The effect of diethylene glycol on pollution from offshore gas platforms

The role of diethylene glycol (DEG) as a co-solvent for selected organic and inorganic pollutants adsorbed onto the particulate matter in produced formation water (PFW) from offshore gas platforms is thoroughly evaluated. Artificial seawater samples were spiked with certified sediments containing several polycyclic aromatic hydrocarbons (PAH) and metals. Aliquots (1 L) containing no DEG and DEG at 3500 and 5000 mg L1 were kept in static and dynamic modes for 24 h before analysis to allow sufficient partitioning time between solid and liquid phases for the selected analytes. The Italian legislation on this matter sets 3500 mg L1 as the highest concentration for DEG in PFW. In our experiments, concentrations equal to and above the set limit were chosen to enhance any possible co-solvent effect. Real PFWsamples were also analysed, both with and without DEG. The analyses were conducted by using GC-MS for the PAH, and ICP-MS for the metals. A minor co-solvent effect was observed for low-molecular-weight PAH in the artificial seawater in static mode. Among metals, only iron showed an increase in solubility in the presence of DEG, demonstrating the co-solvent effect of DEG. The experiments in dynamic mode revealed no increase in the solubility of any other analytes in the liquid phase compared with static mode.