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AEROBIC, ANAEROBIC, AND ANOXIC PROCESSES Cited from: kidswebs.katyisd.org BioE 202 Iowa State University http://iqtma.uva.es/instrat/Presentaciones_pdf/Chapter%203Principles%20of%20Biological%20Wastewater%20Treatment%20_% 20Process%20SelectionR.pdf week 5- aerobic, anaerobic, anoxic 1 Biochemical Environment Aerobic Conditions: Oxygen is used as electron acceptor Anoxic Conditions: Nitrate is the electron acceptor Anaerobic Conditions: absence of oxygen and nitrate and organic compounds are converted to biomass, CO2, CH4 and H2S. Organic matter + H2O CH4 + CO2 + NH3 + H2S+ new cell week 5- aerobic, anaerobic, anoxic 2 Cell Energy (Photosynthesis and Respiration) Notes Energy: • Energy for living things comes from food. Originally, the energy in food comes from the sun. week 5- aerobic, anaerobic, anoxic 3 • Organisms that use light energy from the sun to produce food—autotrophs (auto = self) Ex: plants and some microorganisms (some bacteria and protists) week 5- aerobic, anaerobic, anoxic 4 • Organisms that CANNOT use the sun’s energy to make food—heterotrophs Ex: animals and most microorganisms week 5- aerobic, anaerobic, anoxic 5 Cell Energy: • Cells usable source of energy is called ATP • ATP stands for adenosine triphosphate Adenine Ribose 3 Phosphate groups week 5- aerobic, anaerobic, anoxic 6 • ADP stands for adenosine diphosphate Adenine Ribose 2 Phosphate groups week 5- aerobic, anaerobic, anoxic 7 • All energy is stored in the bonds of compounds— breaking the bond releases the energy • When the cell has energy available it can store this energy by adding a phosphate group to ADP, producing ATP week 5- aerobic, anaerobic, anoxic 8 • ATP is converted into ADP by breaking the bond between the second and third phosphate groups and releasing energy for cellular processes. week 5- aerobic, anaerobic, anoxic 9 Photosynthesis: • Photosynthesis is the process by which the energy of sunlight is converted into the energy of glucose week 5- aerobic, anaerobic, anoxic 10 • Photosynthesis occurs in the chloroplasts of plants week 5- aerobic, anaerobic, anoxic 11 • Light absorbing compound is a pigment—pigments absorb some wavelengths of light and reflect others— the color our eyes see is the color that the pigment reflects week 5- aerobic, anaerobic, anoxic 12 • Chlorophyll is the pigment inside the chloroplast the absorbs light for photosynthesis As the chlorophyll in leaves decays in the autumn, the green color fades and is replaced by the oranges and reds of carotenoids. week 5- aerobic, anaerobic, anoxic 13 •General formula for photosynthesis carbon dioxide + water + light 6CO2 + 6H2O + light week 5- aerobic, anaerobic, anoxic : glucose + oxygen C6H12O6 + 6O2 14 Reactants •Diagram Light H2O CO2 NADP+ ADP + P Light Dependent Reaction Calvin Cycle ATP NADPH Chloroplast O2 week 5- aerobic, anaerobic, anoxic Products C6H12O6 Glucose 15 Summary: • Light Dependent Reaction—H2O is broken down and light energy is stored temporarily in inorganic energy carriers, ATP and NADPH • Calvin Cycle—energy is transferred from ATP and NADPH to the organic compound glucose week 5- aerobic, anaerobic, anoxic 16 Cellular Respiration: (2 kinds—Aerobic and Anaerobic) • Cellular respiration is the process by which the energy of glucose is released in the cell to be used for life processes (movement, breathing, blood circulation, etc…) week 5- aerobic, anaerobic, anoxic 17 • Cells require a constant source of energy for life processes but keep only a small amount of ATP on hand. Cells can regenerate ATP as needed by using the energy stored in foods like glucose. • The energy stored in glucose by photosynthesis is released by cellular respiration and repackaged into the energy of ATP. week 5- aerobic, anaerobic, anoxic 18 week 5- aerobic, anaerobic, anoxic 19 • Respiration occurs in ALL cells and can take place either with or without oxygen present. week 5- aerobic, anaerobic, anoxic 20 Aerobic Respiration: requires oxygen • Occurs in the mitochondria of the cell • Total of 36 ATP molecules produced • General formula for aerobic respiration: C6H12O6 + 6O2 6 CO2 + 6H2O + 36 ATP glucose + oxygen carbon dioxide + water + energy Human cells contain a specialized structure – the mitochondrion – that generates energy. week 5- aerobic, anaerobic, anoxic 21 • Diagram Electrons carried in NADH Mitochondria In Cytoplasm Glucose Krebs Cycle Glycolysis 2 2 week 5- aerobic, anaerobic, anoxic Electrons carried in NADH and FADH2 Electron Transport Chain 32 22 Summary: 3 steps: 1st glycolysis 2nd Krebs cycle 3rd Electron Transport Chain (ETC) week 5- aerobic, anaerobic, anoxic 23 Anaerobic Respiration: occurs when no oxygen is available to the cell (2 kinds: Alcoholic and Lactic Acid) • Also called fermentation • Much less ATP produced than in aerobic respiration week 5- aerobic, anaerobic, anoxic 24 •Alcoholic fermentation—occurs in bacteria and yeast Process used in the baking and brewing industry—yeast produces CO2 gas during fermentation to make dough rise and give bread its holes glucose ethyl alcohol + carbon dioxide + 2 ATP week 5- aerobic, anaerobic, anoxic 25 • Lactic acid fermentation—occurs in muscle cells Lactic acid is produced in the muscles during rapid exercise when the body cannot supply enough oxygen to the tissues—causes burning sensation in muscles glucose lactic acid + carbon dioxide + 2 ATP week 5- aerobic, anaerobic, anoxic 26 • First step in anaerobic respiration is also glycolysis Diagram Anaerobic Respiration Cytoplasm C6H12O6 glucose Alcoholic fermentation Bacteria, Yeast 2 ATP glycolysis Lactic acid fermentation Muscle cells 2 ATP Aerobic Respiration 36 ATP Krebs Cycle ETC Mitochondria week 5- aerobic, anaerobic, anoxic 27 Advantage of anaerobic processes • Less energy requirement as no aeration is needed 0.5-0.75 kWh energy is needed for every 1 kg of COD removal by aerobic processes • Energy generation in the form of methane gas 1.16 kWh energy is produced for every 1 kg of COD fermented in anaerobic process • Less biomass (sludge) generation Anaerobic process produces only 20% of sludge compared with aerobic CO2 + H2O process Soluble BOD 1 kg Biodegradabl e COD 1 kg Aerobic process Anaerobic process week 5- aerobic, anaerobic, anoxic 0.5 kg New biomass 0.5 kg CH4 gas > 0.9 kg New biomass < 0.1 kg 28 Advantage of anaerobic processes • Less nutrients (N & P) required Lower biomass synthesis rate also implies less nutrients requirement : 20% of aerobic • Application of higher organic loading rate Organic loading rates of 5-10 times higher than that of aerobic processes are possible • Space saving Higher loading rates require smaller reactor volumes thereby saving on disposal cost • Ability to transform several hazardous solvents including chloroform, trichloroethylene and trichloroethane to an easily degradable form week 5- aerobic, anaerobic, anoxic 29 Comparison between anaerobic and aerobic processes Anaerobic Aerobic Organic loading rate High loading rates:10-40 kg COD/m3-day Low loading rates:0.5-1.5 kg COD/m3-day (for activated sludge process) (for high rate reactors, e.g. AF,UASB, E/FBR) Biomass yield Low biomass yield:0.05-0.15 kg VSS/ kg COD (biomass yield is not constant but depends on types of substrates metabolized) High biomass yield:0.35-0.45 kg VSS/kg COD (biomass yield is fairly constant irrespective of types of substrates metabolized) Specific substrate utilization rate High rate: 0.75-1.5 kg COD/kg VSS-day Low rate: 0.15-0.75 kg COD/kg VSS-day Start-up time Long start-up: 1-2 months for mesophilic : 2-3 months for thermophilic Short start-up: 1-2 weeks week 5- aerobic, anaerobic, anoxic 30 Comparison between anaerobic and aerobic processes Anaerobic Aerobic SRT Longer SRT is essential to retain the slow growing methanogens within the reactor SRT of 4-10 days is enough for the activated sludge process Microbiology Anaerobic processes involve multi-step chemical conversions and a diverse group of microorganisms degrade the organic matter in a sequential order Aerobic process is mainly a onespecies phenomenon, except for nutrient-removal processes Environmental factors The process is highly susceptible to changes in environmental conditions The process is more robust to changing environmental conditions week 5- aerobic, anaerobic, anoxic 31 Anaerobic degradation of organic substances to biogas Proteins, Carbohydrates, Fats Aminoacids, Sugar, Glycerole, Fatty acids Hydrolyses (facultative anaerobic bacteria) Formation of acids (facultative anaerobic bacteria) HPO42NH4+/NH 3 H 2S H2/CO2 Acetic acid Propionic acid Butyric acid Alkoholes H2/CO2 Acetic acid Formation of acetic acid (acetogenic bacteria) Formation of methane (methanogenic bacteria) ~70% CH4, ~30% CO2 (M. Kolb, Fachhochschule Aalen) week 5- aerobic, anaerobic, anoxic 32 Anoxic carbon removal • There are several definitions of what anoxic conditions are. In WWTPs, this often means that O2 is absent and replaced by nitrate or sulfate as electron acceptor. • Nitrate as electron acceptor C10 H19O3N + NO3- + nutrients → C5H7NO2 + CO2 + N2 + … This process is also known as denitrification (N-removal) • Sulfate as electron acceptor C10H19O3N + SO42- + nutrients → C5H7NO2 + CO2 + H2S+ … H2S formation results in bad smells & corrossion week 5- aerobic, anaerobic, anoxic 33 Denitrification Chemistry • • • • Ammonia First Passes Through Anoxic Zone Ammonia is Converted to Nitrate in Aeration Zone Nitrate are Recycled to Anoxic Zone Nitrate are Converted to Nitrogen gas in Anoxic Zone NO3 Converted to N2 NH3 Converted to NO3 N2 Gas RECYCLE Effluent Influent Anoxic Zone (Denitrification) Aeration Zone (Nitrification) week 5- aerobic, anaerobic, anoxic 3 4 34