Removal Of COD Of Potato Starch Wastewater By Using Flocculants

China is the largest potato-producing country in the world, and nearly a third of the world's potatoes are harvested in China and India. In our country, the amount of potatoes as a raw material for industrial processing was 10%, and 70% of which were processed into potato starch. The biggest problem which troubled the potato industry was its pollution. The Chemical Oxygen Demand(COD) of potato starch industry wastewater was more than 30,000mg/L.Flocculation was a common method of wastewater's treatment. The aim of this study was that: finding appropriate flocculants and their optimum conditions of treatment to reduce the COD of potato starch industry wastewater. Firstly, a new method of measuring COD was built. This method included two parts: opening tube digestion and spectrophotometry. The whole process took less than 1h.Secondly, the cationic starch with high degree of substitution (DS) containing quaternary amino group was prepared via the reaction of tragantine with 3-chioro-2- hydroxypropyl-trimethyl ammonium chloride (CHPTMA) using pre-drying dry process.Thirdly, though single factor and orthogonal tests, the optimal reaction conditions of treating potato starch industry wastewater by using quaternary ammonium type cationic starch were confirmed as follows: cationic starch and CaCl2 were mixed in accordance with the mass ratio of 6:1; addition of mixed flocculants was 800 mg/L; initial pH of wastewater was adjusted to 5; stirring time was 7 min; kept sedimentation time more than 40 min. Based on the above conditions, the COD removal of starch wastewater reached 65.8%.Lastly, the effect of microbial flocculants was researched through single factor tests. Bacillus pumilus was chosen as a kind of flocculant. The experiment results demonstrated that flocculation performance of supernatant and fermented liquid were much better than bacterial suspension. It proves that flocculating substance was secreted to extracellular medium. When CaCl2 dosage was 0.6 mg/L, the COD removal of starch wastewater reached 63.6%. The best pH of water sample was 5, and in this condition the COD removal reached 47.7%. The best culture time was 16h and optimal addition of microbial flocculants was 5mL/L.