rates varying from 46% after 5 days to 31% after
10 days of nutrient starvation and fermented at
95% efficiency after enzymatic pre-treatment.
These fermentation processes also create
protein-rich distiller’s grains, which can be used
as an animal feed supplement if they are not
concentrating heavy metals. As the first commercially viable example of ethanol fermentation, the Andrew Young Foundation conducted a
private research trial using the ecosystem technology, produced by resource recovery experts
Greenbelt Resources Corporation, which was
presented in a feasibility study report conducted
by an independent party Agregy and submitted to
the USDA in 2017. With successful feasibility
determined, the foundation created a corporation
called Duckweed Days LLC, which partnered
with Greenbelt Resources to conduct a pilot
system development project in Paso Robles,
California, USA, in 2018. Leveraging its farming
and agricultural expertise as well as its engineering prowess, Greenbelt has developed a
species agnostic prototype cultivation, harvesting
and processing system. For the biorefining of the
cultivated duckweed, Greenbelt’s proprietary,
partially AI-operated modular machinery uses
membrane filtration to produce anhydrous bioethanol that can be sold as a fuel or solvent, plus
chemically safe distillers’ grains that can be used
as animal feed or a nutritious protein concentrate.
Ethanol is not the only fermentation product,
since Clostridium acetobutylicum bacteria can
convert the sugars of 32% starch content duckweed into a mixture of 68% butanol, with acetone and ethanol coproducts (Cui and Cheng
2015). Ethanol can of course be blended into
gasoline at rates up to 10% or 85% for certain
flex-fuel vehicles, while significantly more
expensive butanol behaves very similarly to
gasoline. Finally, the Argentinian company
MamaGrande experimented with fermentation as
a means to generate lactic acid for polymerization into PLA. Polylactic acid, or PLA, is a
renewable and degradable plastic produced by
enzymatically digesting starch to glucose, fermenting the glucose to lactic acid, and then
purifying and polymerizing it. At the moment,
anaerobic digestion and ethanol fermentation
appear to be the best studied options, while fermentation is the only biofuel in full-scale commercial application.
1.2.4 Animal Feed
Most agricultural wastewater and certain
domestic wastewater streams will have undetectable or legally permissible levels of heavy
metals, enabling a design where duckweed can
recycle nutrients back into the food supply,
provided it is monitored for heavy metals and
other hazards, and legally approved. Agricultural
wastewater, which can come from greenhouses,
livestock barns, anaerobic digesters, or even food
processing facilities, is often heavy metal “free”
and therefore diluted down to 20–50 mg/l total
nitrogen for optimal duckweed growth. Considering the pilot plant examples above, and publicly posted information from Paul Skillicorn’s
Agriquatics Blog, we see the following steps for
domestic wastewater treatment (Fig. 1.3).
First, solids will be removed by screening
and then primary settling lagoons or laminar flow
systems and hydrocyclones, possibly for anaerobic digestion. Secondly, there may be a buffer
lagoon or lagoons, which treat soaps and other
chemicals that may harm duckweed or its
downstream applications. Third will be the
duckweed farm portion, where a diluted influent
with NH 3 concentrations of 10–30 mg/l, BOD of
15–30 mg/l, and pH from 6.0 to 7.0 will fertilize
rapidly growing high-protein duckweed biomass.
Fourth, ponds with slower growing, high starch
content duckweed can polish wastewater as the
final cleaning step. Here, once nitrogen has been
depleted heavy metals will be accumulated, with
the majority of municipal effluents producing
duckweed passing US food and feed safety
standards. HRT can vary from 6 to 15 days
depending on environment, degree of effluent
recirculation, and treatment standards. For
example, the Mirzapur duckweed ponds reduced
NH 3 from 32 to 0.03 mg/l. This high HRT
increases the footprint compared to a conventional system, while providing resilience against
heavy rains or community crashes that
1 Importance of Duckweeds in Basic Research and Their Industrial …
7
10 days of nutrient starvation and fermented at
95% efficiency after enzymatic pre-treatment.
These fermentation processes also create
protein-rich distiller’s grains, which can be used
as an animal feed supplement if they are not
concentrating heavy metals. As the first commercially viable example of ethanol fermentation, the Andrew Young Foundation conducted a
private research trial using the ecosystem technology, produced by resource recovery experts
Greenbelt Resources Corporation, which was
presented in a feasibility study report conducted
by an independent party Agregy and submitted to
the USDA in 2017. With successful feasibility
determined, the foundation created a corporation
called Duckweed Days LLC, which partnered
with Greenbelt Resources to conduct a pilot
system development project in Paso Robles,
California, USA, in 2018. Leveraging its farming
and agricultural expertise as well as its engineering prowess, Greenbelt has developed a
species agnostic prototype cultivation, harvesting
and processing system. For the biorefining of the
cultivated duckweed, Greenbelt’s proprietary,
partially AI-operated modular machinery uses
membrane filtration to produce anhydrous bioethanol that can be sold as a fuel or solvent, plus
chemically safe distillers’ grains that can be used
as animal feed or a nutritious protein concentrate.
Ethanol is not the only fermentation product,
since Clostridium acetobutylicum bacteria can
convert the sugars of 32% starch content duckweed into a mixture of 68% butanol, with acetone and ethanol coproducts (Cui and Cheng
2015). Ethanol can of course be blended into
gasoline at rates up to 10% or 85% for certain
flex-fuel vehicles, while significantly more
expensive butanol behaves very similarly to
gasoline. Finally, the Argentinian company
MamaGrande experimented with fermentation as
a means to generate lactic acid for polymerization into PLA. Polylactic acid, or PLA, is a
renewable and degradable plastic produced by
enzymatically digesting starch to glucose, fermenting the glucose to lactic acid, and then
purifying and polymerizing it. At the moment,
anaerobic digestion and ethanol fermentation
appear to be the best studied options, while fermentation is the only biofuel in full-scale commercial application.
1.2.4 Animal Feed
Most agricultural wastewater and certain
domestic wastewater streams will have undetectable or legally permissible levels of heavy
metals, enabling a design where duckweed can
recycle nutrients back into the food supply,
provided it is monitored for heavy metals and
other hazards, and legally approved. Agricultural
wastewater, which can come from greenhouses,
livestock barns, anaerobic digesters, or even food
processing facilities, is often heavy metal “free”
and therefore diluted down to 20–50 mg/l total
nitrogen for optimal duckweed growth. Considering the pilot plant examples above, and publicly posted information from Paul Skillicorn’s
Agriquatics Blog, we see the following steps for
domestic wastewater treatment (Fig. 1.3).
First, solids will be removed by screening
and then primary settling lagoons or laminar flow
systems and hydrocyclones, possibly for anaerobic digestion. Secondly, there may be a buffer
lagoon or lagoons, which treat soaps and other
chemicals that may harm duckweed or its
downstream applications. Third will be the
duckweed farm portion, where a diluted influent
with NH 3 concentrations of 10–30 mg/l, BOD of
15–30 mg/l, and pH from 6.0 to 7.0 will fertilize
rapidly growing high-protein duckweed biomass.
Fourth, ponds with slower growing, high starch
content duckweed can polish wastewater as the
final cleaning step. Here, once nitrogen has been
depleted heavy metals will be accumulated, with
the majority of municipal effluents producing
duckweed passing US food and feed safety
standards. HRT can vary from 6 to 15 days
depending on environment, degree of effluent
recirculation, and treatment standards. For
example, the Mirzapur duckweed ponds reduced
NH 3 from 32 to 0.03 mg/l. This high HRT
increases the footprint compared to a conventional system, while providing resilience against
heavy rains or community crashes that
1 Importance of Duckweeds in Basic Research and Their Industrial …
7