This paper will address an important area in our life that is often taken for granted, the treatment of our waste. In ancient times populations were small and migratory so we did not have to worry about waste treatment. As civilization developed and populations became more concentrated waste became more of an issue. The diseases of cholera, dysentery, typhoid fever, and enterocolitis have all been major problems due to improper treatment of waste. Modern society has come up with some ingenious methods for handling our waste stream. Our modern sanitary septic system is really quite a biological and engineering marvel and has had an important role in keeping the organic matter and the concentrations of bacteria low in our water supply.
We visited the waste water treatment plant last week and we were reminded of the important job the people and the microbes do there. The process has two main parts, the primary and the secondary treatment. The primary treatment is basically a physical process by which the liquid portion of the wastewater is separated by settling and skimming from the solid portion of the waste. At our plant there were two different influent pipes and each one had a separate type of secondary treatment. The first type is a trickle filter where the fluid is sprinkled over a bed of rocks that have a biofilm of organisms growing on them that decay the organic matter in the fluid. The second type of secondary treatment is called an activated sludge process and this is where the organism is used that I what to discuss in this paper.
Physically the process involves an aeration tank and aeration source so an aerobic environment can be maintained for the activated sludge. It also has a clarifier where the return sludge can be recovered and mixed with the sludge from the primary treatment or a small amount returned to the aeration tanks. The biological component of the activated sludge system is composed of a mixture of microorganisms. The majority of the bacteria in the sludge are heterotrophic. They get energy from carbon in the influent wastewater and release energy in the form of carbon dioxide and water. One of the most important species in the microbial mix is Z. ramigera, it is considered to be the classic floc forming organism. It provides the glue to stick together the living, dead, and inert material into the activated sludge floc. Z. ramigera flocs are easily recognized by their “fingers” which seem to exude from the sludge. After the flocs have degraded the organic material in the waste in the aeration tank it is sent to the clarifier to allow the activated sludge to settle to the bottom and the waste water should now be clean enough to be discharged into the receiving stream. Most of the sludge is now disposed of with the primary sludge but some amount goes back to the aeration tank so the organisms can form more flocs.
The extra cellular polymer strands produced in the capsules of the bacteria form the zoogloeal matrix. There are 9 species of Zoogloea based on the composition and structure of the polysaccharides in the strands of the matrix. Z. ramigera is an aerobic Gram negative bacillus found mostly in organically enriched aqueous environments. It is non-spore forming, has polar flagella, and is approximately 1.5 micrometers by 4 micrometers in size. It is stable in a pH of 3-10 and temperatures of -15 to 90 C . The main polysaccharides in its matrix are glucose, galactose and pyruvic acid. It has a matrix that is slightly water soluble, does not precipitate in the presence of salt, and is highly viscous. Since Z. ramigera possesses all of the above attributes it is an ideal organism to lead the way in reducing the biochemical oxygen demand of the waste water by about 85% in an activated sludge system. It is also useful in absorbing, concentrating, and precipitating out metals such as cadmium, copper, and uranium in a waste water stream via an acid treatment.
I should mention here that the solid sludge is taken to a sanitary landfill or after anaerobic digestion is used as fertilizer on fields where plants are not grown for human consumption and this is the final step in the treatment of the Rolla waste stream. I for one am very grateful that we have a highly developed waste water system in our town and throughout our country.
References:
1. http://www.activatedsludge.info/resources/visbulk.asp
2. http://www.college.ucla.edu/webproject/micro7/studentprojects7/Rader/asludge2.htm
3. Dugan, Patrick R. et al. The Genus Zoogloea. The Prokaryotes. Second Edition Chapter 220. pgs. 3952-3962
4. Perry, Jerome J. et al. Microbial Life. Chapter 32. pgs. 795-797*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.
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