Treatment of reverse osmosis brine by direct contact membrane distillation: Chemical pretreatment approach

- DCMD with chemical pretreatment(s) is promising for the treatment of RO brine.
- Reduction of permeate flux was mainly caused by CaCO3 and CaSO4 precipitation.
- Na2CO3 + NaOH treatment removed all the carbonic species present in the RO brine.
- BaCl2 treatment permitted to remove the sulfate ions from the RO brine.

Different chemical pretreatment strategies followed by direct contact membrane distillation (DCMD) process were adopted for the processing of reverse osmosis (RO) brine. CPT with Na2CO3 + NaOH allowed scale reduction, removing both permanent calcium hardness and temporary calcium hardness whereas the chemical pretreatment with BaCl2 permitted to remove sulfate ions from RO brine. This last chemical pretreatment was found to be the most efficient pretreatment improving the DCMD performance because of the corresponding highest permeate flux, lowest permeate flux decline and best permeate quality. However, it is relatively an expensive pretreatment not recommended for consumption because of the toxic residual barium. The brine was concentrated up to 37 wt% of salts in water, which is above the limiting salt (NaCl) saturation concentration. Therefore, the volume of discharged RO brine can be reduced considerably facilitating its efficient management.

RO brine crystals fouling on the PTFE layer of the membranes, the normalized DCMD permeate flux (Jn) and the normalized feed concentration (Cn) evolution obtained at different chemical pretreatments.151