Abstract:
The use of microfiltration and ultrafiltration in waste water treatment is attracting
increasing interest. The problem of membrane fouling and the high costs associated with
the process has limited large scale applications. This study forms part of a project to
optimise the design of a membrane bioreactor.
A pilot plant has been used to assess the performance of three tubular membrane
modules. The wastewater used has been taken from an existing biological reactor to
simulate the conditions found in a membrane bioreactor. Commercially available
membrane modules of different specification have been tested. The study has centred
around the fouling characteristics of the membranes under varying operating conditions.
The flux produced after 24 hours continuous operation has been used to assess the
degree of fouling present. The hydrodynamic conditions have been varied, and an
optimal cross flow velocity range has been identified.
The feed wastewater has been varied, and the specific flux at different MLSS
concentrations recorded. The specific flux shows a decline with increasing MLSS
concentration. The magnitude and rate of this decline is membrane dependant.
The permeate product water shows a reduction of more than 99% for SS, BOD, and
COD over the feed stream under all conditions used. The DOC also shows a reduction
of up to 72%, indicating that the membranes reject a portion of the high molecular
weight molecules present in the feed stream.
The energy consumption has been estimated from the final permeate flux produced
under each set of conditions. The lowest value has been found to be 1.75 kWhm-3, which
was achieved at the lowest cross flow velocity used during the trials. This illustrates the
influence of pressure drop through the system, which is proportional to the flow velocity
squared.
