# Carbon Footprint Assessment on the Viability of Utilizing Brewer's Spent Grain to Produce Biochar
## 3 Results
### Global Warming Potential (Impact Assessment)
#### 3.3.2 Output Phases  
Wastewater treatment emissions were calculated using the EPA predictive model [28]. Considering the functional unit, where 1.02 kg of wastewater were produced per kg of unprocessed BSG and the wastewater processed from the evaluated system was 0.00076% of what the system processed per hour, this would equate to 6 \(\times\) 10\({}^{-7}\) kg CO\({}_{2}\)e/year for 1 kg unprocessed BSG.  
Fumes from fermentation were vented at a rate of 0.074 kg CO\({}_{2}\) per kg of unprocessed BSG, and, therefore, emitted 0.074 kg CO\({}_{2}\)e per kg of unprocessed BSG.  
Using Equation (3), O : C was found to be 0.047. Using Equation (4), t\({}_{1/2}\) was found to be 719 years. Using Equation (2), CO\({}_{2,\text{sequest}}\) was found to be 3.63 MgO CO\({}_{2}\)e/Mg feedstock processed when TH was 100 years [12]. Sequestration values ranged from 0 to 3.66 Mg CO\({}_{2}\)e/Mg feedstock processed, indicating that the studied pyrolysis conditions yielded an extremely effective carbon sequestration mechanism [31]. To consider the functional unit, 3.63 MgO CO\({}_{2}\)e per Mg feedstock processed was converted to 8.93 kg CO\({}_{2}\)e per kg of unprocessed BSG. Specifically, there are 30,082 seeds of barley per kg of barley plant [32], one barley seed weighs 0.0436 g [33]; BSG accounts for 31% of the original malt weight [14].  
For the biorefining process, it was found that converting bio-oil into gasoline and diesel using the syngas from pyrolysis (Case 1) yielded a GWP value of \(-\)0.0275 kg CO\({}_{2}\)e per kg of unprocessed BSG [34]. However, if the syngas (hydrogen) underwent steam reforming, and the bio-oil was hydrogenated into gasoline and diesel (Case 2), a GWP value of \(-\)0.063 kg CO\({}_{2}\)e per kg unprocessed BSG was found [34]. In the referenced study, the biomass was corn-stover, which was pyrolyzed at 500 \({}^{\circ}\)C with ambient pressure [34]. Because of this difference, and a functional unit of 1 MJ of biofuel produced, data from the study have been extrapolated to match the current study. Based on these results, Case 2 has the more favorable GWP value; however, it also released a higher GWP value for biomass consumption and the pretreatment stage, respectively (8.80, 15.9 g CO\({}_{2}\)e per MJ biofuel produced), than Case 1 (6.70, 12.1 g CO\({}_{2}\)e per MJ biofuel produced). This must be considered when designing a biochar processing facility with bio-oil and syngas recovery. For this study, Case 1 was used, as it required less equipment and processing.  
As presented in Table 2, the primary category contributing to CO\({}_{2}\)e production was the electricity consumed throughout the process, amounting to 9.81 kg CO\({}_{2}\)e. The most significant steps, in terms of electricity use, were pyrolysis, fume hood ventilation, and drying, in that order. Figure 4 illustrates that the top CO\({}_{2}\)e removal category was biochar-soil application (\(-\)8.93 kg CO\({}_{2}\)e). The overall GWP for this system was determined to be 1.18 kg CO\({}_{2}\)e per kg of unprocessed biochar.