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  • jaba53 commented on whatisthisidontunderst's instructable Biogas Digester2 months ago
    Biogas Digester

    I love these digesters! I have one running in my basement which makes the temperature control issue much easier.Your design however has several fundamental flaws which can easily be fixed.1) The feed tube should extend down into (near the bottom, 1/3 from the bottom is a good starting point). That way, a) there is NO loss of gas when feeding. b) the stuff you put in starts at the bottom, as it decomposes and loses mass, it will become lighter and get shoved upwards toward the exit point. You already built a pushing rod which, while not absolutely necessary, can be used to help push everything in ensuring that the feed tube is full of nearly 100% water and no solids. This reduces residual gas production within the feed tube which could escape as part of the feed process.2) The exit t...

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    I love these digesters! I have one running in my basement which makes the temperature control issue much easier.Your design however has several fundamental flaws which can easily be fixed.1) The feed tube should extend down into (near the bottom, 1/3 from the bottom is a good starting point). That way, a) there is NO loss of gas when feeding. b) the stuff you put in starts at the bottom, as it decomposes and loses mass, it will become lighter and get shoved upwards toward the exit point. You already built a pushing rod which, while not absolutely necessary, can be used to help push everything in ensuring that the feed tube is full of nearly 100% water and no solids. This reduces residual gas production within the feed tube which could escape as part of the feed process.2) The exit tube should also extend down into the barrel with half way being optimal. Realize that some things are heavier than water and will collect at the bottom. Some things are lighter (oils, scum, etc.) and will collect at the top. What's in the middle is most likely to be nothing but water and that's what should be coming out as the overflow. The gas pressure (not much, but it is there) pushes the water up the pipe until it flows out. As you have experienced, your exit is so close to the top that the gas is pushing water out until it reaches the exit intake and then gas leaks into the air.Heating/controlling the temperature can be done a million ways. The key is in insulating everything. The bacteria which operate in the biogas digester are anarobic (they consider oxygen poisonous) and will produce no heat of their own. This is a contrast to aerobic bacteria found in a compost pile. Aerobic bacteria love oxygen (which is why you turn the compost) and they generate a fair amount of heat. Actually, some People have comined the two, basically putting the biogas digester in the middle of the compost pile so that the compost heats and insulates the biogas digester.How often you need to empty the digester depends on what you feed it. If you are feeding weeds, try to remove as much sand as possible first (a quick dunk in a water bucket works wonders) because the sand will settle to the bottom and never be digested. Oils are ok but not if they tend to solidify at low temperatures. For example, bacon grease doesn't work well and salad oil does.

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  • LAP - Purifying water with new technologies and algea

    Purifying water with an edible algae does sound like a good idea. I just wonder about eating a plant which was grown in potentially contaminated water. Would not the plant also then be contaminated?

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