Separation of Algae on Water Purification

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1.Coagulation of Alage and Its Blocking by AlgaeThe difference of the coagulation effect between alum and PAC of diatom using scanning electron microscope and energy diversive spectrometer are discussed by the strength of bridging action for coagulation. Freezed and dry method under Low Vaccum is useful to observe algae and the floc. In the stationary and endogeny phase of diatom, total organic substances and the ultara-violet rays absorbance substances are produced and its substances react aluminum injected as the coagulant. These are soluble aluminum, not suspended solid. The concentration of soluble aluminum changes the contact time with organic substances. The concentration of soluble aluminum decreses after reaching the piek value at some contact time. The concentration of piek value and the ratio of soluble aluminum concentration to the amount of aluminum injected are the minimum under the optimum dosage of coagulation of algae. The optimum coagulation process is important on eli … More mination of small size of alminum hydroxide.2.Protection of Clogging of Rapid Sand Filter Caused by DiatomThough the filtration efficiency of diatom such as Asterionella is high in case of combined type and large headloss occurs, the efficiency decreases after broken the formation of Asterionella. The ratio L/d, (L ; filter depth, d ; the filter grain size) is useful index to design the rational filter depth. The ratio means the number of thin layr having the depth with filter grain size. By the filtration experiment of diatom, anthracite-sand double layrs filter has high filtration efficiency on high removal rate, applicapability to wide ranges of length of diatom, deposit in thick filter layr and occurrence of small headloss. The headloss of filter decreases one half or third by setting the anthracite layr 10cm in depth, 1.4mm in effective size on sand layr with long filter run and stable water quality of filtrate. Surface washing sytem has high efficiency to thin anthracite layr such 5 to 10 cm in depth on renewing the filter. The experimental result that the 95 % of total deposit amount is depositted within 100 of L/d, ratio filter depth to grain size, under the condition within 50 of d/s, grain size to length of diatom, is applied to practical filter. Less