Table 6 Treatment Units Unit Operation Unit Processes and Systems for Potato Processing Wastewater

Treatment unit or subsystem_

Unit operation/unit process/ treatment system_

Remarks

In-plant

Pretreatment Primary treatment

Equalization Neutralization Secondary treatment 1. Aerobic processes

Conservation and reuse of water

Process revisions Process control New products

Screening (mesh size: 20 to 40 per inch)

Sedimentation Flotation Earthen ponds Balancing tank/buffer tank Conditioning tank

Natural systems Irrigation land treatment

Reduction of waste flow and load

10-25% BOD5 removal

30-60% BOD5 removal 20-60% COD removal

Constant flow and concentration pH and temperature corrections 80-90% BOD5 removal 70-80% COD removal

— Stabilization ponds and aerated

lagoons

— Wetland systems

• Activated sludge

• Rotating biological contactors

• Trickling filters

2. Anaerobic processes • Upflow anaerobic sludge blanket

• 80-90% BOD5 removal

(UASB) reactors

• Expended granular sludge bed

• 70-80% COD removal

(EGSB) reactors

• Anaerobic contact reactors

• Anaerobic filters and fluidized-bed

reactors

Advanced treatment • Microstraining

• 90-95% BOD5 removal

• Granular media filtration

• 90-95% COD removal

(Sometimes>95%)

• Chemical coagulation/

sedimentation

• Nitrification-denitrification

• Air stripping and ion exchanging

• Membrane technology (reverse

osmosis, ultrafiltration)

Notes: BOD5 and COD removal percentage depended on experience of the German and other developed countries. There are other advanced treatment methods (not mentioned in this table) used for various industrial wastewater such as activated carbon adsorption, deep well injection, and chlorination that are not expected to be highly used in potato processing wastewater treatment.

• collection of floor waste in receptacles instead of washing them down the drains;

• removal of potato solids in wastewater to prevent solubilization of solids.

Water volume can be reduced by reusing process water, with several advantages. First, the size of wastewater treatment facilities can be decreased accordingly. Secondly, with

Potato Processing Water
Figure 7 General treatment scheme for potato processing effluent.

concentration of the waste, the efficiency of a primary settling tank is increased. In the final processing stages, chlorinated water should be utilized to prevent bacterial contamination of the product. Other steps to reduce wastewater volume include alternate conveying methods of transporting potatoes other than water fluming, improved cleaning facilities for equipment and floors (high-pressure nozzles, shut-off nozzles for hoses), collecting clean waste streams, and discharge to natural drainage or storm water systems.

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