Starch Recovery

When potatoes are sliced or diced or chipped the physical action of cutting through the potato cells releases white potato starch that is usually rinsed off with fresh water before going into the fryers or the next process. The potato starch is carried with the wash down water through the effluent system and commonly will go to drain. Alternatively there will be some kind of effluent treatment but everything comes at a cost. The highest cost is no treatment at all in which case the producer will face high and ever increasing trade effluent charges based on the Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) of the waste that is going down the sewer for the water companies to treat.

Ideally the processor will want to find a way of capturing the starch before it ends up going down the drain.

There is also an opportunity to sell the starch if it can be recovered because if the potato has been kept cold before slicing any starch released will have a value either as an animal feed or for sale to companies that specialise in refining starch. However, if the potato has been blanched or heated during processing then the starch will turn gelatinous and will have to be discharged as effluent into the effluent system.

It is estimated that between 1% and 2% of any potatoes sliced will be recovered as starch. The value has fluctuated considerably over the years between £40 and £140 per dry tonne.

There are several processes that can be used to recover starch but these generally produce a product that can be rather wet and unmanageable. Centri-Force are experts in the use of high speed industrial centrifuges for continuous processing, recovering starch in plants across the UK. The decanter centrifuge separates the solids from the water and produces a dry friable material with a moisture content of less than 40%. The liquid phase will have had the bulk of the solids removed and consequently there is a dramatic reduction in load on the sewer and substantial savings in trade effluent charges.

The illustration shows recovered starch from a centrifuge in a collection bag that is ready for shipping off site as saleable material instead of disposal as waste in the effluent.

The picture shows a typical skid mounted centrifuge with control panel. The only other equipment required is a pump to deliver the starch to the centrifuge. All of this equipment is easy to operate and runs continuously without supervision. There is no need for complex installations and the whole process can be up and running in a few weeks. Centri-Force supply a complete range of factory refurbished centrifuges from leading manufacturers that are a cost effective solution ideal for this application. The application itself is now well proven and has been shown to be non aggressive, resulting in low servicing costs and good durability.A typical maintenance cost is less than 5% per annum of the capital cost.

The principal benefit is economic; it saves money, frequently with dramatic pay back potential, particularly if the starch can be sold on. No one particularly “wants” to invest in effluent treatment because there are always prior demands from the mainstream processes. However with rapid payback, or consent issues even the most hardened Finance Directors are having to listen to the arguments.

Of course all companies have to think about how they interact with the environment and reducing the pollution that goes down the drain is an obvious benefit to all concerned. There is also a possibility for reusing the clarified wash water which is certainly worth investigating.