A more detailed
survey by Zhang and Farahbakhsh (2007), showed that primary
plus secondary treatment can remove between 2 and 3 log units
for total and fecal coliform, somatic coliphage and F-specific
coliphage; primary + secondary + tertiary (chlorination, sand filtration
or rotating biological contactor) treatment allow to remove
between 4 and 5 log units of those pathogen indicators, and the
removal rates can be increased up to 6–7 log units for fecal and
total coliform with the use of membrane bioreactors.