Publications Details
Publications Details



Author: T. Ramm, M. Vanossi, F. Durante and D. Setti

Year: 2009

Publisher: European Water Resources Association (EWRA)


Increasing competition for limited water resources and continual pressure to reduce costs are huge challenges for the water treatment industry. The same factors are relevant for both municipal and industrial markets and for water and wastewater treatment. While water reuse is the obvious way of addressing the resource issue it places increased focus on producing water of the appropriate quality for reuse using an economically viable process. As a result the membrane industry is working hard to develop products and processes that achieve the
required technical performance at an acceptable price for all sectors. Reverse osmosis (RO) has been used widely as part of a wastewater recycling scheme. The RO will remove most dissolved solids so the water can be recycled into the process or for secondary uses. However, there are some major challenges for RO systems operating on biologically treated wastewater. One challenge is plugging of the brine spacer due to high levels of suspended solids in the feed. Many RO systems today use ultrafiltration (UF) as pretreatment to remove suspended solids. The UF system does an excellent job of providing water with low suspended solids as measured by SDI (silt density index) to feed an RO. However, the UF system requires additional space and does not effectively reduce the amount of dissolved solids such as organics that are fed to an RO system.
The UF system can also be susceptible to plant upsets from a conventional wastewater treatment plant. Instead of separating the biological treatment process and the ultrafiltration step, the latest wastewater treatment plants
combine both processes in a membrane bioreactor (MBR). The membranes are integrated right into the aeration tank of the biological process. Advantages of this process are that a clarifier is no longer needed, and the effluent quality is considerably better, which improves RO performance. Additionally, the MBR process reduces footprint significantly compared to the combination of wastewater treatment followed by membrane filtration. The membrane bioreactor (MBR) process is being deployed around the world to an ever-increasing degree in
a variety of applications. The scale of these applications is also growing. There are a number of local considerations to take into account such as climatic considerations, availability of land and potential for reuse, and MBR presents a viable solution to all of these difficulties. In addition, MBR produces an effluent suitable as a high quality feed water source for reverse osmosis treatment making the combination of the two techniques an attractive proposition. This presentation will describe the benefits of using MBR as pretreatment for RO systems. Data from MBR systems will be used to show how the pretreatment needs of RO are met.