How to Turn Your Lawn Clippings Into Biogas Fuel

Turning your lawn clippings into biogas fuel is an innovative way to recycle green waste into a renewable energy source. As I discovered, with a few simple steps, anyone can convert their grass clippings into usable biogas to help power generators, cooking appliances, and more.

Gathering the Lawn Clippings

The first step is gathering a sufficient quantity of green waste to feed the biogas production process. Lawn clippings are an excellent feedstock, as they are readily available from routine yard maintenance. Here's what I did:

• Set up a dedicated compost bin or area to collect lawn clippings. This keeps them separate from other compost materials.
• Avoid using clippings treated with herbicides or pesticides, as these may inhibit biogas production.
• Let clippings dry and brown slightly before use, as very green materials may compact and rot instead of digesting.
• Stockpile at least 25-50 gallons of clippings before starting the biogas process. More is even better.

Regular mowing ensures a steady supply of fresh grass clippings all season long. I found that recruiting neighbors to contribute their unneeded clippings helped increase my biogas output.

Breaking Down the Lawn Clippings

Before generating biogas, the tough cellulose and lignin in the lawn clippings must be broken down. This requires:

• Physical breakdown - Chopping or shredding the clippings provides more surface area for microorganisms to act on. I used a chipper-shredder to pulverize clippings.
• Water - Adding water until clippings are submerged helps start bacterial digestion. The slurry should have a porridge-like consistency.
• Heat - Warm temperatures accelerate the decomposition process. I kept my digester at 90-100°F.
• Acid or enzymatic pretreatment - Adding dilute acid or cellulase enzymes further breaks down the biomass for improved biogas yield.

With the pretreated slurry ready, it was time to start making biogas!

Anaerobic Digestion into Biogas

There are several types of anaerobic digesters that can convert biomass into biogas. I used a simple, low-cost plastic tub digester with the following components:

• Air-tight container - A large plastic bin or trash can works well to contain the slurry. All openings must be sealed to maintain anaerobic conditions.
• Inlet and outlet - I used PVC pipes sealed with valves to introduce new material and withdraw digestate.
• Heating - My digester tub was wrapped in insulation and heated with a aquarium heater to maintain optimal temperatures.
• Agitation - An aquarium pump gently stirred the slurry to distribute microbes and improve breakdown.

Over 25-40 days, microorganisms within the heated, oxygen-free digester break down and ferment the organic material into a blend of gases like methane, carbon dioxide, and trace amounts of hydrogen sulfide.

I captured this biogas using an inverted collection barrel sealed over the slurry tub outlet pipe. The rising gas displaced the water inside, collecting in the barrel for easy use.

Using the Generated Biogas

The homemade biogas generated from my lawn clippings had a methane content ranging from 50-70%. After passing it through a water bubbler to remove corrosive hydrogen sulfide, I was able to use the renewable biogas fuel for:

• Powering a converted gas generator to produce electricity
• Fueling a biogas kitchen stove for cooking
• Adding it to a biofuel car's gas tank as vehicle fuel

With some simple DIY equipment like digesters and gas collectors, I was able to produce usable biogas from standard lawn clippings. This allowed me to save on energy costs while recycling green waste into renewable fuel. Though small-scale, it proves that biogas can provide an eco-friendly supplement to conventional fossil fuel usage.