3. Overview of Thailand tapioca starch industry
3.1. Production process in Thailand, processing of tapioca starch is similar among the plants, but it may be different in techniques and machines used in each production stage. Shown in fig. 1 is the production process of tapioca starch to which no reuse and recycling of water in the
production lines are applied. Although most of the studied plants reuse and recycle water at some point, this processing scheme is intended to show potential sources of water consumption and waste water generation. The total amount of water used, waste water
generated, sand and peel, and fibrous residues were averaged from the eight studied plants. The portions of water used and waste water generated in each production stage were obtained from the previous study team [5]. The wet matter mass and water mass balances are based on 1 ton of produced starch. Moisture contents of the matter streams are stated in parentheses.
Cassava roots are firstly delivered to a sand removal drum and then to a rinsing gutter for cleansing and peel separation. After washing, the clean cassava roots are sent to a chopper to chop into small pieces (approximately 20–25 mm) and then taken to a rapper. During rasping, water is added to facilitate the process. The resulting slurry, consisting of starch, water, fiber, and impurities, is then pumped into the centrifuges for extraction of the starch from
the fibrous residue (cellulose). The extraction system consists of three or four centrifuges in series. There are two types of extractors: a coarse extractor with a perforated basket and a fine extractor with a filter cloth. Suitable amount of water and sulfur-containing water are constantly applied to the centrifuges for dilution and bleaching of the starch. The starch slurry is then separated into starch milk and fibrous residue. The coarse and fine pulp is passed to a pulp extractor to recover the remaining starch and the extracted pulp is then delivered to a screw press for dewatering. The dewatered fibrous residue is sold to a feed stock mill. The starch milk from the fine extractor is pumped into a two-stage separator for impurity removal from the protein. After passing to a second dewatering machine, the starch milk has the starch content up to 18–20_ Baume. Then, the concentrated starch milk is pumped into dehydration horizontal centrifuges (DHC) to remove water before drying. The DHC consists of filter cloth placed inside, rotating at about 1000 rpm to remove water from the starch milk. The resulting starch cake has a moisture content of 35–40%. The starch cake is taken to a drying oven consisting of a firing tunnel and drier stack. Drying is effected by hot air produced by oil burners. During the drying process, the starch is blown from the bottom to the top of the drier stack and then fallen into a series of two cyclones in order to cool down the starch. The dried starch with a moisture content of less than 12% is conveyed through a sifter for size separation and finally packaging.