Combination of Activated Carbon with Biological Wastewater Treatment at Full-Scale - Activated Carbon for Water and Wastewater Treatment - page 129

PACT s unit cleans up contaminated surface runoff and meets the stringent
National Pollutant Discharge Elimination System (NPDES) permit in the USA [1].
A full-scale test in which carbon was added to an extended aeration treatment
system at the Sun Oil Refinery in Texas indicated substantial improvement in BOD,
COD, and total suspended solids at even very small carbon dosages (9-24 mg L 1 ).
Carbon dosing also stabilized the effluent quality and led to a clearer effluent; it also
eliminated foam formation. Another field-scale test at the Exxon refinery, for
aeration tank PAC concentrations in excess of 1000mg L 1 , showed significantly
improved effluent quality. It was noted that under such operating conditions the
process stability was improved under shock loading conditions [11].
The wastewater of a refinery plant at a flow rate of 5760 m 3 d 1 , was treated by
PACT in combination with WAR. The system achieved sufficient reduction in
COD, phenols, and sulfides, and met all discharge standards (Table 5.3). The plant
was able to withstand shock loadings of up to 4000mg L 1 COD or 900mg L 1
phenols [8]. The PACT/WAR process produced a high-quality effluent with
minimal residual solids to landfill. Also, no concerns were raised about air
pollution or the escape of toxics, odors, and color to the environment [2].
A full-scale PACT s system treated 280-380m 3 d 1 of a high-strength petro-
chemical industry wastewater emerging from the production of organic acids,
solvents, and aromatics [2]. Preliminary pilot tests showed that PACT decreased
COD from 3600 to 100mg L 1 . In comparison, the effluent from the conventional
activated sludge reactor had a COD of 285mg L 1 , thus exceeding the discharge
limit of 250mg L 1 . The PACT system was selected over conventional biological
treatment both for environmental reasons and cost considerations. At full-scale
PACT the effluent COD was about 135mg L 1 whereas BOD 5 was below 30mg L 1 .
The capital costs of the PACT system were 10% less than those of conventional
biological treatment, primarily because the PACT reactors were more compact and
had a size of about two-thirds that of an activated sludge reactor. Operating costs
were also about 10% less than those of conventional biological treatment despite
the additional expenditure for PAC. The introduction of the PACT provided sig-
nificant savings in man-hours to run the system and in the amount of dewatered
sludge generated (0.5 tons per day with PACT compared to 1.4 tons per day with
activated sludge).

Table 5.3 PACT s system performance for the treatment
of a refinery wastewater (adapted from [8]).

Influent (mg L 1 ) Effluent (mg L 1 ) Parameter

COD 1494 78

BOD 5 718 7

Phenolics 70 0

Sulfides 142 0