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Background & Aims of the Study: Industrial wastewater sludges must be disposed in a safe
way because they have hazardous effects on the human and environment. The aim of this
study is to investigate the physicochemical characteristics and disposal options of sludges
from oil-water separator (OWS) and dissolved air flotation (DAF) clarifier of a Refinery
wastewater treatment plant.
Materials & Methods: Sludge samples were collected in grab sampling manner, in 6
month (April-September 2013) in order to be analyzed for their physicochemical
characteristics. Kolmogorov-Smirnov Z, independent t-test, Mann-Whitney U test, one
sample t-test and Wilcoxon signed rank test were used for statistical analysis. Canadian Soil
Quality Guidelines (CSQG) and Florida Department of Environmental Protection Soil
Cleanup Target Levels (FDEPSCTLs) were used to discuss the disposal fate of the
generated sludge.
Results: As, Cd, Cu, Pb and Se were not detected in the studied sludge. As compared with
CSQG, the investigated sludge were polluted for residential/parkland, agricultural,
commercial and industrial applications, because they contained high concentrations of Cr,
Ni and Zn. Also, according to FDEPSCTLs, the studied sludges were not suitable for
residential and non-residential applications due to their high Al and Ni contents. DAF
sludge had a high Zn concentration for residential application, too.
Conclusions: present sludge management in the studied plant needs to be revised because
metals’ concentrations are above the international standards and guidelines.