50 Gallon Digester for a mix of wastes

Digester design and construction info

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WizBandit
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50 Gallon Digester for a mix of wastes

Post by WizBandit » Thu Mar 04, 2004 3:31 pm

After expanding my small chicken & Goose flock I want to build one or more 50 gallon digesters. I found the plans for a pump fed system here and have a few questions.

I have two surplus pool type pumps, a 1.5HP and a "spa" 1HP. They have strainers and I was wondering if they could be used to pump waste from another 50GAL "holding tank" into the digester?

I have a large amount of Taiwan/Chinese cardboard that needs to be disposed of. Can it be soaked to a mush in the holding tank and used in the digester? I also have a large amount of really fast growing ferns in my woods that I cut down every week during the summer, can they be used in the digester?

My main waste is chicken manure mixed with hay or cardboard and probably an equal amount of Goose manure along with some rabbit manure. About 20 geese and 25 chickens, 3-8 rabbits.

I found some 50 gallon HDPE food grade barrels that were used to hold Greek peppers for about $11 each so I picked up two to play with. Does it make sense to use one to hold the manure/cardboard/fern mix until it's broken down enough to pump and use the strainer in the pool pump to "catch" any straw or solids so as to not plug up the impeller or am I way out on this idea?

Is there "top-loading" manual load digester plans anywhere that might better suit my needs??

Thanks, Jim

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Post by Bob » Sun Mar 07, 2004 2:40 pm

Hi Jim,
I have two surplus pool type pumps, a 1.5HP and a "spa" 1HP. They have strainers and I was wondering if they could be used to pump waste from another 50GAL "holding tank" into the digester?
I wouldn't think so. You'll need a pump that can handle solids, something like a holding tank macerator pump, for example (e.g. as sold by RV and/or marine supply places).
I have a large amount of Taiwan/Chinese cardboard that needs to be disposed of. Can it be soaked to a mush in the holding tank and used in the digester? I also have a large amount of really fast growing ferns in my woods that I cut down every week during the summer, can they be used in the digester?
That sounds like it could work, just make sure that you have an appropriate loading rate and C/N ratio. Also, I'd think that this material would likely be pretty difficult for a pump to handle -- something you might want to do as a batch (see below).
My main waste is chicken manure mixed with hay or cardboard and probably an equal amount of Goose manure along with some rabbit manure. About 20 geese and 25 chickens, 3-8 rabbits.
Did you plug those values into my online calculator, to get a preliminary idea of the size you'll need, and your daily inputs and outputs? What are your goals? To generate fuel gas? How will you use it?
Is there "top-loading" manual load digester plans anywhere that might better suit my needs??
What do you mean by "top-loading"? Batch feed, rather than pumped? Something where you open the digester up, load it, then empty the sludge and do it again, in batches? Depending on your feedstock and how you wish to manage it, that could be a good choice.

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My first 2-stager is built

Post by WizBandit » Mon Mar 08, 2004 5:53 pm

Bob: I finished my first 2-stage digester using your plans. I found some 50 gallon HDPE pepper poly drums with screw-on lids. I used a sealed 5 gallon bucket from work with a rubber gasketed lid in the bottom as stage one. I built the 4" - 2" in/out basicly the same as you except I 90'ed into the bottom of the bucket. The lid has the 2" half way into it as well as out into the main 50 gallon chamber. I used 3/8" poly tubing with quick-connects for the CO2 vent to the lid. Everything else is about the same.

My question now is how do I decide the ratio of Nitrogen / Carbon? Is it done by weight or using the "about this much mass" way? Most of my chicken manure has hay in it. I have a garbage disposal mounted to a 5 gallon bucket feeding another 50 gallon drum. I put an outlet in the bottom and another in the top below the lid. About 8" down I put an inlet from the disposal. I piped the bottom outlet to a 3/4 - 1/10hp (2 speed) spa pump and the outlet of the pump to the top of the drum. I put a valve in the line to adjust the bypass and have a tee under the valve to the digester inlet. Like you said, this might not pump the slurry but I'm going to try. I used to pump mud with the same style pump from the flooded garden years past.

How long (HRT I guess it's called) should the slurry stay in stage one at 5 gallons before pushing it into stage two? Until stage two fills should I bleed the air out? How do you keep the pump from pushing slurry up & out the gas outlet line? The CO2 vent? Keep it higher than the 2" outlet maybe? WHat do you use for a 1-10lb presurre switch?

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Post by Bob » Mon Mar 15, 2004 12:34 pm

Bob: I finished my first 2-stage digester using your plans.
That's great! Do you have pictures you can share? Or sketches?
My question now is how do I decide the ratio of Nitrogen / Carbon?
Yes, it is done by weight. You can use the online calculator for a first approximation. Beyond that, you can do more rigorous testing, if so inclined, or just try to get a reasonable estimate using your best judgement.

Bottom line, C/N is not an overly critical parameter. A wide range of values will still support biogas generation, and, to some extent, the ratio regulates itself. Too much N will generate more ammonia, reducing the amount of N. Too much C will produce more CO2 in the biogas. So, unless you really want to do more detailed testing, just use trial and error, using different mixes until you get the max yield of biogas with the highest CH4 content. Over time, you'll develop the best 'recipe' for your own particular conditions.
How long (HRT I guess it's called) should the slurry stay in stage one at 5 gallons before pushing it into stage two?
My design (and data) are based on about 3 days HRT in the first stage, and about 9 days in the second, for about 12 days total. In mine, the size ratio is about 3:1. In yours, it is about 10:1. I haven't tested it with that wide a variance in HRT, to be able to authoritatively answer your question, but I would guess that much less than 3 days in the first stage would, in effect, function more like a single stage digester because the raw waste just wouldn't be spending enough time in the first stage for the acetogens to do their work. If you do feed it about 1.5 gallons/day to get a 3-day HRT in stage one, then that would be about 33 days HRT in the 2nd stage. This will work fine, but maybe not the most efficient use of the 50 gallon drum.
WHat do you use for a 1-10lb presurre switch?
Dwyer Instruments is a good source. This one costs about $50.

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ANAEROBIC DIGESTER

Post by MASJAVY » Sun Jun 20, 2004 10:47 am

:(
I'm trying to build an anaerobic digester but so far I got nothing...somebody please give me a hand with it...
I needs some plans of something that will work..
I got a 35 gal. with chicken manure and water, 3/4 full, since 10 days and nothing comes out.The pressure meter reads 0...
JORGE ESCOBAR

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Post by Bob » Wed Jun 23, 2004 1:33 pm

Hi Masjavy. Starting up a digester can be tricky. There is some discussion of start-up procedures here on this forum that might be helpful.

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Post by MASJAVY » Sat Jul 31, 2004 11:40 am

thanks Bob.

I tested the gas from my digester and it works just fine .I got blue clear ligth and since it is not much it burned for about 3 minutes...but i feel that i have reach a point.
from here I would like to know more about hanling,storage and use.
can you give me some ideas

Jorge Escobar
JORGE ESCOBAR

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Post by Bob » Mon Aug 09, 2004 2:56 pm

Hi Masjavy,

Sorry for the delay in responding. Yes, I have some ideas about gas handling and use, but first, have some more questions.

First of all, has your biogas yield increased at all yet? Working properly, (i.e. with loading rate, HRT, C/N ratios, temperatures, etc. as specified) you should be able to generate 2-3X the volume of your digester of biogas per day. With this in mind, (assuming that, after any problems have been resolved you will be able to generate that amount of gas), what do you want to do with it? Use it for cooking fuel? Hot water heating?

In general, I prefer using the gas as soon as possible, reducing the requirement (and associated hazards) to store large quantities of flammable fuel on site. One way to do this is to burn it in a gas-fired water heater, storing the energy as heat, rather than as a potentially more hazardous fuel.

If the water heater is appropriately sized to be able to use the anticipated amount of gas per day, you can wire it so that the standard gas valve (must be spark- or hot-plate-ignited) is enabled by a pressure switch on the gas line. Wire it in series with the tank thermostat, so that the burner is enabled when (1) there is gas available (as indicated by pressure switch), and (2) the heater thermostat is calling for heat.

What are your goals for use of the gas?

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anaerobic digester

Post by MASJAVY » Wed Aug 11, 2004 10:24 pm

thanks Bob for your reply..

well I got a 30 gallon plastic container and i get like 5 minute burning every 2 days...the gauge on the container shows almost 5 pounds but since is a plastic, it expands.
and I started to store it in one of those freon tanks with the help of a air condition man...he has the compressor and the gauges.
The tests that you mentioned..the ratio and everything else..i.e. loading rate, HRT, C/N ratios, temperatures, etc. as specified)..I have no idea.how do i do that...my gas yield increased..yes...but it is almost 3 months old allready,it shoul be decreasing right.?
My goal is to store it in a tank and to use it to run my car equipped with lpg system.gasoline in Honduras costs 3 dollars a gal.so...if i run my car one day a week with gas it would be an achivement and I would encourage others to do the same.
I really thank you for your help.
JORGE ESCOBAR

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Post by Bob » Tue Aug 17, 2004 1:48 pm

Hola, Jorge

Here is a formula for estimating gas production from a batch feed process. (My earlier comments were based on the assumption that it was a continuous feed process. Now, reading more carefully, I see that it is a single batch.)

V = Vt(1-e^(-kT))

Where:

V = volume of gas produced at any given time T
Vt = total volume of "possible" gas production (if left to "completion" in, say, 120 days)
e = e -- (2.71828)
k = reaction velocity constant, reciprocal of time it takes to achieve 63% of Vt
T = time (day of interest)

You can only determine the value of k & Vt for your particular feedstock (and temperature), by direct experiment, letting it go to completion, and measuring and recording the amount of gas produced every day. (I've been working on a simple gas measurement device that anyone can build from misc off-the-shelf parts, to facilitate measurement. Let me know if you'd be interested in details...)

When you say that it burns for 5 minutes every 2 days, do you have any idea what the flow rate is?

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ANAEROBIC DIGESTER

Post by MASJAVY » Wed Aug 18, 2004 8:00 am

Hola Bob

I got your formula and i started recording everyday every aspect of the digester.

of course I am interested in the gas measurements device....let me know how to build one.....it would make all this easier for everybody.

The gas flow.....Huh?....well I use a gas regulador that i got from a barbecue grill....hook it up to a burner and when I lit it , a blue flame stars but it just burns upward....i guest it's because it has litlle pressure
and then it justs dies slowly.it last about 5 minutes .my gage shows 5 lbs of pressure.

well now I got a 55 gal. batch feed digester and I use cabbage...just to see if it works.Since getting the chicken manure is tricky here because of the companys regulations of other peoples getting into the farms I decided to used vegetables waste....i just have to pick it up a a local market and i will help with their disposal .
JORGE ESCOBAR

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