How does it work?

Anaerobic digestion is a process in which organic material is broken down by microorganisms in the absence of oxygen into two main products, namely biogas and organic fertilizer.

What type of organic material can be used?

Organic materials such as agricultural waste, manure, organic municipal waste, plant material, green waste, food waste and kitchen waste are ideal for anaerobic digestion and the production of biogas and organic fertilizer.

What is biogas?

Biogas is generated during anaerobic digestion when microorganisms break down organic materials in the absence of oxygen. Biogas is mostly methane (CH 4 ) and carbon dioxide (CO 2 ), with very small amounts of water vapour and hydrogen sulphide (H₂S). Biogas is considered to be a renewable resource as it generates no net carbon dioxide.

What kind of fertilizer is produced?

During the anaerobic digestion process, organic material is broken down into its basic nutrients, elements and minerals. This results in a high-quality organic fertilizer which is quickly taken up by plants and crops.
The actual nutrient content of the fertilizer will vary depending on organic material feedstock, digester type, management, and solid-liquid separation technology.

How much biogas can I get out of my waste?

The amount of biogas you can extract from your organic waste depends on the waste itself and the design of the digester system. Some digesters can yield 20 m 3 of biogas per ton of waste while others can yield as much as 800 m 3 per ton. It all depends on organic waste quality, digester design and proper operation of the system.

As a general rule-of-thumb, by adding around 7kg of mixed food waste/kitchen waste/market waste/organic municipal waste per day around 1m 3 of biogas will be produced per day.

How much organic fertilizer can I get out of my waste?

Generally speaking, with continuous or semi-continuous plug-flow digesters such as the nOa One, whatever volume you put in daily you will get out daily. In other words, if you add 14L volume per day you will receive 14L volume organic fertilizer per day.

How much Energy is there in biogas?

Each cubic meter (m 3 ) of biogas contains the equivalent of 6 kWh of calorific energy. However, when we convert biogas to electricity in a biogas powered electric generator, we get about 2 kWh of useable electricity, and the rest turns into heat which can also be used for heating applications.

What can biogas be used for?

For household use there are a number of appliances that are easily available that run on biogas. These include lamps for lighting, clean stoves, burners and cookers for cooking, water heaters for showering and hot water, heaters for heating and generators for electricity production. For industrial sized applications, raw biogas can be fed into gas grids for household use or used to run combined heat and power (CHP) units to produce electricity and heat for grid and industry insertion. Raw biogas upgraded to bio methane can be used in mobility, stored in cylinders or inserted into the natural gas grids.

Is biogas safe for cooking?

Biogas burns very cleanly, and produces fewer pollutants during cooking than any other fuel except electricity. Biogas provides instant heat upon ignition, no pre-heating or waiting time is required.

Does biogas smell?

The methane (CH 4 ) and carbon dioxide (CO 2 ) of biogas are not poisonous and the hydrogen
sulphide (H₂S) can be smelled if it has not been scrubbed or filtered out when there is a leak in the system; it smells like rotten eggs. However since anaerobic digesters are air and water tight, leaks are uncommon and usually sealed immediately once detected and therefore no unpleasant smell.

Are anaerobic digesters safe?

A properly designed and operated system is very safe. Anaerobic digesters are designed to meet local and national codes for safety. Anaerobic digesters do contain flammable biogas at very low pressures. Therefore appropriate safety measures must be adhered to by the user at all times, such as ensuring that no sparks or flames originate within the vicinity of the digesters.

Is it good for the environment?

Methane has a greenhouse gas (GHG) heating factor 21 times higher than CO 2 . By extracting methane out of waste and using it to produce heat and/or electricity we ensure that the waste will not degrade in an open environment, therefore we are reducing direct methane atmospheric emissions. Moreover, the energy provided by the biogas is likely to displace fossil fuel which is the main contributor to GHG emissions.

Biogas energy is considered carbon neutral, since carbon emitted by its combustion comes from carbon fixed by plants (natural carbon cycle). Furthermore, locally produced organic fertilizers supplement chemically produced fertilizers which are much better for the environment and close the nutrient cycle.

How difficult is it to run a biogas system?

Household biogas systems are generally very easy to run. They need to be fed with an appropriate amount and composition of organic waste on a daily basis and the biogas and organic fertilizer products must be used also on a daily basis. Care must be taken to keep the systems protected from physical damage.

Normally above ground systems are placed in a greenhouse or behind a small enclosure/picket fence to guarantee protection. Commercial plants or facilities can be complicated to run as there are many additional factors and details to consider. Such facilities are normally run by a team of experts.

For how long has anaerobic digestion technology been in existence?

Anaerobic digestion is a natural phenomenon that occurs at the bottom of oceans, lakes and in wetlands, organic material stacks and animal intestines. For centuries humans have harvested the power of anaerobic digestion by recovering naturally formed biogas to use for lighting, cooking, heating or to power mechanical engines.

In Asia, millions of household digesters were built to provide cooking fuel and lighting in rural areas. During WW2, German army trucks were fueled with biogas collected from farmers. Over the last 50 years, remarkable progress has been made in the development of anaerobic digesters (bioreactors) to increase methane (CH 4 ) yield and improve its process flow technologies.

Nowadays, thousands of projects around the world, from small household systems to large municipal plants, are demonstrating that biogas recovery systems are both environmentally and
economically viable.

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