Re: Sewage

Phytoplankton represent the plankton made up of plant or plantlike organisms, while the zooplankton are made up by small animals. You will find more about these in a relevant textbook or in any encyclopedia.

Microaerophilic bacteria are a group (rather small, but including some free-living nitrogen fixers) of bacteria that need oxygen to grow. However, unlike aerobic bacteria, they grow only at low oxygen pressures -- lower than that found in air. When the oxygen concentration is to high they produce superoxide free radicals and peroxides in concentrations that are lethal to them. Their main role in sewege is not that they performe any unique transformations or other processes, but rather their occupation of a zone just under the surface. At the surface the oxygen concentration is toohigh for them to survive. At this location normal aerobic bacteria and maybe fungi will dominate instead. Deeper in the sewege anaerobic and facultative anaerobic bacteria thrive. However, in between these zones, where oxygen diffuses in at low rates, the conditions are right for the microaerophiles.

Admin Note: Some definitions may be helpful..

• Aerobe: An organism that requires oxygen to survive.
• Anaerobe: An organism that cannot survive in the presence of oxygen. Many microbes involved in the breakdown of sewage fall under this category.
• Facultative Anaerobes: Organisms that can adjust to live in the presence or absence of oxygen. A well-known example is the mighty microbe Escherichia coli.
• Microaerophilic: As above, an organism requiring oxygen, but only at levels significantly less than found under standard conditions (~21% O₂ in the atmosphere).