Spectrophotometry, Colour and Turbidity vAim  To distinguish between colour and turbidity.  To know the principles behind the analytical instruments that measure these parameters (Beer-Lamberts Law).  To understand the relevance of these measurements to Environmental Engineering. vReference Sawyer C.N., McCarty P.L., Parkin G.F. Chemistry for Environmental Engineering Outline Importance of Colour Importance of Turbidity Colour Measurement Measurement of Turbidity Spectrophotometry

Colour in Water vWhat is the cause  True Colour (Dissolved Material) –pH linked  Apparent Colour (Suspended Material) vImportance  Aesthetic  THM’s  Industrial Effluent

Colour Measurement vBy Eye  Nessler Tubes  Standard Solution (Potassium chloroplatinate) vVisual Comparison Devices  Nessleriser vBy Spectrophotometer  Light absorbing character vExpress Results in units Hazen  True Colour, Apparent Colour

Spectrophotometry vLight is absorbed by species in solution vTransmittance Transmittance T = I / I 0  Optical Density or Absorbance A = log I 0 / I Sample LAMP Photo multiplier I0I0 I

Spectrophotometry With monochromatic light, following rules apply: vBeer’s Law A = k’c vLambert’s Law A = k’’ l vBeer-Lambert’s Law A = k c l

Spectrophotometry vColorimeter  Filter produces a specific wavelength of light vSpectrophotometer  Prism produces a very specific wavelength of light Filter Sample LAMP Photo multiplier I0I0 I Prism Sample LAMP Photo multiplier I0I0 I

Spectrophotometry vSingle and Dual Beam Spectrophotometer  Wavelengths between nm UV nm Visible vStandard Curve vDirect Measurement  Natural Colour of Water (385nm) vChromophore by Chemical Reaction  numerous Anions, Cations, Organics

Importance of Turbidity vAesthetic vProcess Control  Settled Secondary Effluent –suspended cell growth  Water Supply (Sand Filtration) –Requirement for Coagulation –Pre-Treatment vDisinfection

Lamp Photomultiplier Burner Gas + Sample Light Path Atomic Absorption Spectroscopy (AAS)

Turbidity of Water vDefinition  Turbidity is due to Suspended or Colloidal Particles. vTurbid samples affect light in two ways.  Light may be Absorbed  Light may be scattered Refraction Internal Reflection External Reflection Absorbed

Turbidity - Measurement vTurbidity can be measured by:  Spectrophotometer (Interference / Absorbance)  Jackson Candle Turbidimeter (Interference / Absorbance)  Secchi Disk (Interference / Absorbance)  Nephelometry (Reflected Light) vNephelometry Sample Photo multiplier Light Trap LAMP Lens

Turbidity - Measurement vUnits of Turbidity  Nephelometric Turbidity Units (NTU)  Calibrate with:SiO 2 Suspension (1mg/l) Standard Formazin Suspensions Bead Suspensions in a Gel vPrecautions  Sample Dilution  Air Bubbles, Condensation, Stray Light  Large Suspended Particles

Spectrophotometry, Colour and Turbidity vSummary  Definition and Origins of Colour, Its Measurement, and its Significance in EE.  Definition and Origins of Turbidity, Its Measurement, and its Significance in EE.  The general application of Spectrophotometry in water analysis.