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1、Bacterial Metabolism in Wastewater Treatment Systems,index,1.2 Decomposition of Organic CarbonCompounds in Natural andManmade Ecosystems,1.1 Introduction,Basic Biology, Mass, and Energy Balance of Aerobic Biopolymer Degradation,1.2.1,Mass and Energy Balance for Aerobic Glucose Respiration and Sewage
2、 Sludge Stabilization,1.2.1.1,1.1 Introduction,Water that has been used by people and is disposed into a receiving water body with altered physical and/or chemical parameters is defined as wastewater. If only the physical parameters of the water were changed, e.g., resulting in an elevated temperatu
3、re after use as a coolant, treatment before final disposal into a surface water may require only cooling close to its initial temperature. If the water, however, has been contaminated with soluble or insoluble organic or inorganic material, a combination of mechanical, chemical, and/or biological pu
4、rification procedures may be required to protect the environment from periodic or permanent pollution or damage. For this reason, legislation in industrialized and in many developing countries has reinforced environmental laws that regulate the maximum allowed residual concentrations of carbon, nitr
5、ogen, and phosphorous compounds in purified wastewater,before it is disposed into a river or into any other receiving water body.In this chapter basic processes for biological treatment of waste or wastewater to eliminate organic and inorganic pollutants are summarized.,Catabolic processes of microo
6、rganisms, algae, yeasts, and lower fungi are the main pathways for total or at least partial mineralization/decomposition of bioorganic and organic compounds in natural or manmade environments. Most of this material is derived directly or indirectly from recent plant or animal biomass. It originates
7、 from carbon dioxide fixation via photosynthesis ( plant biomass), from plants that served as animal feed ( detritus, feces, urine, etc.), or from fossil fuels or biologically or geochemically transformed biomass (peat, coal, oil, natural gas). Only because the mineralization of carbonaceous materia
8、l from decaying plant and animal biomass in nature under anaerobic conditions with a shortage of water was incomplete, did the formation of fossil oil, natural gas, and coal deposits from biomass occur through biological and/or geochemical transformations. The fossil carbon of natural gas, coal, and
9、 oil enters the atmospheric CO2 cycle again as soon as these compounds are incinerated as fuels or used for energy generation in industry or private households.,1.2 Decomposition of Organic Carbon Compounds in Natural and Manmade Ecosystems,Biological degradation of recent biomass and of organic che
10、micals during solid waste or wastewater treatment proceeds either in the presence of molecular oxygen by respiration, under anoxic conditions by denitrification, or under anaerobic conditions by methanogenesis or sulfidogenesis. Respiration of soluble organic compounds or of extracellularly solubili
11、zed biopolymers such as carbohydrates, proteins, fats, or lipids in activated sludge systems leads to the formation of carbon dioxide, water, and a significant amount of surplus sludge. Some ammonia and H2S may be formed during degradation of sulfur-containing amino acids or heterocyclic compounds.R
12、espiration in the denitrification process with chemically bound oxygen supplied in the form of nitrate or nitrite abundantly yields dinitrogen.If anaerobic zones are allowed to form in sludge flocs of an activated sludge system, e.g., by limitation of the oxygen supply, methanogens and sulfate reduc
13、ers may develop in the center of sludge flocs and form traces of methane and hydrogen sulfide, found in the off-gas.,1.2 Decomposition of Organic Carbon Compounds in Natural and Manmade Ecosystems,Under strictly anaerobic conditions, soluble carbon compounds of wastes and wastewater are degraded ste
14、pwise to methane, CO2, NH3, and H2S via a syntrophic interaction of fermentative and acetogenic bacteria with methanogens or sulfate reducers. The complete methanogenic degradation of biopolymers or monomers via hydrolysis/fermentation, acetogenesis, and methanogenesis can proceed only at a low H2 p
15、artial pressure, which is maintained mainly by interspecies hydrogen transfer. Interspecies hydrogen transfer is facilitated when acetogens and hydrogenolytic methanogenic bacteria are arranged in proximity in flocs or in a biofilm within short diffusion distances. The reducing equivalents for carbo
16、n dioxide reduction to methane or sulfate reduction to sulfide are derived from the fermentative metabolism, e.g., of clostridia or Eubacterium sp., from oxidation of fatty acids, or the oxidation of alcohols. Methane and CO2 are the main products in anaerobic environments where sulfate is absent, but sulfide and CO2 are the main products if sulfate is present.,1.2 Decomposition of Organic Carbon Compounds in Natural and Manmade Ecosystems,
