Technology developments in forward osmosis to address water purification

Abstract

Forward osmosis (FO) is a natural process, occurring in the cells of all living things when liquids of differing solute concentrations are separated by a semipermeable membrane at ambient temperatures. FO differs from reverse osmosis (RO) in that natural osmotic pressure, resulting from the difference in solute concentration in the two liquids, is the sole driving force for the transport of water across a membrane. The purpose of this paper is to illustrate the energy/cost of water trade-offs when comparing RO and FO technology for water purification. Trials of the FO system were conducted by a third party consulting firm, Carollo Engineers and the US Navy to monitor energy consumption, with results demonstrating the feasibility of operating an FO plant at one-sixth the electrical energy of current RO systems, i.e. 0.8 kilowatt hours per cubic meter of water. The FO process uses “waste” or low-grade thermal heat to drive the systems energy requirements of <70 mega joules per cubic meter of water. The availability of a low-cost heat source largely dictates the selection of the proposed technology. FO has two claimed advantages over RO, (1) lower energy consumption and (2) lower fouling. In this paper, we will discuss the findings of both in a year-long sea water desalination trial.