Environmental Chemistry
Homework Assignment 8 (20 points)
- Most plants assimilate nitrogen as nitrate ion. However, ammonia (NH3) is a popular and economical fertilizer. What essential role do bacteria play when ammonia is used as a fertilizer? Do you think any problems might occur when using ammonia in a waterlogged soil lacking oxygen?
- Of the four classes of microorganisms—algae, fungi, bacteria and virus—which has the least influence on water chemistry? Explain your answer.
- Wastewater containing 8 mg/L O2, 1 x 10-3 M
NO3-, and 1.00 x 10-2 M soluble organic
matter {CH2O}, is stored isolated from the atmosphere in
a container richly seeded with a variety of bacteria. Assume that denitrification
is one of the processes that will occur during storage. After the bacteria
have had a chance to do their work, which of the following statements
will be true? (a) No {CH2O} will remain, (b) some O2
will remain, (c) some NO3- will remain, (d) denitrification
will have consumed more of the organic matter than aerobic respiration,
(e) the composition of the water will remain unchanged. The equation
for dinitrification is:
4 NO3- + 5 {CH2O} + 4 H+ → 2 N2 + 5 CO2 + 7 H2O
- A lake with a cross-sectional
area of 1 km2 and a depth of 50 meters has a euphotic zone
that extends 15 meters below the surface. What is the maximum weight
for the biomass (in grams of carbon) that can be decomposed by aerobic
bacteria in the water column of the lake below the euphotic zone during
the summer when there is no circulation in the upper layer? The bacterial
decomposition reaction is:
{CH2O} + O2 → CO2 + H2O
The solubility of oxygen in pure water saturated with air at 20 °C is 8.9 mg/L; 1 m3 = 1,000 liters.
- Assume that algae need carbon, nitrogen and phosphorus in the molar ratios 106:16:1. What is the limiting nutrient in a lake that contains the following concentrations: total C = 20 mg/L, total N = 0.80 mg/L, and total P = 0.16 mg/L? If it is known the half the phosphorus in the lake originates from the use of phosphate detergents, will banning phosphate builders slow down eutrophication?
ENV 440 Homework