Removal of NOM, Nutrients, and Micropollutants in BAC Filtration - Activated Carbon for Water and Wastewater Treatment - page 298

concentrations and an EBCT of 5 min, 80% of perchlorate was removed, whereas
complete removal was possible for EBCT Z 9 min. At an EBCT of 15 min the BAC

gL 1 perchlorate in the influent, and

filtration was robust even in the case of 300 m

gL 1 was not exceeded [111].
Concurrent removal of bromate and perchlorate in BAC filtration is also
addressed. In contrast to bromate removal, perchlorate removal was biological only.
This ion was not removed by reduction on GAC surface or ion exchange [114].
Using bench-scale BAC filters following ozonation, complete bromate and
perchlorate removal was observed when the influent concentrations were in the
range of 10-50

4 m

gL 1 , EBCTs were at 15 and 25 min, and influent DO was
0-2mg L 1 . No external carbon addition was required to achieve this removal. In
pilot-scale treatment, complete removal of 25 and 50

m

gL 1 bromate and perchlorate
was achieved, respectively, without the addition of an external electron donor [114].
The advantages of GAC over nonadsorbing media are also obvious in the case of
perchlorate, particularly under dynamic loading conditions. Chemisorption of oxy-
gen onto the GAC surface can enhance the stability of biological perchlorate reduc-
tion. It was shown that with nonadsorptive glass beads perchlorate reduction was
negatively affected when DO was raised from 1 to 4mg L 1 . In contrast to this, the
BAC reactor was robust to short-term increases in influent DO up to 8mg L 1 since
the surface of GAC chemisorbed a substantial fraction of the oxygen, a competing
electron acceptor, as shown in Figure 9.12. However, long-term exposure to influent
DO concentrations of 8.5mg L 1 led to slow increases in effluent perchlorate and DO
concentrations. Subsequent exposure of the BAC reactor bed to low DO concentra-
tions partially regenerated the capacity of GAC for oxygen chemisorption [18].

m

9.7
Integration of PAC and GAC into Biological Membrane Operations

9.7.1
Effect of PAC on Membrane Bioreactors

In general, microfiltration (MF) and ultrafiltration (UF) processes are the widely
employed membrane processes for production of drinking water. Initially, they
were introduced to provide a high level of particle, turbidity, and microorganism
removal. Currently, they are being involved with other unit processes to provide
removal of inorganic and organic materials [115].
The Membrane Bioreactor (MBR) for drinking water treatment is considered to
be a new technology. These reactors can also be used in conjunction with PAC
adsorption [116, 117]. The benefits of PAC addition to MBR can be summarized as
follows: (i) removal of specific organic micropollutants, (ii) removal of DBP pre-
cursors, (iii) decrease in DOC and SUVA, and (iv) reduction in membrane fouling
and flux decline.
As in the case of wastewater treatment (Chapter 3), compared to the stand-alone
MBR process, PAC has the benefit of relieving the accumulation of organics in the
mixed liquor, particularly the dissolved organics, and improving the removal