Integration of Ultrafiltration and Reverse Osmosis on purification of brackish waters: optimization trials

Abstract

Ultrafiltration (UF), due to its reliability, robustness and stable quality of the water produced , offers technical advantages over conventional pretreatments such as sand filtration coupled with coagulation/flocculation or activated carbon. In this study, the real case of a prototype designed, commissioned and operated consisting of an advanced Ultrafiltration unit (DOW™ UF) followed by a Reverse Osmosis system (Filmtec ™ Reverse Osmosis elements) is evaluated. The work presented has been obtained wihtin the framework of the UFTEC LIFE+ project financed by the European Union. The prototype, which is located in the Drinking Water Treatment Plant in Sant Joan Despí (Barcelona), treats surface brackish water from the Llobregat River. The raw water has a turbidity ranging between 1--500NTU and Total Suspended Solids (TSS) content around 50-250mg/l. The article discusses the economic optimization of the Ultrafiltration system by experimentally finding which operating conditions enable the lowest operating costs without compromising the overall capacity of the unit and the sustainability of the process. A detailed Design of Experiments has been undertaken in order to assess the impact on the final cost of water of each one of the key operational parameters, such as: operational flux, backwash frequency and sequence, chemical enhanced backwash frequency, sequence and chemicals consumption, etc.. Normalization software tools provided by DOW are used to evaluate the operational data generated by the prototype (Ultrafiltration and Reverse Osmosis). The on-line measurements coupled with the off-line laboratory results demonstrate that the quality of the UF product is not influenced by the quality of the raw water.