Which of the following methods is commonly used to purify waste streams?

Electrodialysis is a method commonly used to purify waste streams, particularly those containing dissolved salts and other ions. This technique utilizes an electric field to drive the migration of ions through selective ion-exchange membranes, effectively separating contaminants from the water or solution. It is especially beneficial in applications such as desalination and the treatment of industrial effluents, where reducing salinity or recovering valuable materials from wastewater is essential.

In contrast, excavation involves physically removing contaminated soil or waste but does not treat or purify the waste itself. Chemical fertilization relates to the enhancement of soil nutrient content, which is not directly applicable to the purification of waste streams. Gas flaring is a process used to burn off excess gas, primarily in oil and gas operations, and does not pertain to the purification of waste materials. Therefore, electrodialysis stands out as the correct method for wastewater purification in this context.