iii) At CF=2 – Experiments run in total recirculation mode:
the trans-membrane pressure was varied from 200 to
800 kPa and the permeate fluxes were measured.
iv) Experiment in Concentration Mode: at this stage, 45 l of
fresh wastewater was added into the feed tank and permeate
was continuously removed at a constant pressure
of 625 kPa until a Concentration Factor of 3.5 was
reached.
v) At CF=3.5 – Experiments run in total recirculation
mode: the trans-membrane pressure was varied from
690 to 900 kPa and the permeate fluxes were measured.
vi) Experiment in Concentration Mode: at this stage, the
permeate was continuously removed at a constant pressure
of 800 kPa until a Concentration Factor of 5 was
reached. The final concentrate volume in the nanofiltration
unit was 19 l.
After effluent nanofiltration the membrane module was
first flushed with water at room temperature and, after that,
washed with a solution of Ultrasil 11 at 1 g/l during 10 min.
and at transmembrane pressure of 400 kPa, with a recirculation
flowrate of 1,200 l/min at 35ºC. The initial hydraulic
permeability of the membrane was completely recovered
after this procedure.