25.1 In what forms does nitrogen normally occur in natural waters?

25.2 Discuss the significance of nitrogen analysis in water pollution control.

25.3 Analyses for various forms of nitrogen were made at three points in a stream as follows:

Nitrogen, mg/L



DO, mg/L






Point of waste discharge







5 km downstream







10 km downstream






On the basts of your knowledge of the nitrogen cycle, explain the processes involved in the relative changes in each nitrogen form, as well as the decrease in total nitrogen in moving downstream from point 1 to point 3.

25.4 Would you expect to find the highest concentration of each of the following in raw domestic wastewater or in the effluent from an aerobic biological waste treatment plant? Why? (a) Organic-N; (b) NHrN; (c) NOj-N; (d) N03"-N,

25.5 What biological processes might be used to reduce the total nitrogen content of a wastewater?

25.6 What limit is placed on the nitrogen content of drinking water and why?

25.7 What is NO, and what environmental problems are associated with it?

25.8 What is the general source of N20 in the environment, and what environmental problems can it cause?

25.9 What are the oxidation states of nitrogen, and what environmental problem or problems may be associated with each?

25.10 What environmental problems may be associated with ammonia discharge to a river?

part 2 Water and Wastewater Analysis

25.11 Why might one wish to suppress nitrification in a biological wastewater treatment plant? Is it always a good idea to do this? Why?

25.12 How can advantage be taken of the need to nitrify a wastewater in order to reduce the oxygen demand for treatment?

25.13 Of what significance is ammonia nitrogen in water disinfection?

25.14 What four analytical methods can be used for ammonia nitrogen measurements?

25.15 How may organic nitrogen concentration in a wastewater be determined?

25.16 Describe the chemistry of the colorimetric method for nitrite determination.

25.17 What methods are available for analysis of nitrate nitrogen?

25.18 Describe two procedures for determining total nitrogen in a water sample.

25.19 Determine the total nitrogen concentration in mg/L of a water sample containing 0.25 raM ammonia, 0,02 mM nitrite, 0.75 mM nitrate, and 1.3 mg/L organic nitrogen.

25.20 Determine the total nitrogen concentration in mg/L of a water sample containing 1.3 mg/L ammonia, 0.25 mg/L nitrite, 15.1 mg/L nitrate, and 0.9 mg/L organic nitrogen.

25.21 The total nitrogen concentration of a water sample is found to be 11.2 mg/L. How might the organic nitrogen content be determined without chemical analysis for the organic nitrogen content of the sample? What is the advantage and disadvantage of your method over direct chemical analysis for organic nitrogen?

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