Algal alginate: A potential coagulant for drinking water treatment

Due to its gelling abilities, calcium alginate has been investigated in this work as a possible coagulant to be used in turbid water treatment. Sodium salts of commercially available alginic acid with low and high viscosities were used in the study. A standard jar test was conducted in 500 mL of synthetic turbid water samples with different initial turbidities of 150, 80 and 10 NTU. These samples were treated using different doses of calcium (varying between 30 and 200 mg/L) and alginate (varying between 0.001 and 10 mg/L).Results of the study indicated that at especially high turbidity values (150 NTU and 80 NTU) calcium alginate proved to be a very effective coagulant causing turbidity removals generally over 98%. In these samples turbidity values as low as 1 NTU were achieved even at very low doses of alginate (0.02 mg/L). The effectiveness of calcium alginate decreased for the sample with lowest initial turbidity (10 NTU). The use of a high viscosity alginate helped to improve the performance of the process at 10 NTU. In addition, when the mixing regime was modified to increase the rapid mixing period and speed, low final turbidity values close to 1 NTU were achieved.

► We used calcium alginate as a coagulant for the first time in literature.
► We tested the coagulant for three different initial turbidity values.
► We analyzed the turbidity removal efficiencies.
► Calcium alginate acts as a good coagulant particularly for high turbidity in waters.
► Performance can be improved by changing mixing regime in waters of low turbidity.