If raw water is pre-chlorinated, what color on the inside walls of filters and the filter media indicates the presence of both iron and manganese?

If raw water is pre-chlorinated, what color on the inside walls of filters and the filter media indicates the presence of both iron and manganese?

• A. Black
• B. Green
• C. Red
• D. Brownish-black

Answer: (D)

When raw water is pre-chlorinated, iron and manganese are oxidized and form solid deposits on the filter media and walls. Iron oxide/hydroxide tends to be reddish-brown, while manganese oxide is dark/black. If both metals are present, their oxidation products mix on the filter surfaces, creating a brownish-black color. This color indicates that both iron and manganese are present and being deposited. The other colors align with different single-contaminant scenarios or other conditions, so brownish-black is the telltale sign of both metals together.

When raw water is pre-chlorinated, iron and manganese are oxidized and form solid deposits on the filter media and walls. Iron oxide/hydroxide tends to be reddish-brown, while manganese oxide is dark/black. If both metals are present, their oxidation products mix on the filter surfaces, creating a brownish-black color. This color indicates that both iron and manganese are present and being deposited. The other colors align with different single-contaminant scenarios or other conditions, so brownish-black is the telltale sign of both metals together.