania. (accessed: 01 Oct. 2007).

 

United States. Department of Energy Hydrogen Program. Hydrogen Fuel Cells. (Oct. 2006). (accessed: 01 Oct. 2007).

 

United States. Environmental Protection Agency. Biosolids Technology Fact Sheet: Multi-Stage Anaerobic Digestion. (Sept. 2006). accessed (01 Oct. 2007).

 

Other Interesting and informative Articles:

 

Levin, D.B. et al. “Potential for Hydrogen and Methane Production from Biomass Residues in Canada.” (2006). Science Direct. (01 Oct. 2007).

 

Nishio, N. and Nakashimada, Y. “Recent Development of Anaerobic Digestion Processes for Energy Recovery from Wastes.” (2007). ScienceDirect. (01 Oct. 2007).

 

Ting, C. H. and Lee, D. J. “Production of Hydrogen and Methane from Wastewater Sludge using Anaerobic Fermentation.” (2006). ScienceDirect. (01 Oct. 2007).