טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentRakefet Kovalio
SubjectStudy of Three Systems for Treatment and Reuse of Greywater
for Toilet Flushing
DepartmentDepartment of Civil and Environmental Engineering
Supervisor Full Professor Friedler Eran


Abstract

This research studied examined the technological feasibility of greywater reuse for toilet flushing and the quality of effluent produced from a pilot plant treating light greywater from 7 residential flats. Light greywater (originating from the bath, shower and washbasin) was collected and treated by three parallel treatment systems:

  • Sand Filtration - The system produced effluent that cannot be reused without further treatment: unpleasant odor, CODtotal 130 mg/L, turbidity 30 NTU and faecal coliform 105 CFU/100ml.

  • RBC (Rotating biological contactor) followed by sand filtration - The system produced “excellent-quality” effluent: CODtotal 42 mg/L, turbidity 0.5 NTU and faecal coliforms 102-104 CFU/100 ml.

  • MBR (Membrane Bio-Reactor) - Tubular side stream ultrafiltration membrane. The MBR produced “excellent-quality” effluent: CODtotal 40 mg/L, turbidity 0.22 NTU and faecal coliforms 27 CFU/100 ml (zero in 65% of samples).

Faecal Coliforms (FC) and Heterotrophic Plate Count (HPC) were examined in undisinfected and disinfected effluents after 0.5, 3, 6 hours and one week, which simulates residence times in full scale systems, under normal and exceptional operation. Disinfection prevented regrowth of HPC in short storage time, while on long term some regrowth was detected. No FCs were detected after disinfection.


Both biological treatment systems produced very high quality effluent that well meets the “excellent-quality” category set by the Israeli Ministry of Health regulations (2003). The combination of low organic matter, nutrients and microbial indicators reduces regrowth and fouling potentials in the reuse system, thus ensuring safe reuse of the treated greywater for toilet flushing.