Wastewater treatment in petroleum activities: example of “SEWAGE” unit in the BG Tunisia Hannibal plant

This paper provides a detailed analysis of the sewage system procedure, as well as the occurring problems during the operation of the system and the required corrective actions that should be taken. In the Hannibal gas plant, the used water is exploited from a local deep well drilled in the plant. However, before being used in both of gas process and domestic activities, this water is treated in a specified unit called “Metito Unit” to obtain an over-purified water that can meet with the chemical requirements of the oil/gas process and the health and environment standards. After several steps of the process, the polluted wastewater resulting from several activities within the plant is treated in the “Sewage Unit”. This unit decontaminates wastewater from polluting factors, using the “Extended Aeration Method”. We have shown that in spite of the efficient methods used in the sewage system procedure, several problems can occur during the operating of the system such as hydraulic overloading, high SVI, high Fm ratio, which causes high level of organic pollutants (BOD5 = 42 mg/l), chemical pollution (COD = 85 mg/l), high level of pH 8, chloride (1900 mg/l), and iron (8300 mg/l). We suggest that the quality of the treated wastewater should be improved by the addition of other processes such as constructed wetland process, photo-catalytic oxidation technique which is one of the most efficient methods of wastewater treatment, to produce water quality that is very similar to that of the natural waters.