The working principle of this tool is to use the DO meter or probe oxygen electrode consists of a cathode and an anode immersed in an electrolyte solution. DO meter on the instrument, typically using a cathode of silver (Ag) and an anode lead (Pb). Overall, this electrode is coated with a plastic membrane that is semi-permeable to oxygen. The chemical reaction that will occur at the electrodes are:
Cathode: O2 + 2 H2O + 4 ho- 4EA
Anode: Pb + 2 ho- à PbO + H20 + 2e
The flow of the reaction depends on the flow of oxygen at the cathode. Diffusion of oxygen from the sample to the electrode is proportional to the concentration of oxygen terlarut.Sampel used is distilled water or distilled water. Measurement of dissolved oxygen using a DO meter is relatively easier than the titration method. measurements by inserting the tip of the electrode in water samples that have been prepared.
DO meter generally is portable so that measurements can be performed directly in the field. to maintain the accuracy of measurement, every certain period instruments need to be calibrated by comparing the measurement results to the results of the measurement instrument with Winkler titration method to the same water sample. the tools must also be calibrated to temperature and barometric pressure (altitude location) local, tools also need to be set on the temperature and salinity of the water in question at the time of measurement.
BOD (Biochemical Oxygen Demand)
BOD is the amount of oxygen needed by microorganisms in the decomposition of organic materials. so BOD describe a process for the oxidation of organic material by microorganisms that occur in waters. the process of decomposition of organic matter in the water occurs gradually, to achieve 96% organic matter decomposes, it takes ± 20 days. pengamatana standards for BOD taken within 5 days, for allegedly within 5 days of decomposition process has been going on 75% organic matter has decomposed, so it is considered sufficient to provide an overview of BOD value. BOD measurement is also using the Winkler titration method
Tool :
Bottle Winkler
Pipette drops
Pipette volumetric
Erlenmeyer
Buret and the stand
Material :
Water samples
alkali iodide (perekasi Winkler)
concentrated H2SO4
Manganese sulfate solution / MnSO4 48%
Sodium thiosulfate 0,025 N
Indicator amylum 1%
Ways of working :
Filter 100 mL water samples from the mud.
Taken 75 mL sample of water that has been filtered, diluted with distilled water and put into a 100X 2 bottles Winkler.
Kept in the dark (wrapped in paper or plastic carbon black) and a dark place. Dicata water temperature and hours of storage. Its calculated levels of O2 after 5 days later.
To sample also calculated the levels of O2 moment.
Recorded levels.
Calculation:
BOD (mg / L) = (DO momentary – DO5) X dilution