Removal of model waste-water bacteria by magnetite in water and waste-water treatment processes

Conventional disinfection processes used for water and waste-water treatment such as chlorination, and ozonation produce disinfection by products, some of which have been found to be carcinogenic to living organisms. The use of magnetite as an alternative method of removing pathogenic microorganisms from the water streams was proposed as it does not produce any harmful by products. The removal of three model bacteria Escherichia coli ATCC RTM 25922(TM), Pseudomonas putida ATCC RTM 17453(TM) and Micrococcus luteus ATCC RTM 4698(TM) using magnetite and the mechanism of removal has been studied in this thesis. It was found that the optimal cell : magnetite ratio was 1:50 and could remove bacterial cells as follows: 96.8% for E. coli, 94.8% for P. putida and 99.7% for M luteus. To better understand the removal mechanism the effect of buffers, pH, mixing and contact times were also studied. The addition of buffers reduced the removal efficiency of magnetite by about 10% in most cases but still remains above 90% at a pH of 7.5. Optimum mixing time at 200 RPM was found to be between 10 to 12 minutes. Water and magnetite interaction study indicated that each gram of magnetite releases 1.084 mg/l dissolved oxygen in water. Further the functional groups on the surface of bacteria were also studied to better understand the interaction of magnetite with the bacterial cells. These analyses indicate that magnetite could be efficiently used for disinfection processes in water and waste-water treatment industry.