Composition of Tapioca Processing Wastewater
Tapioca starch production generates a lot of polluted wastewater with solid waste being another major concern. Wastewater from sedimentation and centrifugation is especially problematic. The amount of wastewater produced is around 12 cubic meters per ton of starch produced, which causes severe pollution to the surface water and air in South Vietnam.
Large-Scale Industry
The chemical and physical properties of primary and secondary settling wastewater from cassava starch factories can vary greatly. For example, in a large-scale tapioca processing factory in Kerala, India, the COD concentration in primary settling wastewater ranges from 33,600-38,223 mg/L, while it’s only 3,800-9,050 mg/L in secondary settling wastewater.
| Parameters | Unit | Primary settling wastewater | Secondary settling wastewater |
| pH | – | 4.50 – 4.70 | 4.50 – 4.70 |
| Total solids | mg/L | 35,640 – 42,000 | 3,200 – 9,600 |
| Total suspended solids | mg/L | 33,200 – 37,320 | 980 – 4,078 |
| COD | mg/L | 33,600 – 38,223 | 3,800 – 9,050 |
| BOD5 | mg/L | 13,200 – 14,300 | 3,600 – 7,050 |
| Free sugar as glucose | mg/L | 425 – 1,850 | 735 – 2,060 |
| Total hydrolysable reducing sugar as glucose | mg/L | 22,614 – 29,275 | 1,120 – 2,761 |
| Total ash | mg/L | 1,450 – 1,680 | 265 – 820 |
| Total nitrogen | mg/L | 97 – 182 | 62 – 86 |
Researchers like Balagopalan et al. (1988) found that extracting starch from cassava roots requires a lot of water, leading to significant wastewater being released. This has resulted in many tapioca factories being situated near rivers or lakes, and the customary practice of discharging wastewater into water sources has become a serious environmental threat in rural areas. The pollution problems caused by these factories have also been described by researchers in Thailand and India.
Mai et al. (2001) and Oanh et al. (2001) conducted studies on wastewater from two different tapioca factories in Vietnam, and found that the centrifuging process generates wastewater with extremely high organic concentrations, with up to 23,000 mg/L of BOD5 and 41,000 mg/L of total COD. They also found that rinsing wastewater from one of the factories contained mainly inorganic matter with a total COD concentration ranging from 320-520 mg/L and suspended solids ranging from 220-3,389 mg/L.
| Parameters | Unit | Phước Long Tapioca Co. | Việt Thái Tapioca Co. | Tây Ninh Tapioca Co. | KMC Tapioca Co |
| pH | – | 4.90 – 5.70 | 4.50 – 5.10 | 4.30 – 4.50 | 3.78 – 4.53 |
| SS | mg/L | 500 – 3,080 | 3,750 – 4,100 | 1,588 – 2,650 | 330 – 4,400 |
| CODtt | mg/L | 7,000 – 14,243 | 14,262 – 41,406 | 10,701 – 15,560 | 9,221 – 20,648 |
| COD-VFA | mg/L | – | – | 682-930 | – |
| BOD5 | mg/L | 6,200 – 13,200 | 7,125 – 23,077 | 5,600 – 8,950 | 6,757 – 15,280 |
| N-NH3 | mg/L | 45 – 73 | 38 – 102 | 71.4 – 88.1 | 37.8 – 84.5 |
| N-Org | mg/L | 90 – 367 | 96 – 188 | 174 – 212 | 220 – 237 |
| P-PO4 | mg/L | 10 – 45 | 15 – 24 | 53 – 59 | 47 – 58 |
| SO42- | mg/L | 26 – 73 | 13 – 21 | 10 – 25 | 21 – 28 |
| CN– | mg/L | 19 – 28 | 28 – 61 | 30.0 – 33.6 | 32.5 – 36.5 |
The water in the tapioca production process contains highly toxic cyanide which is fatal to fish at concentrations of about 1 mg/L. The water can have up to 96 mg/L of cyanide, which is too polluted for fish to survive. Large amounts of cyanoglycosides are released during production, and these compounds decay rapidly to cyanide, depending on the type of cassava used. The cyanide concentration in the wastewater can be as high as 200 mg/L.
Household- and Medium-Scale Industry
Studies conducted at two medium-sized tapioca factories in Tay Ninh and Binh Dinh provinces have shown that the wastewater produced by these factories has high organic content and low pH levels. The BOD5 and COD concentrations were between 7,400-11,000 mg/L and 13,000-17,700 mg/L, respectively.
Nandy et al. (1995) conducted a survey on small-scale tapioca production and found that wastewater from the root-rinsing stage has low BOD5 and COD concentrations and a neutral pH. On the other hand, wastewater from sedimentation is slightly acidic and has high BOD5 and COD concentrations, causing heavy pollution to the receiving surface water.
Flow Rate of Tapioca Processing Wastewater
The amount of wastewater produced during tapioca production is an important factor to consider when designing a wastewater treatment plant. The quantity of starch in cassava root varies, but typically it takes four tons of fresh cassava roots to make one ton of tapioca starch. The amount of wastewater produced varies depending on the size of the production operation and the stage of processing. In household-scale production, most of the wastewater comes from the settling stage, while in large-scale production, it comes mainly from the centrifuge stage. A survey conducted by ARRPET (2003, 2005) found that the flow-rate of household-scale wastewater ranges from 3.5-5.5 cubic meters per ton of fresh cassava roots, while large-scale production generates 3.0-5.0 cubic meters per ton of fresh cassava roots.