Abstract:
The present work aims to assess the feasibility of using an ostensibly low-cost
polypropylene (PP) material for processing municipal wastewater from the University
sewage works. Two different types of hydrophilic membranes were employed, both
being macroscopically homogenous (i.e. isotropic) in their physical nature. These were:
• An extruded polymeric membrane (EPP) containing microscopic glass beads as a
fibrulating agent (0.5 jam pore size), and
• A non-woven felt of microscopic fibres (NWPP) of 1.5, 3 and 5 jam pore size.
The membrane materials were mounted on plate and frame modules and used in a
submerged membrane bioreactor (MBR) run at 0.06 bar, fed continuously with primary
effluent. Membrane performance was assessed in terms of specific flux and rejection,
the latter with respect to indicator bacteria. Overall bioreactor performance was
measured in terms of BOD5 and COD removal and the extent of nitrification. An initial
economic analysis was also undertaken to identify major costs in treating municipal
wastewater with the two configurations of MBR. Analysis of these two areas concluded
that:
• flux decline is most significant in the first few hours of filtration,
• bacterial rejection increases with the formation of the dynamic membrane,
• organics removal is high even when mixed liquor suspended solids are low,
• sludge production is reduced due to long solids retention times and substrate inhibited microorganisms, and
• economics point to submerged MBRs being more cost efficient than side-stream
MBRs due to their lower operating costs.
Only one NWPP membrane (5 jum pore size) could be concluded to be suitable for use
to treat municipal wastewater, and only if disinfection was not required. The other
NWPP membranes where highly susceptible to fouling, therefore producing a permeate
flux unacceptable for commercial treatment processes. The PS membrane showed the
most suitable characteristics for treatment of municipal wastewater in submerged
MBRs.
