What is the maximum turbidity level that direct filtration can effectively treat?

Direct filtration is a water treatment process designed to remove suspended solids and some other contaminants without the use of a coagulation or sedimentation step. The effectiveness of direct filtration is closely tied to the turbidity levels of the source water being treated. Generally, direct filtration can effectively treat water with a maximum turbidity level of about 25 NTU (Nephelometric Turbidity Units).

At this level, the filtration system can adequately remove the particulates present in the water, ensuring that the treated water meets safety and quality standards. Higher levels of turbidity significantly challenge the direct filtration process, as the filters may become quickly overloaded and unable to maintain the necessary flow rates or water quality. Therefore, the 25 percent turbidity level represents a threshold for effective treatment, which aligns with standard practices in water treatment.

In comparison, options suggesting higher turbidity levels would exceed the typical capacity for effective filtration without additional treatment processes. This is why the correct maximum turbidity level for effective direct filtration is 25 percent.