Potato Products & Starch Recovery

Hiller machines provide world-class high-performance decanter centrifuges applicable to a variety of snack food, potato and root crop processing plant starch recovery and pretreatment wastewater applications. The majority of centrifuges applications found at snack food, potato chip, french-fry, flake and potato packers will typically fit into four (4) liquid / solids separation and dewatering application groups:

1. Starch recovery and starch dewatering
2. Potato meal
3. Wash water recycling / cleaning (mud dewatering)
4. Wastewater effluent treatment

Starch Recovery and Dewatering: Abrasive peeling, slicing and or cutting potatoes and or other root crops causes the cells to release starch which is typically is rinsed off with fresh water before frying or taking the next process step. This potentially valuable starch is often left to wash down through the drain and to the plant wastewater treatment system where it will impact the Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) limits and treatment cost. Ideally many processors will want to find a solution for minimizing this added BOD / COD waste load on their treatment facility and recover the potentially more valuable starch selling to other processers specializing in starch refining or as animal feed. Hydro-cyclones and other systems are commonly used for starch recovery but these generally produce a wetter and more unmanageable starch when compared to a decanter centrifuge. Plus these systems typically do not recover the starch with the same separation efficiently as the decanter centrifuge. The decanter centrifuge separates the solids from the water and produces a dry friable cake material with an average moisture content of less than 40%, and the liquid phase will have had the majority of the solids removed which consequently provides is a dramatic reduction in the BOD / COD load on the plant or city treatment system providing a substantial savings in effluent charges.

With many installations in this sector and excellent co-operation with our clients, we have extracted considerable data from on-site processing results. The majority of the centrifuges installed for starch recovery are operated as lower “G” reduced speed type decanters since these machines can operate at less than 2,000 x “G” and produce the desired results. Other processing plant wastewater treatment applications require more traditional decanter centrifuge operation.

Units installed to recover wash water starch from cutting and / or slicing potatoes at a potato chip manufacturer would on average produced approximately 2-3 tons of recoverable starch from every 100 tons of potatoes processed. The separated starch cake discharged from the decanter centrifuge at 60% dry solids on average with a values ranging up to $180. This proved to be a significant advance in comparison with the traditional hydro-cyclones and other system, which involved hauling the slurry away at 25 to 30% dry weight solids. The reduction in process area and transport costs is also an attractive and valued factor. Whether or not the purchaser of the starch re-slurries the material for further treatment is irrelevant, but it is important to move the starch within a few days of production especially in hot weather (alternatively cold storage) to prevent deterioration of the product.

As results of the success of with potato chip manufactures machines were also installed at French-fry producers. Naturally, the starch yield is less in the case of straight cut French-fries and represents approximately 0.3 - 0.5 % of the potato being processed as recoverable starch at 60% dry weight solids.

• Machine Wear Characteristics: No signs of wear to the bowl and screw conveyor.
• Process Issues: Gelatinized starch produced by the blanching process or by steam peeling, can cause process concerns with variations in the starch solids being discharged from the centrifuge:
  • Starch 57 - 60 % dry solids
  • Gelatinized (slimy) starch at 25 % dry solids

After testing several machine design changes and still experiencing two (2) different starch variations the client modified the potato fiber screen removing the gelatinized starch before reached the decanter centrifuge.

Starch Dewatering Conclusion: The Hiller DecaPress Decanter centrifuge is very well suited for starch dewatering. Where some manufacturers accept the starch as part of their wastewater effluent, there are several incentives to remove the starch upstream of plant or city wastewater treatment facilities:

1. sell recovered / dewatered starch
2. Reduce wastewater treatment and effluent costs
3. Recycle centrate to the pre-wash area
4. Reduction of fresh water requirement

Potato Meal: Potato peel combined with reject potatoes, and substandard products can be pulverized into slurry. Water is then added and the potato meal slurry can be centrifuged to produce a cake of approximately 40 % dry weight solids.

Potato Meal Conclusion: Potato meal commands a higher price than the potato waste in its original form. The proportion of cooked potato in the feed largely influences the dryness of the cake.

Potato wash water recycling / cleaning (mud dewatering): Use of the decanter centrifuge on a closed loop to the potato pre-washer or potato flume/transport water leads to the continuous removal of earth, mud, soil, potato debris etc. from the washing water. The solids are discharged as a stackable cake at up to 50% ds. The cleaned liquid discharge is returned to the washer for reuse thus reducing the amount of water used at plant and allowing the washer to be run for extended periods before emptying. The addition of a flocculent is not normally required but may be used to improve the superfine capture if needed, and achieve a centrate of < 100 ppm suspended solids.

• Machine Wear Characteristics: In order to minimize wear, the bowl speed is reduced. The welded scroll wear protection operates for 15,000 to 20,000 hours before attention or tiled scrolls can be used to extend service intervals. No significant wear is found on any of the other parts.

Wastewater / Effluent Treatment: Prior too many decanter centrifuge installations the typical processing plant effluent treatment program was a screen system with grit removal followed by a crude settling tank, primary clarifier, or lagoon. Typically underflow from a clarifier was thickened from 5% to 20% in a cone thickener prior to land disposal by tanker. The centrifuge is often installed to replace the thickener and cakes of up to 40 % were easily achieved without flocculent addition. Often the product is saleable to farmers as an animal feed additive. Suspended solids in the water discharged to the city are routinely reduced from 1,200 ppm to less than 300 ppm.

When steam peeling is used instead of abrasive peelers, gelatinized starch affects the cake and the dry solids content will not be as high but the resulting cake discharge at 20 to 25% is still a stackable and saleable product.

• Machine Wear Characteristics: After approximately 10,000 hours, the effluent centrifuge was disassembled finding minor wear on the scroll and in the feed chamber. Hiller now makes use of added wear protection on the scroll flights and a comprehensive tungsten carbide (or a similar material) protection liner in the feed chamber, to extend the scroll life beyond 12,000 hours.

Wastewater / Effluent Treatment Conclusion: The low speed decanter centrifuge is ideally suited for effluent derived from the potato process. Clients who have used belt presses have complained of high maintenance costs and excess water use in comparison with Hiller decanter centrifuges and have also replaced rotary vacuum filters for similar reasons.

And if your snack food or potato / root crop processing plant features an on-site wastewater pretreatment facility that requires liquid / solids separation and dewatering sludges or thickening of biological sludges, the Hiller decanter centrifuge series has been developed for maximum cake dryness at high throughputs with significantly reduced polymer consumption.

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