New WRRF reports on MBR disinfection and ion-exchange

The WateReuse Research Foundation has published reports on: disinfection in satellite water-reuse facilities; and use of ion-exchange in desalination concentrate management.

The project Disinfection Guidelines for Satellite Water Recycling Facilities (WRF-08-07), by principal investigator Joseph G Jacangelo of MWH Americas, sought to characterize membrane bioreactor (MBR) effluent water quality requirements necessary for operation with lower disinfection requirements.

Results from the study demonstrated the ability of the MBR process to produce oxidized, nitrified effluents that have very low concentrations of particles and pathogens. Microbial inactivation studies conducted on effluents from satellite MBR facilities and pilot MBR systems showed that a free available chlorine CT of 30 mg‑min/L and turbidity of ≤ 1.0 were sufficient to achieve a 5‑log removal of seeded male-specific bacteriophage and total coliform bacterial concentrations at or below 2.0 CFU/100 mL.

The report concludes that, in order to employ these low CT values at satellite facilities, implementing a process control strategy that will ensure production of high-quality effluent by the MBR process with respect to particles and ammonia is critical.

Kerry J Howe of the University of New Mexico led the ion-exchange project, Selective Salt Recovery from Reverse Osmosis (RO) Concentrate Using Interstage Ion Exchange (WRF-06-010E), which tested the use of sequential cation and anion exchange between two RO stages.

The study concluded that sequential ion‑exchange had the potential to generate salts from RO concentrate and to increase water recovery from RO systems.

Bench-scale tests showed that ions of interest could be recovered from higher ionic strength solutions using ion-exchange, despite some selectivity decrease. Modeling and regression relationships developed from batch isotherms tests could be used to predict breakthrough curves.

Calcium and magnesium selectivity was too similar for ion-separation by regeneration variation, but gypsum could be recovered by mixing cation and anion regeneration solutions from an optimized system.