title: Trade-off between carbon emission and effluent quality of activated sludge processes under seasonal variations of wastewater temperature and mean cell retention time.
abstract: Over the seasonal cycles, the mean cell retention time (MCRT) of the activated sludge process is varied to compensate the wastewater temperature variations. The effects of these variations on the carbon footprint (CFP) and effluent quality index (EQI) of a conventional activated sludge (CAS) process and a nitrification/denitrification (NDN) process were quantified. The carbon emission included both biogenic and non-biogenic carbon. Carbon emissions of wasted biosolids management were also addressed. Our results confirmed that the effluent quality indicated by EQI was not necessarily improved by increasing MCRT. Higher MCRT increased the carbon emission and reduced excess sludge production, which decreased the potential for biogas energy recovery. The NDN process was preferable to the CAS process from the perspective of effluent quality. This consideration extended to the whole plant CFP if the N2O emitted during NDN was limited ([N2O]<1% [NH4(+)]removed) as the carbon emission per unit effluent quality achieved by NDN process is less than that of the CAS process. By putting forward carbon emission intensity (γ) derived from CFP and EQI, our work provides a quantitative tool for decision makers evaluating process alternatives when there is a trade-off between carbon emission and effluent quality.
authors.affiliation: School of Civil and Architecture Engineering, Northeast Dianli University, Jilin 132012, PR China. Electronic address: guojingbo640@163.com.
authors.forename: Jingbo
authors.initials: J
authors.lastname: Guo
authors.affiliation: School of Civil and Architecture Engineering, Northeast Dianli University, Jilin 132012, PR China.
authors.forename: Xin
authors.initials: X
authors.lastname: Fu
authors.affiliation: Ciencia e Ingeniería del Agua y el Ambiente, Pontificia Universidad Javeriana, Carrera 7 No. 40-62, Bogotá D.C., Colombia.
authors.forename: G
authors.initials: G
authors.lastname: Andrés Baquero
authors.affiliation: Water-Energy Nexus Center, University of California, Irvine, CA 92697-2175, USA.
authors.forename: Reza
authors.initials: R
authors.lastname: Sobhani
authors.affiliation: Water-Energy Nexus Center, University of California, Irvine, CA 92697-2175, USA; Nolasco y Asociados, S.A., Congreso 1908, Piso 2D, Buenos Aires C1428BVB, Argentina.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Nolasco
authors.affiliation: Water-Energy Nexus Center, University of California, Irvine, CA 92697-2175, USA; Department of Civil and Environmental Engineering, University of California, Irvine, CA 92697-2175, USA.
authors.forename: Diego
authors.initials: D
authors.lastname: Rosso
keywords: Carbon footprint; Conventional activated sludge process; Effluent quality index; Mean cell retention time; Nitrification/denitrification process; Temperature