BOD5, Iron, Manganese, Sulphates LAB 7 & 8 PDF

Manual LAB 7 and 8: BOD5, iron, manganese, sulphates BOD The biochemical oxygen demand (BOD) is the amount of dissolved oxygen needed by aerobic microorganisms to mineralize organic compounds present in a water sample. This process can be repre...

Manual LAB 7 and 8: BOD5, iron, manganese, sulphates BOD The biochemical oxygen demand (BOD) is the amount of dissolved oxygen needed by aerobic microorganisms to mineralize organic compounds present in a water sample. This process can be represented schematically by the following equation: bacteria, enzymes organic compounds + O2 CO2 + H2O + bacteria The BOD method can be divided into two stages: Stage I: oxidation of simple organic compounds, i.e. proteins, simple sugars, starch oxidation of complex organic compounds, i.e. fats, cellulose, lignin and pectins Stage II: which begins after 6-10 days of incubation : nitrification - oxidation of nitrogen compounds in aerobic conditions by autotrophic bacteria: NH4+ → NO2- → NO3- BOD Method 1) Fill the Winkler bottles with the samples according to the scheme below. 2) Determine the dissolved oxygen concentration using the Winkler method in the samples of set 1 3) Stop the bottles from set 2 (make sure there is no air under the glass stoppers). Leave the set 2 for 7 days for incubation. After this time, determine the concentration of dissolved oxygen using the Winkler method in the samples of set 2. Preparation of dilutions 1) Using a graduated cylinder, measure the specified amount of water according to a given dilution and fill the cylinder with dilution water up to 500 mL. Mix the sample and fill two Winkler bottles with the prepared dilution. Example: Dilution 1:5  taking into account that the total amount of the sample is 500 mL, it can be concluded that it contains: 100 mL of water and 400 mL of dilution water To calculate the amount of water, you need to divide the total amount of the sample (500 mL) by the dilution (for this example it is 5, because the dilution is one to five (1:5))  500 mL/5 = 100 mL 2) In the graduated cylinder leave 250 mL of the sample (or slightly less) and add the dilution water in the same amount. This will result in a dilution that is twice as large. Mix the sample and fill two other Winkler bottles with the prepared dilution.  Manual LAB 7 and 8: BOD5, iron, manganese, sulphates Set 1 Set 2 DW 1:5 1:10* DW 1:5 1:10* measurement of dissolved oxygen concentration incubation (7 days) *the second dilution is twice as large as the first measurement of dissolved oxygen concentration DW (dilution water) contains the following: - phosphate buffer, magnesium sulphate, calcium chloride, and magnesium chloride in appropriate amounts; - microorganisms - it is saturated with oxygen ( 8 mg/L) - has an adjusted pH value of 7.2 Calculations* (𝒄 − 𝒅) ∙ 𝑴 𝟏𝟎𝟎𝟎 𝑩𝑶𝑫𝟕 = [(𝒂 − 𝒃) − ]∙ 𝟏𝟎𝟎𝟎 𝒎 a – oxygen concentration (mg O2/L) in the sample prior to incubation b – oxygen concentration (mg O2/L) in the sample after incubation c – oxygen concentration (mg O2/L) in dilution water prior to incubation d – oxygen concentration (mg O2/L) in dilution water after incubation M – the amount of dilution water (mL) contained in 1 L of the sample m – the amount of water (mL) contained in 1 L of the sample 1000 – conversion factor, mL to L Calculate BOD5 taking into account that: BOD5 = 68% of BODtotal BOD7 = 80% of BODtotal  Manual LAB 7 and 8: BOD5, iron, manganese, sulphates Analytical sheet Dilution 1: ……………….. Total amount of the sample The amount of water The amount of dilution water 500 mL – for the analytical procedure 1000 mL – for the calculations m= M= Dilution 2: ……………….. Total amount of the sample The amount of water The amount of dilution water 500 mL – for the analytical procedure 1000 mL – for the calculations m= M= Dillution 1 Dillution 2 Parameter DW (dilution water) ……………….. ……………….. the amount of sodium thiosulphate used for the sample Set 1 titration prior to incubation oxygen concentration (mg O2/L) in the sample prior to incubation the amount of sodium thiosulphate used for the sample Set 2 titration after incubation oxygen concentration (mg O2/L) in the sample after incubation  Manual LAB 7 and 8: BOD5, iron, manganese, sulphates Iron (Fe) and manganese (Mn) Metals naturally occur in soils, rocks, and minerals. When groundwater comes into contact with these solids, the metals dissolve and are released. At higher concentrations of iron and manganese, the usefulness of water can be seriously impacted. The taste (the metallic taste of the water causing consumer objection)) and odour of the water may deteriorate. There are also favourable conditions for the growth of iron and manganese bacteria resulting in clogging of pipelines. Elevated levels of aluminium in drinking water are likely to contribute to the development of Alzheimer's disease. The degree to which Fe and Mn dissolve in groundwater depends on the amount of oxygen in the water. Iron, for example, can occur in two forms: as Fe2+ and as Fe3+. When the levels of dissolved oxygen in groundwater are greater than 1-2 mg/L, iron occurs as Fe3+, while at lower levels of dissolved oxygen, iron occurs as Fe2+. When groundwater is pumped to the surface, the dissolved iron reacts with the oxygen coming from the atmosphere, changes to Fe3+ (it is oxidized) and forms deposits of rust colored according to the reactions: Fe(HCO3)2 + 2H2O = Fe(OH)2 + 2H2O+ 2CO2 (hydrolysis) 2Fe(OH)2 + ½O2 + H2O = 2Fe(OH)3  (oxidation) Maximum permissible value for drinking water: - iron 200 g/L - manganese 50 g//L - sulphates 250 mg//L Methods* *After each of the reagents has been added to the sample, it should be mixed Iron 1) Using the Nessler cylinder, measure 50 mL of water sample onto the lower meniscus 2) Add 1 mL of hydroxylamine hydrochloride 3) Add 2 mL of acetate buffer 4) Add 2 mL of 1.10 phenanthroline 5) Place the cylinder in the dark for 15 min. 6) Check the iron concentration with the use of the spectrophotometer, wavelength 510 nm Manganese 1) Using the graduated cylinder, measure 100 mL of water sample onto the lower meniscus and pour it into the conical flask 2) Add 2 mL of the special reagent (mixture of HgSO4, HNO3, AgNO3) 3) Add a small spoon of ammonium persulfate 4) Put the conical flask into the heating basket, bring to a boil and cook for 1 min. 5) Cool the sample to room temperature 6) Transfer the sample to a Nessler cylinder and fill with distilled water up to 100 mL 7) Check the manganese concentration with the use of the spectrophotometer, wavelength 525 nm Sulphates 1) Add to the cuvette test: - 5.0 mL of water sample - 1 spoon of ‘A reagent’ 2) Cap the vial and shake it for 2 min. 3) Check the sulphate concentration with the use of the DR3900 spectrophotometer, wavelength 430 nm