Turbidity

What is turbidity?
Turbidity is “the decrease in the transparency of a liquid caused by the presence of undissolved
substances” (DIN EN 27027). Thus, clear water has a lower turbidity measurement than muddy
water containing suspended particles, such as bacteria, sediments or sewage.

How is it measured?
In nephelometric turbidity measurement, entering light is scattered and measured at 90° using
a detector. The signals are characteristically non-linear. Thus, samples with very high turbidity,
like untreated wastewater, show a decreasing signal with increasing turbidity. For added security,
these samples are investigated in transmission (attenuation of translucent light) as well as by
classic nephelometry. The combined result is the “NTU ratio”.