Carbon dioxide sewage treatment

These tanks at a water treatment facility are used to generate a mixture of methane and carbon dioxide by anaerobic digestion of sewage. The methane produced provides much of the power needed to run the facility. 

One common step in the treatment of sewage is aeration, a process by which air is pumped through water, destroying the bacteria contained in it and converting them to carbon dioxide, water, and other harmless products. (Rosenfeld Images Ltd. /Photo Researchers, Inc.)... 

Part of the North Branch of the Potomac River runs crystal clear through the scenic Appalachian Mountains, but it is lifeless—a victim of acid drainage from abandoned coal mines. As the river passes a paper mill and a wastewater treatment plant near Westemport, Maryland, the pH rises from an acidic, lethal value of 4.5 to a neutral value of 7.2, at which fish and plants thrive. This happy "accident comes about because calcium carbonate exiting the paper mill equilibrates with massive quantities of carbon dioxide from bacterial respiration at the sewage treatment plant. The resulting soluble bicarbonate neutralizes the acidic river and restores life downstream of the plant.1... 

Important is the conclusion that a significant amount of C02 may not be found in the exhaust gas but rather trapped in the culture liquid in the form of bicarbonate or even carbonate (in alkalophilic cultures). For example, Ponti [327] estimated that up to 25% of total carbon mineralized in sewage sludge treatment was captured as bicarbonate and not released via the gas phase. Disregarding this fact must result in systematically erroneous determinations of respiratory quotient (RQ), carbon dioxide production rate (CPR) and carbon recovery. However, taking all these factors into account allows the determination of the RQ-value, even in mammalian cell cultures, with reasonable accuracy even though bicarbonate and low gas turnover rates hamper the measurements [38]. 

The secondary treatment is also called biological treatment because it uses organisms—natural decomposers and detritus feeders. Basically, an environment is created to enable these organisms to feed on the colloidal and dissolved organic material, and break it down to carbon dioxide arid water via their cell respiration. The sewage water from primary treatment is the food- and water-rich medium. 

Effluents from sewage treatment plants are not allowed to contain residual chlorine in excess of tolerable values as determined by water quality standards. For example, in discharges to trout streams, the residual chlorine should not exceed 0.02 mg/L. Thus, chlorinated effluents should be dechlorinated. Sulfur dioxide, sodium sulfite, sodium metabisullite, and activated carbon have been used for dechlorination. Because sulfur dioxide, sodium sulfite, and sodium metabisulfite contain sulfur, we will call them sulfur dechlorinating agents. Dechlorination is an oxidation-reduction reaction. The chemical reactions involved in dechlorination are discussed next. 

Lee, H. B., Peart, T. E., Bennie, D. T., and Maguire, R. J., Determination of nonylphenol polyethoxylates and their carboxylic acid metabolites in sewage treatment plant sludge by supercritical carbon dioxide extraction, J. Chromatogr. A, 785, 385-394, 1997. 

As far as disposal of materials is concerned, the environmental effects of materials are handled in a similar way to product safety. The environmental fate of chemicals must satisfy certain criteria for their use to be desirable or even legal. For organic materials, one of the most important parameters is the fate of a material in a typical sewage treatment plant. The ease with which sewage bacteria will convert the material to carbon dioxide and water can be measured in laboratory equipment which replicates the first stage of sewage treatment and this... 

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