Separating algae from water from a raceway pond

[Curbie]

I've been toying with the notion of anaerobic methane production of
bio-mass (algae from a raceway pond). I need compost anyway for my
garden, so a algae pond has appeal on it's own, but I read a couple of
books one by Jean Pain and the other by John Fry, so by anaerobic
composting I'll still get same amount of compost but also a surprising
amount of methane as a bonus.

Since methane is chemically 4/5 hydrogen it has sort of the same
storage problem that hydrogen has, which is to say that neither gas is
very portable, but is interesting for both cooking and stationary
engines.

I've been playing with sketch-up in an effort to visualize what would
be involved with constructing such a notion, came up with this:
http://i825.photobucket.com/albums/zz177/Curbie_Pics/RacewayV02.jpg

What you're looking at is a raceway paddle-wheel that provides water
movement, the intake gate funnels a portion of water/algae and a
filter by the exit gate concentrates algae in the channel on the left.

Then the gates are both closed and the concentrated algae/water is
pumped out of the channel into the digester where the water is again
filtered out by gravity and return to the channel. When the water
pressure equalizes between the channel and the raceway, the gate are
opened again.

Any help on the function of this notion would be appreciated.

Thanks,

Curbie

 

[Curbie]

I would try batch production first to learn and improve the process.
Jim,

I will, for me anyway, the base question is an algae pond practical to
produce compost for a large garden, even if I was just pumping into a
pile on the ground and letting it compost aerobically, if it is, the
methane produced is gravy.

In his book, Jean Pain used the formula of 5kg of vegetable bio-mass
produces 1m^3 of GAS, John Fry give the rough composition of the GAS
as methane 63%, CO2 33%, and the rest N2, H2, CO, O2, and H2S. I
don't know if I believe these numbers but if there even half correct,
the ability to produce large volumes of bio-mass would have multiple
appeals.

This notion brings me to growing indigenous algae in a raceway pond.
I'm also thinking about digesters, gas scrubbers, compression and
storage, but all that is dependant on my base question.

The great thing about experimenting on bio-mass from indigenous algae
is that is practically free, not to mention I would really groove on a
couple tons of compost.

Curbie

 

[Curbie]

Raceway, paddlewheel, water movement. Sounds more aerobic

than anaerobic.

"I've been toying with the notion of anaerobic methane production of
bio-mass (algae from a raceway pond)."

The notion is algae grown in, and collected from a raceway pond, the
bio-mass (algae) is then composted in an anaerobic digester to produce
compost and methane.

Which anaerobic Witch is Which.

Curbie

 

[Curbie]

Jim,

Generally, as Michael points out, smelly algae come from anaerobic
digestion of bio-mass producing hydrogen sulfide (think rotten eggs),
the purpose of the paddle-wheel is to keep the algae in motion during
peak sunlight hours for CO2 sequestration and shading (depth of algae
in pond, algae partially shaded by algae above it).

Since the paddle-wheel is necessary to maintain algae at a higher
exponential growth rate and to help prevent smelly anaerobic digestion
in the raceway pond anyway, I'm trying to use the paddle-wheel to also
concentrate the algae (think replacement of high volume pumps, feeding
a centrifuge). A DIY translation of the commercial process.

Curbie

 

[Curbie]

Micheal,

Anaerobic means without oxygen. So if it's in an airtight container,
the bacteria are forced into a condition of anaerobic metabolism,
and they will make methane. Rather like the "swamp gas" you
can read about. Those swamps are more often in warm climates,
the warm water holds less or no oxygen, the bacteria function in
an anaerobic metabolism. Like in a septic tank.

You and I are on the exact same page up to this point.

But in the raceway you describe and diagram, oxygen exposure
would be enhaned by the paddlewheel, the shallow depth, the
overall water exchanges. Not saying you couldn't do it, but that
from the descriptions, I would be expecting aerobic metabolism,
without methane, without hydrogen sulfide.

Here is where I haven't been clear enough; there are two processes at
play here, 1) the growing and collecting of algae for bio-mass in a
raceway pond, and 2) the anaerobic digestion of the bio-mass in a
separate digester. In this post I am focusing on the growth and
collection process and the digester hasn't been depicted out here.

"The notion is algae grown in, and collected from a raceway pond, the
bio-mass (algae) is THEN composted in an anaerobic digester to produce
compost and methane."

What I'm mainly looking for is feedback on filtering the algae via the
paddle-wheel and concentration channel notion pictured in the image in
an effort not to convolute or complicate any step of the process.

Curbie

 

[Curbie]

Morris,

Is it possible to configure a raceway such that a single transit of the
raceway would provide sufficient algae to justify algae/water separation
at the output end of the raceway?

The algae is just driven around the raceway like cars round a
racetrack, if I understand the concept behind your use the phrase
"single transit" as a single trip around the raceway, my answer would
be probably, but keep in mind that the primary function of the
paddle-wheel is to maintain algae at a higher exponential growth rate
and to help prevent smelly anaerobic digestion
in the raceway pond. Collecting all the algae from the pond in one
circuit would greatly impede further growth.

Growth and collection happens all season, it's a continuous process as
long as the temperatures are within the algae's growth range.

Would re-use of the recovered water enhance algae growth in subsequent
"cycles" (I'm assuming that there would be water and heat conservation
benefits)?

The temperature of the pond is primarily dictated by indigenous
algae's preferred maximum growth rate temperature and ambient
temperatures. The algae growth process takes place in the warmer
months (just solar heat gain), so I don't have a use for low
temperature heat at that point in time.

In the plan I'm looking at, the concentrated algae is moved to an
anaerobic digester where the water is drained of to equalize the
pressure between the channel and the raceway so the gates will open
again.

Could the raceway be "featured" in such a way as to induce non-aerobic
churning/turbulance throughout its length?

Maybe, but the reason the growth raceway and a separate digester is
that they are two different process. I don't want digestion in the
raceway where the gases produced by anaerobic digestion (CH4 + C02)
are produced where they can't be captured, and algae won't grow in a
digester.

Is there an actual process advantage to separating the growth and
digestion stages, or is this separation primarily for convenience?

The separation is necessary to my understanding.

Curbie

 

[Curbie]

Jim,

Good option, I think the key to this will be testing, what a
location's indigenous algae's doubling-rate at different temperature
within it natural-growth temperature-range, once I figure that out, I
can test to see what improvement (if any) in the algae's doubling rate
the different rates of circulation has.

Depending on the results, I now have two options and can choose the
option that best fits the need; I think if the raceway needs high
circulation the paddle-wheel will be better, but if high circulation
is not needed your Archmedian screw idea seems to have a lower power
consumption.

I think all I'll need to test indigenous algae's doubling-rate at
different temperature within it natural-growth temperature-range will
be a thermometer, a couple dozen clear 2-liter soda bottles, and a
log.

If the results seem reasonable to produce enough compost, then a 1:12
model should give me all the answers I need for compost, although I'd
still like to test Jean Pain's (1kg of bio-mass produces 1m^3 of gas)
claim.

Your algae sticking to rocks point I haven't considered; another
potential fly in the ointment to think about.

Thanks,

Curbie

 

[Curbie]

Jim,

If indigenous algae doubles fast enough to be grown in a small raceway
AND the total volume of bio-mass produces gas at anywhere near Jean
Pain's claims, the bio-mass will produce enough methane to power a
small converted gasoline engine for compression, circulation, methane
for cooking and some left over.

Jean Pain CLAIMS he produced all his heating needs by aerobic compost
to heat anaerobic composting (for the gas), his house, his water, used
the gas produced for cooking, compression, and to drive his car, I not
sure I believe his claims, and they are real short of the numbers, but
John Fry is NOT short on the numbers, so there seems to enough there
to do a little experimenting.

If I can get couple tons of organic compost, through a fairly labor
free process I'd be happy, and if at the end of the day I had compost
and enough gas to perpetuate the process and extra for cooking I'd be
ecstatic.

Again, the great thing here is that the real numbers for real answers
won't cost spit, I'm just trying to visualize the process so I'll know
what number I need.

Curbie

 

[Curbie]

On Mon, 14 Dec 2009 14:10:27 -0800 (PST),
Michael,

Thanks for the feedback, I read that waist-water document today.

Curbie

 

[Curbie]

A digester/raceway concept is depicted here:
http://i825.photobucket.com/albums/zz177/Curbie_Pics/RacewaySystemV2.jpg

The notion here is that the algae grows in the raceway, concentrated
(somehow) by the raceway and then the concentrated algae is pumped to
the batch digesters, keep in mind that nothing is of a calculated
size, and I have no clue whether the digesters should be many
55-gallon drum size or fewer of the large size pictured, and same with
the size of the raceway and concentration area. No data yet.

The digesters have a concentrated algae input, a gas output, heated
water in and out, and a compost drop. The digesters needs to maintain
about 97°F for methane bacteria and I'm thinking solar for the colder
months; grow algae in a raceway, concentrate it, fill the digesters
with concentrated algae, collect gas in the winter, and compost in the
spring.

Curbie