Membrane and Desalination Technologies - TCE Moodle Website

492 P. Kajitvichyanukul et al.
rDNA were a common structure response to ozone application and operating temperature, but
no response to different ozone application points (69).
Biofiltration with GAC as a media to support biological growth successfully removed both
geosmin and 2-methylisoborneol (MIB), and taste and odor causing compounds in drinking
water (70). In biofiltration, while biomass is breaking down naturally occurring organic
matter, cometabolism of taste and odor compounds, such as geosmin and MIB, also occurs.
MIB removal can be accomplished with biofiltration at varying empty-bed contact times, or
bed depths. An Arizona utility increased removal (up to about 67%) by increasing empty-bed
times and the addition of PAC at 10–20 mg/L. The combination of ozonation and biofiltration
can provide an excellent and low-cost solution for removing high percentages of taste and
odor compounds, while the GAC serves as a backstop against any taste and odor escaping the
plant (70).
The respirometric method was developed and applied for the measurement of biomass
activity in bench-scale drinking water biofilters (65). The results obtained with BRP, indicated
a high sensitivity allowing the quantification of the activity of low amounts of biomass.
The ratio between biomass activity and the amount of viable biomass (phospholipid) at
different filter depths indicated a substantial increase of this ratio with filter depth, where
biofilm thickness is low. The comparison of the filter profiles of biomass activity and
dissolved BOM, expressed as theoretical oxygen demand, showed a high correlation between
these profiles. Consequently, BRP results appear to be good indicators of the BOM removal
capacity of the filter biomass and can potentially be used in certain cases instead of BOM
measurements for the assessment of the BOM removal capacity of drinking water biofilters,
operated under different conditions (65).
4.1.3. Application of Fixed-Film Bioreactor in Nitrate Removal
Fixed film bioreactor is one type of biofilm reactors that is widely used in NO 3 – removal. In
this reactor, bacteria grow on inert packing. In the aerobic process, oxygen is provided by air
sparging. In some cases, GAC is utilized as a media providing benefits for microbial growth
in sorption of contaminants on activated carbon surface.
Soares et al. (71) utilized sand as a media in denitrification of groundwater containing
NO3 at 22.6 mg NO3–N/L using a downflow sand column. In this process sucrose is used as
a substrate. It was reported that complete NO3 – removal was achieved at a C:N ratio of two.
Kappelhof et al. (72) described the application of upflow fixed bed denitrification reactors
using three kinds of support media including expanded schist, anthracite, and sand. The
support media were compared based on their ability to attach biomass, NO 3 – removal
capacity, ease of stripping the biomass, and abrasivity. Sand was found to be the most
preferable support media.
Harremoes et al. (73) and Hoek et al. (74) addressed the issue of clogging of fixed bed
bioreactors. The presence of dissolved nitrogen and oxygen can affect the operation of fixed
bed denitrification reactors. Release of nitrogen bubbles requires special care to avoid gas
entrapment and filter blockage. The presence of oxygen can lead to production of biomass
and can cause clogging of the reactor. To solve the problem, vacuum degassing preceding
biological denitrification is an effective method to control the clogging problem.