The trickling-filter system and the activated-sludge systems in wastewater treatment both require
a. the addition of large amounts of chlorine to kill pathogens.
b. the addition of large amounts of ammonia as nutrients to support decomposers.
c. high levels of oxygen to promote aerobic decomposition.
d. high levels of carbon dioxide to adjust the pH of the water for bacterial action.
Answer: c. high levels of oxygen to promote aerobic decomposition.
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While a pair of objects move closer to each other due to gravity, the force between them
A. decreases. B. increases. C. remains constant. D. is more uncertain.
In a flower, the sticky structure that helps to trap pollen is known as the
A) stamen. B) anther. C) ovary. D) stigma.
The UN's HDI considers development to be a function of three factors: a decent standard of living, access to knowledge, and a long and healthy life
Indicate whether the statement is true or false.
What is the source of most of the dissolved materials found in the ocean?
a. Outgassing b. Convection currents c. Dissolving and weathering of crustal rocks d. Biological activities