Which of the following procedures can be used for measuring residual sulfide concentration?

Using an ORP (Oxidation-Reduction Potential) meter is a suitable method for measuring residual sulfide concentration because sulfides in wastewater can affect redox conditions. An ORP meter can provide insights into the overall oxidation and reduction potentials of a sample, and since sulfide ions are typically reduced species that can lower the ORP, their concentration can influence the readings. By understanding the relationship between ORP values and sulfide concentrations, operators can infer the level of sulfides present in the wastewater.

This method is beneficial in wastewater treatment applications as it allows for real-time monitoring of redox conditions, which is crucial for maintaining optimal treatment processes.

Other methods, while useful in their contexts, do not directly measure residual sulfide concentration in the same comprehensive manner. For instance, filtration provides a way to separate solids from liquids but does not measure concentration levels. pH testing can indicate the acidity or alkalinity of a solution, which indirectly might relate to sulfide conditions, but it does not quantify sulfide levels specifically. Spectrophotometry is a technique that can be used for various analyses, but it requires calibration for specific compounds and may not be as direct as using an ORP meter for sulfides.