Membrane Filtration in Drinking and Industrial Water Production

2 3 Initially, reverse osmosis (RO) was considered as an expensive luxury and applied only in arid regions for desalting sea and brackish water. Advances in membrane manufacturing and process conditions have led to a dramatic decline in costs for not only RO but also the other pressure driven membrane filtration processes; nano (NF), ultra and micro-filtration. Consequently, these processes are increasingly being applied for all water sources e.g. sea, ground and surface water in potable water production and in water reuse and recycling to achieve various water treatment goals e.g. removal of salts, pesticides, Giardia and Cryptosporidum , bacteria etc. Today, membrane filtration has emerged as a cost competitive and viable technology and is taking over market share from competing technologies. However, membrane scaling and fouling may exert severe limitations on future growth in membrane filtration. Scaling, occurring only in RO and NF, refers to the deposition of “hard scale” on the membrane due to the solubility of sparingly soluble salts being exceeded. Whereas, fouling refers to the deposition of various material e.g. organics, particulates and occurs in all membrane filtration processes. Particulate fouling (suspended matter, colloids and micro-organisms) is an especially persistent problem. One undesirable consequence of scaling and fouling is a decline in membrane flux (water production) or increased operating pressures to maintain flux with an ensuing increase in energy costs. Presently, no reliable parameters exist to predict and monitor the scaling and particulate fouling potential of feedwater in order to prevent these phenomena. Therefore, pilot plant operation is commonly used prior to designing full scale systems. However, although this method generally provides reasonably good reproducibility, it is time consuming and expensive. At RO pilot plants operating in the Netherlands treating River Rhine Water, barium sulphate scaling (BaS0 4 ) and particulate fouling problems occurred. At one plant despite preventative measures i.e. antiscalant addition, BaS0 4 scaling occurred, while under other operating conditions without antiscalant addition, no scaling occurred despite the high scaling tendency predicted for the concentrate. When scaling occurred several cleanings were required to remove it. Whereas, particulate fouling generally requires cleaning on a regular basis. The goal of this research is to contribute to the understanding of the processes involved in (BaS0 4 ) scaling and particulate fouling in membrane filtration systems, and to develop methods to predict and prevent these phenomena. These methods can be used as tools to determine the efficiency of scaling and particulate fouling prevention techniques, for improvements thereof in the absence of expensive pilot plant studies and ultimately reduce costs. 4