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Membrane Filtration Regulations and Determination of Log Removal Value 193
After system stabilization (based on dye flow tests), three filters were used to monitor the
effluent concentration from each system for 80 min. The effluent monitoring filters were all
absolute pore size filters (Nuclepore # 641505 filters) designed to capture all Giardia cysts
and Cryptosporidium oocysts.
The first run of the test facility was on Monday, June 2, 1997. Additional runs were
conducted every other Monday through October 20, and the final run was on Monday,
October 27, 1997. The engineering reports that document the experimental plants, experimental
conditions, challenge testing procedures, results, and recommendations can be found
from the refernces (37–39).
The following are the conclusions drawn from the case studies (37):
1. Both MF and CBUDSF systems produced finished water quality in compliance with existing
regulatory standards for potable water (e.g., consistent effluent turbidities less than 0.1 NTIJ;
complete coliform bacterial kill).
2. Both systems reduced influent BOD 5 and TSS to less than 1 mg/L.
3. The MF system achieved an average reduction of total phosphorus of 68%, resulting in an
average effluent total phosphorus concentration of 0.099 mg/L. The reduction was achieved with
the addition of PAC or PASS polymers as coagulants. Peak concentrations reached 0.41 mg/L.
The use of coagulants increases the frequency of system CIP (clean-in-place caustic cleaning)
from biweekly to weekly. Combined average and peak concentrations without coagulant addition
were 0.412 mg/L and 2.4 mg/L, respectively.
4. The CBUDSF system achieved an average reduction of total phosphorus of 96%, resulting in an
average effluent phosphorus concentration of 0.013 mg/L. The coagulant used to achieve this
reduction was PASS polymer. Combined peak concentrations reached 0.29 mg/L. Coagulant
addition is required for normal operation of this system.
5. There was no reduction in ammonia (typically less than 0.1 mg/L in the pilot influent) nor nitrate
through either tertiary filtering system.
6. The extremely low levels of BOD5, TSS, and particularly phosphorus in the final effluent(s)
dictate extremely sensitive sampling and analytical procedures.
7. Twelve protozoan spike challenge events to both filtering systems were completed. The MF
system average removal for Cryptosporidium oocysts was 6.47 log. The CBIJDSF system
average removal for pathogens was 7.00 log.
8. Oxidants (e.g., sodium hypochlorite) will deteriorate the polypropylene hollow fiber membranes
and cannot be introduced into the MF unit. The filter modules must be cleansed with a caustic
solution as specified in the testing procedure.
9. The chlorination required by the CBIJDSF unit prevents biofilm accumulation and may provide
additional wastewater disinfection due to the detention time afforded within each filter unit.
10. 80 amp of electrical service were supplied to the MF unit, whereas 10 amperes of electrical
service were supplied to the CBUDSF system.
11. To accurately measure the filtrate particulates from the MF and CBUDSF systems, on-line
turbidimeters and particle counters must be employed. Coordination of monitoring equipment
results with visual observations of the process train must be performed by operations staff.
12. The net water production during this pilot study for the MF unit was 90%. The net water
production for the CBUDSF unit was 95%.
13. System downtime during this pilot study for the MF unit was 16 days out of 159 days or 10%. For
the CBUDSF system, downtime was 4 h out of 159 days or 0.1%. During this pilot study, on-site