Activated sludge aeration waste heat for membrane evaporation of desalination brine concentrate: a bench scale collaborative study

Desalination processes produce highly concentrated brine effluent which is costly to dispose of for inland desalination facilities. The current study uses membrane evaporation process to reduce brine concentrate 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 the proposed process appear favorable because energy demands can be neglected when using waste heat. Fouling was observed in experiments for brine concentrate solutions 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 concentrate 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.