Watch A Methane Biodigester Primer – it will open a new window!
Then come back and read about our design based on a design by Shaun Hermans of Shaun’s Backyard.
Our Main Objective!
The main objective of this project is to promote the development of renewable energy sources and technology and to establish a basic concept and bench mark for a future biogas plant.
- The proposed project seeks to demonstrate a proven technology for our anaerobic digestion system and to promote the development of renewable energy sources and technology providing an integral approach to the solution of environmental pollution problems by waste disposal.
- To create a local capacity for properly managing a treatment of municipal solid waste particularly the water hyacinth and draw lessons to replicate elsewhere.
- To increase community awareness and participation in environmental management at the local government level.
In addition, this is going to be a project to see if we can use the water hyacinth plant to produce a biogas. If we’re successful on this small scale, we will scale up our system for an introduction to the Stockton, CA City Council with the hope of taking their yearly hyacinth removal to a whole different level.
Our goal will be to have a concert event called the Water Hyacinth Festival with sponsorships provided by most if not all of the local businesses within San Joaquin County at the Stockton Arena.
At the present time, they remove the water hyacinth plant to local landfills; we hope to provide a mobile solution. But for now we’re going to create this three barrel digester to see how feasible a larger scale program would be, and of course, we will document the process with pictures and videos.
“Biogas is the perfect solution to modern sustainable cooking.”
Biogas is a mixture of gasses that are produced as anaerobic bacteria break down organic matter. It is flammable, capable of producing a clean flame for cooking and heating, and it can be derived from as simple a feedstock as your kitchen rinse water.
A biogas digester is a container holding water and bacteria, which can be ‘fed’ organic matter to be broken down, and which collects the resultant biogas, to be tapped off either to a collector for storage, or directly for burning.
- Creates Flammable Gas
- Creates Fertilizer
- Safe and Clean
- 200 Liter Blue Plastic Barrel (2)
- 100 Liter Blue Plastic Barrel (1)
- PVC Pipes and Fittings
- PV Hoses and Fittings
- Silicone Sealer
As noted above, we are using a design by Shaun’s Backyard. This project is designed to see if The Water Hyacinth Plant can efficiently by converted into biogas, and as a home project, I will hopefully be able to decide if we should take it to a larger scale.
My biogas digester, and biogas collector, will be using a 200 Liter (50 gallon) blue plastic barrel. It will be my aim to create a system capable of producing enough biogas using water hyacinth to produce enough biogas to burn in a gas lamp, and use those results to scale up the project.
Sealed, with two screw-in lids at the top, and a slight dome shape top which will became an important factor.
The input pipe, gas-out valve and output pipe all fitted to the top of the barrel
A biogas digester requires an input pipe (a place to deposit fresh feedstock), and an output pipe of some kind (for contents to be displaced out of). Since there were already two screw-in lids which sealed perfectly, we will take advantage of them, but have the discharge going 3/4 way down the barrel. The biogas output will be located at the top of the barrel.
The digester was designed to be gas-tight, so that no biogas could escape the unit except through the gas-out valve, which was a simple polytube irrigation valve. However, if for some reason pressure should build up in the system, it would simply push the contents out through one or both of the input/output pipes.
The input pipe will run through one of the lids of the blue plastic barrel, and extended almost to the bottom of the barrel. This meant that fresh feedstock would enter the digester at the bottom. The output pipe ran only to the center of the barrel, which meant that as fresh feedstock entered, existing liquid would be displaced from the center of the barrel, and exits the unit into an effluent bucket. Since solid particles of organic matter usually either float or sink, it would be mostly only liquid which comes out as effluent, leaving the larger particles in the digester to break down further.
The pink line shows the water level inside the digester. Note the gas-out valve is above this level.
We will be able to set the output pipe almost at the level of entry into the barrel, which left a pocket inside the dome of the top of the barrel for biogas to collect, and it was at the very top of the barrel that I fixed my gas-out valve. T
his means that at any given time there would be very little biogas stored in the digester – the digester would be almost completely filled with liquid, and almost all biogas would be expelled via the gas-out valve to the collector.
The collector (empty) is an inverted plastic garbage bin submerged in water
The collector was simply a blue plastic barrel with its top cut off, 3/4 filled with water, with a plastic garbage bin inverted and submerged, with a gas input and a gas output valve fitted to it. Biogas produced by the digester would collect in the garbage bin, and as the garbage bin filled, it would rise out of the water.
If the biogas unit became too filled with biogas, the biogas would simply leak out the side.
Filling The Biogas Digester:
We plan on filling the biogas digester with water and about 30lbs. of cow manure and 20lbs. of water hyacinths. The idea is to breed the various kinds of intestinal bacteria from the manure, so that they can process feedstock the same way they do in a cow’s intestines, breaking it down into fertilizer and creating a flammable gas. It might take a couple weeks or so for the bacteria to settle in and begin digesting feedstock from what we’ve read.
Feeding The Biogas Digester:
Shaun uses kitchen rinse water, effluent is displaced into a bucket which goes straight on the garden. We will take advantage an follow his lead to get the process started adjusting it with water hyacinths as gas is created.
Feeding the biogas digester will be easy.
Just turn off the gas-out, and open the lids on the input and output pipes.
Shaun pouring in his kitchen rinse water, the excess effluent pours out into a bucket, then use as garden fertilizer.
Shaun says; biogas is fart gas, the same as what a cow produces! It smells as you’d imagine, but when it is burnt the smell is the same as from a clean natural gas burner.
Burning biogas alone produces a large yellow sooty flame, which will turn the bottom of pots black, and will not heat very efficiently. It is when air is allowed to mix with the biogas just before it is burnt that a hot, clean, blue flame is produced.
To make his unit efficient, Shaun created a bunsen-burner type tip to test the variables involved.
Shaun Made Gas Restrictors:
Shaun’s Bunsen burner is made from scrap PVC pipe, a spare polytube sprinkler fitting, and some circular wooden doweling fashioned into a gas restrictor. I made a few of these restrictors with different sized holes to experiment with, and drilled holes through a pvc collar into the main pipe, which allows air to enter and mix with the stream of biogas.
The collar can be rotated to limit air flow. It took him a few tests to find the most efficient combination of factors to get a nice hot flame.
Shaun attached his home-made burner to the bottom of an old gas barbecue. Using the existing supports, he can cook a pot over the biogas flame. I place a weight of either 5kg or 10kg on top of the biogas collector bin to apply some pressure to the biogas. The 5kg weight allows for a modest flame capable of boiling a liter of water in about 15 minutes. The 10kg weight forces biogas out quicker and a liter of water can be boiled in 10mins.
Emptying The Biogas Digester:
Most digester designs include a ‘sludge-out’ pipe toward the bottom, so that the unit can be moved and emptied easily, which I will include.
Shaun’s biogas digester project was successful; the digester is capable of producing more than 30mins worth of biogas per day, and the collector can just hold this amount of biogas. However, he has decided not to go to the trouble of grinding/chopping/blending/mincing up kitchen scraps to fully feed the digester, and have instead been feeding it the rinse water from his kitchen which amounts to about 4 Liters per day – a mix of water, liquids and food particles from rinsing cups and plates. From just this feedstock I have been generating about 15mins worth of biogas per day – enough to steam some veggies in the morning and make a cup of tea.
His system is limited by the collector – it can only store about 30mins worth of biogas, while the digester itself can produce more than double this if it is fed substantially. For his purpose, a larger collector is unnecessary, but he encourages anyone planning to do all their cooking on biogas, to consider multiple collectors or scaling up using larger containers.
A Frequently Asked Question:
What else can I use to make a biogas digester?
Any large plastic container is fine. Do not use steel drums or any metal parts for your design, as the hydrogen sulphide component of biogas will quickly corrode these parts. So far he’s seen no deterioration of any of the parts I’ve used (PVC, Polyvinyl, and Polyethylene) in contact with biogas and/or effluent. Consider olive barrels, or for a larger scale digester consider 1000L tanks (with cage).
My Question Written on Shaun’s Blog:
I’ve spent most of the late night/early morning reading everything, and I must say that I’m about to jump on this bandwagon. Although my project is quite different, I am the experimenter and will attempt to make it work.
We are working on converting the aggressive water hyacinth plant into a usable bio fuel.
We are following your design and would like your input on if you it is possible. We will be grinding the plant up, adding it to a slurry of cow manure and crossing our fingers. It is a small scale test at this time but we are hoping that we can make it a producing test.
Shaun Takes the Time to Answer:
Thanks for your comments. Its a great idea you have, and if it works I hope it can serve as a model for others.
There’s a very simple way to test how much gas a particular feedstock can generate.
- Mix hyacinth, cow manure and water into a condom and tie it shut.
- Use the same manure on its own with water in another condom as a control (manure alone will produce some gas).
Leave it for a day or two in warm (but dark) conditions. I saw a guy do this test for a range of feed stocks, attempting to find what would produce the most biogas. (beans took the cake).
You can also whip up a small digester using bottles, and capture biogas with a balloon. These prototypes, as opposed to the condom test, will allow you to do a burn test to confirm that you’ve made biogas and not some other gas (like co2 from yeasts).
Also, you may not need to add cow manure after your initial fill, as the bacteria multiply themselves. Mine has only had one dose of manure and has continued to produce gas for a year+.
If you’re only feeding your system hyacinth, the effluent coming out will only contain what nutrients are in hyacinth, and so will only be so good as a fertilizer. I’m not sure if other problems may arise from feeding a digester only one type of feedstock. On a home scale there’s a variety of materials going in, so I cant vouch for a single feedstock, you’ll have to let me know.
Keep me posted. I’d love to see a photo of your setup, and know how you’re grinding materials and what you plan to do with the biogas and effluent.
Good luck with your project!
Michael Burton Sr.
AAAA Hyacinth Harvesting