Effect of Activated Carbon on Biological Treatment of Specific Pollutants and Wastewaters: Laboratory- and Pilot-Scale Studies - Activated Carbon for Water and Wastewater Treatment - page 100

mainly due to the removal of nonbiodegradable organics since OUR was com-
parable in PAC-added and control reactors. On the other hand, through adsorption
of toxic compounds, PAC addition also enhanced the biological removal of cyanide
and thiocyanate by autotrophic microorganisms which can utilize cyanide as a
carbon and nitrogen source. With PAC addition, influent cyanide at 40-80mg L 1
and influent thiocyanate at 90-180mg L 1 were reduced to below 4 and 20mg L 1 ,
respectively. The control reactor could achieve less (and insufficient) cyanide
removal (82%) and poor thiocyanate removal. However, the cyanide metabolism
produced ammonia which could not be nitrified at a sludge age of 15 days, even in
PAC-added cases.
Coke oven plant wastewater was simulated by a synthetic mixture containing the
inhibitory chemicals, phenol, thiocyanide, and cyanide at concentrations up to 1400,
270, and 100mg L 1 , respectively. For comparison purposes, PAC was dosed both to
a biological continuous-flow stirred tank reactor (CSTR) and to a Sequencing Batch
Reactor (SBR). Although efficient removal was observed in both, the performance
of SBR was better than that of CSTR. Toxicity reduction amounted to up to 90% in
the SBR, whereas it was limited to about 60% in the CSTR. In the SBR reactor, up
to 93% of COD was removed, corresponding to an effluent COD below 400mg L 1 ,
while the COD in the CSTR effluent was higher than 600mg L 1 [33].
Wastewater from an abondoned toxic waste storage site clean-up was tested for
its treatability by a pilot-scale PACT system [34]. The wastewater contained
chlorinated aliphatic, aromatic, and polyaromatic hydrocarbons, nitrobenzenes,
phenols, oils, solvents, thinners, pesticide production wastes, and so on. Pre-
treatment by wet air oxidation (WAO) aimed to produce biodegradable organics
for subsequent removal in the PACT system. In pretreated and diluted waste-
waters, BOD 5 and COD values were about 9000-10 000 and 17 000-19 000mg L 1 ,
respectively. In the PACT system, BOD 5 decreased to below 1mg L 1 with an
efficiency exceeding 99%, while COD decreased to below 900mg L 1 with effi-
ciencies above 95%. The aim was also to decrease the extractable organic
chlorine (EOCl) to below 0.1mg L 1 . At influent EOCl concentrations as high
as 150mg L 1 , the removal efficiency exceeded 99%. Based on the pilot study
results, the PACT system was selected and designed for full-scale treatment.
The nature of pollutants and the high salinity had an unfavorable effect in
activated sludge treatment of a wastewater produced in an oilfield. However, PAC
addition successfully stabilized the process. The positive effect of PAC was
attributed to the adsorption of pollutants and immobilization of microorganisms
on PAC surface. Immobilization prevented bacteria from washout at high
hydraulic loads. Addition of PAC also improved sludge settling [35].
High-strength wastewater from an acrylonitrile manufacturing wastewater in
which COD and cyanide concentrations were 25 000mg L 1 and 15-20mg L 1 ,
respectively, was treated in a laboratory-scale activated sludge system. PAC addi-
tion raised the COD removal in activated sludge from about 70% to 80%. OUR was
significantly increased in the system whereas the SVI decreased from about 90 to
60 mL g 1 , indicating enhancement of substrate removal and sludge settling,
respectively [36].