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Biogas from wastewater treatment as replacement for fossil support fuels in biomass burning
Published on 21 December 2020
Finland
Etelä-Suomi
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About this good practice
Pulp mills wastewater treatment process (WWTP) is very expensive (chemicals and energy), and it also generates wet bio sludge which needs to be landfilled. COD (chemical oxygen demand, carbon) of the wastewater is lost. Normally, WWTP only generates costs. Also, pulp mills burn their waste biomass, such as bark in bark boilers to produce electricity and heat for the plant's own use. To burn low quality biomass like bark, high-quality support fuel is needed which is usually fossil fuel. Producing biogas from wastewater sludge reduces the need for expensive wastewater processing and the resulting gas can be burned immediately in the bark boiler where it can replace fossil fuels.
In Stora Enso pulp and paper mill in Heinola there has been implemented an anaerobic bacterial granular based process which is capable of generating biomethane directly from wastewater. Wastewaters can be characterized to evaluate which streams can be collected to such reactor. The reactor and granules inside can cut up to 80 % COD and turn it to biomethane. Granular bacteria are valuable and have a positive value (compared to wet bio sludge waste from the aerobic process). Idea is to put the anaerobic process in front of regular wastewater treatment, leaving less COD meaning less chemical, energy and sludge treatment cost.
The process has worked well and is easy to operate. There are no rotating parts inside the reactor, so the maintenance costs are low.
In Stora Enso pulp and paper mill in Heinola there has been implemented an anaerobic bacterial granular based process which is capable of generating biomethane directly from wastewater. Wastewaters can be characterized to evaluate which streams can be collected to such reactor. The reactor and granules inside can cut up to 80 % COD and turn it to biomethane. Granular bacteria are valuable and have a positive value (compared to wet bio sludge waste from the aerobic process). Idea is to put the anaerobic process in front of regular wastewater treatment, leaving less COD meaning less chemical, energy and sludge treatment cost.
The process has worked well and is easy to operate. There are no rotating parts inside the reactor, so the maintenance costs are low.
Resources needed
Cost of the reactor depends the amount of wastewater treated. The total cost of the projects 25 000 kg COD/d capacity reactor was ~5 M€. System is largely maintenance-free requiring some monitoring. System received aid from the Ministry of Industry providing 30 % of project cost: 647 550€.
Evidence of success
Biogas produced: in 2017: 4387 MWh, in 2018: 5289 MWh, in 2019: 4840 MWh.
Wastewater treatment energy use is reduced by 35 % and the total use of fossil fuels by the plant is reduced by 5 %.
Wastewater treatment energy use is reduced by 35 % and the total use of fossil fuels by the plant is reduced by 5 %.
Potential for learning or transfer
The system can be used in any pulp mill or pulp and paper to increase the use of renewables and replace fossil fuels. The system is considered novel in Finland, so there is much potential to apply the same system to other plants. A similar system has already been implemented in some other Stora Enso’s plants in Central Europe.
COD from wastewater is a resource we should not forget. It has been seen only as a cost before. Bio gas is a renewable fuel. By traditional activated sludge process, a lot of chemicals is needed, also electricity and especially wet wastewater sludge problem are globally getting bad. This can be one part of the solution.
This system serves as example of kind of new technology in renewable energy that should be encouraged and invested in, for example through government subsidy.
COD from wastewater is a resource we should not forget. It has been seen only as a cost before. Bio gas is a renewable fuel. By traditional activated sludge process, a lot of chemicals is needed, also electricity and especially wet wastewater sludge problem are globally getting bad. This can be one part of the solution.
This system serves as example of kind of new technology in renewable energy that should be encouraged and invested in, for example through government subsidy.
Further information
Website
Good practice owner
You can contact the good practice owner below for more detailed information.
Organisation
Lab university of applied sciences
Finland
Pohjois- ja Itä-Suomi
Contact
RDI specialist