Characterization and treatment proposals of shipboard slop wastewater contaminated by hydrocarbons

Abstract

Shipboard slop wastewaters are produced by the activity of washing of oil tankers with seawater, and are characterized by high salinity and hydrocarbons. In this context, harbor authorities are forced to respect the international regulation IMO-MARPOL 73/78 and they must treat slop wastewater before discharging to the sea. This study compared data from three stand-alone treatments working with the same real slop wastewater: (1) a chemical treatment of coagulation-flocculation with aluminum sulphate as coagulant and an anionic flocculant (A57), (2) a physical treatment of adsorption on granular activated carbon (GAC), (3) two biological treatments represented by a membrane bioreactor (MBR) and a moving bed biofilm reactor (MB-MBR). GAC treatment registered the highest removal efficiency of total petroleum hydrocarbons (ηTPH) next to 85%, since the activated carbon had excellent adsorption properties towards organic substances. The coagulation-flocculation treatment reported the lowest ηTPH ≈ 57% due to the presence of emulsified hydrocarbons that were not affected by the coagulant and flocculant action, so remaining in liquid phase. ηTPH ≈ 70% obtained with MB-MBR fed with 100% volume of slop, suggested biomass acclimation to salinity and hydrocarbons. Based on the results of each process, three main treatment chains are proposed depending on the hydrocarbons load of the real slop wastewater.