Effect of particle size and suspended sediment concentration on turbidity

ABSTRACT

This study evaluates the effects of particle size and variations of CSS on turbidity readings of three optical-nephelometric sensors using sediment samples collected in the field. Samples were collected in fluviometric station at Turcato basin (19.5 km²), located in the South region of Brazil. The collected material underwent screening and pipetting processes for fractionation in sand and silt grain size. For each diameter were separated fractions with different sediment concentration ranging between 0.01 and 5.00 g.L^-1. The results demonstrate great influence of CSS and particle size on turbidity readings. The increase in turbidity is opposite to particle size and directly related to CSS. Variations in turbidity, expressed in CSS function (sensor sensitivity), are higher for smaller diameters, reaching almost constant values for sand particles. Turbidity readings of the three sensors showed no significant difference in the level of 5% by the Mann-Whitney rank sum test. For a given CSS, the turbidity reading may be different, depending on the granulometric class analyzed. Turbidity recorded by the sensor to the silt-class is equivalent to a sensor response observed for a CSS ten times lower for the sand class.

Keywords:
water quality monitoring; concentration of suspended solid; grain size; optical sensor