scholarly journals Greenhouse Gas Emission Assessment of Simulated Wastewater Biorefinery

Resources ◽  
2021 ◽  
Vol 10 (8) ◽  
pp. 78
Author(s):  
Carla Silva

A wastewater treatment plant (WWTP) can be considered a system where dirty water enters and fresh water (by means of treatment processes) and other co-products such as sludge and biogas exit. Inside the system, typically, the following steps occur: preliminary treatment, primary treatment, secondary treatment, tertiary treatment, disinfection, and solids handling. The system transforms biomass into several energy and non-energy products, which fall into the definition of a biorefinery. This research compares three simulated WWTP in terms of their environmental greenhouse gas (GHG) emission release to the atmosphere: a generic one (without co-product valorization), one that converts co-products into fertilizer, heat, and electricity, and a third one that converts co-products into heat, electricity, fertilizer, and bioplastic. Heat and electricity are used to provide its energy needs. The chosen impact category is GHG, and the aim is to project the best scenario to the European context in terms of GHG avoidance (savings). The scope is the upstream electricity and natural gas production, the in-use emissions, and the avoided emissions by substituting equivalent fossil-based products. The functional unit is 1 L of sewage (“dirty water”). The GHG savings are evaluated by comparing a generic WWTP scenario, without co-product valorization, with alternative scenarios of co-product valorization. Conventional LCA assuming all the emissions occurs at instant zero is compared to a more realistic environment where for each year, the average of the variable emission pulses occurs. Variable emissions pulses are taken from variable inflows data publicly available from European COST actions (COST Action 682 “Integrated Wastewater Management” as well as within the first IAWQ (later IWA) Task Group on respirometry-based control of the activated sludge process), within the later COST Action 624 on “Optimal Management of Wastewater Systems”). The GHG uncertainty is estimated based on the inputs benchmark data from the WWTP literature and by having different available global warming potential dynamic models. The conventional LCA versus dynamic LCA approach is discussed especially because a WWTP is by nature a dynamic system, having variable inputs along time and therefore variable output GHG emission pulses. It is concluded that heat needs are fully covered by biogas production in the anaerobic digester and combustion, covering its own energy needs and with a potential for heat district supply. Only 30–40% of electricity needs are covered by combined heat and power. Bioplastics and/or fertilizer yields potentially represent less than 3% of current European needs, which suggests the need to reduce their consumption levels. In comparison to generic WWTP, GHG savings are 20%, considering the uncertainty in the benchmark input assumptions. The former is much higher than the uncertainty in the dynamic global warming potential model selection, which means that the model selection is not important in this case study.

2020 ◽  
Author(s):  
Ronley Canatoy ◽  
Seung Tak Jeong ◽  
Pil Joo Kim

<p>Biochar is a carbon-rich black stable solid substance that when utilized as soil amendment can effectively mitigate greenhouse gas (GHG) emission. However, during the pyrolysis process of organic feedstock (i.e. manure) greenhouse gases are released as the feedstock undergo thermochemical degradation. Many studies were reported with regards to the effectiveness of biochar to mitigate greenhouse gas emission and to maintain soil quality via carbon sequestration. However, no clear investigation was done regarding biochar utilization on reducing GHG emission in an integrated perspective that starts from pyrolysis (production) to field application (utilization). To evaluate the integrated influence of biochar utilization on the overall Global Warming Potential (GWP) and (Greenhouse Gas Intensity) GHGI at different temperature, the fluxes of GHGs during feedstock pyrolysis to soil application were calculated. The key components include GHGs released during production processes and biogenic GHG emissions taking place in the soil via short-term incubation experiment in lowland and upland condition treated with biochar pyrolyzed at different temperature. Highest pyrolysis temperature of 700<sup>o</sup>C emitted 6.92 Mg CO<sub>2</sub>-eq ton<sup>-1</sup> biochar, wherein 8.7% and 91.2% was contributed by Carbon dioxide (CO<sub>2</sub>) and Methane (CH<sub>4</sub>) effluxes, respectively, during pyrolysis. This GHG emission during pyrolysis at 700<sup>o</sup>C was 5.6, 2.2, and 1.5 times higher than at 400<sup>o</sup>C, 500<sup>o</sup>C and 600<sup>o</sup>C, respectively. Meanwhile, biochar produced at lowest temperature (Biochar400) when utilized as soil amendment emitted 43.4 and 38.2 Mg CO<sub>2</sub>-eq ha<sup>-1</sup> in lowland and upland condition, respectively. In addition, this emission value under lowland (and upland) condition was 1.38 (1.36), 1.51 (1.56) and 1.86 (1.91) times higher than Biochar500, Biochar600 and Biochar700, respectively. Combining the GWP during the production and the utilization processes in lowland and upland condition reveal that at 400<sup>o</sup>C emanates the lowest overall GWP of 93.3 and 88.1 Mg CO<sub>2</sub>-eq ha<sup>-1</sup>, respectively.  Moreover, under lowland (and upland) condition, overall GWP at 400<sup>o</sup>C was noted to be 65.7% (71.7%), 131.6% (140.4%) and 221.9% (237.1%), lower than at 500<sup>o</sup>C, 600<sup>o</sup>C and 700<sup>o</sup>C, respectively. In conclusion, the use of lower temperature during biomass pyrolysis and utilization of its derived biochar could be a practical approach to mitigate GHG emissions.</p><p> </p><p>Keywords: Biochar, Pyrolysis, Greenhouse gas, Methane, Global warming potential, Greenhouse gas intensity</p>


2021 ◽  
Vol 21 (6) ◽  
pp. 4699-4708
Author(s):  
Ian Enting ◽  
Nathan Clisby

Abstract. Many metrics for comparing greenhouse gas emissions can be expressed as an instantaneous global warming potential multiplied by the ratio of airborne fractions calculated in various ways. The forcing equivalent index (FEI) provides a specification for equal radiative forcing at all times at the expense of generally precluding point-by-point equivalence over time. The FEI can be expressed in terms of asymptotic airborne fractions for exponentially growing emissions. This provides a reference against which other metrics can be compared. Four other equivalence metrics are evaluated in terms of how closely they match the timescale dependence of FEI, with methane referenced to carbon dioxide used as an example. The 100-year global warming potential overestimates the long-term role of methane, while metrics based on rates of change overestimate the short-term contribution. A recently proposed metric based on differences between methane emissions 20 years apart provides a good compromise. Analysis of the timescale dependence of metrics expressed as Laplace transforms leads to an alternative metric that gives closer agreement with FEI at the expense of considering methane over longer time periods. The short-term behaviour, which is important when metrics are used for emissions trading, is illustrated with simple examples for the four metrics.


RSC Advances ◽  
2019 ◽  
Vol 9 (60) ◽  
pp. 34827-34836 ◽  
Author(s):  
Yuan Tian ◽  
Xiaoxing Zhang ◽  
Bowen Tang ◽  
Zhaolun Cui ◽  
Guozhi Zhang ◽  
...  

SF6 is a greenhouse gas with extremely high global warming potential (GWP).


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