Greenhouse gas emissions from on-site wastewater treatment systems
Citation:SOMLAI-HAASE, CÉLIA TINA, Greenhouse gas emissions from on-site wastewater treatment systems, Trinity College Dublin.School of Engineering, 2019
CeliaSomlaiPhDThesis.pdf (PhD Thesis) 15.36Mb
Domestic wastewater is rich in carbon and nitrogen and given the biogeochemical transformations that these compounds undergo during diﬀerent treatment processes can be signiﬁcant sources of greenhouse gas (GHG) emissions. However, most research focus in relation to GHG emissions and wastewater treatment has been on large-scale treatment units with only a small number of studies carried out directly on domestic on-site wastewater treatment systems (DWWTSs) in the ﬁeld. In the Republic of Ireland, around 500,000 dwellings rely on on-site treatment and disposal of their wastewater, 87 % of which use septic tanks (STs) followed by some form of soil treatment unit (STU). Considering the large number of DWWTSs in Ireland, as well more internationally, septic systems are potential signiﬁcant sources of GHG emissions. The main aim of this research, therefore, was to develop a better understanding of the contribution of the DWWTSs to the GHG inventories. Four DWWTSs were investigated during this study. One site had a simple one chamber ST with a soakaway, which is common of many older systems in existence, Site 1. Two sites were recently constructed following the latest Irish EPA standards including a two-chamber ST, and/or a packaged secondary treatment unit discharging eﬄuent into an engineered STU, Site 2 and 3. The fourth site had a two-chamber ST followed by a willow-based evapotranspiration system, Site 4. In the STs as well as over the STUs and evapotranspiration systems, discrete and long-term CO 2 and CH 4 ﬂux measurements were carried out using automated ﬂux chambers and a closed-transient measurement approach. In addition discrete samples were taken for laboratory analysis of N 2 O. The soil of the soakaway (Site 1) consumed overall 0.03 kg CO 2Eq. yr −1 less CH 4 and emitted 7.3 kg CO 2 yr −1 more CO 2 than a similarly sized area of control soil. The net GHG emissions were compared from diﬀerent stages (i.e. ST and STU) of two recently constructed DWWTSs as well as how inclusion of up-front packaged secondary treatment units impact on the net emissions from STU (Site 2 and 3). The total net emissions from the systems were 17.0 and 21.9 kg CO 2Eq. cap −1 yr −1 at the two diﬀerent sites, respectively. Over 80 % of the total net emissions was in the form of CO 2 , around 15 % in CH 4 and less than 2 % in N 2 O. GHG ﬂuxes had strong spatial and seasonal variation from the willow bed, Site 4.
Author: SOMLAI-HAASE, CÉLIA TINA
Publisher:Trinity College Dublin. School of Engineering. Disc of Civil Structural & Environmental Eng
Type of material:Thesis
Availability:Full text available