According to the author, oil separator
devices have no efficiency in removing this oil, due to the formation
of stable emulsions in the wastewater caused by detergents
used in the cleaning steps of vehicles. On the other hand, Hamada
and Miyazaki (2004) and Al-odwani et al. (2006) reported low
concentrations (lower than 25 mg L−1) of oil in automatic vehicles
washing facilities in Japan and Kuwait, respectively. Table 5 shows
that the oil concentration in wastewater herein was quite low, in
average below 10 mg L−1 (emission limit). In this work, wastewater
sampling were carryout downstream of the oil separator (Fig. 1).
As this gravity device is known to separate free and/or dispersed
oil droplets, it could be stated that the detergents used were not
responsible for oil stabilization. Besides, phenol concentration was
quite small (0.02 mgC6H5OH L−1), much lower than the local limit
(0.1 mgC6H5OH L−1).