Minimize the Use of Chemicals in Sea Water Reverse Osmosis: Impact on Scaling & Concentrate Disposal

In the last decade, pressure driven membrane filtration processes; e.g., reverse osmosis (RO); nanofiltration (NF); ultrafiltation (UF) and microfiltration (MF); have undergone steady growth. Drivers for this growth include rapid growth in the desalination market and the removal of various materials to comply with the increasingly strict regulations.

Innovations in membrane manufacturing and process conditions have led to a dramatic decrease in membrane filtration costs. Consequently, this emerging technology is becoming a viable and cost effective alternative to conventional methods generally used in water treatment process. However, membrane scaling, biofouling, and organic fouling still exert a severe limitation on further market expansion.

Problems arising from scaling and fouling are a reduction in water production or increase of operating pressure to maintain the same production level; in other words an increase in the operational cost. Membrane cleaning to remove scaling and fouling results in increased down time, energy and chemical use. In addition, if membrane cleaning is not successful, membranes may have to be replaced. Intensive chemical use in Sea Water Reverse Osmosis plants (SWRO) increases the operational costs in addition to the environmental issues relating to brine disposal with this chemicals.

The goal of this project is to decrease the operational cost of a SWRO plant by eliminating or decreasing chemicals used to minimize scalants, especially antiscalants that inhibit calcium precipitation. A comparison of results will be made between laboratory experiments using synthetic water versus pilot tests using real sea water. Pilot studies will be performed at a later stage to demonstrate differences between laboratory results and those with real sea water. Process modeling will be part our scope based on the safe recoveries determined.

A wide range of recoveries and four types of commercially used antiscalants will be applied on one type of membrane. A limited number of tests will be done on another kind of membrane to ensure that results are not membrane specific. NF shall be used in a later step as pretreatment for the SWRO membrane. Modeling of the process will be the final objective based on our findings.

Recommendations will be based on experimental findings (safe recoveries, chemical doses and ionic strength). The reduction in operational costs will be emphasized.

Key words: Membranes, Reverse Osmosis, Scaling, induction time, chemical