Bench scale continuous clariflocculation of saline industrial wastewater contaminated by hydrocarbons

Abstract

In this study the outcomes obtained whit the treatment of clariflocculation applied to industrial wastewater coming from oil tanker of Augusta (Sr) harbour are analyzed. This wastewater is characterized by high salinity and contain recalcitrant pollutants predominantly of hydrocarbon origin. Therefore, the application of a chemical-physical treatment is preferred rather than biological treatment, since the simultaneous effect of salinity and hydrocarbons plays an inhibitory role in biomass growth. In the clariflocculation process, the first phase of coagulation aims at electrical destabilization of pollutants’ particles, whereas the flocculation phase allows destabilized particles to aggregate and form flocs that can be removed from effluent by sedimentation or flotation, depending on physical features of wastewater fed to the system. The novelty of this experimentation consists in the optimization of the continuous treatment of the wastewater whit economic advantages and in terms of flexibility of treatment. Results’ analysis has shown that the process allows high removal efficiency of the main pollutants that have been the object of this study. In particular, the efficiency of removal of SST always stood at values ​​greater than 90%, while the efficiency of removal of TPH was even almost close to 100%. Instead, lower performances were obtained for the removal of the organic substance in terms of COD and TOC. Therefore, in the outlet wastewater the levels of the contaminants were usually lower than law limits to allow the discharge into the receiving water body. Between the different tests carried out, the best was the one in which the slop fed to the system of clariflocculation was previously subjected to a treatment in which the oil was removed. In this case, the residual pollutants have been removed after the final sedimentation phase and the removed sludge also contain most of the aluminium dosed to allow coagulation.