The 3rd Conference on Technology

O-STARCH-03

Water Minimization in the Starch Production Industry: A Decision Support System

Natthakan Rungraeng1, Kanchana Saengchan1, Annop Nopharatana2 and Warinthorn Songkasiri3 1Department of Food Engineering, Faculty of Engineering, Food Engineering Practice School, King Mongkut’s University of Technology Thonburi, Ratchburana, Bangkok 10140, Thailand 2Pilot Plant Development and Training Institute (PDTI), King Mongkut’s University of Technology Thonburi, Bangkhuntien, Bangkok 10150, Thailand 3Biochemical Engineering and Pilot Plant Research and Development Unit (BEC), National Center for Genetic Engineering and Biotechnology (BIOTEC), 83 Moo 8 Thakham, Bangkhuntien, Bangkok, 10150, Thailand

Abstract A typical tapioca starch manufacturing process consumes freshwater approximately 10 to 30 m3 per ton of starch produced. The amount of consumption can be reduced considerably by the recycle of wastewater. This research utilizes a water pinch technology as a tool to minimize water consumption in the starch production process. The water pinch decision support system, called the W-Pinch program, was generated by the Starch Engineering and Process Optimization (SEPO) Program, King Mongkut’s University of Technology Thonburi (KMUTT). The W-Pinch modelling system includes 7 composition balances of water, starch, , pulp, sand, peel, and sulfur. Water composition is correlated to freshwater and wastewater calculations and the moisture content of the product. Starch and pulp compositions demonstrate the extractor efficiency. Peel, sand, protein, and sulfur compositions are the control parameters to monitor and control the final product quality after applying the water recycling patterns. Each composition stream was balanced for each unit in the starch production process, i.e., root receiver, washer/cutter, rasper/grinder, coarse extractor, fine extractor, separator I, separator II, separator III, centrifugal dewater unit, and flash dryer. A user inputs the removal efficiency of each component and the maximum allowable concentrations of each composition at that specific unit into the W-Pinch input file. Five recycling patterns were designed to evaluate the water minimization in the starch process. All the water streams do not require the water treatment before the reuse of water. In addition, the W-Pinch program allows a user customize his own recycling pattern. The W-Pinch model was validated with the data from one tapioca starch factory with a capacity of 200 tons starch per day. The W-Pinch simulations showed that, with a recycling water stream, the water consumption was reduced by 25 percent of that of the non-recycling system.

Introduction Tapioca starch, one of the major export products of Thailand, is produced from the tuberous roots of the tapioca plant. The starch manufacturing process can be divided into the following stages: 1. Fresh roots are passed through the sand removing drum to separate out sands and dirts, then roots are washed, peeled, and rasped before the addition of water to become starch slurry. 2. Starch slurry is passed through extractors twice to extract starch from cassava pulps using centrifugal forces. Several extractors are interconnecting in series with different mesh sizes. 3. Freshwater is added to the starch milk in separator units to separate of the fruit water and its soluble contents, i.e. root protein. 4. Water is removed by draining, centrifuging and drying with pneumatic dryer. 5. Then, the starch is ready to pack.

However, the starch producing processes consume freshwater approximately 10 to 30 m3 per ton of starch produced (Jirasaowapak, 1998). Thus, this research utilizes a water pinch technology as a tool to minimize water consumption in the starch production process by the reuse and recycle of water. The water pinch decision support system, called the W-Pinch program, was generated by the Starch Engineering and Process Optimization (SEPO) Program, King Mongkut’s University of Technology Thonburi (KMUTT).

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Water pinch technology is a mass-exchange network involving the optimization of water- using operations in the production process (Srinophakun et al., 2000). The water pinch technology can be divided into three steps: (1) analysis Identifying, a priori, the minimum freshwater consumption and wastewater generation in water-using operations (2) synthesis Designing a water-using network that achieves the identified flow rate targets for freshwater and wastewater through water reuse, regeneration, and recycle (3) retrofit Modifying an existing water-using network to maximize water reuse and minimize wastewater generation through effective process changes. Jirasaowapak (1998) reported that the amount of water consumption can be reduced from 12 m3 per ton starch to around 5 m3 per ton starch by reusing the treated wastewater. Moreover, Prakotpol (2003) established a genetic toolbox for water pinch technology the program was written in MATLAB. The program can be used to minimize freshwater consumption for both single and multi contaminants according to user data inputs.

2. Methodology 2.1. The W-Pinch Model The W-Pinch program is written in FORTRAN language. The program consists of mass balance equations of each compostion around each production units as shown in the following equation.

Flowouti, j Flowini, j u Efficiencyi, j ---(1) where i is the unit operation j is the compositions A user inputs the removal efficiency of each component and the maximum allowable concentrations of each composition at that specific unit into the W-Pinch input file.

The compositions are 1. Water (W) 2. Starch (ST) 3. Protein (PR) 4. Pulp (PP) 5. Sand (SN) 6. Peel (PE) 7. Sulfur (SF) Water (W) composition is linked in the calculation of the flow rate of freshwater and wastewater and the moisture content of the starch product. Starch (ST) and pulp (PP) contents are the parameters used for the evaluation of the extraction efficiency. Peel (PE), sand (SN), protein (PR), and sulfur (SF) are the unwanted compositions for customers. They are included in this model to monitor and control the quality of the final product after applied water reused patterns. The units in the starch production process in the W-Pinch program are 1. Root receiving unit 2. Washing and cutting unit 3. Rasping and grinding unit 4. Coarse Extractor 5. Fine Extractor 6. Separator I 7. Separator II 8. Separator III 9. Centrifugal Dewatering unit 10. Flash Drying unit

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In addition, the pulp released from coarse and fine extractors are re-extracted in the pulp extractor. The wasted pulps are pressed to remove water and are sold as animal feeds. The amount of water, protein, pulp, sand, peel, and sulfur released from each unit depend on the machine efficiency specified by a user.

2.2. Reused Patterns Five recycling patterns were designed to evaluate the water minimization in the starch process. Note that all the water streams do not require the water treatment before the reuse of water.

Pattern I (shown in Figure 1) - Water effluent from the pulp pressing and pulp extractor were reused in the washing and cutting unit - Water effluent from the separator I was reused in the rasping and grinding unit - Water effluent from the separator II was reused in the coarse extractor - Water effluent from the separator III was reused in the fine extractor

Pattern II (shown in Figure 2) - Water released from the pulp pressing and pulp extractor were reused at the rasping and grinding unit - Water released from the separator I was reused at the washing and cutting unit - Water released from the separator II was reused at the coarse extractor - Water released from separator III was reused at fine extractor

Figure 1 Water Reused Pattern I F igure 2 Water Reused Pattern II

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Pattern III (shown in Figure 3) - Water released from the pulp extractor was reused at the rasping and grinding unit - Water released from the separator I and the pulp pressing unit were reused at the rasping and grinding unit - Water released from the separator II was reused at the fine extractor - Water released from the separator III was reused at the coarse extractor

Pattern IV (shown in Figure 4) - Water released from the pulp extractor with the pulp pressing and the separator II were reused at the rasping and grinding unit - Water released from the separator I was reused at the coarse extractor unit - Water released from the separator III was reused at the fine extractor

Pattern V (shown in Figure 5) - Water released from the pulp extractor and pulp pressing unit were reused at the rasping and grinding unit - Water released from the separator I was reused at the washing and cutting unit - Water released from the separator II was reused at the fine extractor - Water released from the separator III was reused at the coarse extractor.

Figure 3 Water Reused Pattern III Figure 4. Water Reused Pattern IV

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Figure 5. Water Reused Pattern V

2.3 Model Calculations The amount of freshwater consumption without water reused network was calculated, and then the freshwater consumption of each reused pattern were calculated and shown in the table in the output file for the result comparison.

2.4 Model Validation This model was validated with the data from one of the tapioca starch factory in Thailand. After validation, the amount of freshwater consumption was approximately 23 m3 per ton of starch.

3. Results and discussion Table 1 shows the comparisons of water consumptions, amount of product, and starch compositions from each pattern of water reused.

Water Consumption Water consumption of the no-recycle line is 22 m3 per one ton product and the amount of product is 96.4 tons daily. After apply 5 patterns for water recycle the water consumption are reduced to 17.97, 17.24, 17.02, 18.14, and 17.17 m3 per one ton product in pattern I to pattern V, respectively.

Amount of Product With the no-recycle pattern, a factory produces 96 tons per day. A factory could increase the starch production of up to 123 tons per day if applying the recycle patterns. The increasing yield may come from the recovery of starch particles suspended in the water effluent of each unit.

Product Compositions Consumers specifies the product compositions, e.g., the starch should have moisture content less than 13 % dry basis and contain a small amount of protein and sulfur, so the amount of water protein and sulfur should be calculate and monitor. In this example, we specified the removal efficiency of protein and sulfur to be almost 100% in each pattern. However, the user could specify the machine efficiency to control the quality of the product.

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4. Conclusions and recommendations Conclusions The W-Pinch Program can be used to calculate freshwater consumption for a tapioca starch plant. From the program calculations, the freshwater consumption without water reused pattern is approximately 21.8 m3 per ton of starch and amount of product of 96 tons daily. While the recycle patterns provided lower freshwater consumption and helped increase the production process yield. The result shows that the water recycle pattern III reduced freshwater consumption to 17.02 m3 per and ton of starch and amount of starch produced was increased to 123.35 tons daily. The amount of freshwater consumption depends on the unit operation efficiency and the process pathway at which the recycle stream has passed through. The starch producing factory can reduce the freshwater consumption to minimize its freshwater cost, wastewater treatment cost, and simultaneously to optimize its natural resource utilization.

References Jirasaowapak, S., 1998. Application of Pinch Technology for Better Water Utilization in Tapioca Starch Factories, Master of Engineering Thesis, Chemical Engineering, King Mongkut’s University of Technology Thonburi. J.G. Mann, Y.A. Liu, Industrial Water Reuse and Wastewater minimization, McGraw-Hill, New York, 1999. Prakotpol, D., 2003. Development of MATLAB Toolbox with Genetic Algorithm for Water Pinch Technology, Master of Engineering Thesis, Chemical Engineering Practice School, King Mongkut’s University of Technology Thonburi. Srinophakun, T., Suriyapraphadilok, U., Tia, S., 2000, Water-Wastewater Management of Tapioca Starch Manufacturing Using Optimization Technique, ScienceAsia, 26: 57-67.

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