[Digestion] Concentration of digestate centrate

[Matt Coen]

Hello all,

 

We are designing a wheat-fed fuel ethanol plant, routing whole stillage
to AD for biogas/CHP utilization and compost/fertilizer recovery.

 

How is anyone concentrating their liquid digestate fraction after
decanting (or screw/belt press, gravity thickening, etc)? I understand
land application is the preferred end-use, but our volume (150,000 gpd)
and nitrogen content (1.5%) would require over 30,000 acres - using a
liberal N application rate of 200 lbs/acre/year.  I need to remove as
much water as technically/economically feasible in order to transport or
store the concentrate, while capturing most/all the nutrient value and,
ideally, retaining the "certified organic" status of this fertilizer.

 

Is there consensus on membrane filtration vs. evaporation? Research has
been done at University of Nevada-Reno (US) using forward osmosis as a
pretreatment to reverse osmosis, but has not been proven commercially.
I just contacted a German firm, GBU:Society for Biogas and Environmental
Technology, whose "evaporation plant" uses fluidized bed multi-effect
evaporators after degassing and acidification.  What is the proven
technology for removing water from this type of effluent stream in
Europe?  Info and expertise (outside of manure and POWT applications)
are relatively scarce in the States (no offense to present company of
American experts)....any references or opinions appreciated.

 

I have only recently discovered this forum, but the exchange has been
most informative. Thanks to all contributors.

 

Matt Coen

Essential Consulting Oregon 

1328 W. 2nd Ave

Eugene OR 97402

p: (541) 485-9095

c: (541) 228-5386

e: matt at ecoregon.com