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

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CHAPTER 1.0INTRODUCTIONThis study was conducted to determine the emission of greenhouse gases (GHGs) fromconventional septic tank systems used for the management of domestic wastewater. The projectbackground, objectives, approach, and report organization are discussed below.1.1 BackgroundConcerns with climate change have led to an effort to reduce the emission of GHGs,especially in the state of California, which has enacted regulations related to GHG inventory andmitigation (i.e., AB 32). Methane has been identified as a potent greenhouse gas; equivalent to25 times that of carbon dioxide. Similarly, nitrous oxide has a reported potency factor of 298times that of carbon dioxide (IPCC, 2007). Using the IPCC methodology, the U.S. EPA (2009)has determined that a majority of the methane emissions associated with wastewater originatefrom conventional septic tank systems, due to the large number of individual septic systems nowin use. However, the actual data currently available on the emission of methane from septicsystems are insufficient to produce an accurate GHG inventory for these systems.In the IPCC (2007) method used currently to compute GHG emissions from septic tanksystem it is assumed that half of the influent organic matter is converted to methane. Using theIPCC model, the carbon dioxide equivalent (CO 2 e ) of the methane released from individualdomestic septic tanks is about 0.24 tonne CO 2 e/capita⋅yr. However, based on historical studies ofmethane emissions from septic tank systems, the value is estimated to range from about 0.09 to0.16 tonne CO 2 e/capita⋅yr. In addition, these estimates only consider emissions from the septictank and do not account for emissions from the soil dispersal systems. Thus, there is a need todevelop a more detailed model of the production of GHGs from septic tank systems.1.2 ObjectivesThe principal objective of the research was to obtain more accurate data on GHGemissions from septic tank systems, focusing on methane emissions from conventional septicsystems. To achieve the proposed objective the following activities were performed:♦♦♦♦Extensive literature review on septic tanks and gas formation pathways.Construction of flux chambers and development of a method for gas sampling fromseptic tanks.Development of sampling techniques and a protocol for gas sampling from septic systemdrainage and ventilation piping.Identification and selection of appropriate field sites for collection of study data.Evaluation of Greenhouse Gas Emissions from Septic Systems 1-1
♦♦Collection of gas samples from the septic tank liquid surface, vent system, and soildispersal system over a six-month period.Analysis of results and determination of estimated GHG emission rate values.1.3 Project ApproachMethods for the measurement of GHG emissions from soil-plant ecosystems using fluxchambers are well established; however, little information is available on gas flux measurementsfrom the liquid/solid surface of septic tanks. Hence, for this research a flux chamber design,based on the design used for soil-based measurements, was constructed and tested, along withthe development of a corresponding sampling methodology. The flux chamber method was alsoused for gas sampling of the soil dispersal system. In addition, a sampling device andmethodology were developed to measure the mass flow of GHGs through the vent system.Methane, carbon dioxide, and nitrous oxide emission rates were measured in this study.1.4 Report OrganizationThis report is organized into seven chapters. The first chapter provides an introductionand purpose for this project. A detailed literature review on septic tank systems, characteristics,processes, and GHG emissions is presented in Chapter 2.0. The methods employed during and insupport of field monitoring are described in Chapter 3.0. A description of the field sites ispresented in Chapter 4.0. The results of the gas flux measurements in the septic tank, ventingsystem and soil dispersal system, a mass balance analysis, and the sources of variability in thegas emission rates are discussed in Chapter 5.0. The implications of the results from the researchstudy are presented in Chapter 6.0. Findings and recommendations for further study aresummarized in Chapter 7.0. Calculations and support materials are presented in the appendixes.1-2
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: RecommendationsBased on the finding
Page 21 and 22: 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
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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
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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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