Comparison of membrane options for water reuse and reclamation

The reuse of effluents for irrigation and indirect potable water uses is rapidly developing as an alternative to seawater desalination. This paper explores two membrane-based options available to treat sewage for water reuse, tertiary filtration (TF) of the effluent from a conventional activated sludge (CAS) process and an integrated membrane bioreactor (MBR). These options are compared from technical, performance and cost points of view using ZeeWeed® immersed membranes. The analysis shows that an integrated MBR is less expensive than the CAS-TF option. The total life cycle costs for the treatment of sewage to a quality suitable for irrigation reuse or for feeding reverse osmosis decrease from 0.40$/m3 to 0.20$/m3 as plant size increases to 75,000 m3/d. It is also shown that the incremental life cycle cost to treat sewage to indirect potable water reuse standards (i.e. by ultrafiltration and reverse osmosis) is only 39% of the cost of seawater desalination.

Two membrane options to reuse water were presented, conventional activated sludge followed by tertiary filtration (CAS-TF) and integrated membrane bioreactor (MBR). Both treatment trains provide equivalent effluent quality from the point of view of suspended solids and Silt Density Index and are suitable to feed a reverse osmosis (RO) polishing step. However, the MBR is superior for the removal of organic contaminants and nutrients (nitrogen and phosphorus) because the membranes work in synergy with the bioreactor.