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Abstract
A pilot study was conducted over a period of 18 months at the Point Loma Wastewater
Treatment Plant (PLWWTP) in San Diego, CA to evaluate the operational and water quality
performance of six selected membrane bioreactor (MBR) systems at average and peak
flux operation. Each of these systems was operated at peak flux for 4 h a day for
six consecutive days to assess peak flux performance. Virus seeding studies were also
conducted during peak flux operation to assess the capability of these systems to
reject MS-2 coliphage. When operating at steady state, these MBR systems achieved
an effluent BOD concentration of <2 mg/L and a turbidity of <0.1 NTU. Peak flux for
the MBR systems ranged from 56 to 76 L/m2/h (liters per square meter per hour) with
peaking factors in the range of 1.5-3.2. When switching from average to peak flux
operation, a reversible drop of 22-32% in temperature-corrected permeability was observed
for all submerged MBR systems. The percent drop in permeability increased as MLSS
concentration in the membrane tank increased from 11,100 mg/L to 15,300 mg/L and was
observed to be highest for the system operating at highest MLSS concentration. Such
trends were not observed with an external MBR system. Each MBR system was able to
sustain a 4-h-a-day peak flow for six consecutive days with only moderate membrane
fouling. The membrane fouling was quantified by measuring the drop in temperature-corrected
permeability. This drop ranged from 13 to 33% over six days for different submerged
MBR systems. The MBR systems achieved microbial removal in the range of 5.8-6.9 logs
for total coliform bacteria, >5.5 to >6.0 logs for fecal coliform bacteria and 2.6
to >3.4 logs for indigenous MS-2 coliphages. When operating at peak flux, seeded MS-2
coliphage removal ranged from 1.0 to 4.4 logs, respectively. The higher log removal
values (LRVs) for indigenous MS-2 coliphage among different MBR systems were probably
the result of particle association of indigenous coliphage. Differences in membrane
pore size (0.04-0.2 microm) amongst the MBR systems evaluated did not have a substantial
impact on indigenous MS-2 coliphage removal, but seeded MS-2 coliphage removal varied
among the different MBR systems.