o Is pre-treatment of materials needed for the BEKON process?
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 three ways:
- Recirculation of part of the digestate (up to 40 %)
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.