Digestion – biogas production, fallow equipment
These are biological equipment that bacteriologically separate organic matter under anaerobic conditions. Methane separated during separation is used as fuel for production of electricity and heat. It is a cheap and effective energy that can be used for personal needs or supplied to a network, as well as an environmentally-friendly, cost-effective and viable fuel that can be obtained from the following raw materials:
- Animal manure and slurry.
- Wastewater treatment plant sludge.
- Food industry waste, agricultural products, corn silage.
- Green waste (grass, leaves) and other organic raw materials.
- Biodegradable waste sorted from landfills.
Raw materials are supplied to a biogas power plant through pipelines from a waste source (farm, production workshop) or transported with trucks. All waste enters the collection tank where the biomass is mixed and stored. The biomass is periodically supplied from this tank through pumps to the bioreactors. Substrate in the reactor is maintained for some time, therefore it is necessary to refill the reactors every day, and remove the used biomass. The reactors contain mechanical stirrers that maintain a homogeneous mass and do not allow it to be layered, thus sediments do not accumulate in the bottom of the reactor and are pushed towards the exhaust vents. The reactor continuously performs the anaerobic process, maintains a mesophilic or thermophilic environment and continuously maintains proper temperature. Reactors are heated – heat is emitted by cogeneration power plants by burning biogas. Biogas emitted during the anaerobic process accumulates in the upper parts of the reactor and enters the gas storage facility due to the pressure. Gas is cleaned of additives and sulfur compounds through mechanical and chemical filters. Biogas reserve is accumulated in the storage facility. Accumulated biogas is burned in internal combustion engines (cogenerators) that rotate an electric generator, thus producing electric power. Engines are cooled with water that heats up during engine cooling and produces heat. Processed biomass can be used for the production of concentrated fertilizer or compost. In this case, the substrate is separated and the thick fraction is composted or granulated. The liquid part is used to fertilize fields.
One of the methods to process organic waste is to compost them. Different compost can be obtained after the composting cycle, depending on the raw materials or waste that we want to compost. Composting helps us to properly and in a controlled manned
- Open, when composting occurs in open piles in the fields. This composting method requires large areas. The composting cycle occurs in the natural environment. Unpleasant smells are produced during this process, which can cause issues with the society.
- Closed, when composting occurs in closed tunnels. This composting method does not require large areas. The entire cycle is well controlled according to the set time parameters. The process is carried out under anaerobic or aerobic conditions, depending on the technological cycle. Proper substrate moisture is continuously maintained. If necessary, the substrate is watered. Air removed from the tunnels is cleaned in biofilters, therefore no unpleasant smells are emitted into the environment.
- For the fertilization of green zones, recultivation of forests and restoration of the plant layer.
- For filling landfill polygon piles.
Which waste and raw materials are suitable for composting
- Sludge which is produced after wastewater cleaning and fallow processes.
- Biodegradable fraction which is sorted from household waste in a waste sorting plant.
- Food and vegetable waste from catering facilities.
- Green waste (leaves, grass, sticks, etc.).
- Animal manure.
- All other organic waste suitable for fallow.
Sludge drainage and desiccation equipment
Technological processes produce waste called “excess sludge” which needs to be processed in order to use it in further processes. Depending on the requirements, different technological equipment and solutions may be selected for sludge drainage in order to meet the requirements. Flocculants are additionally inserted into water in order for them to be able to pass through sludge more easily. Sludge is transformed into flakes and water is able to pass through it more easily during the technological process. Flocculants are dosed through an automatic flocculant dosing station.
Sludge is formed during the following technological processes
- In wastewater treatment equipment.
- In biogas power plants.
- After the flotation process.
Depending on the need, sludge can be prossesed through
- Compression – process during which sludge is drained up to 6 % of dry residue. Compression is usually carried out through a belt press. It is a simple device where sludge is added and drained by using the belt and the gravitation method.
- Drainage – process during which sludge is drained up to 25 % of dry residue. Drainage is carried out depending on the sludge type: in the filtpress or decanter. Filtpress is a device similar to the belt press, however it contains several belts. When sludge appears on the belt, it is transported into a roller system where it is pressed between rollers, thus undergoing a pressing process. The decanter, also known as a centrifuge, is a device containing two simultaneously rotating cylinders, however one cylinder is rotating one step slower than the other. This way water is extracted from the sludge.
- Desiccation – process during which sludge is dried up to 6 % of dry residue. Drying is a complex process during which sludge on the belt is heated and water is evaporated from it. It is the final process to prepare sludge for incineration or use it in fertilizer processing.
Waste sorting equipment
Waste is a material or object which is discarded by its owner. It can be of various types, dimensions and compositions:
- Household: everything that is thrown into a trash bin in our homes.
- Secondary: paper, glass, plastic, metal.
- Green: grass, sticks, leaves.
- Hazardous: drugs, chemicals.
- Household objects: furniture, windows, bicycles, textile waste, etc.
- Construction: concrete, blocks, etc.
Household waste is collected with special vehicles and delivered to a waste sorting plant where the waste is sorted according to its type. All waste brought in special vehicles is dumped in an unsorted waste area installed inside a building, where waste is loaded into a crusher or bag shredder. The purpose of the latter is to shred the contents of a bag and crush the waste to a fraction of 300 mm to the extent possible. After the waste is crushed, it is transported to a cylinder separator where waste is separated according to its fraction. Waste that is smaller than 80 mm passes through the cylinder mesh and is directed towards an electromagnetic separator to trap iron and towards a turbulent current separator to trap metal without iron. After undergoing metal filtering, all waste is directed towards a container where it will no longer be sorted. Waste larger than 80 mm enters the transporter and is carried into the 3 D device where it is sorted into two groups according to weight and size. One waste group is transported on conveyors to an area where it will be hand sorted by people who separate plastic, glass and metal from all the waste. After the waste is hand sorted, it is passed through a paper separator, thus separating paper which is sorted and removed from the general waste flow. The remaining waste is placed into a container where it will no longer be sorted. The second waste group is placed in an electromagnetic separator for trapping iron, then it is transported to an air separator where plastic and aluminium cans are removed from the general waste with the help of air. Remaining waste is directed towards a glass separator where glass is separated from the general waste and the remaining waste is then directed towards a container where it will no longer be sorted. Secondary waste which is biodegradable and suitable for further processing is moved from the air separator to the waste processing equipment.
Waste Incineration Plants
Different waste management regulations are applicable in different countries. Each country selects its own waste management method.
One of the methods is incineration of the collected waste at a specifically equipped plant. The electricity and heat produced during this incineration process are successfully applied for the city’s utility needs as a source of renewable energy:
- for production of hot water;
- for household heating;
- for production of electricity.
Such plants are widely operated around the world and help us reduce the amount of non-recyclable waste disposed of in the natural environment. Incineration plants are built in big cities generating large amounts of waste or such a single plant is built for servicing several towns located in a close range.
Incineration plants are safe and have no adverse impact on the environment because they are equipped by strictly following safety requirements. Any particles released within the process of incineration are retained by specially equipped filters.
Advantages of incineration plants
- Safe waste processing
- Low operating costs
- Maximum energy efficiency
- Fast return of investment
- Occupies a small territory
- Does not emit unpleasant odours
- Reduced gas emissions
- There is no need for landfills
Facilities for Gas Extraction from a Landfill
It has been a long-standing practice that all domestic waste should be brought directly to a landfill without recycling it and making piles of it. At that time nobody stopped to think about any potential hazards we would face and what negative impact this decision could have on the natural environment.
It was decided to extract gas from landfills and to use it as a form of renewable energy for production of electricity and heat in order to preserve the environment and reduce gas emission to the environment.
Any pile on a landfill consisting of unsorted waste is a huge biochemical reactor. Waste of vegetable and animal origin start decomposing due to anaerobic conditions inside of it resulting in production of biogas also known as landfill gas. Such processes start while the landfill is still operational and continue decades after it is closed. Therefore, these are long-term day-to-day processes. The composition of landfill gas may include many different trace elements. Certain concentrations thereof are toxic and dangerous.
Technical parameters of landfill gas:1 m³ of gas
- Potential production of 1.5 kWh of electricity.
- Potential production of 2 kWh of thermal energy.
Landfill gas equivalent in comparison to natural gas is 0.8 m³.
At present there is a solution for gas extraction from a landfill. Wells could be drilled deeper into the pile in order to collect gas to be fed to a gas treatment plant where the gas would be treated and such treated gas could be fed to a generator. The gas would fuel the generator and it would produce electricity and heat to be supplied to the city’s utility facilities.