Investigation of coagulation and microfiltration for Danube water as the first step of make-up water production

A comparison of coagulation with two coagulants, poly-aluminum chloride (PACl) and ferric chloride (FeCl3), followed by microfiltration, was evaluated to obtain a better coagulant for an efficient pretreatment method for make-up water preparation from Danube water for thermal power plants. Efficiency was determined by chloride concentration and retention based on the total suspended solid content of the treated water samples. Results were compared to microfiltration working alone as a chemical-free pretreatment. Addition of PACl resulted in the lowest total suspended solid content (18.0 +/- 1.3 mg/L), slightly lower than obtained for microfiltration alone (19.6 +/- 2.5 mg/L) and significantly lower than for FeCl3 (25.0 +/- 3.3 mg/L). Regarding the retention values, coagulation with PACl followed by microfiltration, microfiltration working alone and coagulation with FeCl3 followed by microfiltration represented retention values of 68%, 66.21%, and 56.89%, respectively. Considering the chloride concentration, it remained constant after microfiltration alone; meanwhile, adding coagulants showed a significant rise, similar to 6.4- and 5.7-times higher than the raw water's value after adding FeCl3 and PACl, respectively. From environmental viewpoint, microfiltration alone is recommended because it can provide a steady flux and low total suspended solid content without additional load of chloride ion which shall be eliminated in the further desalination step.