Key Points

1. Biochemical operations use the carbon and nitrogen cycles to remove organic and nitrogenous pollutants from wastewaters.

2. The microorganisms in biochemical operations can be classified in several ways. Among the most important are: the type of electron donor used, the type of electron acceptor employed, their physical growth characteristics. and their function.

3. The microorganisms in acrobic/anoxic suspended growth bioreactors may be divided into five overlapping groups: (1) Hoc-forming organisms, (2) saprophytes. (3) nitrifying bacteria, (4) predators, and (5) nuisance organisms.

4. Attached growth bioreactors have more diverse microbial communities encompassing more trophic levels than suspended growth bioreactors.

5. Methanogenic anaerobic cultures are highly interdependent ecosystems with mans complex interactions between Bacteria and Archaea. Acetic-acid and H- play a central role in those interactions, being products of Bacteria and substrates for Archaea.

6. There are two major groups of methanogens: (1) those that oxidize H: and (2) those that cleave acetic acid. Both are essential to the proper functioning of anaerobic cultures receiving complex substrates.

7. In most situations, biomass growth and substrate utilization are coupled, with the true growth yield, Y, serving as the coupling factor. The yield is the amount of biomass formed per unit of substrate removed. Its value depends on the nature of the substrate, the organism involved, and the growth environment.

8. Heterotrophic bacteria obtain their energy from the oxidation of organic carbon. Hence, chemical oxygen demand (C'OD). which is a measure of available electrons, is a convenient way in which to express the concentration of organic matter in wastewaters. When an organic compound is mineralized, all of the electrons available in it must end up either in the biomass formed or in the terminal electron acceptor. Consequently, COD is also a convenient technique for expressing the concentration of biomass.

Yield values for heterotrophic biomass cover a very broad range, but seldom exceed 0.75 mg biomass COD formed per mg substrate COD removed because of the energy required for synthesis.

10. As a result of maintenance energy needs and decay, death, and lysis, biochemical reactors exhibit two characteristics: (1) the observed yield is less than the true growth yield, and (2) active, viable bacteria make up only a fraction of the "biomass."

11. Soluble microbial product formation is associated with substrate utilization and with biomass decay and lysis. As a consequence, much of the soluble organic matter leaving a biochemical operation is of microbial origin.

12. Hydrolysis reactions are important for the biodégradation of particulate substrates and cellular components released by biomass death and lysis.

13. Ammonilication is the release of ammonia nitrogen as nitrogen containing organic compounds undergo biodégradation.

14. PAOs will only store large amounts of phosphorus as polyphosphate granules when they are cycled between substrate-rich anaerobic and substrate-poor aerobic environments.

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