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Potable Water Biotechnology, Membrane Filtration and Biofiltration 509
removed more DOC than did nonozonated, chlorinated Filter 8. However, both filters
removed equivalent amounts of THMFP and HAAFP.
The type of backwash disinfectant had an impact on biofiltration performance. Preozonated,
chloraminated Filter 2 developed more biomass and removed more DOC, THMFP, and
HAAFP than did preozonated, chlorinated Filter 1. Filter 2 developed as much biomass and
removed as much DOC and HAAFP as preozonated, NC Filter 3. As in the previous pilotscale
study, the use of anthracite/sand versus sand only as a filter material had no impact on
biological filtration performance. Preozonated, NC Filters 3 and 5 developed equivalent
amounts of biomass and removed almost identical fractions of DOC, THMFP, and
HAAFP. However, the use of exhausted GAC significantly improved biological filtration
performance. Preozonated, NC Filter 4 (GAC) developed more biomass and removed roughly
twice as much DOC, THMFP, and HAAFP than did Filters 3 and 5. All of the preozonated
filters in the current study removed larger DOC fractions than did equivalent filters during the
previous study. This was most likely due to the higher filter influent DOCs.
5.4.1. Impact of Temperature
Three biological filters were acclimated at 5, 20, and 35 C during a 73-day study in order
to investigate biomass development and PM control as a function of temperature (120). For
the first 44 day of the study, the filters were acclimated with ozonated ORW. During days
45–73, the filters were acclimated with an ozonated, isolated solution of NOM. The NOM
was isolated by nanofiltration from a Florida ground water low in particulates and high in
DOC. Prior to ozonation, the isolated NOM solution was diluted to a DOC concentration of
4.2 mg/L with dechlorinated tap water. The temperature in the 5 and 35 C filters was
regulated using water-jacketed columns. The cooling or heating fluid was recirculated from
the columns through constant temperature water baths. The temperature in the 20 C filter was
maintained by the ambient internal building temperature. The tops of the filter media were
sampled for biomass development on a regular basis. The filters were defined to have reached
a biological steady-state when consecutive biomass samples did not vary by more than 20%.
During the last 2 weeks of the study, the filters were sampled intensively for DOC and
HAAFP control. Formation potentials were measured under uniform formation conditions. At
the conclusion of the study, the filters were sacrificed and sampled for biomass development
with respect to depth. Biomass profiles are summarized in Fig. 11.8, and PM control is
summarized in Table 11.4. All filters were operated at 3.6 m/h loading rates. Top of filter
biomass development was more extensive in the 20 and 35 C filters than in the 5 C unit.
However, middle of filter biomass levels were higher at 5 C than at the two higher temperatures.
DOC removal at 5 C was lower than at the two higher temperatures. There were no
significant differences in DOC removals between 20 and 35 C. HAAFP removals at 5 C were
about half the level reported for 20 and 35 C. HAAFP removals did not vary significantly
between 20 and 35 C.
5.4.2. Full-Scale Evaluation of Temperature Effects
A study was performed to assess the impact of temperature on biomass growth and PM
control in eight full-scale drinking water filters (120). Filters in these plants were sampled in