Both biogas and composting turn wasted organic material into something useful. Biogas makes methane, which is collected and burned to generate electricity. Composting makes organic fertilizer, which is used by gardeners, golf course managers and farmers to grow plants. Let’s dig into depth about their similarities and differences.
Scale: All Sizes
Both systems can work on any scale. Biogas is usually done on a large scale by a municipality or energy company. Some adventurous households tackle it themselves with DIY biogas generators. Composting can be done on a small scale in a household, for an entire apartment building or campus, or on a massive municipal basis.
Both processes need organic matter, such as kitchen scraps, left-over vegetables and fruits, wasted plant material from farming and the food processing industries, spoiled or unsold produce from grocery stores, and coffee grounds and uneaten fruit salads from coffee shops. This material needs to be separated and collected.
Most composting requires the inputs be low in oils. Animal products like dairy and meat can attract pests and stink up the process. Composting worms are often used to speed up the process, and they prefer vegetation.
Biogas can take pretty much any type of organic matter. It’s not as fussy because it uses a different process. It can use food waste, manure, municipal waste, agricultural waste, sewage, and plant material.
Process: Anaerobic vs. Aerobic
Organic matter ends up in either an oxygen-rich (aerobic) environment or a low-oxygen (anaerobic) environment.
Note: Incinerating anything can produce electricity, but it also creates toxic gasses and toxic ash. Biogas is a superior method for handling organic waste.
- If food scraps end up in a landfill, they are buried in a low-oxygen environment. Anaerobic bacteria grow and slowly start breaking down the scraps. If there is not enough oxygen, the process stops. This is why intact-looking food can be found in old landfills. The process of breaking down food anaerobically produces methane, a greenhouse gas. Landfill gas is around half methane. This gas can cause sudden explosions, so it might be vented and/or burned off (flared). Landfill gas also contains carbon dioxide, and it may have contaminants from all the trash in there. In some cases, landfill gas can be used as biogas.
- Biogas (bio-gas) usually involves creating an anaerobic (low-oxygen) environment for breaking down organic matter. It can also be done using a fermentation process. Housed in a biogas plant, the mixture stews away, producing gasses. The gasses are mostly methane, plus carbon dioxide, and hydrogen sulfide. This type of energy is renewable. It can be designed to have a very small carbon footprint.
- Composting is done in the presence of oxygen. Simply leaving organic matter in a bin or pile automatically triggers bacteria and fungi to break down the scraps. The process is sped up by adding composting worms – this is called vermiculture. With worms, the bin is started using bedding such as shredded paper, coconut coir and/or pure peat moss. Kitchen scraps and other organic material are gradually added. Compost piles and bins may need to be turned to keep the oxygen flowing; worm bins may not need this because the worms dig tunnels. Bins can be simple totes or 50-gallon plastic drums, or more elaborate tray-based composters that go indoors or out. Composting scales up, from a single apartment dweller to an entire municipality.
Outputs: Different but Useful
Biogas can be compressed and shipped to another facility. Depending on their exact composition, they may be burned or oxidized; and they can produce electricity or heating fuel. The solids that are left behind from the process is called digestate. Digestate can be used as a soil conditioner, but it is not technically compost.
Composting produces finished compost for the garden, which is rich in nutrients, soil-friendly bacteria, and nitrogen. If worms are used, they produce worm castings, which are even better. These prized, chemical-free fertilizers are ideal for organic farming, lawns, vegetable gardens and indoor plants of all types. Just use it for growing starts, work it into the soil, use as a side dressing, or spray it.
Composting and biogas harness the power of organic matter. They use very different processes. Biogas requires far more machinery than composting, and its resulting output is flammable. On the other hand, mixing organic matter into the trash is a no-win scenario. Therefore, separating food waste from the trash helps the environment, whether the material is used to make organic compost or electricity.