Question 1 Explain the terms \'biochemical oxygen demand\' and \"chemical oxygen

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Question 1 Explain the terms 'biochemical oxygen demand' and "chemical oxygen demand, and bring out in detail their relative significance and importance in wastewater analysis a. Explain why we do not carry out tests for the presence of specific pathogens in water. Discuss the role of 'indicator organisms in water quality testing. b. Discuss, citing examples, the important health hazards from pathogens and toxic substances which may be present in water. c. Marks: 4+4+4 Chemical oxyqen demond Aloo) 0 nts (4A

Explanation / Answer

Biochemical oxygen demand can be defined as the oxygen content required by the bacteria in wastewater to completely biodegrade the biodegradable organic matter present in the sewer. It is an indicator of the strength of the sewage or the wastewater.

Chemical oxygen demand is the oxygen required for oxidation of all the organic matter, by using an active oxidation agent such as potassium dichromate. It is an indicator of the toxicity of the sewage.

2)

Th tests for specific pathogens are not carried because of the differences in their growth rates in different environments; The indicator organism should be easy to identify and measure. So, the E-coli bacteria have been used an indicator in the biological analysis of wastewater. Coliform is not a harmful group, but it has more resistance to adverse condition and can survive in harsh conditions for longer durations. So, if it is possible to minimize the number of coliforms, the harmful species can be assumed to be very less. Pathogenic organisms cause water-borne diseases, but non-pathogenic bacteria such as E.Coli are commonly found inside the human body.

3)

The most common type of health hazards from pathogens includes deadly epidemics such as Cholera. Viral fevers, Encephalitis and other types of pathogens like the Salmonella, Shigella, and Vibrio can cause gastroenteritis bacillary dysentery, typhoid fever, and cholera.

Toxins in the wastewater generally include the Nitrites. They have partially oxidized nitrogen products which are very toxic. They may cause the Impairment of vision, dysentery, Blue baby disease, methaglobanemia and other sicknesses.

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