Preparation And Application Of Cationic Starch Flocculant To Molasses Alcohol Wastewater Treatment

The aim of this paper was to prepare a modified starch flocculant in order to provide basis for establishing new technology of treating molasses alcohol wastewater.Firstly, the cationic starch with high degree of substation (DS) containing quaternary amino group was prepared via the reaction of corn starch with 3-chloro-2-hydroxypropyl- trimethyl ammounium chloride (CHPTMA) using pre-drying dry process. Through single factor tests and orthogonal tests, the optimal reaction conditions of preparing high DS cationic starch were confirmed as follows: the amount of CHPTMA was 55% of mass of starch, the molar ratio of sodium hydroxide to CHPTMA was 1.2, water content of the systerm was 25%, reaction temperature was 85℃and reaction time was 4h. Then the self-made cationic starch with different DS was taken as flocculant to treat molasses alcohol wastewater. The influences of the dosage of cationic starch, the DS, the initial pH of wastewater, stiring and adsorption time on the removal rate of CODcr and the decoloration rate were discussed. The results showed that when the amount of cationic starch was 500mg/L, the DS was 0.39, the initial pH of wastewater was 9.0 and the adsorption time was 5min, the removal rate of CODcr reached 70.8% and the decoloration rate reached 53.6%. Further, through Zeta potential and scanning electron microscope (SEM), the mechanism of cationic starch flocculant to molasses alcohol wastewater treatment was discussed.Secondly, the cross-linked starch with high degree of cross-linking was prepared via the reaction of corn starch with epichlorohydrin (ECH) using temperature-programmed method. Through single factor tests and Response Surface Methodology (RSM), the optimal reaction conditions of preparing high degree of cross-linking were confirmed as follows: the amount of corn starch was 50g, the dosage of ECH was 0.98mL, sodium hydroxide was 0.75g, the first-programmed reaction temperature was 25℃, the first-programmed reaction time was 5.5h, the second-programmed temperature was 79℃and the second-programmed time was 3h. Then the cross-linking cationic starch was prepared using the cross-linked starch with different degree of cross-linking. The results showed that the DS of the cross-linking cationic starch with different degree of cross-linking was similar, all was about 0.4. Then the self-made cross-linking cationic starch with different degree of cross-linking was taken as flocculant to decolor molasses alcohol wastewater. The results showed that the effect of the degree of cross-linking to the decolorization of molasses alcohol wastewater was little. At the room temperature 28℃, when the amount of cross-linking cationic starch was 4.5g/L, the initial pH was 9.0 and the adsorption time was 7min, the decolorization rate was up to 85.7%.Based on the experiment results: the decolorization rate reached 85.7% when using cross-linking cationic starch to treat molasses alcohol wastewater, and the decolorization rate only reached 53.6% when using cationic starch. So the low-cost cationic etherifying agent CHPTMA was prepared using temperature-programmed method. Under the condition of the high content of CHPTMA, the by-products such as ECH, 1,3-dichloro-propanol wasn't removed, but as cross-linking agent. So the process of removing the by-products could be deleted, and the cost of cationic etherifying agent was lower, correspondingly the cost of cationic starch was lower. Through single factor tests and orthogonal tests, the optimal reaction conditions were obtained as follows: the molar ratio of ECH to trimethylamine hydrochloride(TMAC) was 1.1, pH was 8.0, TMAC concentration was 75%, the first-programmed reaction time was 3h, the first-programmed reaction temperature was 15℃, the second-programmed time was 2h and the second-programmed temperature was 50℃. Then the cationic starch with DS 0.39 and cross-linking cationic starch with DS 0.40 was prepared using the low-cost cationic etherifying agent, and the structure was identified by IR. Finally, the cationic starch with DS 0.39 and cross-linking cationic starch with DS 0.40 was used to treat molasses alcohol wastewater. Under optimal conditions, the removal rate of CODcr reached 81.9% and the decoloration rate reached 79.4% when using cationic starch as flocculant; the removal rate of CODcr reached 90.3% and the decoloration rate reached 86.0% when using cross-linking cationic starch as flocculant.