Aeration waste heat for membrane evaporation of desalination brine concentrate

The desalination processes produces highly concentrated brine effluent which is costly to dispose of for inland desalination facilities. The current study uses a membrane evaporation process to reduce brine volumes. Membrane evaporation was evaluated at the bench scale for different brine flow rates, airflow rates and air temperatures, extent of fouling and possible means to control fouling. The evaporation rate was found to increase with airflow rate and air temperature and decrease with brine flow rate. Model predictions, derived based upon literature values for heat and mass transfer correlations, agree well with the measured evaporation rate. The economics of membrane evaporation appears only marginally competitive with deep well injection if only disposal of brine is considered. However, in this application a high quality permeate is produced and comparisons are more favorable if water production costs are considered. Fouling was observed in experiments for brines with and without ferrous iron. Cleaning of the membranes by flushing the fibers with brine at higher flow rates was not able to alleviate fouling. Fouling could be alleviated when the pH of the brine solution was lowered for the durations of the studies conducted. Full evaluation of the process will require longer-term studies and future studies should also consider possible sources of supplemental waste heat to increase the overall amount of water treated.