Numerical and experimental study of floc characteristics induced by fully baffled mixing tank agitated with retreat curved impeller

Abstract

This study examines the impact of mixing methods in enhancing the coagulation-flocculation process. Two types of coagulants: Aluminum Sulfate Hydrate [Al2(SO4)3.16H2O] and Magnesium Chloride [MgCl2] were used. The polymer polyacrylamide (C3H5n) was utilized as a flocculent aid. A fully baffled mixing tank agitated with retreat curve impellers rotates in the range of 60-105 rpm as an increment step and a mixing time of 600 sec. was used in the present study. The present investigation includes two methodologies: the first is based on numerical solutions using MIXSIM 2.0 and ANSYS Fluent, while the second is based on experimental work. The Kaolin particles were utilized to represent the suspension collides in natural raw water. The image analysis technique was used to determine the surface area of producing flocs. The results established that the most appropriate impeller rotational speed for the flocculation process is in the range of 90 and 105 rpm for alum coagulants. The maximum surface area of the floc was found to be 3.252 mm2 produced at 60 rpm with 240 sec. of mixing time and the maximum final floc surface area was 1.91 mm2 at 90 rpm and 600 sec. of mixing time. For magnesium chloride coagulant the max surface area of floc was 1.19 mm2 produced at 75 rpm and 360 sec. of mixing time, the best impeller rotation speed was 75 rpm produced the final surface area of floc which is 0.783 after 600 sec. of the mixing tank. These types of floc are appropriate for the sedimentation process to be followed by the normal procedure of drinking water treatment.