Abstract:
Membrane clogging is a major obstacle to the
successful operation of the membrane separation process. A
submerged hollow fibre membrane with powdered activated
carbon (PAC) adsorption (adsorption-membrane hybrid
system) was used for the removal of organics from a
synthetic wastewater representative of biologically treated
sewage effluent. PAC usage successfully adsorbs the
majority of the organics, and then the organic laden PAC is
separated by the membrane reducing the direct organic
loading to the membrane. However, membrane clogging
still occurs.
This study involved the development of an
automation system and Supervisory Control and Data
Acquisition (SCADA) system for performing an
investigation and evaluation of three automated declogging
techniques.
The first de-clogging method involved the use of
periodic relaxation, whereby permeate production for 12
minutes was periodically stopped for 3 minutes and the
shear forces created by the aeration system and the absence
of suction pressure during the relaxation period were used
to de-clog the membrane. The second de-clogging method
involved the use of a series of periodic back flush
experiments with varied frequencies and durations toforce
permeate in the opposite direction out through the
membrane pores. The optimal results in terms of declogging
the membrane were achieved using a 15 second
backflush after 15 minutes of permeate production. The
third de-clogging method involved the application of an
understanding of results of the periodic backflush series of
experiments to design an automation system with a new
approach to backflushing where an upper limit of a
transmembrane pressure (TMP) increase each cycle was
used to initiate the backflush. The transmembrane pressure
represents the pressure measured across the membrane and
it is a vital parameter indicating the degree of fouling of the
membrane.
A periodic backflush was found to be significantly
more effective in terms of increasing the total quantity of
wastewater treated than was achieved using periodic
relaxation and was investigated in detail during the study.For the periodic backflush, an optimal frequency and
duration was determined for treatment of wastewater with a
fixed foulant concentration. The new approach to
backflushing using more advances in the control system
incorporating the TMP increase each cycle resulted in a
40% reduction in the number of backwashes required and
was capable of self-optimising operating parameters under
an unsteady foulant concentration of wastewater.
