Energy usage and carbon dioxide emission saving in desalination by using desalination concentrate and wastes in microalgae production

Abstract

Energy usage and CO2 emission between traditional electrodialysis reversal (EDR) and innovative EDR desalinations were compared. The difference between traditional and innovative EDR desalination depended on which concentrate treatment was employed. Traditional EDR desalination consists of electrodialysis as concentrate treatment, while innovative EDR desalination consists of Dunaliella salina production as concentrate treatment. Microalgae species D. salina and Arthrospira (Spirulina) platensis were cultured in used bottles (3.7 L) as reactors and using desalination concentrate and supernatant from anaerobic digested sludge (SADS) as growth medium and nutrients. D. salina was grown in reactors D1, D2, D3, and D4. Spirulina platensis was in S1, S2, S3, and S4. SADS was supplied to reactors D1, D2, S1, and S2 as nutrient. Bold’s Basal Medium was supplied to reactors D3 and D4 while F2 was supplied to reactors S3 and S4 as nutrient. Conductivity of desalination concentrates used in reactors D1 and D3 was 31.8 and in D2 and D4 25.4 mS/cm, respectively. Conductivity of concentrate in reactors S1 and S3 was 35.9 and in S2 and S4 21.5 mS/cm, respectively. Dry weight concentrations of D. salina grown in reactors D1 and D2 with SADS (1.36–1.49 g/L) were achieved which were more than that with Bold’s Basal Medium (0.84–1.04 g/L) in reactors D3 and D4. Dry weight concentrations of S. platensis with SADS (1.41–1.98 g/L) in reactors S1 and S2 were achieved which were more than that supplied with F2 (0.68–1.20 g/L) in reactors S3 and S4. In those cases where SADS was the nutrient, low conductivity mediums provided the higher microalgae dry weight concentrations. Dry weights of both species achieved by reusing concentrate and SADS in our studies were 1.49 g/L (D. Salina) and 1.98 g/L (S. platensis) that are comparable to that of literature data where sea water and pretreated sea water were used. Both species gain a negative net energy ratio. Energy content of 3.02–4.24 kJ/L is required for a positive net energy ratio in microalgae growth culture. Conductivities of growth mediums from all reactors in which D. salina were grown are less than the conductivity of drinking water quality required for sheep. Net energy ratio of D. salina is less than that of S. platensis. For conservative and reusable drinking water for sheep, D. salina was used as microalgae to treat concentrate in our analyses. Energy usage and CO2 emission saved from innovative integrated desalination were 4–14%.