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

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5.3 Sources of Variability in Gas EmissionsA number of factors contributed to the wide variability in the gas emission measurementsrecorded for the septic systems included in this study. The influence of factors such as waterhardness, presence of scum layer, pumping intervals, turnover events, presence of invertebrates,temperature, and the septic tank effluent filter are discussed in this section.5.3.1 Water Hardness Influence on Carbon Dioxide EmissionsAs mentioned previously, the water supply for the Auburn Lakes Trails (ALT)development, encompassing Sites 1 through 7, originates in the Sierra and flows into theStrumpy Meadows Reservoir; it has an average hardness content of 9 mg/L as CaCO 3 (GDPUD,2009) which indicates a soft water supply. In contrast, the water that serves the tank located inDavis is pumped out from a groundwater well and has an average hardness of 212 mg/L asCaCO 3 (CDPW, 2009) indicating a hard water supply.A comparison of the carbon dioxide emission rates data between the sites located in ALTand the tank for Site 8 (Figure 5-2) indicates different distributions. It is hypothesized that thehardness content of the water supply in each area may be a reason for this differing behavior. Inaddition to the difference in source water, Site 8 had other distinguishing characteristics thatpotentially impacted emissions. Unique aspects at Site 8 include the diversion of laundry waterto a gray water system, a higher number of occupants per tank volume, and the vegetarian diet ofthe house occupants. It is conceivable that these aspects may also influence the overall anaerobicand facultative processes occurring in the tank and hence the carbon dioxide emission rates.5.3.2 Influence of Scum Layer on Gas EmissionsTwo different groups of sites were compared to determine the influence of the scum layerin the overall emissions from the septic tank. The first group was composed of the tanks fromSites 2, 3, and 7 that share as a common characteristic a thick scum layer varying from 3 to 5inch in depth, with similar appearance, black color, humus like texture and usually covered theliquid surface of the septic tank. The septic tanks at Sites 1, 5, and 6 formed the second group;these tanks were characterized by patchy, light scum (less than 1"), with a light brownish color.As shown on Figure 5-9, the average methane and carbon dioxide emission rates from the sitesthat have a thick scum layer are similar to the sites without scum and the slopes are also similar.The data from the septic tank at Site 8 (light scum, hard water) was plotted separately forcomparison.5.3.3 Emissions from Recently Cleaned TankThe septic tank located at Site 4 was not a typical septic tank. It did not have any scumformation; the sludge was less than 14" in depth, with a light brown coloration and a particularpine odor was emitted when the tank lids were opened. The tank was last pumped out in late Julyof 2009 (measurements took place during September 2009). The methane and carbon dioxide gasemission rates from the tank at Site 4 in g/capita·d, averaged 0.2 and 3.2, respectively. Nitrousoxide emission rates were negligible. From the results of the overall GHG emission rate and thecharacteristics of the tank discussed above, it can be assumed that methanogenesis was notoccurring in this tank, which is consistent with results reported by Weibel et al. (1955) forrecently pumped septic tanks, which had a lag phase in the gas production.Evaluation of Greenhouse Gas Emissions from Septic Systems 5-11
(a)(b)Figure 5-9. Gas Emission Rates Results Grouped Based on Presence of Scum: (a) Methane and (b) Carbon Dioxide.5-12
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D e c e n t r a l i z e dEvaluation
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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
Page 23 and 24: 2.2 Septic Tank CharacteristicsSept
Page 25 and 26: 2.2.3 General Conversion Processes
Page 27 and 28: increase in thickness with daily so
Page 29 and 30: environmental damage and/or health
Page 31 and 32: Figure 2-6. The Intermediate Steps
Page 33 and 34: In anaerobic reactors, the alkalini
Page 35 and 36: epresentative concentrations. Inhib
Page 37 and 38: 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: The septic tank effluent CO 2 equiv
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
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Page 87 and 88: B. Based on COD Loading1. Determine
Page 89 and 90: C-2
Page 91 and 92: 2. First row of Table 23 from Sasse
Page 93 and 94: Biogas production = (COD inflow - C
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Page 97 and 98: SAMPLING FROM SOIL SURFACEDate:Hour
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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
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Philip, H., S. Maunoir, A. Rambaud,
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Winfrey, M.R. and J.G. Zeikus (1977
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Fort Worth, City ofHouston, City of
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W E R F P r o d u c t O r d e r F o
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