08/06/2022 to 12/06/2022
What is black water ?
Blackwater is wastewater from bathrooms and toilets which contain fecal matter and urine. It is Also called sewage or brown water. Blackwater contains pathogens which can cause many diseases that must decompose before they can be released safely into the environment.
In this study, blackwater treatment is performed by using different systems. The observation is focused on decrease in Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), TDS during processing.
- The three systems used for blackwater treatment –
- system without bubbler
- System with bubbler
- Flood and drain system
Model plant | Water Hyacinth | Canna indica |
System – 1 | Without bubbler | Without bubbler |
System – 2 | With bubbler | With bubbler |
System – 3 | Flood and drain | Flood and drain |
- The design of system referred from http://vadic.vigyanashram.blog/2022/04/11/treatment-of-black-water-by-bio-beds/
13/06/2022 to 18/06/2022
1st trial for the Black water recycling system –
For the examination of the blackwater system, BOD, COB and TDS of the initial black water was calculated by using following method –
Biological Oxygen Demand (BOD)
- Objectives –
- To estimate the concentration of organic matter in waste water samples (black water).
- To assess the quality of surface waters.
- To understand the characteristics of Dissolved oxygen contained in water and wastewater.
- Theory and Principle –
BOD is measure of amount of oxygen required by organism to complete oxidation of organic matter in waste water sample. The amount of oxygen consumed is directly proportional to amount of oxidisable amount of water in organic matter. It is very important to provide conditions suitable for proliferation of heterotrophs and prevent growth of nitrifying bacteria. This is because under aerobic condition and in presence of sufficient amount of ammonia nitrification occurs where ammonia is converted into nitrate and finally into nitrate. Therefore, to supress the growth of nitrifying bacteria, BOD sample is incubated at low temperature, continuous organic matter can be oxidised at low temperature by aerobic and facultative anaerobic organisms. The micro-organism present in sewage will oxidise organic matter by using dissolved oxygen from diluvent.
The dissolvent oxygen is determined by Whinkeler’s modified alkali method which is a titrimetric method. In this method dissolved oxygen is precipitated by conc. H2SO4 and oxidation at MnSO4 occur under alkaline condition. Precipitated oxygen reacts with specific amount of potassium iodide (KI) and liberated iodine is titrated against 0.1N sodium thiosulphate using starch indicator. From titration BOD value is calculated by using formula,
BOD = (A – B) × N × dilution factor × 1000 / Amount of sample taken for titration
Here,
A = SI – SF
B = BI – BF
N = normality of sodium thiosulphate i.e. 0.125N
1000 = dilution factor.
- Materials required –
- BOD bottle
- Water bottle
- Pipettes
- Measuring cylinders
- BOD Incubator
- Burette and burette stand
- Standard flask
- Reagents –
- Alkali azide solution
- Manganese sulphate reagent
- Con. Sulphuric acid (H2SO4)
- Starch solution
- 0.025N sodium thiosulphate solution
- preparation of reagents –
- MnSO4 reagent –
- MnSO4.H2O – 364 gm
- distilled water – up to 1 lit
- 2% starch indicator –
- starch – 2 gm
- distilled water – 100 ml
- alkali azide solution –
- solution A –
- NaOH – 500 gm
- KI – 150 gm
- Distilled water – up to 1 lit
- solution B –
- sodium azide – 10 gm
- distilled water – 40 ml (mix solution A and B)
- solution A –
- 0.125 N Sodium thiosulphate –
- stock solution-
- sodium thiosulphate – 24.8 gm
- distilled water – up to 1 lit
- working solution –
- stock solution – 125 ml
- distilled water – 1 lit.
- stock solution-
- MnSO4 reagent –
- Procedure –
- Incubation for BOD –
- Distilled water is aerated for 2 hours then this aerated water is used for diluting sewage sample.
- BOD bottles were taken and labelled as Blank Initial (BI), Blank Final (BF), Sample Initial (SI), Sample Final (SF).
- BI and BF bottles were added with distilled water as blank sample and then filled with aerated distilled water.
- SI and SF bottles were added with sewage sample and then filled with aerated distilled water.
- The BF and SF bottles were kept for incubation at 260 C for 5 days.
- The BI and SI bottles were immediately taken for analysis of dissolved oxygen.
- Determination of dissolved oxygen –
- 2 ml of each MnSO4 and alkali azide solution were carefully added in SI and BI bottles. while adding reagents to the bottles pipette must be dipped at least 3/4 to bottles.
- observe for the brown ppt and shake the bottles.
- 2 ml of conc. H2SO4 was added to dissolve the ppt.
- From bottles 50 or 100ml sample was taken and in that 2-3 drops of starch indicator was added and blue colour of solution was observed.
- solution was titrated against 0.125 N sodium thiosulphate till blue colour disappear.
- Same procedure was repeated after the 5 days of incubation of BF and SF bottles.
- Incubation for BOD –

- Observation –
Sample | Burette reading |
Blank initial (BI) | 5 |
Sample initial (SI) | 4 |
Blank final (BF) | 5 |
Sample final (SF) | 2 |
Here,
A = SI – SF
= 4 – 2 = 2
B = BI – BF
= 5 – 5 = 0.
BOD = (A – B) × N × dilution factor × 1000 / Amount of sample taken for titration
= (2 – 0) x 0.125 x 1500 x 1000 / 50
= 750 mg/lit .
- Conclusion – thus, the BOD of black water sample is 750 mg/ lit.
Chemical Oxygen Demand (COD)
- Objective –
- To estimate chemical oxygen demand (COD) of waste water sample.
- to determine the chemical characteristics of waste water.
- Theory and Principle –
COD is an amount of oxygen required for complete oxidation of biologically oxidisable as well as biological non-oxidisable organic matter presence in effluent or sewage by means of chemical agents. COD is based on the fact that all the organic matter with the exception of few chlorides are oxidised to carbon dioxide and water by the action of strong oxidising agent like Potassium dichromate. The amount of utilized oxygen is directly proportional to the amount of organic matter in the sample. oxidation of organic matter is carried out with excess of potassium dichromate in presence of solution of sulfuric acid as an chemical catalyst. Sample is refluxed with known amount of potassium dichromate and remaining potassium dichromate after digestion is titrated against the 0.1N FAS. The amount of oxidisable matter is measured as oxygen equivalence consumed by potassium dichromate for oxidation.
COD = ( A – B) x N x 8 x 1000 / Amount of sample taken
Here,
A = Blank reading
B = Sample reading
N = Normality of FAS ( 0.1N)
8 = Atomic number of oxygen
1000 = Conversion factor ( ml to Lit )
- Material Required –
- COD Flask
- COD reflux unit
- Water Sample
- Pipettes
- Measuring cylinders
- Burette and Burette stand
- Standard flask
- Reagents –
- 0.25 N Potassium dichromate ( K2Cr2O7)
- 0.1 N FAS ( Ferrous ammonium sulphate )
- Ferron indicator
- Sliver sulphate , Mercury sulphate
- conc. Sulfuric acid
- Preparation of Reagents –
- 0.25 N Potassium dichromate –
- K2Cr2O7 – 12. 25 gm
- Distilled water – up to 1 Lit
- 0.1 N Ferrous ammonium sulphate –
- FAS . 6 H2O – 39.2 gm
- Conc. H2SO4 – 20 ml
- Distilled water – up to 1 lit
- Potassium Hydrogen Phosphate solution –
- KHP – 0.425 gm
- Distilled water – up to 1 lit
- Ferroin indicator –
- 1, 10 – Phenolthroline – 1.46 gm
- Ferrous sulphate – 0.695 gm
- Distilled water – up to 1 lit
- 0.25 N Potassium dichromate –
- Procedure –
- For COD, distilled water is taken as blank sample, KHP is taken as standard for COB and 2 samples were taken for COD.
- 0.4 gm. AgSO4 (silver sulphate) was taken in COD tubes.
- All reagents were added as per given table.
Sample | Reagents in COD flask |
Blank sample | 40 ml distilled water + 10 ml K2Cr2O7 + 20 ml H2SO4 |
KHP | 20 ml KHP + 20 ml Distilled water +10 ml K2Cr2O7 + 20 ml H2SO4 |
Grey water sample | 2 ml sample + 38 ml Distilled water + 10 ml K2Cr2O7 + 20 ml H2SO4 |
Black water sample | 2 ml sample + 38 ml Distilled water + 10 ml K2Cr2O7 + 20 ml H2SO4 |
- Sample were refluxed for 2 hours in COD reflux unit.
- after refluxing , flask were removed , cooled and total volume was made 130 ml using cold distilled water.
- 2 – 3 drops of ferroin indicator added in the solution and titrated against 0.1 N FAS.
- Colour change from green hue to red wine was observed and readings were recorded.
- Observation table –
Sample | Readings after titration |
Blank sample | 7 |
KHP | 4 |
Grey water sample | 5 |
Black water sample | 6 |
COD = ( A – B) x N x 8 x 1000 / Amount of sample taken
By using COD formula, COD of waste water was calculated.
- COD of Grey water sample – 900 mg/lit.
- COD of Black water sample – 1800 mg/lit.
- Conclusion – thus, the COD of black water sample is 1800 mg/lit.
Total Dissolved Solids (TDS)
TDS stands for total dissolved solids, and represents the total concentration of dissolved substances in water. Total dissolved solids (TDS) is a measure of the dissolved combined content of all inorganic and organic substances present in a liquid in molecular and ionized , or micro-granular suspended form. TDS concentrations are often reported in parts per million (ppm). TDS is made up of inorganic salts, as well as a small amount of organic matter. Common inorganic salts that can be found in water include calcium, magnesium, potassium and sodium, which are all cations, and carbonates, nitrates, bicarbonates, chlorides and sulfates, which are all anions.
The two principal methods of measuring total dissolved solids are gravimetric analysis and conductivity. Gravimetric methods are the most accurate and involve evaporating the liquid solvent and measuring the mass of residues left. This method is generally the best, although it is time-consuming. If inorganic salts comprise the great majority of TDS, conductivity-based methods are appropriate. Electrical, or specific, conductivity of water is directly related to the concentration of dissolved ionized solids in the water. Ions from the dissolved solids in water create the ability for that water to conduct an electric current, which can be measured using a conventional conductivity meter or TDS meter. TDS concentrations are often reported in parts per million (ppm). 1 ppm indicates 1 mg of dissolved solids per kg of water.
The TDS of black water is calculated by using TDS meter. The TDS of Black water is 775 ppm.
This way, the Initial BOD, COD and TDS of black water was calculated.
- Conclusion –
BOD | COD | TDS |
750 mg/lit | 1800mg/lit | 1266 ppm |
20/06/2022 to 27/06/2022
BOD , COD and TDS after 6 days –
Sample | BOD (mg/lit) | COD (mg/lit) | TDS (ppm) |
Without bubbler (Water hyacinth) | 712.5 | 1620 | 1093 |
Without bubbler ( Canna indica) | 675 | 1710 | 967 |
With bubbler (Water hyacinth) | 525 | 1260 | 690 |
With bubbler ( Canna indica) | 487.5 | 1170 | 548 |
Flood and drain (Water hyacinth) | 300 | 630 | 430 |
Flood and drain (Canna indica) | 337.5 | 810 | 421 |
Conclusion –
We observed that COD, BOD and TDS was decreased in every system. But maximum decrease is found in flood and drain system compared to others system. The Initial COD -1800mg/lit, BOD – 750 mg/lit and TDS – 1266ppm. After 6 days after treatment COD – 810mg/lit, BOD – 337mg/lit, TDS – 421ppm was observed. Inflood and drain system COD, BOD and TDS drops near 50% in 6 days.