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 ThreeStage 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