Introduction: Make Energy From Weeds

Picture of Make Energy From Weeds

Solar, wind, water, geothermal and biomass are sources of producing renewable energy. Production of energy from sun, wind, water and geothermal need costly equipment. Even the smaller scale models of solar and wind energy for a medium sized home costs more than 1000 US Dollars. Individuals can not think of energy from water and geothermal as the required infrastructure will cost the heaven. They also require regular maintenance of moving parts, batteries and other things. Renewable energy from biomass is the cheapest form of all sources mentioned above, which require minimum initial investment and practically no maintenance at all. The biomass fuels like vegetation, crop residues, cattle waste, kitchen waste and aquatic plants are abundant in nature and also easily available throughout the year. A medium sized biomass digester can be built with about 200 US Dollars.

Here, I have experimented with producing energy from anaerobic digestion of weeds.

we had a very good rainy season this year in our area and everyone is happy. The rains also helped weeds to spread and grow at a faster phase covering open areas. road sides, home gardens and all ! There are weeds, weeds, weeds everywhere...

Few of our neighbors hired some help to weed out their patch of land. Some threw them out and few heaped them to make compost. Also, some farmers used chemical weed killers / herbicides to completely destroy all those weeds from their agricultural land. And me, left all those weeds in our home garden to make an experiment on making energy from them.

This instructable is aimed at the common man with simple to follow steps explaining how we can efficiently extract energy from all those unwanted weeds and use the remains as compost.

Please read on and offer your comments and suggestions

Step 1: How Can We Extract Energy From Weeds ?

Picture of How Can We Extract Energy From Weeds ?

How can we extract energy from weeds ?

Energy from weeds can be extracted by anaerobic digestion process which breaks down the weeds and produce methane. Methane is an odorless & colorless gas and combustible in nature. So it can be used as energy for lighting, cooking, heating, fuel for vehicles and for running generators to produce electricity.

How it Works...

The biogas process happens in three simple steps namely Hydrolysis, Acidogenesis and Methanogenesis. Different groups of bacteria are responsible for each step to turn weeds into energy.

Hydrolysis

During hydrolysis, protein, carbohydrate and fat polymers present in the weeds are broken down to small molecules by different specialized bacteria. They produce a number of specific enzymes that accelerate the decomposition of the weeds. Lignin, an important plant component, cannot be decomposed under anaerobic conditions at all. In plant tissue cellulose and hemicellulose function as supporting material in the cell walls. These are tightly packed in lignin and are therefore difficult for bacteria to get at. So, by lightly pulverizing the weeds, we make it easy for the bacteria to break down the weeds.

Acidogenesis, also known as Fermentation

In acidogenesis or fermentation process, the broken down weeds are converted into acetic acid, carbon dioxide, hydrogen and volatile fatty acids.

Methanogenesis

The third and last step of biogas production is done by the methanogenic bacteria, which are divided into two groups. One group converts acetic acid into methane and the other from carbon dioxide and hydrogen. Degradation of acetic acid is responsible for about 70% of the methane produced, and the remaining 30% comes from carbon dioxide and hydrogen. These processes are finely balanced and inhibition of one will also lead to inhibition of the other.

Earlier I have posted an instructable on constructing a medium sized anaerobic Biogas digester using only a hacksaw blade and a knife as tools, which you can see at this link here :

https://www.instructables.com/id/Constructing-a-Med...

Here, I have used the same biogas digester to make this experiment / study using only weeds as feed material to produce biogas.

I have started feeding the biogas digester with pulverized weeds since last week of September 2014 and still continuing with it. In the mean time, I have also collected the data of how much biogas can be produced and how much energy can be derived from weeds.

The subsequent steps will explain how simple it is to extract energy from weeds.

Step 2: Collect Weeds

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The capacity of the digester in the biogas plant I have built earlier is 750 liters. Leaving about 50 liters for free board, we can consider the net capacity as 700 liters. Considering 30 to 35 days of retention time, I can feed about 2.5 to 3.5 kilogram of weeds per day in this plant. For my experiment with weeds, I choose to feed about 2.5 kilograms of freshly collected weeds mixed with enough water to make it to about 20 liters of diluted feed material. The mixture will also have a retention time of about 35 days in the digester. I will also get about 20 liters of composted slurry everyday, which can be diluted and applied as compost to plants in the garden

I have experimented with all type of weeds from the home garden and surrounding areas. They include weedy plants, weed creepers, leaves of trees, grass and whatever available nearby. Due to rains the ground was very soft and I could pull out most of the weeds with roots. About 4 kilograms of these freshly collected weeds will give 2.5 kilograms of feed material after trimming out the roots and removing the woody parts. Otherwise, you can just collect the weed clippings without the roots and use them as they are. You can also collect three to four days requirement in advance and keep them separately.

Step 3: Remove Roots and Chop Weeds

Picture of Remove Roots and Chop Weeds

In the pictures above you can see that I have trimmed away unwanted roots and stems from the weeds. Then using a garden shear, I have also chopped down the weeds to manageable size.

To make an assessment of how much weeds make a kilogram, I have weighed about one kilogram of chopped up weeds in a bag. The red basket in the picture here contains about two and a half bags, that is, 2.5 kilograms of chopped weeds ready to be pulverized.

I feel it is not necessary to weigh the weeds again and again every day as the basket-full of chopped up weeds will make the daily requirement.

Step 4: Pulverize the Chopped Weeds

Picture of Pulverize the Chopped Weeds

I have observed that feeding the chopped weeds directly into the plant did not digest the feed material fully. On closer examination of the slurry, I could find some partially digested chopped weeds drained out with the slurry. So, it is better to pulverize the weeds before feeding the plant.

using a spare metal jar of a mixer grinder, the weeds were ground with little amount of water in small batches. I have recycled the water collected from the kitchen which was used for rinsing rice and lentils and used it for dilution. The pulverized weeds were then collected in a small bucket and transferred to another larger one near the biogas digester. I have also reused the water used for cleaning the metal jar after use, for diluting the pulverized weeds.

For pulverizing about 2.5 kilograms of chopped weeds in small batches, I use a 550 watt mixer / grinder. It takes less than 10 batches and about 15 to 20 seconds per batch. The total running time used is between 3 to 4 minutes per day for which the electricity charges comes to less than a Dollar per month.

A word of caution here... Do not use chlorinated water. Also do not use soapy water used for cleaning the utensils. We use bore-well water at home which do not contain chlorine or any other chemical.

Step 5: Dilute With Water and Feed the Biogas Digester

Picture of Dilute With Water and Feed the Biogas Digester

I have used a 20 liter capacity bucket to transfer and dilute the pulverized weeds near the feeding point. More water is added up to the brim of the bucket to make to 20 liters. The diluted crushed mixture is then fed into the biogas digester through the feed pipe. This is a repetitive process and should be done everyday to get uninterrupted production of gas.

There may be some soil particles collected along with the weeds. These particles may get deposited at the bottom of the diluted mixture. So, do not empty the bucket containing pulverized weeds in to the feed pipe and discard the soil deposit away.

Step 6: A Study on Production of Energy

Picture of A Study on Production of Energy

How much gas is produced per day ?

Calculating energy produced by this way may seem to be not in accord with the procedures followed by scientists in a controlled manner in laboratories. But I do not have that sort of facilities available with me. Moreover, I am using this gas for cooking purpose only, so I have compared it with normal LPG consumption at our home.

In terms of cubic meters

with 2.5 kilogram of pulverized weeds, let us see how much cubic capacity of gas is produced:

Inner diameter of gas holder = 80 centimeters (0.80 meters) (Radius is 0.40 meters)

Average height raise due to gas production = 45 centimeters (0.45 meters)

Cubic content of gas produced : 3.1428 X (0.40 X 0.40) X 0.45 = 0.226 cubic meters.

The above quantity also contains impurities like Carbon Dioxide, Nitrogen and Hydrogen Sulfide.

Liquefied Petroleum Gas (LPG) versus Biogas

Another test to find out the actual efficiency of the biogas is to compare with Liquefied Petroleum Gas (LPG) normally used in our household.

In our home, a full LPG cylinder containing nearly 15 kilograms of gas normally lasts for about 30 days. So, our consumption works out to about 500 grams of LPG per day.

As you can see in the pictures above, I have placed both the systems (one using LPG and another with Biogas) side by side. On 13 October 2014 we installed a new LPG Cylinder and started using both LPG and Biogas simultaneously. The LPG cylinder was fully emptied on 24 November 2014 and replaced with a new one.

The LPG cylinder which normally lasts for only 30 days has now been utilized for 41 days in conjunction with Biogas. At the rate of 500 grams of LPG per day, the additional 11 days X 500 grams = 5500 grams of equivalent LPG has been supplemented by Biogas.

Production of Biogas per day from weeds equivalent to LPG = 5500 grams /41 days = 134.15 grams

So, 0.226 cubic meter of biogas produced everyday ( mixed with Carbon Dioxide, Nitrogen and Hydrogen Sulfide), gave us 134.15 grams of equivalent calorific value of energy in comparison to LPG.

Step 7: Output Slurry

Picture of Output Slurry

Whenever the biogas digester is fed with pulverized weeds, the equal volume of digested slurry is drained out through the outlet pipe. Here also, I have used a 20 liters bucket to collect the slurry, which can be used as compost in the garden.

Step 8: PH of Slurry

Picture of PH of Slurry

I have tested the pH of the output slurry with the help of pH test strips. The pH was measured between 7 and 8 in comparison to the Test chart provided with the kit. The slurry is slightly alkaline due to the presence of Ammonia produced by the weeds. I think this slurry is well suited as compost for our garden's red soil which is little bit acidic in nature.

Step 9: Maintenance of the System

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The anaerobic digester needs very little maintenance. However the following steps will help in uninterrupted gas production.

The anaerobic process creates heat and some water vapor also gets mixed with the biogas. This water vapor will condense and may get trapped in gas pipe. To prevent this, keep the outlet valve closed at the gas holder tank after using the gas. This will help in most of the condensed water to fall back into the tank. Disconnect the gas pipe once in a week and drain out any condensed water from the pipe line.

Secondly, the slurry in the tank needs to be agitated to prevent the formation of surface crust. I do this after every feed using a vented ram through the feed pipe.

Step 10: Bottom Line

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It takes less than an hour for me to collect, clean,chop, pulverize and feed the weeds in the anaerobic digester. It requires less than 5 minutes of mixture-grinder time to pulverize 2.5 kilograms of weeds in small batches, which is more than compensated by the output biogas and digested slurry as compost.

Advantages of the system

  • Our home garden gets a regular weeding operation
  • The weeds are utilized to extract bio-fuel
  • The digested slurry is recycled as compost for the plants
  • The bio-fuel meets 25 % of our cooking gas requirement
  • Does not involve any running costs other than few minutes of electricity for pulverizing the weeds
  • It is also eco-friendly

Some Do's and Don'ts

  • Feed the Biogas digester regularly
  • Do not over feed. Keep the excess weeds for tomorrow
  • Do not collect weeds from areas where pesticides / herbicides were used
  • Do not use chlorinated water. We use bore-well water for all our needs.
  • Recycle water wherever possible.
  • Do not use soapy water used for cleaning kitchen utensils.

It is almost three months since I started using weeds to produce energy. The Biogas digester is stabilized and producing regular supply of gas as well as composted slurry everyday. Every four months I save one full LPG cylinder which is being supplemented by biogas which is almost free of cost. As my biogas digester can support more load, I am planning to gradually increase the input from 2.5 kilograms to about 3.5 kilograms.

I hope I have explained everything in easy to follow simple steps here. Your inputs, comments and suggestions are most welcome.

Comments

SHOE0007 (author)2017-11-17

Cool, do you think it is possible to generate electricity if you scaled this Up? Cody lab he made a methane collector and there were issues there. I am all for alternative energy however the limitation is bacteria that convert biomass into gas. I am sure with bio-enhanced bacteria or fungi this can be done.

A while back I made a bio battery reactor with steel and copper and sludge from soil and nutrients for a friendly bacteria it did work but it was not very effective at making electricity even if Oxygen from the air was pumped in.

I even add a mixture of Potassium ferrocyanide with 3% Hydrogen peroxide it did not work well even though Literature said in the right conditions it can.

antoniraj (author)SHOE00072017-11-27

you can run a generator using biogas and generate electricity. I'm not sure of other methods.

Chukz4real (author)2016-06-06

Under normal temperature, what size of biogas digester and quantity of feed can produce up to 12kg of gas daily? Can the gas be used to power generator or cook without first removing the impurities? ferdinand.obuluku@gmail.com

antoniraj (author)Chukz4real2016-06-06

Please go through the files sent to your mail which will help you in designing the Biogas digester as per your requirement. I have also included construction plan for a large scale model which you can keep it as reference. You can use the gas to power a generator. The gas produced initially contains lots of impurities and will not burn. So no use in trying to burn that gas. Just empty the gas holder few times till you get burnable gas

utomii (author)antoniraj2017-10-27

Please sir, help with files/materials on design of biodigesters for cooking and electricity as applied in temperate region (Africa).
Thank you. chukaiweka@yahoo.com

antoniraj (author)utomii2017-11-24

You can download the files from the following Dropbox link

https://www.dropbox.com/sh/hjpq1o8qbe3r8db/AAD63dDpvb3SMSCye_eXPeRca?dl=0

utomii (author)antoniraj2017-10-27

Also forward the above files you sent to him(chuks4real) dated 2016-06-06, on biogas to me please.
Thank you

antoniraj (author)utomii2017-11-24

You can download the files from the following Dropbox link

https://www.dropbox.com/sh/hjpq1o8qbe3r8db/AAD63dDpvb3SMSCye_eXPeRca?dl=0

OmotayoO1 (author)2017-09-18

Wow!.... You deserves best world award from all parts of the continent.
Sir, if possible... I will like to have your mail and phone contact. Send to: omotayoolaoye@gmail.com
Best regard.

kelms1 (author)2017-08-28

I love this nice job

antoniraj (author)kelms12017-08-28

thank you...

Daniel434 (author)2017-02-04

Actually we can recondition batteries at home - simple way

jasonsj (author)2016-06-25

I couldn't find how to attach the pic as a reply after my comment so here you have a pic of a water trap i suggested you to intall

antoniraj (author)jasonsj2016-06-26

thank you for the suggestion and picture. I will see how I can do this...

BrandonM164 (author)2016-06-07

Great instructable! Is there any way you could share a hardware diagram or a few more pictures of the biodigester?

antoniraj (author)BrandonM1642016-06-08

I have given a link to my other instructable on constructing a medium sized Biogas Plant in Step-2.

Here is the link for you...

https://www.instructables.com/id/Constructing-a-Medium-Sized-Biogas-Plant-Using-Kit/

SelineH (author)2016-05-23

Is there any other way to make this without biogas digester?
Thank you

antoniraj (author)SelineH2016-05-23

You can make compost with weeds but you can not collect the gas. Anaerobic Digestion using the Biogas digester is the only way to make this.

malexander15 (author)2016-05-19

I'd encourage you to get a gas sample and bring it to a lab near you. Some gaseous products of these methanogenic bacteria are harmful. In the mean time use your gas in an open, ventilated area. Great project overall!!!

antoniraj (author)malexander152016-05-23

I do not have a lab near me to get the gas sample tested. However, we use the gas in a well ventilated area. Thank you very much for your appreciation...

ybaggi (author)2016-05-21

So if I'm reading this correctly, this size biogas digester can handle or needs
2.5kg of organic material (weeds in this case) everyday?

So if I build two and feed them in parrallel everything should be doubled right?

Thanks

antoniraj (author)ybaggi2016-05-23

Yes, you are right. This digester can handle about 2.5 to 3 kilograms of organic material. If you build a parallel one of the same size, everything will be doubled up. You can also connect both gas holder tanks together with gas pipe line. The outlet pipe line can also be connected together.

jannie.lloyd (author)2016-04-24

You can come and collect my weeds - as long as you show me how to connect this "free" gas to my cooker.

antoniraj (author)jannie.lloyd2016-04-25

please see my other instructable where I have explained everything including construction of the system, gas pipe line and also how to connect it to the Biogas Stove...

https://www.instructables.com/id/Constructing-a-Medium-Sized-Biogas-Plant-Using-Kit/

anagchaudhuri (author)antoniraj2016-04-26

Do u need any bacteria ( cow manure) for the gas production ? It seems you are using only pulverized weed ... does that in itself take care of the bacteria needs for the anaerobic digestion process ?

antoniraj (author)anagchaudhuri2016-04-27

You need cow dung slurry only for the initial feed. Afterwards the bacteria present in the cow dung slurry adjust themselves to the input and take care of the anaerobic digestion process. It is more than year this system is in operation and I never used cow dung slurry except for the initial feed

anagchaudhuri (author)antoniraj2016-05-10

Thanks. I would be interested in having some of my students work on this. I am no anaerobic digester expert, but generally it is known that cow's stomach has the bacteria to digest grass, weed etc and produce methane. Can u give me a little more detail on quantities of weed and cow manure involved and other logistics.

antoniraj (author)anagchaudhuri2016-05-10

Please see my other instructables on Biogas Digester where I have explained everything in detail

https://www.instructables.com/id/Constructing-a-Med...

https://www.instructables.com/id/Bio-gas-plant-usin...

jannie.lloyd (author)antoniraj2016-04-25

Thanks. I guess I missed that bit. Teach me to read things properly.

sivaprasadc (author)2016-05-02

This is very informative and usefull , particularly urban population should learn to live natural way , this is best exercise.

antoniraj (author)sivaprasadc2016-05-02

Thank you...

TxPuddleDuck (author)2016-05-01

How do you build the Biogas Digester for the weeds?

also if we are short on weeds, do you think we can pulls weeds on the side of highways?

Thanks

antoniraj (author)TxPuddleDuck2016-05-01

I have given a link in Step 1 of this instructable on building a medium sized Biogas Digester. Here is the link for you...

https://www.instructables.com/id/Constructing-a-Medium-Sized-Biogas-Plant-Using-Kit/

You can pull out weeds from anywhere, but make sure chemical pesticides or weed killers were not used on them. You can also use kitchen waste to feed the digester

innerlight2111 (author)2016-04-26

I was wondering what was left in the spent slurry at the end of the process. You stated that it can be used as fertilizer I am interested if you know the chemical breakdown specifically the nitrogen levels. thanks great project.

antoniraj (author)innerlight21112016-04-27

The spent slurry is fully composted organic material mixed with water. It is almost odorless and little bit alkaline due to the presence of small amount of Ammonia. You can directly add the waste slurry to plants

ilhampenta (author)2016-04-26

Thank's man. Hope i can make for myself

antoniraj (author)ilhampenta2016-04-27

thank you...

guruji1 (author)2016-04-27

Wow regards Antoniraj this is geniously done thanks for sharing this. Is there a need of a bubbler for safety so that there would no back fire to digester?

Thanks

antoniraj (author)guruji12016-04-27

Thank you... I am using this system for more than a year and did not find any need for a bubbler. For safety and to prevent back-flow of Methane, I have placed about 40 kilograms of weight on top of the gas holder tank. This produces enough pressure and prevents back fire.

bowen5400 (author)2016-04-25

I am a little disappointed. A general description of the digesting bin and a photo are pretty slim. Where in the world can you get one, and what are the exact specifications as a reference. I have never seen a tub/barrel/bin like that in 61 years, 44 of them focused on this and other self sufficiency strategies. Not to mention years in commercial and residential construction and maintenance. A little to vague. And the linchpin of and only critical one of a kind item in the design. A 50 gallon drum needs some moderate level modifications.but the picture and the text are difficult to collate from the lack of labeling, or materials that are applicable...it is the centerpiece of the system, yet I get zero idea how to go about aquiring one. The author doesn't even say what the thing is called by the manufacturer. Can't even google it. Just this picture is what I used, and it's triple walled? Please understand, I appreciate the time, effort, and info, but the author seems to think his readers are mind readers. Or that they have an encyclopedia of industrial containers in their heads. No clue what the containers product name is, or what it is usually used for, or where to get one. Just "anything like this is good". I also noticed a lack of an x-ray image or cutaway view, or a schematic for non experts to use in configuring one from other vessels. It is the only critical part of the entire apparatus.

Kaljakaaleppi (author)bowen54002016-04-26

There are lots of DIY-related forums on the net and I frequent some of them. Some places discourages spoonfeeding, you can get some quite nasty replies if you don't do your own research.
Instructables is not one of those.

Thanks to the author for a great Instructable, especially paired with the other biogas one. It has more than enough info to work on. If I would to build one (which I'd love to but I live in a very cold climate) I'd put the drainage tube in the lowest point of the incubator. It'd mean a bit more of work but then the accumulation of sand trough soil wouldn't be a problem as it would drain when draining the slurry.

We have lots of reed growing here (Phragmites australis) and I have been toying with the idea of harvesting it for burning. I had a plan in mind to use a lawnmower blade and rig it in a bucket to cut the reed for further processing. Maybe one could crush the weeds with a rig like this also. Blenders tend to break down when used in a home-industrial scale. Found it out when processing apples for juice/cider :)

antoniraj (author)bowen54002016-04-26

If you have gone through this instructable, you might have noticed that I have given a link in Step 1 on How to construct a medium sized Biogas plant including all required material, tools, Biogas stove and all necessary pipe line connection. Here is the link for you...

https://www.instructables.com/id/Constructing-a-Medium-Sized-Biogas-Plant-Using-Kit/

Hexacyanoferrat (author)2016-04-13

Thank you for this great instructable (and the other 2 you did on biogas production). I am planning to implement a similar construction here in Germany, but am a bit worried about our resident temperatures. I did some research and found that the bacteria (especially those for methanogenesis) prefer temperatures between 20°C and 50°C to thrive and don't like large temperature differences (for example day-night-cycle). Those values are for industrial sized biogas production -- where a constant gas output is needed -- so I don't know how much they apply to smaller scale garden systems.

Can you tell me a bit about your experience with temperature variation? I am not familiar with your local climate, but I guess it's a lot warmer than mine. What was the coldest temperature your biogas plant still worked with? Did it ever stop working due to cold temperatures? What is the highest day-night-difference in temperature you get?

I plan on starting in the summer -- where the heat is at it's maximum -- but even then nights can get pretty cold and in spring and autumn there is usually some freezing.

Do you have any information about this problem?

Kindest Regards,

Hexacyanoferrat

Germany is one of the leading countries in renewable energy production. Our place never experience much temperature variations. In our area the lowest temperature is about 14°C in winter and maximum 38°C in summer.

In cold places the Biogas digester is buried in the ground and part of the Biogas produced is used to keep the slurry warm.

Please go through the articles in the following links

http://www.wecf.eu/download/2008/Biogascoldclimates_WEB-WECF0608.pdf

http://www.ramiran.net/doc08/RAMIRAN_2008/Sommer.pdf

You can also download a paper "Biogas production in climates with long cold winter" from the following site

http://www.susana.org/en/resources/library/details/855

Bury the Digester & use an insulated cover for the top etc.

That's a good idea in general I think, but it probably won't help when the ground is frozen. In that state it would probably be even better to have it standing above ground :D

If I am really bored I might try both to get some measure of comparison.

DamonS1 (author)Hexacyanoferrat2016-04-24

It is true that as long as the system is insulated it will probably generate enough heat to keep itself running. Look at compost heaps and melon growing... which is often used here in the uk where temperatures are also cooler.

Hexacyanoferrat (author)DamonS12016-04-24

Ah, but compost heaps have aerobic digestion! that produces more heat than anaerobic, as far as I know.

But speculation aside, I will try the insulation and if all else fails I have to use some burned biogas to heat a water hose running around the digester.

The oxygen gets depleated quickly beneath the surface unless the pile is very small, or very thin. That is why it is recommended to turn compost regularly, especially in warm weathrr.

DamonS1 (author)Hexacyanoferrat2016-04-25

Fair point! Thanks, of course you are right.. i suppose you could construct a small greenhouse (or geodesic dome) type of arrangement around the
digestion chamber... this should provide some protection from extremes of temperature... just a thought

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