Which alkaline substance typically produces the least amount of sludge when treating an industrial wastewater stream?

The alkaline substance that typically produces the least amount of sludge when treating an industrial wastewater stream is caustic soda. Caustic soda, or sodium hydroxide, is highly effective in neutralizing acids and raising the pH of wastewater while reacting more efficiently with contaminants. Because it is a pure chemical compound, it creates fewer insoluble byproducts compared to other alkalizing agents, which can lead to increased sludge production.

In contrast, lime, while widely used, generates a significant amount of sludge due to the formation of calcium carbonate, which precipitates out of solution. This precipitation can contribute to higher volumes of settled solids. Sodium bicarbonate also produces some sludge, particularly when it reacts with acids in wastewater, as it can form insoluble carbonates. Although sodium bicarbonate is less potent than caustic soda, the neutralization reaction still results in sludge generation.

Although sodium hydroxide is technically the same as caustic soda, the term "caustic soda" generally refers to its application in wastewater treatment. Its efficiency in chemical reaction and minimal generation of precipitates makes it the preferable choice for minimizing sludge production.