• Principle for the determination of 
     Chemical Oxygen Demand(COD)
    • It  is  a  rapidly  measurable parameter for 
     stream and industrial waste studies and 
     control  of  water  treatment  plants.  The 
     method  is  based  on  the  chemical 
     oxidation of material in the presence of a 
     catalyst by Cr O 2-in 50% H SO4.
                    2 7           2
    • The  amount  of  unreacted  Cr O 2is  then 
                                      2  7
     determined  by  titration  with  a  standard 
     Mohr’s salt solution.
    • Ag SO catalyses the oxidation of straight 
        2   4
     chain  aliphatic  compounds,  aromatic 
     hydrocarbons  and  pyridine.  HgSO4ties 
     upCl-as soluble complex and prevents its 
     interference.
              Biochemicaloxygen demand(BOD)
     • The degree of microbially mediated O consumption in 
                                                   2
       water  is  known  as  the  biochemical  oxygen  demand. 
       This parameter is commonly measured the quantity of 
       Outilised by suitable aquatic microorganisms during 5-
        2
       day period.
     • Where D = DO of diluted sample; D = DO of diluted 
                 1                               2
       sample  after  incubation;  B and  B are  DO  of  dilution 
                                      1       2
       water containing seed before and after incubation .f= 
       ratio  of  speed  in  sample  to  seed  in  control  and  P  = 
       decimal fraction of sample used.
                  Total Organic Carbon(TOC)
     It  is  an  instrumental  method  and  superior  than  COD 
     method  and  is  quit  popular.  The  oxidising  agent  is 
     K Cr O and the oxidation is promoted by the free radical 
      2  2  8
        .
     HOGenerated from UV light.
     At  the  end  of  the  oxidation,  CO is  sparged  from  the 
                                          2
     system  and  measured  with  a  gas  chromatographic 
     detector or by absorption in ultrapure water followed by 
     conductivity measurement.
          COD is always higher than BOD
   • BOD (Biological Oxygen Demand) means the amount of oxygen (in 
    mg/l) microorganisms like bacteria need to 'consume' the organic 
    pollutants (sugars, fat, proteins etc.).BODvalue in polluted water is 
    normally  higher  than  the  fresh  water.  Increased  BOD  can  be 
    resulted due to domestic sewage, petroleum residues and organic 
    wastes etc,
   • COD (Chemical Oxygen Demand) is the amount of oxygen required 
    to  degenerate  all  pollution  in  a  chemicalway.In  general  with 
    industrial  waste  that  typically  has  high  inorganic  loads  you  can 
    remove  more  pollution  via  chemical  destruction  than  with  the 
    biological way.
   • As BOD is only a measurement of consumed oxygen by aquatic 
    microorganisms to decompose or oxidize organic matter and COD 
    refers the requirement of dissolved oxygen for both the oxidation of 
    organic and inorganic constituents. COD levels in waste streams are 
    always higher than BOD.