Wet and readily degradable residues
Peel residues and starch-containing process waters are generated continuously, have limited storage stability and require reliable utilisation and transport routes.
Process solution for potato processing
Biogas from potato waste, potato pulp and process water
Potato pulp, peelings, starch-rich process water and other potato-processing residues are converted through anaerobic digestion into biogas, biomethane, process energy and organic NPKS fertilisers.
Initial situation
Typical challenges with potato pulp, peelings and process water
High operational energy demand
Potato-processing plants require continuous electrical and thermal energy and, in some cases, cooling energy. Rising energy prices directly increase production costs.
Protein-rich material streams and inhibitors
Protein-rich peel residues can lead to elevated ammonium and hydrogen sulphide concentrations in the digestion system and thereby impair biological process stability.
Wastewater, odour and logistics impacts
Production wastewater, sludge, interim storage and residue transport generate additional costs and can constrain expansion of production capacity.
Process principle
From potato pulp and peelings to biogas and fertiliser products
Collect and suspend residues
Peel residues, starch-containing process waters, cleaning residues, organically loaded cleaning media and suitable wastewater sludge are combined into a pumpable biosuspension. High-dry-matter additives and process water are used to establish a dry-matter content of approximately 12 to 18%.
Aerobic hydrolysis
The biosuspension undergoes hydrolytic pretreatment with intensive air supply at elevated temperatures. This opens up lignocellulosic structures in particular and prepares the material for subsequent methane formation.
Culture-retaining main digestion
The hydrolysate is fed to a hydraulically and only partially mixed main digester. A mixed methane-bacteria culture adapted to protein- and lignocellulose-rich feedstocks is retained and continuously reproduced in the system.
Multi-stage anaerobic digestion
A robust mesophilic main digestion stage is combined with a downstream, preferably thermophilic post-digestion stage. This balances varying residue qualities, increases degradation and supports hygienisation.
Separate digestate and recover nutrients
The fermentation residues are separated into a solid fertiliser fraction and biofiltrate. The solid phase can be used as an organic NPKS fertiliser.
Remove inhibitory compounds
Where required, ammonium and sulphur compounds are removed from the biofiltrate before it is recycled. The resulting nitrogen- and sulphur-rich washing liquids are recovered as liquid fertiliser concentrate.
Treat and energetically utilise biogas
The biogas produced is desulphurised, dried and compressed where required. It can be used in particular for combined generation of electrical and thermal process energy.
Suitable feedstocks
Potato pulp, peelings, process water and other residues
Peel residues
Wet residues with valuable organic and energy content from the processing of potatoes and comparable starch-rich root crops.
Starch-containing process waters
Aqueous material streams and settled starch fractions from cleaning and processing the root crops used.
Cleaning media and wastewater sludge
Organically loaded media from plant cleaning and sludge from on-site aerobic or anaerobic wastewater treatment.
Stillage and press cakes
Residues from an optional upstream yeast-fermentation and bioethanol-production stage using starch-containing material streams.
Other starch-rich root crops
The process principle can also be assessed on a project-specific basis for residues from processing sweet potatoes, manioc, tapioca and cassava.
High-dry-matter additives
For example cereal chaff, mill dust, brushing dust and comparable lignocellulose-rich residues for adjusting the biosuspension.
Client benefits
More value from on-site residue streams
Reduced process-energy costs
The biogas produced can cover a substantial share of the plant's electricity and heat demand and reduce dependence on fossil energy sources.
Greater disposal security
The plant becomes less dependent on short-notice collection of wet peel residues, fluctuating feed markets and external disposal routes.
Organic NPKS fertilisers
Plant nutrients are recovered in solid fertiliser fractions and liquid nitrogen- and sulphur-rich concentrates for further use.
Less wastewater, odour and transport
Integrating process water and wastewater sludge can reduce wastewater load. At the same time, interim storage, odour emissions and plant-related truck traffic are reduced.
More stable biological operation
Aerobic hydrolysis, culture-retaining digester technology and targeted inhibitor removal support stable treatment of protein- and lignocellulose-rich residues.
Additional value creation
Surplus energy, marketable fertiliser products and verifiable greenhouse-gas reductions may, depending on the project and applicable schemes, create additional revenue potential.
Technical background
The process solution presented is based on German patent specification DE 10 2014 001 910 B4. The specific technical and commercial design must always be tailored to the project, site and material flows.
Project assessment