FREQUENTLY ASKED QUESTIONS (FAQ)
Biogas is a mixture of different gases produced by the decomposition of organic matter in the absence of oxygen.
The biogas produced in a BEKON plant usually has the following composition:
- Methane (CH4): 55 %
- Carbon dioxide (CO2): 45 %
- Hydrogen sulfide (H2S): < 1 %
- Oxygen (O2): < 1 %
o What are the requirements for organic waste to be treated in a BEKON plant?
The materials should have less than 70 % moisture content (equivalent to ≥ 30 % dry matter content) and should be stackable, as they are moved with a front loader. If different materials are used in a BEKON plant, the parameters of the mixture need to fulfill these conditions.
o What are the typical waste materials used in BEKON plants?
Typically, BEKON plants work with these substrates:
- Source separated organics (SSO): Organic household waste that is separated by every household and collected from dedicated bins. It contains kitchen and garden waste.
- Green waste: Gardens and park waste that consists of twigs, leaves and grass
- Organic fraction of municipal solid waste (OFMSW): The organic part of mixed household waste that is separated by a sorting process. Typically, the fractions ≤ 60 mm or ≤ 80 mm are used. In contrast to source separated organic waste, this waste material contains more plastics, glass and other contaminants.
- Cow dung from deep litter systems: Cow dung mixed with straw or saw dust.
o Can sewage sludge be treated in BEKON plants?
Usually, sewage sludge is too wet for our process. If it is dewatered, it can be used for a BEKON plant along with dryer substrates as long as the general conditions for the waste mixture are met.
o Can chicken manure be treated in BEKON plants?
Yes, however only around 30 % of the overall input to a BEKON plant should be chicken manure. This is due to the high nitrogen content in the chicken manure which inhibits the biological process if concentration gets too high.
o What is the recommended C/N (carbon/nitrogen) ratio?
The recommended C/N ratio is between 20 and 30.
o How much biogas can be produced from one ton of organic waste?
The biogas yield depends very much on the type of organic waste. For our typical substrates, the following assumptions can be made:
- Source separated organics (SSO): 85 to 95 m³/ ton of waste
- Green waste: 60 to 90 m³/ ton of waste
- Organic fraction of municipal solid waste (OFMSW): 100 to 120 m³/ ton of waste
- Cow dung from deep litter systems: 75 to 85 m³/ ton of waste
o How much electricity and heat can be produced from one ton of organic waste?
The electricity production depends on the biogas yield of the material and the efficiency of the combined heat and power unit. Approximately, 165 to 260 kWh of electricity can be produced from one ton of waste. Approximately the same amount of heat will be produced.
Calculation: Biogas yield (m³/t) x calorific value of biogas (kWh/m³) x electrical efficiency (%) = produced electricity (kWh/t)
Sample calculation for source separated organics (SSO): 90 m³/t x 5,5 kWh/m³ x 40% = 198 kWh/t
The most important factors for a successful business case of a BEKON plant are the revenue streams. For a plant operator, the main revenue streams are the revenues per ton of waste accepted (called tipping fee or gate fee) and the revenues per kWh or biomethane injected to the grid (feed-in tariff). The higher these two revenue streams, the better for the business case. Other revenue streams such as revenues for heat or compost sale are usually much smaller, but of course are also beneficial for the business case
o How much space is required for a BEKON plant?
Our smallest plants (BEKON MINI) with an approximate capacity of 3,000 t need at least 750 m² of space. The bigger the capacity, the larger is the footprint of the plant. Detailed space requirements are dependent on plant capacity, storage amounts and times, minimum distance requirements for CHP/gas upgrading plants etc. and thus need to be evaluated on a project basis. In case a composting plant is not yet available, the necessary space also needs to be considered.
o How high are maintenance costs for a BEKON plant?
Typically, 1 % of the overall investment (civil works + mechanical and electrical equipment, excluding CHP) is necessary for annual maintenance.
o What is the typical payback time for a BEKON plant?
The payback time depends very much on revenues and investment & operational costs that differ a lot between different projects. Usually, a payback time of 5 to 10 years is realistic.
o How much is the cost per kW installed power?
If you are asking this question, it is likely you are coming from the energy industry. We consider ourselves as waste treatment company with the benefit of producing renewable energy alongside. From our point of view, it is thus not correct to compare our technology with wind power or solar power. The overall cost per kW installed power is between 5,000 € and 16,000 €. The larger the plant, the cheaper is the cost per kW installed.
o Does BEKON provide warranties?
Yes, BEKON gives the following performance warranties:
- Availability of the BEKON plant
- Achievement of certain biogas yield
- Maximum parasitical consumption of electricity
o How much is the price of a BEKON plant?
The overall investment of a BEKON plant depends on many factors, e.g.,
- Plant capacity and configuration
- Plant location (transport cost, local civil works costs)
- Available site
- Choice of gas utilization method
- Supplementary equipment
- etc.
As an indication, the overall investment needed for the construction of a small plant (BEKON MINI with 10,000 t of capacity) in Germany is approximately 2.5 Million €. Strong economies of scale apply for larger plants.
o How high is the parasitical energy consumption of a BEKON plant?
Our BEKON dry fermentation plants have a parasitical energy consumption of
- 5 to 10 % of electricity produced
- 20 to 30 % of heat produced
In case a composting system is integrated, the parasitical energy demand is likely to be higher.
No pre-treatment of materials is needed. However, if most of the material enters the plant in plastic bags, a bag opener may be installed to increase the biogas yield. For green waste a shredding is useful to reduce the volume.
o Is post-treatment of materials needed for the BEKON process?
The material coming out of the dry fermentation process is called digestate. The post-treatment depends on the input quality and on the use of the output. If the input is clean (e.g. cattle manure) the digestate can be directly applied in agriculture (depending on local regulation). For digestate from source separated organics (SSO) and green waste a composting and screening step is needed to meet the end-user requirements. For OFMSW at least a composting step is required to achieve landfill requirements.
o Why is a percolate system needed for the BEKON process?
Percolate is the liquid draining from the waste material. It is collected at the rear end of the fermenter and then pumped into a percolate fermenter. As the percolate contains bacteria, it is used to inoculate fresh material and to allow for a stable biological process. In addition, biogas is also produced in the percolate fermenter.
o How many fermenters does a plant consist of?
The smallest plant in our portfolio (BEKON MINI) has 4 fermenters. This is the minimum in order to ensure an even biogas production at all times. Our biggest plant so far consists of 18 fermenters.
o How large are the fermenters?
For our BEKON MINI plant, the inner width of the fermenter is fixed at 5.50 m. Depending on the desired capacity, the length varies between 10 and 25 m.
For our larger sized plants, the inner width of the fermenter is fixed at 6.50 m.
Depending on the desired capacity, the length can go up to 35 m.
The height of the fermenters is between 4 and 5 m.
o How long does the material stay inside the fermenters?
The retention time inside the fermenters is between three and four weeks.
o How is fresh material inoculated?
In order for the biogas production process to start, anaerobic bacteria need to populate the fresh waste material. This process is called inoculation and is achieved in two ways:
- Recirculation of part of the digestate (up to 40 %)
- Percolation
Thanks to the creation of optimal conditions for anaerobic bacteria through temperature control (floor and wall heating) and quick establishment of anaerobic atmosphere the bacteria will increase in number and starts working.
o How large is the mass reduction in a BEKON plant?
Approximately, 10 to 15% of weight are lost during the fermentation process.
o What reduction of volatile solids is achieved in a BEKON plant?
Volatile solids are a measure of the decomposable biomass. During the dry fermentation process, approximately 40 % of volatile solids are decomposed into biogas.
o How is the biogas quality and quantity monitored?
A gas analysis instrument is installed in our plants and connected to the central control system. Thus, gas quality and quantity can always be monitored and necessary adjustments to the process can be made
o In case a CHP is used, how does the desulphurization of biogas take place?
Before the biogas enters the CHP, it is dried, compressed and run through an active carbon filter. The active carbon filter takes out the hydrogen sulfide.
o Does BEKON supply combined heat and power units?
If a combined heat and power unit (CHP) is chosen for the biogas utilization, we always include a CHP into our offer. We only work with high quality CHP suppliers from renowned brands and ensure a perfect fit to our plant. However, if clients prefer to source the CHP themselves, they are of course free to do so.
o Does BEKON supply biogas upgrading plants?
If a gas upgrading unit is chosen for the biogas utilization, we can provide an offer on request. However, if clients prefer to source the gas upgrading unit themselves, they are of course free to do so.
o Are there any leachates that need to be treated?
Depending on the waste materials used, there may be more percolate than necessary. This applies mostly for rather wet substrates with moisture contents of 60 to 70 %. Consequently, the percolate fermenter fills up and percolate has to be taken out the system every now and then. Depending on local legislations, the percolate can either be brought to a waste water treatment plant or treated with heat (sanitation) and applied as a fertilizer in agriculture. If excess liquid shall be avoided at all cost, the excess percolate can be used in the composting stage. Many of our plants do not have any excess percolate at all.
Together with our sister company Fechtelkord & Eggersmann GmbH or other experienced construction companies, we can take over the civil works part of BEKON plants and thus provide complete turnkey solutions. This applies mostly to Central European countries and is decided on a project basis. Outside Europe, the civil works scope normally falls under the clients’ responsibility.
o I would like to do the mechanical/electrical supply and installation myself. Is that possible?
The main part of our mechanical equipment is located inside a skid called rear wall unit that is manufactured in our factory in Germany. Likewise, most of the electrical engineering is done inside our factory in Germany. So, there is basically no engineering left to be done by the client as we prefer our technicians to finish the installation work on site. Based on our experience, it is not cheaper if this effort is done locally despite possibly lower salaries.
o How long does it take to build a BEKON plant?
Depending on the size of the plant, the construction takes between 8 and 14 months.
o Does BEKON also operate plants?
While BEKON itself does not operate plants, our sister company Kompotec GmbH operates a number of BEKON plants in Germany. We are always happy to discuss opportunities for plant operation.
o How are BEKON plants serviced and maintained?
BEKON has an own service crew to do maintenance works on site. Because a lot of tasks are easy they are often done directly by the operator.
o Does BEKON co-invest in plant construction?
For projects within Europe, a co-investment is possible, but needs to be discussed on a case by case basis.
The BEKON process produces
- digestate that can be turned into valuable compost. In case of OFMSW the digestate can be turned in a mass and volume reduced resource derived fuel (RDF) or landfill material
- biogas that can be turned into electricity and heat or upgraded to biomethane
o Can we use the generated heat for cooling?
In countries, where heat is not needed, the exhaust heat of the CHP can be used for cooling via an absorption refrigeration unit.
o Can the digestate be incinerated?
While it is of course possible to incinerate the digestate, we do not recommend incineration due to the water contained in the digestate. In the case of municipal solid waste, the material can be dried and further processed into resource-derived fuel (RFD).
In most European countries, composting of digestate is obligatory. If you want to further refine the digestate, e.g. run it through a screening process, it is absolutely necessary to compost it to get moisture content down to maximum 40 % (equivalent to dry matter content of minimum 60 %)
o Which quality does the compost have?
The quality of the compost depends a lot on the input materials for the dry fermentation process. The purer the input, the purer the compost will be. Depending on the technology chosen for the composting process as well as the retention time in the composting stage, we are able to achieve even the highest composting quality in Germany (Rottegrad V) which is equivalent to self-heating below 30°C.
o What type of composting is recommended?
The choice of composting system is dependent on many factors, e.g.
- Process goals
- Available space
- Personnel cost
- Requirements for odor emissions
- Available budget
Together with our sister companies, we are able to supply all types of composting systems (open windrow composting with windrow turning, composting with lane turner, membrane-covered composting, closed tunnel composting)
o Is it necessary to add fresh material to the composting process?
During the dry fermentation process, only the anaerobically available VS will be degraded and you will still have enough VS inside the digestate to allow for the aerobic composting process. However, if you have more fresh waste material such as green waste at hand, it can be added to the composting stage to accelerate the process. Because the digestate is wetter as the original input, it is in any case necessary to add dry material to the digestate to create a compostable mixture.
o Can compost from the organic fraction of municipal solid waste (OFMSW) be applied to agriculture?
In most European countries, it is not possible to use compost from OFMSW in agriculture due to European regulations. Instead, the OFMSW compost can be used to recultivate fallow areas or cover landfills.
Feel free to contact us if you want to go on a guided tour of one of our plants. As we have plants in many countries, the nearest one may be not too far from you.