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II: STOICHIOMETRY NITROGEN IN ENERGY METABOLISM AND CELL SYNTHESIS AMMONIA OXIDATION IN WASTEWATER TREATMENT All terms in stoichiometric relations expressed in units of nitrogen (N, MW = 14 g/mole) Oxidation of ammonium-nitrogen (NH4-N) Bacteria: autotrophs (chemolithotrophs) which use reduced nitrogen species: ammonia oxidizing bacteria (AOB) use ammonia, NH3/NH4+ (oxidation state -3) and nitrite oxidizing bacteria (NOB) use nitrite, NO2- (oxidation state +3) as electron donors. Product of AOB metabolism is nitrite; product of NOB metabolism is nitrate (NO3-). Generally, but not always, oxygen is the electron acceptor. Chemolithotrophs fix CO2 for cell compound synthesis. AOB (common genera: Nitrosomonas, Nitrosococcus, Nitrosolobus) Molar stoichiometry for oxidation (no synthesis uptake): NH4+ + 1.5O2 NO2- + 2H+ + H2O (Microbiologists think that unionized ammonia, NH3, is the actual substrate) NOB (common genera: Nitrobacter, Nitrospira, Nitrospina) Molar stoichiometry for oxidation (no synthesis uptake) NO2- + 0.5O2 NO3Usually AOB and NOB grow in proximity since nitrite intermediate is consumed by NOB. Nitrite is fairly unstable and accumulation in treatment processes (or natural environments) is evidence of inhibition or process upset caused by oxygen deficiency, toxicity or other conditions. High concentrations of both ammonia and nitrite have been reported to inhibit AOB and NOB. Overall molar stoichiometry for complete nitrification: NH4+ + 2O2 NO3- + 2H+ + H2O Mass stoichiometry (NH4+ is reference compound) 1.00NH4+ + 3.555O2 3.444NO3- + 0.111H+ + 1.00H2O = 1.00 g 2 = a2MW2/MW1 = 2(32)/18 = 3.555 g 3 = a3MW3/MW1 = 1(62)18 =3.444 g 4 = a4MW4/MW1 = 2(1)/18 = 0.111 g 2 = a5MW5/MW1 = 1(18)/18 = 1.00 g 1 Check: 1.00+3.555 = 3.444 + 0.111 + 1.00 4.555 = 4.555 COD equivalent stoichiometry, NH4 as reference: COD equivalents of NH4 = 3.555 g-COD/g-NH4 COD equivalents of O2 = -1g-COD/g-O2 COD equivalents of NO3-, H+, and H20 = 0 1 NH4-COD 1 O2-COD 0NO3- + 0H+ + 0H2O Y1 = Y2 = Y3 = Y4 = Y5 = (COD1/COD1) = 1.00 (3.55/3.55) = 1 2(COD2/COD1) = 3.555(-1.00)/3.555 = -1 3 (COD3/COD1) = 3.444(0)/3.555 = 0 4 (COD4/COD1) = 0.111(0)/3.55 = 0 5 (COD5/COD1) = 1.00(0)/3.55 = 0 1 Check: 1 1 = 0 COD of ammonium expressed as nitrogen = CODNH4-N 3.555 (g-COD/g-NH4)(18g-NH4/14g NH4-N) = 4.57 g-COD/g-NH4-N CELL SYNTHESIS WITH SIMPLE CARBOHYDRATE AS SOURCE Molar stoichiometry, reference compound is product cells (C5H7NO2) 5CH2O + HCO3- + NH4+ C5H7NO2 + 4H2O + CO2 Mass stoichiometry with cells as reference (MW = 113) 1.327CH2O + 0.540HCO3- + 0.159NH4+ 1C5H7NO2 + 0.637H2O + 0.389CO2 = 1 (cells) then numbering from left to right: 2 = a2MW2/MW1 = 5(30)/113 = 1.327 g 3 = a3MW3/MW1 = 1(61)113 =0.540 g 4 = a4MW4/MW1 = 1(18)/113 = 0.159 g 5 = a5MW5/MW1 = 4(18)/113 = 0.637 g 6 = a6MW6/MW1 = 1(44)/113 = 0.389 g 1 Check: 1.327 + 0.540 + 0.159 = 2.026 = 1 + 0.637 + 0.389 COD stoichiometry with cells as reference 1CH2O-COD + 0HCO3- + 0NH4+ 1C5H7NO2-COD + 0H2O + 0CO2 COD equivalents of CH2O= 1.07 g-COD/g-CH2O COD equivalents of C5H7NO2 = 1.42 g-COD/g-C5H7NO2 COD equivalents of HCO3-, CO2, and H2O = 0 COD equivalents of NH4 = 0 g-COD/g-NH4 in this reaction (no e- transfer since oxidation level of cell nitrogen = -3, same as ammonia) Y1 = Y2 = Y3 = Y4 = Y5 = Y6 = (COD1/COD1) = 1.00 (1.42/1.42) = 1 2(COD2/COD1) = 1.327(1.07)/1.42 = 1 3 (COD3/COD1) = 0.540(0)/1.42 = 0 4 (COD4/COD1) = 0.159(0)/1.42 = 0 5 (COD5/COD1) = 0.637(0)/1.42 = 0 6 (COD6/COD1) = 0.389(0)/1.42 = 0 1 NITROGEN UPTAKE IN CELL SYNTHESIS KEY POINT: As with COD, a portion of wastewater ammonia consumed in a ...

STOICHIOMETRY II nitrogen

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