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BioEnergy Production from Food Waste

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BioEnergy Production from Food Waste Powered By Docstoc
					BioEnergy Production from
Food Waste
By: Quinn Osgood
Background Information
• It has become apparent that the world needs to find an energy
  source other that the non-renewable ones we use today.

• A potential solution can be found in food waste, which is produced
  in great quantity and is very rich in organic material and stored
  energy.

• Several methods have been tested to harvest the energy stored in
  this waste, most of which strive to gather Methane and Hydrogen.
Hydrogen and Bioenergy
• Hydrogen shows great potential as a fuel source that is both efficient
  and environmentally safe.

• Another use for Hydrogen is as an additive for Compressed Natural
  Gas, which reduces the formation of Nitrogen Oxides by up to 50%

• Given the importance that Hydrogen may have in our energy future,
  efficient methods for production will be very important.
Two-Stage anaerobic fermentation for H2 and
CH4 production
 • Anaerobic dark fermentation of food waste followed by either light
   or dark anaerobic fermentation for H2 production

 • Generally result in high CH4 production but comparatively low H2
   production

 • Poor H2 yield results from the main organic acids present after
   anaerobic fermentation being acetate and butyrate which more
   readily form other compounds
Development of a novel three-stage
fermentation system converting food
waste to hydrogen and methane

         Dong-Hoon Kim and Mi-Sun Kim
Abbreviations
•   COD = Chemical Oxygen Demand
•   LFE = Lactate fermentation effluent
•   I/S ratio = inoculum to substrate ratio
•   VS = volatile solids
Objective
• To develop of a novel three-stage fermentation
  system converting food waste to hydrogen and
  methane with an emphasis on high H2 yield.
Methods Overview
• The food waste was collected from a cafeteria, diluted two times by
  volume and shredded into pieces < 5mm in diameter.
• The COD of the carbohydrates in the food waste was then adjusted
  to 30 ± 2 g/L
• Stage 1 of fermentation: The food waste is fermented for one day for
  the production of lactate.
• The LFE was then centrifuged
• Stage 2 of fermentation: The supernatant is removed and used for
  H2 photo-fermentation
• Stage 3 of fermentation: The residue is removed and used for CH4
  production via anaerobic digestion
• H2 and Ch4 content was measured with gas chromatography, other
  compounds were measured with HPLC and quantities such as VS
  and COD were determined with standard methods
Schematic
Methods: Stage 1
• There is no initial inoculum, but instead relies on organisms already
  present in the food waste.

• The fermentor used had a working volume of 2.5 L and was
  equipped with a pH sensor and a mechanical agitator.

• pH was initially 7± 0.1 and dropped to 5.0 due to fermentation
  products and was then held there (± 0.1) by addition of KOH.

• Temperature was held at 35°C and the agitator was held at 100 rpm

• Later testing showed that the primary bacteria present were
  Lactobacillus sp. and Streptococcus sp.
Methods: Stage 2
• The inoculum used in the photo-fermentation was R. sphaeroides
  previously isolated from mud on an island in the West Sea of Korea

• The bottles were inoculated with 0.56g of the cells, then 50 mL of
  the diluted supernatant from the LFE and a trace metal solution
  were added.

• The bottles were then held at 30°C and were agitated with a
  magnetic stir bar at 100 rpm

• The media was exposed to light with an intensity of 110W/m^2 with
  a halogen lamp
Methods: Stage 3
• The inoculum used for CH4 production was a sample taken from an
  anaerobic digester at a local waste water treatment plant.

• The solid portion of the LFE, inoculum and tap water were added to
  the bottle for a working volume of 100mL

• The initial pH of the media was set to 7.5 by the addition of KOH
  and HCL

• The sample were held at 35°C in a shaking incubator
Results: Stage 1
 Results: Stage 2




A maximum of 2570 mL of H2 was produce/ L of broth with the addition of 0.5mL/L
Trace metal solution. This corresponds to 994 mL H2 per g COD
Results: Stage 3
Results: Summary
Discussion
• From the results it was determined that 41% and 37% of the energy
  content of the food waste was converted into H2 and Ch4
  respectively
  ▫ This corresponds to an electrical energy yield of 1146 MJ/ ton food waste
    which is 1.4 time more that the next best two-stage system
  ▫ About 3.6 MJ = 1 kWh, so the electrical energy yield is about 318 kWh

• This method produced the highest efficiency H2 yield of any study
  that made use of waste products by converting 8.38 mol H2 per mol
  of hexose, which has a theoretical maximum yield of 12 mol H2

• This method, while having some down sides, is a definite step in the
  right direction for the development of efficient H2 production
  mechanisms
Comparison
Critiques
• Not using a pure culture for lactate formation
  ▫ This would result in higher lactate yield and thus higher H2 yield

• Figure 4 is not easily read but contains significant data
  ▫ Much of this is resolved if Table 2 and Figure 4 were to be place
     next to each other

• The phrase “a certain amount” is used in place of actual quantities in
  multiple places in the text and I feel that this damages the
  reproducibility of the experiment.

• Overall I thought this was a quality paper that included novel ideas
  and good results.
Future Directions
• Using a pure culture in lactate fermentation to increase lactate yield

• Exploring other H2 producing microorganisms and optimization of
  H2 producing pathways

• Lactate fermentation followed by a two stage dark/photo H2
  fermentation system

• Performing this test in a different region where different food wastes
  would be more abundant.

• Development of a mechanism for removing ammonium from
  solution after lactate fermentation
References
• Kim, Dong-Hoon, and Mi-Sun Kim. "Development of a Novel Three-
  Stage Fermentation System Converting Food Waste to Hydrogen
  and Methane." Bioresource Technology 127 (2013): 267-74. 1 Oct.
  2012. Web. doi: 10.1016/j.biortech.2012.09.088

				
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