FIELD AND LABORATORY WORK Laboratory work

Laboratory work (optional) Peter Kelderman UNESCO-IHE Institute for Water Education Online Module Water Quality Assessment 2

3 PHYSICO-CHEMICAL ANALYSIS Conventional, cheap methods (titrations, colorimetry..) Advanced, expensive methods (AAS, GC..)  specialised, central labs Compare (relative) investment and operational costs; labour time (ECU~ US$)

4 PHYSICO-CHEMICAL ANALYSIS Conventional, cheap methods (titrations, colorimetry..) Advanced, expensive methods (AAS, GC..)  specialised, central labs. These instrumentations need good facilities, much manpower, expertise and maintenance, and good quality control. See example of price list (2009) of analyses in an Asian Certified lab: Nutrients: 5-10 US$/analysis Heavy metals: US$/sample (multiple HMs) Pesticides: US$ (per group of pesticides)

5 Certified Water Laboratory Nusantara, Manado, Indonesia Clockwise, starting Electrodes for pH, EC,.. AAS for heavy metals Colorimeter for phosphate, ammonia, nitrate, etc.

6 CONVENTIONAL CHEMICAL ANALYSIS TECHNIQUES Titrations: used for e.g. chloride, Mg 2+, Ca 2+, alkalinity…. Adding known amount of chemical A to unknown amount B  from reaction A  B you can calculate concentration of B. Colorimetry/spectrophotometry: used for phosphate, nitrate, ammonia, iron, etc. By adding specific chemicals you can make coloured solution (e.g. phosphate  blue). Colour intensity is proportional to concentration  measure in spectrophotometer Electrodes: for pH, dissolved oxygen, conductivity, fluoride,.. ; calibration necessary at known values.

7

8 MEASUREMENT OF pH pH can be measured with the help of a glass electrode: Diffusion of H + ions across the glass membrane Difusion rate proportional to pH of solution  redox reaction  electrical current  reading Calibration is essential: e.g. at pH = 4.0; 7.0; 10.0

9 ELECTRICAL CONDUCTIVITY (EC) EC is reciprocal of electrical resistance; it indicates presence of cations (K + ; Na +,Ca 2+…. ) and anions (Cl - ; HCO 3 - ; SO 4 2- …) Unit: μS/cm or mS/m (S=Siemens). Values in most natural waters: μS/cm Measure electrical current in the solution by using electrical circuit with two platinum plates. EC is often used as (fully automated) water quality check for TDS (total dissolved solids), e.g. for drinking water. In agriculture for quality of the irrigation/drainage water.

10 TURBIDITY Indicates “Total suspended solids” (TSS) in water High turbidity in e.g. monsoon period “Turbidimeter”: measures light scattered at 90 0 Turbidity unit: JTU = FTU= NTU: Nephelometric turbidity units. WHO guideline 5 NTU. In some (tropical) rivers during monsoon:1000 NTU!

11 REDOX POTENTIAL (E h ) Connected with “aerobic” vs “anaerobic” conditions of surface/groundwaters Expressed in (milli)Volts. - At low redox potential (e.g. : -200 mV), we can expect presence of “reduced” components: S 2- ; CH 4 ; Fe 2+ ; NH 4 +, … - At high redox potential (e.g.: +500 mV), we can expect presence of “oxidized” components: O 2 ; NO 3 - ; Fe 3+ ; SO Measurement: with E h electrode

12 DISSOLVED OXYGEN Alternative (especially at very low DO): “Winkler titration” Oxygen is measured with oxygen electrode O 2 diffuses through membrane at a rate proportional to [O 2 ]; inside electrode redox reaction  "volts" on meter (calibration needed !) Solubility of dissolved oxygen in fresh water

13 NUTRIENTS NH 3 /NH 4 + NO 3 -, (NO 2 - ) Phosphate (PO 4 3-, HPO 4 2-,..) Analysis: colorimetric or with I.C. (“ion chromatography”; can measure “all” ions); see slides on “Gas chromatography”  Total N and P: by “destruction” in strong, boiling acid and measure as nitrate /phosphate

14 Often very low concentrations --> accurate working; clean glassware, very pure chemicals and distilled water! Also good “Quality Control” is vital ! Absorption wavelength  specific for element Intensity of absorption  concentration MEASUREMENT OF TRACEMETALS WITH ATOMIC ABSORPTION SPECTROMETRY (AAS) AAS :Atom M  M* (“excited state”) light absorption

15 Work with a flame of C to get the metal atoms

ANALYSIS MOSTLY BY GAS CHROMATOGRAPHY Injection mixture of organics in gas stream Separation in a column with stationary medium (adsorbent) Identification by “retention time” or GC-MS Concentration: peak height or area ORGANIC MICROPOLLUTANTS (DDT, PCBS,..)

17

18 MICROBIOLOGICAL INDICATORS Human faeces: Salmonella; Shigella; Escherichia Coli; …; extreme health risks (water-borne diseases) Separate analysis very costly; therefore often E-coli taken as “indicator organism”; E-coli WHO standard: ca. 100/100 mL for recreation water ; 0 (zero) for drinking water In wastewater: E-coli > 10 8 /100 mL; 90-99% reduction in conventional wastewater treatment Analysis by counting colonies on plate in lab, after few days at 37 0 C  MPN: “most probable number”.