NAMS 2002 Workshop - ICOM 2008

Drinking and Wastewater Applications I – 3
Monday July 14, 10:45 AM-11:15 AM, Maui
Impact of Seasonal Water Quality Changes on Low Pressure Membrane
Filtration of an Activated Sludge-Lagoon Effluent.
F. Roddick (Speaker), RMIT University, Melbourne, Australia, felicity.roddick@rmit.edu.au
T. Nguyen, RMIT University, Melbourne, Australia
L. Fan, RMIT University, Melbourne, Australia
J. Harris, RMIT University, Melbourne, Australia
Increasing demands on Melbourne’s water resources due to population growth
and drought have emphasized the need for multiple use of water, including the
treatment and recycling of wastewater. Western Treatment Plant (WTP) treats
approximately 52% of Melbourne’s sewage, a total of approximately 485 million
liters/day, using a sequential activated sludge-lagoon (AS- lagoon) process. WTP
employs two AS-lagoon systems in which sewage is treated by passing through
ponds and an activated sludge plant with anoxic and aeration zones. The
biologically treated effluent then passes through a clarifier and a chain of lagoons
before it is transferred to the head of the road storage pond (HORS). The
recycled water is currently used for various on-site and off-site purposes,
however, due to catchment issues such as industrial waste input and saline
aquifer infiltration, it contains salt which limits its long term use for some
applications, such as agriculture, without additional management practices. Pilotscale
trials, which utilized microfiltration (MF) or ultrafiltration (UF) as a pretreatment
prior to reverse osmosis (RO), demonstrated that the product water
was suitable for various applications including agriculture and domestic use.
Since the effluent from WTP contains algae and algal products from the lagoon
process, as well as some residual products from the AS process, the resultant
membrane fouling and permeate properties may be more problematic and differ
from those arising from separate AS and lagoon processes. As the performance
can vary, and the lagoons are subject to algal blooms over the warmer months,
the aim of this study was to characterize the properties of the AS-lagoon effluent
and to determine their influence on the performance of the MF and UF processes
to determine the impact of seasonal variation. These data will be used as a basis
for the development of a fouling mitigation strategy. The filterability was
measured as specific permeate volume at a final flux rate of 55 L m h- 1 using a
dead-end stirred cell fitted with 0.22 µm PVDF or PES (100 kDa MWCO)
membranes.
The trends for a range of feed parameters over the eighteen month sampling
period were established and their influence on MF and UF filterability statistically
analyzed. During this period, there was a major algal bloom with consequential