COMPARATIVE EVALUATION OF MBR/RO AND PAC ENHANCED MBR/RO TREATMENT OF REFINERY OILY WASTEWATER

Saudi Aramco operates its facilities in one of the driest countries in the world and values its wastewater as a resource rather than a wastewater treatment responsibility. Saudi Aramco approached Siemens Water Technologies (Siemens) to perform bench/lab scale testing to determine the economics associated with treating a wastewater stream that contains sanitary wastewater combined with the API separator effluent from a refinery. The goal of this testing is to determine what treatment steps are required to obtain an effluent quality such that it could be used as feed to a Reverse Osmosis (RO) unit. This Paper details the results of side-by-side testing of a Siemens Powdered Activated Carbon (PAC) Membrane BioReactor (MBR) unit (PAC Petro™ MBR, Siemens interim name) and a conventional MBR (Petro™ MBR) to determine whether the application of PAC to a conventional MBR reduces the refractory organics to levels low enough to allow the effluent to be fed to an RO system.It was anticipated that applying PAC in combination with an MBR flow scheme as pre treatment to the RO would provide a more reliable, economical and smaller biological and reuse system; one that is economically viable for feed to an RO unit. Work previously performed by Siemens had demonstrated that using PAC with MBR gives better treatment of wastewater than conventional MBR and other bio-treatment processes, such as activated sludge, for treating toxic, higher strength, bio-refractory and/or bio-inhibitory compounds. Data collected from other tests indicated Carbon Oxygen Demand (COD) removal to be about twice that from a conventional MBR, with a reduced probability of membrane fouling. Other references have indicated that the addition of PAC enhances the removal of bio-refractory, inhibitory, and toxic compounds from the wastewater as well as enhancing the removal or mitigation of compounds and materials that could potentially foul or degrade ultra filtration and RO membranes. PAC has also been documented to remove compounds that can inhibit nitrification.Saudi Aramco collected representative oily wastewater samples from one of its facilities in Saudi Arabia and shipped them to Siemens' pilot facility for bench scale testing. Siemens characterized the water and then started two MBR laboratory bench/lab scale test units to conduct the side-by-side testing of the Siemens PAC Petro MBR and a conventional Siemens Petro MBR. Effluent from both units was analyzed and treated by identical brackish water RO units.The test results demonstrated a clear difference in effluent quality between the two MBR systems as well as a difference in the ability of an RO unit to treat the MBR effluents. The PAC Petro MBR effluent was significantly lower in refractory organics and was noticeably clearer in color. While the PAC Petro MBR effluent was effectively treated by an RO unit, the conventional Petro MBR effluent was not able to be treated by an RO because of excessive fouling.