Integrated membrane operations in desalination processes

Today there are many reverse osmosis (RO) plants in operation all over the world for desalination processes. The operating costs for both seawater and brackish water desalination are already competitive with those of thermal operations. These costs are mainly related to the costs of the pretreatment steps, which for seawater desalination might reach 60% of overall costs. By introducing integrated membrane operations, a possible reduction might be possible with an increase of water quality. For example, cross-flow microfiltration (MF), ultrafiltration (UF) and eventually nanofiltration (NF) units might be introduced in the pretreatment line for purifying and clarifying the feed streams and for reducing bivalent ions concentration. If the removal of dissolved gases (CO2, O-2, etc.) is suggested, the possibility of also introducing membrane contactors before the RO treatment might be considered. Moreover, the recovery factor of the RO process could be enhanced by introducing membrane distillation (MD) units to treat the RO brine. In the present work, integrated membrane operations such as the ones described above are analyzed for a seawater desalination system. Preliminary experimental results will be discussed confirming the possibility of reaching a seawater recovery factor of 87%.