- Biogas definitions
- Materials suitable for biogas production
- Types of biogas systems
- Wet biogas system
- Dry biogas system
- Types of small scale biogas digesters
- Fixed dome plants
- Floating drum plants
- Low-cost polyethlene tube digester
- Balloon plant
- Various stages of biogas production
- Collection, transport and processing of biogas feed-stocks.
- Biogas production, upgrading and injection into the gas network.
- Biogas distribution logistics.
- Emissions from biogas use. tank to wheel, TTW.
- Steps used in biogas production.
- Methane formation
- Importance of biogas.
- Waste treatment benefits
- Energy benefits
- Environmental benefits
- Economical benefits
- Advantages and disadvantages of using biogas
- How to efficiently Service and Maintain biogas digester
- Benefits of rigorous / regular maintenance of biogas plant
- How to stop biogas from smelling
- How to minimize risks and ensure safety during every step of your biogas project
- Plant design
- Project construction
- Biogas plant commissioning
- Biogas plant operation
1. Biogas Definitions
Biogas has been defined in various different ways;
- Biogas is a mixture of gases, primarily consisting of methane, carbon dioxide and hydrogen sulphide, produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste and food waste. It is a renewable energy source. (Wikipedia)
- A type of biofuel naturally produced from the decomposition of organic matter when exposed to an environment without oxygen they free a blend of gases. (youmatter)
- A renewable biofuel naturally produced by the breakdown of decomposition of organic matter, such as food scraps and animal waste, when exposed to an environment without oxygen.
- Any gas fuel derived from the decay of organic matter, as the mixture of methane and carbon dioxide produced by the bacterial decomposition of sewage, manure, garbage, or plant crops.(dictionary.com)
- Biogas is a gaseous mixture generated during anaerobic digestion processes using waste water, solid waste (e.g. at landfills), organic waste, and other sources of biomass. (climate technology centre & network)
In summary from the above definitions biogas is;
- A mixture of gasses i.e carbon dioxide, methane and hydrogen oxide.
- Biogas is a biofuel/gasfuel
- Biogas is a mixture of methane and carbondixide
- Biogas is a renewable fuel.
All the definitions are in agreement that biogas is derived, produced or generated from decomposed waste materials, organic matter, waste water, and solid waste or plant crops. In absence of oxygen.
Biogas is produced through the processing of various types of organic waste such as food waste, human waste, sewage, paper waste, manure, green waste, biodegradable plastic, and slaughterhouse.
Biogas production also helps in the easy disposal of organic wastes and is eco-friendly because combustion of biogas does not cause much pollution. It has high calorific value and is a non-polluting renewable source of energy
Biogas production starts from the arrival of feed-stocks at the biogas plant. A diverse range of solid as well as sludge-like feed-stocks can be used.
2. Materials Suitable for Biogas Production
- Biodegradable waste from enterprises and industrial facilities e.g. surplus lactose.
- Spoiled food from shops, homes, hotels and institutions.
- Bio-waste generated by consumers
- Sludge from wastewater treatment plants
- Manure and field biomass from agriculture
3. Types Of Biogas Systems
There are two types of biogas systems depending on the moisture content of the feed-stocks;
- Wet biogas system– it’s the most common digester style. A wet digester or low solids AD system generally processes feedstock with less than 15 percent solids content
- Dry biogas system – Dry digesters keep the substrates in a stackable form and remain in a pile during the digestion process. Food waste is mixed with green wastes such as yard debris for structure and porosity and is put into a long, rectangular vessel in a stack. The vessel is then sealed tight and warmed.
4. Types Of Small Scale Biogas Digesters
The table below gives a first comparison of the different types of biogas;
|Factors||Fixed done||Floating drum||Tabular design||Plastic container|
|Gas storage||Internal Gas storage up to 20 m³ (large)||Internal Gas storage drum size (small)||Internal eventually external plastic bags||Internal Gas storage drum sizes (small)|
|Gas pressure||Between 60 and 120 mbar||Upto 20 mbar||Low, around 2 mbar||Low around 2mbar|
|Skills of contractor||High; masonry, plumbing||High; masonry, plumbing, welding||Medium; plumbing||Low; plumbing|
|Availability of Material||yes||Yes||yes||Yes|
|Durability||Very high >20 years||High; drum is weakness||Medium; Depending on chosen liner||medium|
|Agitation||Self agitated by Biogas pressure||Manual steering||Not possible; plug flow type||Evtl Manual steering|
|Sizing||6 to 124 m³ digester vol||Up to 20 m³||Combination possible||Up to 6 m³ digester vol|
- FIXED DOME– A fixed-dome plant comprises of a closed, dome-shaped digester with an immovable/ fixed rigid gas-holder and a displacement pit, also named ‘compensation tank’. Gas pressure increases with the volume of gas stored, i.e. with the height difference between the two slurry levels.
- There are no moving or rusting parts involved.
- Its design is compact hence saves space and is well insulated.
- It’s a Source of employment during construction for both locals and skilled people.
- Has a long life span if well constructed and fixed.
- The underground construction saves space and protects the digester from temperature changes.
- Low initial and construction costs and long useful life-span;
- Masonry gas-holders require special sealants and high technical skills for gas-tight construction
- Gas leaks occur quite frequently
- Fluctuating gas pressure complicates gas utilization
- Amount of gas produced is not immediately visible.
- Fixed dome plants need exact planning of levels.
- Excavation can be difficult and expensive in bedrock.
- Constructed and supervised by highly experienced biogas technicians.
- FLOATING-DRUM PLANTS– Floating-drum plants consist of an underground digester (cylindrical or dome-shaped) and a moving gas-holder. Floating-drum plants consist of an underground digester (cylindrical or dome-shaped) and a moving gas-holder. The gas-holder floats either directly on the fermentation slurry or in a water jacket of its own.
They are chiefly used for digesting animal and human feces on a continuous-feed mode of operation.
They are used most frequently by small to middle-sized farms (digester size: 5-15m3) or in institutions and larger agro-industrial estates (digester size: 20-100m3).
The floating-drum must not touch the outer walls. It must not tilt, otherwise the coating will be damaged or it will get stuck.
- The steel drum is relatively expensive and maintenance-intensive.
- Removing rust and painting has to be carried out regularly.
- The life-time of the drum is short (up to 15 years while in tropical regions about 5years
- The gas-holder gets “stuck” If fibrous substrates are used in the resultant floating scum.
- The floating gas drum can be replaced by a balloon above the digester.
- Readily available materials are used to construct the digester.
- LOW – COST POLYETHYLENE TUBE DIGESTER- The tubular polyethylene film is bended at each end around a 6 inch PVC drainpipe and is wound with rubber strap of recycled tire-tubes. With this system a hermetic isolated tank is obtained.
- Easy to solve the technical problems arising in the polyethylene tube digester.
- Economically, it saves the producer costs of buying liquid gas, firewood and chemical fertilizers. Low cost biodigester.
- It helps minimize health hazards such air pollution
- Reduces environmental threats, due to decrease in use of chemical fertilizers and organic waste exposures.
- There is also reduced deforestation from firewood use for energy purposes.
- Has a short lifespan meaning the biodigester is not long lasting.
- There is no reliable back up support.
- PTDs suffer from effects of variable temperatures.
- The bio digesters can only function properly and last a little longer if the farmer takes good care of the digester.
- BALLOON PLANTS– A balloon plant consists of a heat-sealed plastic or rubber bag (balloon), combining digester and gas-holder. The gas is stored in the upper part of the balloon. The inlet and outlet are attached directly to the skin of the balloon. Gas pressure can be increased by placing weights on the balloon. The useful life-span does usually not exceed 2-5 years. Safety valves are placed to regulate gas pressure.
- Standardized prefabrication at low cost
- low construction sophistication
- Ease of transportation
- Shallow installation suitable for use in areas with a high groundwater table
- High temperature digesters in warm climates
- Uncomplicated cleaning
- Emptying and maintenance
- Low gas pressure may require gas pumps
- scum cannot be removed during operation
5. Various Stages Of Biogas Production
Biogas is produced using well-established technology in a process involving several stages:
- Collection, transport and processing of biogas feed-stocks– Raw materials or Feedstocks used in biogas production are delivered to biogas plants and the emissions put into account. Biowaste is crushed into smaller pieces and slurrified to prepare it for the anaerobic digestion process. Slurrifying means adding liquid to the biowaste to make it easier to process Feedstock processing and odor control also is put to consideration in this stage.
- Biogas production, upgrading and injection into the gas network- s regards biogas production and upgrading, emissions from heat and electricity consumed at biogas plants, emissions from the production of chemicals used in the biogas process and emissions related to water consumption and wastewater treatment are taken into account
- Biogas distribution logistics– Emissions related to biogas transmission in the gas pipeline network consist of methane emissions and carbon dioxide emissions from compressor stations and transmission pipelines. Containers are also used for biogas transport.
- Emissions from biogas use (tank to wheel, TTW)- In the final stage, the gas is purified (upgraded) by removing impurities and carbon dioxide.
6. Steps Used in Biogas Production
It involves the conversion of polymeric organic matter (e.g., polysaccharides, lipids, proteins) to monomers (e.g., sugars, fatty acids, amino acids) by hydrolysis secreted to the environment by microorganisms.
Acidification increased biogas and carbon dioxide production in five cases, increased methane production and reduced nitrogen production in four cases, and reduced methane content in biogas in four of five cases.
- Methane formation
In practice this means that microbes feed on the organic matter, such as proteins, carbohydrates and lipids, and their digestion turns these into methane and carbon dioxide.
7. Importance Of Biogas
Biogas systems protect our air, water, and soil by recycling organic waste into renewable energy and soil products. Biogas is beneficial in the following categories;
- Waste treatment benefits
- Natural waste treatment process
- Mature technology
- Smaller physical footprint (vs. composting)
- Reduces volume of waste for transport, land application, (vs. not using digestion)
- Very efficient decomposition
- Complete biogas capture
- Nutrient recovery and recycling
- Energy benefits
- Net-energy producing process
- Multiple existing biogas end-use applications, including; heat-only, electric-only, combined heat & power, pipeline quality biomethane and transportation fuel.
- Baseload/dispatchable energy source(vs. intermittent wind and solar)
- Distributed generation (which means lower transmission / transportation costs and higher reliability)
- Direct replacement for non-renewable fossil fuel
- Environmental Benefits
- Dramatic odor reduction
- Reduced pathogen levels
- Reduced greenhouse gas emissions
- Platform for reducing nutrient runoff
- Increased crop yield
- Economic Benefits
- Jobs (temporary/construction and permanent)
- Turns cost item (i.e., waste treatment) into revenue-generating opportunity
- Can operate in conjunction with composting operations
- Improves rural infrastructure and diversifies rural income streams
- Digestate produced by the system can replace synthetic fertilizer or bedding purchase
8. Advantages & Disadvantages of Using Biogas
- Biogas is Eco-Friendly.
- Biogas Generation Reduces Soil and Water Pollution.
- Biogas Generation Produces Organic Fertilizer.
- It’s A Simple and Low-Cost Technology That Encourages A Circular Economy.
- Healthy Cooking Alternative for Developing Areas.
- Little Technological Advancement. An unfortunate disadvantage of biogas today is that the systems used in the production of biogas are not efficient.
- Contains Impurities.
- Effect of Temperature on Biogas Production.
- Less Suitable For Dense Metropolitan Areas.
- Highly toxic
- Potentially explosive
HOW TO EFFICIENTLY SERVICE AND MAINTAIN BIOGAS DIGESTER
9. How to Efficiently Service and Maintain Biogas Digester
Maintaining a biogas plant involves;
- Doing minor repairs to the equipment,
- Changing its oil as needed,
- Removing debris from organic matter that falls to the bottom of the tank,
- Solving problems in the process
- Removing debris from organic matter that falls to the bottom of the tank
- Breaking and removal of any scum formed at the top of the slurry.
- Leakage test trouble shooting along the gas line.
- Inspection of any clogged/blocked joints at the utilization point
- Check the air blower on monthly basis.
10. Benefits Of a Rigorous / Regular Maintenance Of Biogas Plant
Among other things, the advantages include:
- Prevention of technical failures or problems in the process
- Increase in the life cycle of the equipment
- Prevention of accidents and safer plant environment
- Optimization of a plant operation or of biogas production.
11. How To Stop Biogas From Smelling
The method comprises the following steps:
(1) Firstly coarsely filtering through a mechanical grid, separating biogas residues from biogas slurry and introducing the biogas slurry into a reaction tank.
(2) Adding ferrate into the reaction tank and performing oxidation and deodorization;
(3) Introducing the biogas.
12. How To Minimize Risks and Ensure Safety During Every Step Of Your Biogas Project
The operator and the plant designer have to take certain measures at every step of a project. The goal is to ensure safety and minimize risks.
1. Plant design
This step is particularly important to ensure the safety of the biogas plant. The operator and the plant designer have to pay attention to:
- The norms, guidelines and all other codes that apply to biogas plants
- The classification of explosion zones, since the electric system installed on the biogas must be suited according to the risks of explosion
- Avoiding confined space
- Potential risks that can happen during the operation of the plant
2. Project construction
- Make sure to plan the project rigorously
- Hire an onsite expert to insure the workers apply the health and safety measures that are established
3. Biogas plant commissioning
Commissioning of a biogas plant can be the most dangerous step of a project.
Accidents that can happen include:
- Structural failure rarely happens when the tank is being filled or the high-pressure pipes are being tested
- Accidental hydraulic discharge during the pre-operation test of the pumps and valves
- Lack of calibration of the health and safety equipment
- Higher risks of explosion when the air inlets are opened and the air reach biogas
4. Biogas plant operation
During this step, a lot of accidents and incidents happen. To avoid them, the operator must:
- Train every operator of the plant for the work in confined space, portable gas detection, process and equipment use
- Apply strict procedures for equipment locking
- Regularly verify health and safety equipment to make sure they are calibrated and offer precise measurements
- Do a visual screening of all equipment to detect leaks and verify the state of equipment
- Make sure all workers apply health measures to avoid pathogen diseases
- Train all plant workers for basic firefighting skills and CPR
The biogas production process is the same for all types of biogas, and it leverages chemical reactions that are 100% natural. By placing biomass (organic waste) in a digester, you enable bacteria to break down the organic elements and turn them into biogas, which can then be used to generate energy.
It’s a zero-waste process that reduces the amount of waste that ends in landfills while permitting you to produce cleaner energy than by using fossil-fuel sources.
The process can occur at a large scale in industrial plants, but it can also be adapted for domestic usage, so you can easily have a small biogas station and produce energy for your house’s needs.