A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Environment, Resources and Development

Thesis (M.Eng.) - Asian Institute of Technology, 1998

This study was carried out to study the pretreatment process for manganese removal from raw water and assess its effect on membrane fouling. Manganese is considered to cause aesthetic problems such as colored water, turbidity, staining and taste. It has also been found that manganese was major cause of membrane fouling. The study was aimed towards biological pretreatment for manganese removal. The fluidized bed pretreatment reactor containing tubular polypropylene pellets was, therefore, seeded with the slimes considered to contain manganese oxidizing bacteria and no chemical oxidant was added. Laboratory scale dead end microfiltration process was carried out under constant flux of 0.50 mid. Prefiltered tap water augmented with manganese, potassium dihydrogen phosphate, and ammonium chloride was used as feed water. Duration of forty days was required for startup of pretreatment reactor with media and was efficient in removing manganese after the color of media changed to black due to coating of insoluble oxides of manganese. The media was effective in adsorption and oxidation of manganese even without the aid of chemical oxidant. More than 95 percent of manganese was biologically or chemically removed in fluidized bed pretreatment. Trans-membrane pressure increased very slowly in the beginning of the experiment in the membrane filtering pretreated water. Later when the membrane color changed to dark brown, TMP increased at a rapid rate. Resistance exhibited by both membranes filtering water with and without pretreatment was not of difference. Manganese was found to be major cause of membrane fouling, however, the ratio of attached iron and manganese was factor behind membrane resistance. Lower ratio of attached iron and manganese demonstrated higher resistance.