Removal of starch from starch dispersions by tangential flow filtration

Siong, Samantha Ling-Chee (2015) Removal of starch from starch dispersions by tangential flow filtration. Masters thesis, Universiti Malaysia Sarawak, (UNIMAS).

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Abstract

Absence of systematic wastewater treatment in sago industries in Sarawak has resulted in improper discharge of effluent into our rivers. Tangential flow filtration (TFF) is an attractive alternative for treatment of sago effluent. The main aim of this study was to employ TFF for sago starch separation from two model dispersions (1% and 3% w/v). The laboratory-scale studies used polysulfone membrane filter cassettes (0.45 µm) with membrane area of 0.1 m2 , 0.2 m2 and 0.3 m2 . This study is essential for next in-situ sago effluent treatment in order to have good filtration efficiency with low fouling rate. Each model dispersion was filtered and concentrated to a minimum factor of 3.33 with a final volume of less than 15 L. High concentration of starch caused high degree and rates of fouling in the filtration membrane. Consequently, it deteriorates the performance of membrane filtration. Membrane backflushing is a way to reduce fouling of membrane during filtration process. By this, the time of operation for treatment of 3% starch dispersion had been successfully reduced by 5 hours. In treatment of 1% starch dispersion, expanding the filtration area (0.1 m2 to 0.2 m2 , and to 0.3 m2 ) have improved the filtration efficiency by shortening the filtration time from 1 hour to 30 minutes and also increased the removal of water by 4%, from 81% to 85.4%. In contrast, the normalized permeate flux (NPF), specific volume (SV), normalized retentate flux (NRF), normalized instantaneous specific flux (NISF), transmembrane pressure (TMP) and water recovery (WR) decreased with filtration area at fixed feed flow of 4.5 LPM. These parameters except TMP decreased with operational time due to membrane fouling. However, the parameters were improved when the TMP was reduced after backwashing the membrane and thus increases the filtration efficiency of membrane. Meanwhile, total suspended solids (TSS), turbidity and chemical oxygen demand (COD) were not detected in the permeate generated unless overfouling of membrane, and all showed significant differences (p < 0.05) between before and after treatments. Based on the laboratory study, it is suggested to use 0.3 m2 membrane and employ backflush in TFF for in-situ study. In treatment of actual sago effluent, similar results were obtained where most of turbidity, TSS, COD and biochemical oxygen demand (BOD) were successfully eliminated after the TFF process. The main problem faced in this in-situ study was the sago fibres in sago effluent which will greatly reduce the filtration efficiency of TFF process. This has caused the TMP to increase drastically and decrease of NPF, SV as well as NISF within 10 minutes. However, further investigations regarding the pre-removal of all sago fibres prior to treatment using TFF system is necessary. In terms of membrane cleaning, soaking membrane in 0.2 M NaOH solution is found to be the most effective method to recover the membrane permeability (up to 91%) within the shortest time (within 72 hours).

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