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

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CHAPTER 2.0LITERATURE REVIEWTo assess the potential for the release of greenhouse gases from septic tanks, thecharacteristics of onsite systems are reviewed in this chapter. The subjects considered in thisreview include an overview of the development of septic tank systems, the physicalcharacteristics and operation of septic tanks, the fundamentals of the anaerobic processesoccurring in septic tanks, and the information that exists on the emissions from septic tanks andother wastewater sources.2.1 Overview of Septic Tank SystemsThe septic tank is one of the oldest units available for the primary treatment ofwastewater from decentralized sources. The historical background of the septic tank and itsimportance in decentralized wastewater treatment systems are discussed in this section. Anintroductory overview of gaseous emissions from septic tanks is also presented along with a briefdescription of venting systems and the soil absorption field.2.1.1 Historical BackgroundWastewater from individual buildings and small communities is often managed usingonsite wastewater systems when a centralized wastewater collection system is not available.Nearly all onsite wastewater systems incorporate a septic tank for primary treatment of influentwastewater (Crites and Tchobanoglous, 1998). A septic tank is a buried, watertight tank designedand constructed to receive and partially treat raw wastewater (U.S. PHS, 1957; U.S. EPA, 2009).It is estimated that about 25 million septic tanks are currently in use in the United States (U.S.EPA, 2002).Septic tanks were first reported as wastewater treatment systems in the 1860s in France.The Fosse Mouras automatic scavenger was patented in 1881, based on the work of AbbeMoigno and Louis M. Mouras (Dunbar, 1908; Winneberger, 1984). An illustration of the FosseMouras septic treatment process is presented on Figure 2-1. The process configuration since thattime remains almost unchanged when compared to modern septic systems (Crites andTchobanoglous, 1998).2.1.2 Onsite Wastewater Treatment SystemsThe key functions of the septic tank are to separate and retain settleable solids (sludge) andfloatables (scum) from the incoming wastewater. Subsequently, the treated wastewater isdischarged typically into a soil dispersal system, also known as a leach field. The captured solidsare retained in the septic tank and undergo a passive (naturally occurring and uncontrolled)anaerobic digestion (Tchobanoglous and Schroeder, 1985). The combination of septic tank andleach field, shown on Figure 2-2, is the most commonly used onsite wastewater treatmentsystem. Other types of primary treatment processes used in decentralized wastewater systemsEvaluation of Greenhouse Gas Emissions from Septic Systems 2-1
include Imhoff tanks, anaerobic baffled reactors, and upflow anaerobic sludge blanket reactors(Crites and Tchobanoglous, 1998; U.S. EPA, 1999). However, these alternative primarytreatment processes are not used commonly due to their more complex construction andoperation. As shown on Figure 2-2, the septic tank is connected to a building through subsurfacedrainage pipes and the treated wastewater (septic tank effluent) is discharged to the soil dispersalsystem (U.S. EPA, 2000).Figure 2-1. Illustration of the Mouras Automatic Scavenger. Adapted from Dunbar, 1908.Figure 2-2. Onsite Wastewater Treatment System Consisting of a Septic Tank and Soil Dispersal System.Adapted From Tchobanoglous, G. and F.L. Burton, 1991.2-2
Page 1 and 2: D e c e n t r a l i z e dEvaluation
Page 3 and 4: The Water Environment Research Foun
Page 5 and 6: ABSTRACT AND BENEFITSAbstract:This
Page 7 and 8: 3.1.2 Flux Chamber Inserts for Sept
Page 9 and 10: LIST OF TABLESES-1 Summary of Metha
Page 11 and 12: 3-7 Use of Flux Chamber in the Soil
Page 13 and 14: Evaluation of Greenhouse Gas Emissi
Page 15 and 16: tank is converted anaerobically. Fu
Page 17 and 18: RecommendationsBased on the finding
Page 19: ♦♦Collection of gas samples fro
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
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noted that in this approach it is a
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The septic tank effluent CO 2 equiv
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(a)(b)Figure 5-9. Gas Emission Rate
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Figure 5-11. Emission Rates from Si
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(a)(b)Figure 5-13. Views of the Eff
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It is important to note that the U.
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♦ Methane generated during the an
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A-2
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B. Based on COD Loading1. Determine
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C-2
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2. First row of Table 23 from Sasse
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Biogas production = (COD inflow - C
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E-2
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SAMPLING FROM SOIL SURFACEDate:Hour
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F-4
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G-2
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DateSamplelocationGas measurement (
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After the initial inspections, Site
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H-2 Site 2The scum layer in the fir
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Table H-10. GHG Emission Rates From
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Table H-14. Summary of the Water Qu
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Table H-18. Summary of the Water Qu
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Table H-22. GHG Emission Rates from
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Sample Gas measurement (g/capita·d
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H-9 Summary of ResultsA summary of
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I-2
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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
Page 132:
W E R F P r o d u c t O r d e r F o
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