טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentTomita Masahiro
SubjectGreywater Treatment by Electrocoagulation through
Oscillatory Mixing
DepartmentDepartment of Civil and Environmental Engineering
Supervisor Professor Eran Friedler
Full Thesis textFull thesis text - English Version


Abstract

Greywater reuse has gained attention due to the ever-increasing water demand coupled with growing water scarcity. One method for greywater treatment is electrocoagulation (EC). Rotational and hydraulic mixing have been the conventional mixing method for rapid and slow mixing for EC. In this research, mixing in EC will be achieved by a novel wave-like oscillatory mixing. The oscillatory EC device creates sinusoidal motion, mixing the water in an oscillatory manner. The electrodes in this combined treatment method have a dual function as a source of coagulant and as mixing paddles. The aim of the research is to develop and study the novel oscillatory EC for different types of water: synthetic surface water (SSW), synthetic greywater (SGW), and real greywater (RGW). For greywater, conventional radial chemical coagulation was also studied for comparison with the new method. Experiments with SSW revealed the distance between the electrodes should be in the range of 0.8 - 1 cm. The oscillatory EC efficiently removed turbidity from the SSW. For SGW both oscillatory EC and the jar test (representing conventional chemical coagulation) removed pollutants effectively. EC removed 96%, 91%, 34%, 42%, and 2% of the turbidity, TP, COD, DOC, and TN respectively. The jar test's removal was almost the same. In oscillatory EC, floatation by gas babbles formed in the process removed pollutants effectively, and the slow mixing time could be shortened from 30 minutes to 10 minutes, implying smaller volumes of mixing tanks. For RGW, both EC and the jar test removed pollutants effectively as well. EC removed 96%, 47%, 72%, 35%, and 11% of the turbidity, TP, COD, DOC, and TN respectively at pH 8. Also, at the original RGW pH (7.5), EC removed turbidity efficiently. Thus, we can conclude that oscillatory EC is a viable option to treat greywater, requiring less pH adjustment, having lower footprint, less sludge production, no addition of chemical coagulants, and easy operation and maintenance over the conventional chemical coagulation. Further assessment for microbiological removal by EC, the effect of passivation, and study on gas flotation by EC on RGW are recommended.