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Membrane Filtration Regulations and Determination of Log Removal Value 191
Table 4.15
Cryptosporidium, Giardia, and virus log inactivation values for UV (Source: US EPA)
Log credit Cryptosporidium dose (mj/cm 2 ) Giardia dose (mj/cm 2 ) Virus dose (mj/cm 2 )
0.5 1.6 1.5 39
1.0 2.5 2.1 58
1.5 3.9 3.0 79
2.0 5.8 5.2 100
2.5 8.5 7.7 121
3.0 12 11 143
3.5 15 15 163
4.0 22 22 186
Table 4.16
Chlorine dioxide and ozone disinfection for Giardia inactivation (Source: US EPA)
CT Values (CT99.9) for 99.9% inactivation of Giardia lamblia cysts by chlorine dioxide and ozone a
Degrees ( C) 1 5 10 15 20 25
Chlorine dioxide 63 26 23 19 15 11
Ozone 2.9 1.9 1.4 0.95 0.72 0.48
a These CT values achieve greater than a 99.99% inactivation of viruses. CT values between the indicated pH
values may be determined by linear interpolation. If no interpolation is used, use the CT99.9 value at the lower
temperature for determining CT 99.9 values between indicated temperatures
equivalent. Moreover, the U.S. EPA Region 2 Filtration Avoidance Determination issued in
May of 1997 also requires all WWTPs discharging into NYC’s Catskill and Delaware
watersheds utilize by May 1, 2002 either microfiltration or an approved equivalent.
Accordingly, NYC DEP developed and implemented protocols for a study that compares
the pathogen removal capabilities of microfiltration (MF) and continuous-backwash-upflow,
dual-sand (CBUDS) filtration by operating a pilot facility of each system, side by side, with
the same influent and testing methods, shown in Fig. 4.8. The test units are located at the
Stamford Wastewater Treatment Plant (WWTP), immediately downstream of the secondary
clarifier. This plant treats mostly domestic wastewater. The microfiltration unit is Memtec
America Corporation’s Memcor 6M10C unit. The CBUDS test unit consists of two Parkson
Corporation Dynasand filters operated in series. Both the CBUDS and the microfilter test
units were operated using the manufacturer’s standard operating procedures.
During each run of the pilot facility, the mean concentration in the spike solution tank,
from which the spiking material was pumped into the influent stream, was approximately
1 10 8 units per 100 L for both Giardia cysts and Cryptosporidium oocysts. Approximately
42 L (11 gallons) of this solution was delivered to each effluent stream. Hence, the total
numbers of Giardia cysts and Cryptosporidium oocysts delivered to each unit was approximately
4.2 10 7 .