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Optimal addition of flocculants for the treatment of municipal wastewater

Apostolou Maria

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Summary

Nowadays, the cost of consuming chemicals and handling large quantities of sludge in chemical wastewater treatment plants is quite high. In addition, coagulation and flocculation processes require high area capacity. A Norwegian Technology AS has provided a new polymer, "IN-ut 338", which aims to simplify the cleaning process and thereby save money. The following work took into account the dosage of the polymer and its rate of mixing, with the aim to give the highest cleaning effect. The dosage of polymer from an economic point of view has also been taken into account. Experimental tests were carried out using a jar testing method but adapted to IN-ut 338. The cleaning result was evaluated based on Suspended Solids (SS) and turbidity, but with emphasis on suspended solids. The wastewater used in the tests was collected from the IVAR North Jæren (SNJ) plant in Stavanger, Norway. A mixing time of 15 seconds was selected. The mixing rate for dosing tests was 500/600 (rpm). The results show that the initial content of suspended solids (SS) in sewage influences the effectiveness of IN-ut 338 dosages. Low IN-ut 338 (≤ 4.5 mg L-1) showed the highest cleaning effect of suspended solids SS) for sewage containing small amounts of suspended solids (SS) - about 50 mg L-1. For sewage containing approximately 100 mg SS L-1with a mixing rate of 600 rpm, the IN - ut 338 5.5 mg L-1 displayed the highest cleaning result, corresponding to 14.4 ± 1.4 mg SS L-1. The optimal turbidity dose was observed in the range of 6.0 to 6.5 mg L-1. The velocity gradient (G value) of 2900 s-1 exhibited the highest cleaning effect for suspended solids (SS) at a dose of IN-ut 338 of 5.5 mg L-1. The G value was applied to both sewage containing approximately 70 mg SS L-1 and to waste containing approximately 190 mg SS L-1 at a rate of 88 ± 3% and 87 ± 1.1%, respectively. The lower dose of IN-ut 338 yielded a content of ≤ 20 mg SS L-1 and therefore was considered sufficient at work at 4 mg L-1. A mixture with a G value of about 2900 s-1 was used.

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