Combination of Activated Carbon with Biological Wastewater Treatment at Full-Scale - Activated Carbon for Water and Wastewater Treatment - page 131

downstream of a biofilm reactor. In the PAC reactor, COD went down from about
2000mg L 1 to less then 600mg L 1 , achieving the target. Also, residual BOD 5
values approached insignificant levels, and almost full nitrification took place.
Based on these positive results, the full-scale system was designed for an average
flow rate of 550 m 3 d 1 . The average influent COD concentration to the PAC
system was 2893mg L 1 , whereas the effluent COD from the secondary clarifier
was 1042mg L 1 . The combination of the biofilm reactor with the PACT system
reduced the concentration of organics by 95% on average, provided complete
nitrification, and met the overall treatment requirements.

5.1.1.5
Treatment of Priority Pollutants
An extensive test at DuPont's Chambers Works Plant [8] showed that priority
aromatic pollutants could be more successfully removed with PACT s compared to
activated sludge (Table 5.4). The effluent concentrations of priority pollutants had
to be kept at levels of a few m gL 1 . However, in general, in conventional activated
sludge systems it is very difficult to achieve such low target values. Fortunately,
PAC addition enabled the removal of these compounds to the level required in
discharge standards. The removal of some aromatic compounds exceeded 90%
after PAC addition, although biodegradation efficiencies of these compounds were
much lower in most cases. The off-gas from activated sludge may contain volatile
priority organic chemicals such as chlorobenzenes, toluene, and xylene. PAC
addition eliminated the stripping of these volatiles almost totally, whereas up to
90% of the influent could appear in the off-gas of a conventional system [8]. In
other work, the removal efficiencies for priority pollutants at the Chambers
Works PACT s system were reported to vary in the range of 81-99% for volatiles
(benzene, carbon tetrachloride, chlorobenzene, chloroform, ethylbenzene, methyl
chloride, PCE, toluene, TCE, and so on), 44-99% for base-neutral extractables
(dichlorobenzene, dinitrotoluene, nitrobenzene, and trichlorobenzene), 94-98%
for acid extractables (phenol, 2-chlorophenol, 4-nitrophenol, 2,4-dinitrophenol),
and up to 52% for heavy metals [4].

Table 5.4 PACT s System performance for the treatment of priority pollutants (adapted
from [8]).

PACT s
removal (%)

Parameter Influent concentration,

(

Activated sludge
(AS) removal (%) gL 1 ) l

1,2-Dichlorobenzene 18 90.6 W 99

2,4-Dinitrotoluene 1000 31 99

2,6-Dinitrotoluene 1100 14 95

Nitrobenzene 330 94.5 >99

1,4-Dichlorophenol 19 0 93

2,4-Dinitrophenol 140 39 >99

4-Nitrophenol 1100 25 97