Evaluation of Greenhouse Gas Emissions from Septic ... - Geoflow

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APPENDIX DESTIMATE OF METHANE EMISSIONS FROMSEPTIC TANK SYSTEM BASED ON SASSE (1998)The model presented below was developed by Sasse (1998) based on observations of septic tankoperation primarily from developing countries. The model parameters, including BOD 5 , waterconsumption per capita, COD/BOD ratio, septic tank dimensions, and dissolved methane contentin water were adjusted to be consistent with typical septic tank design parameters in the U.S.1. Table 22 from Sasse (1998), wastewater production per capita. The highlighted values inthe table were calculated using the following assumptions:⋅ Population: 1⋅ BOD: 85 g/capita⋅d (Table 4.12, Crites and Tchobanoglous, 1998)⋅ Water consumption: 300 L/capita (Average water used in individual residences, Critesand Tchobanoglous, 1998)⋅ COD/BOD: 2.33 (COD and BOD values taken from Table 4.12, Crites andTchobanoglous, 1998)Table D-1. Wastewater Production Per Capita.UserBOD 5 peruserWaterconsumptionper userCOD /BOD 5ratioDaily flow ofwastewaterBOD 5conc.CODconc.(1) (2) (3) (4) (5) (6) (7)Given Given Given Given Calc. Calc. Approx.Number g/d L/dmg/L /mg/L m 3 /d mg/L mg/L1 85 300 2.33 0.3 283 6601.1 Calculation of daily flow of wastewater, m 3 /d – Column (5)Daily Flow of wastewater = number of users x water consumption per userDaily Flow of wastewater = 1 x 300 L/d x 10 -3 m 3 /L = 0.3 m 3 /d1.2 Calculation of BOD 5 concentration, mg/L – Column (6)BOD 5 = BOD 5 / Daily Flow of wastewaterBOD 5 = (85 g/d) / (0.3 m 3 /d) = 283 mg/L1.3 Calculation of the approximate COD concentration, mg/L – Column (7)COD = COD / BOD 5 x BOD 5COD = 2.33 x 283 mg/L = 660 mg/LEvaluation of Greenhouse Gas Emissions from Septic Systems D-1
2. First row of Table 23 from Sasse (1998), general spread sheet for septic tank, input andtreatment data. The highlighted values on the table were calculated using the previousvalues from Step 1 and assuming 12 hours as the time of most wastewater flow andSS/COD ratio equal to 0.42 mg/L.Table D-2a. General Spread Sheet for Septic Tank, Input and Treatment Data.Daily wastewater flowMax flowat peakhoursTime of mostwaste water flowCODinflowBOD 5inflow(1) (2) (3) (4) (5)Given Given Calc. Given Givenm 3 /d h m 3 /h mg/L mg/L0.3 12 0.025 660 283COD/BOD 5 2.33Table D-2b. General Spread Sheet for Septic Tank, Input and Treatment Data (Continued).HRT insidetankSettleableSS/COD ratioCODremoval COD outflowBOD 5outflow(6) (7) (8) (9) (10)Chosen Given Calc. Calc. Calc.h mg/L / mg/L % mg/L mg/L24 0.42 36% 421 1752.1 Calculation of maximum flow at peak hours, m 3 /h – Column (3)Maximum daily flow = Daily wastewater flow, m 3 /d / time of most wastewater flow, hr/dMaximum daily flow = 0.3 m 3 /d / 12 h/d = 0.025 m 3 /h2.2 Calculation of the COD removal, % – Column (8)To calculate the COD removal, Sasse (1998) propose a factor of 0.6. This factor takesinto account that in a septic tank the COD removal rate depends on the amount ofsettleable solids, their COD content, and the intensity of inoculation of fresh inflow. TheCOD removal is calculated based on the chosen HRT (24 hr).COD removal = (SS / COD) / 0.6 x {[(HRT – 3) x (0.15 / 27)] + 0.4}COD removal = 0.42 / 0.6 x {[24 - 3] x (0.15 / 27)] + 0.4} = 36%2.3 Calculation of the COD outflow, mg/L – Column (9)COD outflow = (1 – COD removal rate) x COD inflowCOD outflow = (1 -0.36) x 660 mg/L = 421 mg/L2.4 Calculation of the BOD removal, %The equation to calculate the BOD removal is related to Fig. 65 in Sasse (1998), thesimplified curve of change in the COD/BOD ratio during anaerobic treatment. The BODremoval is based on the COD removal rate (36%).For a COD removal less than 0.5, the COD/BOD removal ratio is 1.06Therefore, BOD removal is (0.36)(1.06) = 0.38 or 38%2.5 Calculation of the BOD outflow, mg/L – Column (10)BOD outflow = [1 – (BOD removal)] x BODBOD outflow = [1 – (0.38)] x 283 mg/L = 175 mg/LD-2
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D e c e n t r a l i z e dEvaluation
Page 3 and 4:
The Water Environment Research Foun
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ABSTRACT AND BENEFITSAbstract:This
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3.1.2 Flux Chamber Inserts for Sept
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LIST OF TABLESES-1 Summary of Metha
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3-7 Use of Flux Chamber in the Soil
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Evaluation of Greenhouse Gas Emissi
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tank is converted anaerobically. Fu
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RecommendationsBased on the finding
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♦♦Collection of gas samples fro
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include Imhoff tanks, anaerobic baf
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2.2 Septic Tank CharacteristicsSept
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2.2.3 General Conversion Processes
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increase in thickness with daily so
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environmental damage and/or health
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Figure 2-6. The Intermediate Steps
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In anaerobic reactors, the alkalini
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epresentative concentrations. Inhib
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2.4 Gas Emissions from Septic Syste
Page 39 and 40: Figure 2-9. Flux Chamber Designed b
Page 41 and 42: due to settling and anaerobic diges
Page 43 and 44: total methane production value of 1
Page 45 and 46: 2-26
Page 47 and 48: The main body of the flux chamber w
Page 49 and 50: 3.1.3 Flux Chamber Design for Use i
Page 51 and 52: 3.2 Sampling ProtocolsThe three pri
Page 53 and 54: 3.2.3 Sampling Method for Vent Syst
Page 55 and 56: 3.3 Gas AnalysisThe gas samples wer
Page 57 and 58: ppm (raw data from laboratory) were
Page 59 and 60: gal. Sites 5, 6, and 7 were the onl
Page 61 and 62: Table 4-2. Continued from previous
Page 63 and 64: Three of the septic tanks that appe
Page 65 and 66: steeper than that for the rest of t
Page 67 and 68: espectively, and for methane were 4
Page 69 and 70: oth before and after the septic tan
Page 71 and 72: noted that in this approach it is a
Page 73 and 74: The septic tank effluent CO 2 equiv
Page 75 and 76: (a)(b)Figure 5-9. Gas Emission Rate
Page 77 and 78: Figure 5-11. Emission Rates from Si
Page 79 and 80: (a)(b)Figure 5-13. Views of the Eff
Page 81 and 82: It is important to note that the U.
Page 83 and 84: ♦ Methane generated during the an
Page 85 and 86: A-2
Page 87 and 88: B. Based on COD Loading1. Determine
Page 89: C-2
Page 93 and 94: Biogas production = (COD inflow - C
Page 95 and 96: E-2
Page 97 and 98: SAMPLING FROM SOIL SURFACEDate:Hour
Page 99 and 100: F-4
Page 101 and 102: G-2
Page 103 and 104: DateSamplelocationGas measurement (
Page 105 and 106: After the initial inspections, Site
Page 107 and 108: H-2 Site 2The scum layer in the fir
Page 109 and 110: Table H-10. GHG Emission Rates From
Page 111 and 112: Table H-14. Summary of the Water Qu
Page 113 and 114: Table H-18. Summary of the Water Qu
Page 115 and 116: Table H-22. GHG Emission Rates from
Page 117 and 118: Sample Gas measurement (g/capita·d
Page 119 and 120: H-9 Summary of ResultsA summary of
Page 121 and 122: I-2
Page 123 and 124: Treatment in Decentralized Wastewat
Page 125 and 126: Philip, H., S. Maunoir, A. Rambaud,
Page 127 and 128: Winfrey, M.R. and J.G. Zeikus (1977
Page 129 and 130: Fort Worth, City ofHouston, City of
Page 132: W E R F P r o d u c t O r d e r F o
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