Gemidan Ecogi’s Process to Codigest Garden Waste & Food Waste : IN DEPTH: Pulp Fraction - A Green Future for Anaerobic Digestion
While effective at processing garden waste, composting does not capture energy from this organic waste stream. Danish firm, Gemidan Ecogi A/S, has developed a new pulping technology that allows this waste to be co-processed with food waste and digested to produce biogas.
Gemidan, supported by the Danish Market Development Fund, was originally founded in 2012 with the purpose of developing a new pre-treatment technology to process source separated food waste, producing a high-quality pulp for Anaerobic Digestion (AD) plants. For the past six years the Gemidan facility in Holsted, Denmark has been testing and refining its ECOGI pulping system. During the last four years the facility has also operated at commercial scale.
According to the company, as well as processing food waste it is also effective in co-process light garden waste, allowing energy to be recovered from materials which would otherwise have been composted.
Following a Danish public procurement process the firm has now secured a contract to establish a 24,000 tonne per year facility to process waste collected from six municipalities in South Zealand. Once operational the plant will produce a high-quality pulp-based substrate which will be distributed to local AD facilities.
The site benefits from an onsite energy from waste operation and a supply of process water from a nearby water treatment plant. Pulp from the new facility will mainly be used to generate bio-gas for upgrade and injection into the Danish natural gas grid.
The Process
The ECOGI batch based process loads source separated food wastes and water into a pulping vessel. Tony Pickess, UK Sales Director at Gemidan Ecogi A/S, likens the process within the pulper to a “very sophisticated washing machine” where turbulence in the vessel, created by the rotation of a central screw to agitate the mixture, causes food waste to break down and separate from any non-organic materials.
When the pulping stage of the process is complete a valve opens and the contents pass into the separator. This is where the rejects (non-organic contaminents) are removed creating a very pure pulp based substrate.
To ensure the capture rate of organic content in the feedstock is maximised the rejects undergo two washing phases; the first wash using process water and the second wash using clean water. This two stage wash process raises capture rate of the organic fraction to 95%. The reject materials are finally passed through a screw press to recover the residual water before the rejects are stored for subsequent recycling or recovery. All the water used during this washing stage is recycled back into the pre-treatment system which helps minimise overall water usage.
“ECOGI is very effective at taking non-organic material out of food waste to produce a pulp that testing confirms to be circa 99.95% pure” explains Pickess. “Most of the more conventional pre-treatment systems are more aggressive and reduce the non-organic fraction of feedstock to very small fragments which are then much more difficult to remove from the substrate.
As a result further processing is often required in an effort to remove this contamination from the digestate following the anaerobic digestion process to allow the digestate to be used as a fertiliser on farm land.
The system is proven to be capable of achieving these very high levels of pulp purity even when processing material with 20% contamination, at the same time as recovering 95% of the organic matter in the feedstock. “ECOGI treats plastics, films, bottles, cans, glass – the whole gambit of packaging found in food waste,” Pickess tells WMW.
“ECOGI is a comprehensive pre-treatment technology rather than simply a depackaging operation” explains Pickess. “The pulping phase of the process also breaks down the organic part of the food waste and reduces 60% of it to a particle size below 100 micron and 90% to below 1.3 mm.”
He adds that the benefit of such a reduction in organic matter particle size is that methanogens have a greater sufarce area to work on, meaning when pulp is ultimately fed into a digester it starts to produce bio-gas much quicker. This early generation of gas also reduces retention times in the digester.
The process produces a pulp based substrate between 15 to18% dry solids, which Pickess says is ideal as the pulp retains the consistancy of a liquid and can be easily handled using standard pumping equipment. The dry solid content of the pulp can also be adjusted to match the specification the customer (AD operator) requires for their final anaerobic digestion process.
“The very low OPEX associated with the ECOGI technology results from the process relying purely on friction generated by water turbalence in the pulper. All the hard work is done by the water itself and not by mechanical based processes, thereby reducing wear and tear to a minimum” says Pickess. “In addition, the whole process is computer controlled and can be remotely operated. The pre-treatment operation can be run by a single person, who’s main roles are to feed the equipment using a loading shovel and to monitor the computor management system.”
R&D in Holsted
The company has been using its Holsted facility to develop its process using domestic food waste, as well and commercial and industrial materials.
“We regularly test the technology by putting more problematic materials through it,” says Pickess. “We recently processed several truck-loads of reject salad dressings and cream cheeses in glass packaging and the technology processed that material very effectively, removing virtually all glass fragments from the finished pulp. We also recently received 400 tonnes of off-spec dry milk powder packaged in plastic bags or metal cans, which we are presently processing mixed with other waste types.”
At the Holsted plant the resulting pulp from the process is distributed to a number of local anaerobic digestion plants. Most of the bio-gas produced is upgraded and injected into the Danish natural gas grid, but at smaller AD plants the bio-gas is used for heat/power generation.
Gemidan has also used the facility to have its process formally verified as part of the EU ETV programme for new and developing environmental based technologies. This approval means the purity of the substrate that ECOGI produces is formally endorsed, thereby ensuring the nutrient-rich and contaminant-free digestate-based fertiliser can be used on nearby farmland without risk of pollution.
“The ETV verification is important for us because it gives us the seal of approval that our ECOGI technology effectively and efficiently processes source separated food waste that incorporates up to 20% contaminants in the form of plastic, glass, metal, etc.
The process produces a high quality ‘pulp’ for use in bio-gas production that is confirmed to be 99.95% free from contamination,” comments Lars Ravn Nielsen, Gemidan Ecogi’s CEO. “At the same time the ECOGI technology optimises the recovery of the organic content - measured to be more than 95% - from the original feedstock.”
Pickess adds that the system can be used as a front end pre-treatment system at an AD plant or, as with the Holsted operation, as part of a dedicated pulp making facility serving a network of local AD plants. Either way, the ECOGI technology could provide a much needed solution for food waste producers with ambitions to achieve a zero waste operation.
A Green Solution
In addition to being able to process food waste, the ECOGI system is able to co-process green waste, a capability which helped it secure the South Zealand deal. According to Pickess, it is very difficult to process garden waste in hammer mill systems typically used to process food waste.
“The ECOGI system can take up to 20% light garden waste (typical kerbside collected garden waste),” he says. “It’s quite unique in being able to handle both materials at once. Garden waste usually goes to composting, which is effective in treating the material and fulfilling the legislation requirements. But it’s an intensive operation and there’s no energy recovery. It is better for the envirnment if you can put that material through AD – but you’ve got to be able to process it.”
He adds that another big advantage the ECOGI system has over more conventional pre-treatment systems, being a less aggressive process, is that it requires less maintenance (routine or due to failure) and this maintenance can largely be completed between operational shifts.
The Future
When it comes to the future for the company and its technology Pickess is bullish and says the financial pressures local authorities are under, together with the drive to increase recycling presents Gemidan Ecogi A/S with an opportunity. Food waste, he says, is an excellent waste stream to target to boost recycling rates and improve environmetnal performance.
“Our technology offers the option of a relatively low cost solution to maximise the recovery of organic matter, and thereby energy recovery. It makes the digestion process more efficient and enables a greater throughput of materials through the digester,” he asserts. “By doing that and reducing some of the process costs it makes collection a more viable operation for local authorities.”
He concludes by noting that a number of major commercial food producers and retailers are moving towards zero waste and want a process where they can maximise the recovery of materials. While he says this already presents the company with a big opportunity, it is also looking to co-develop an additional piece of equipment to increase the recovery of recyclables from the reject material. Watch this space…
