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Large blooms of algae result from high nutrient loading in rivers and lakes, for example, as a result of runoff of fertilizers from agricultural fields. When the algae die, they biodegrade and consume oxygen. The amount of oxygen consumed is called the biochemical oxygen demand (BOD). If the level of oxygen dissolved in water becomes too low, fishes become stressed and susceptible to viral or bacterial infections. In severe cases, fish kills result. A simplified empirical formula for algae is C6H15O6N.

a) Write a balanced chemical reaction for the conversion of 1 mole of algal cells to
carbon dioxide, water and ammonia (NH3).

b) Calculate the theoretical BOD of algae (g BOD/g algae).

#### Solution Preview

a) 1C6H15O6N + aO2 <-> bCO2 + cH2O + dNH3
Because the problem statement asks for a balanced reaction for the conversion of 1 mole of
algal cells, the fist coefficient in this reaction is fixed at 1. Therefore, the unknowns to solve for are the moles of O2, CO2, H2O, and NH3, denoted as a, b, c, and d respectively.
By carbon balance: 1*6 = b <-> b = 6
By nitrogen balance: 1*1 = d <-> d = 1
By hydrogen ...

#### Solution Summary

Large blooms of algae result from high nutrient loading. Calculation biochemical oxygen demand (BOD).

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