# Carbon Footprint Assessment on the Viability of Utilizing Brewer's Spent Grain to Produce Biochar
## 2 Materials and Methods
### Carbon Footprint Assessment (CFA) Model Assumptions and Equations
#### 2.3.1 Inventory of BSG-to-Biochar Process Inputs and Outputs  
Data collection was categorized by the industrial phases of: soaking (1); drying (2); grinding (3); weighing (4); and pyrolysis (5). The resulting quantities of BSG after each phase, starting from 1 kg of unprocessed BSG were: 0.3 kg post drying; 0.299 kg post grinding; 0.299 kg post weighing; and 0.0825 kg post pyrolysis.  
Phase 1 inputs considered fume hood usage, while the outputs were wastewater and vented fumes. Fume hood data was collected using the Lawrence Berkeley National laboratory calculator for determining the energy usage of a fume hood, considering sash height and a variety of other parameters. The tool was set to Sacramento, CA with an opening of 62 by 29 in (horizontal by vertical); a face velocity of 100 ft/min; temperature maintenance at 55 \({}^{\circ}\)F; a delivery air temp of 65 \({}^{\circ}\)F; and the energy type being fuel. The volume of wastewater was collected at the laboratory scale after caustic adsorption for 48 h. The volume of CO\({}_{2}\) produced from fermentation was determined at the laboratory scale by closing the system for 48 h and measuring the volume of collected gas. These were considered biogenic carbon emissions, which could be considered climate-neutral; however, we are including these in this analysis for a complete assessment of emissions.  
The major input for drying, phase 2, was the electricity used to power the oven; the major output was water vapor from the BSG. The modeled equipment was a Shel Lab Forced Air Oven SMO3 110-120 Voltage. The wattage of this oven was 1610 W, with a capacity of 85 L. The water-vapor volume was assumed to be equivalent to the mass loss of the BSG, post drying.  
The inputs of phases 3 and 4 were primarily electricity, the MJ inputs were calculated considering the conversion of \(\mathrm{Power}_{(\mathrm{Watts})}=\frac{\mathrm{Energy}_{(\mathrm{Joules})}}{ \mathrm{Time}_{(\mathrm{seconds})}}\). There were no considerable outputs for these phases.  
Phase 5, pyrolysis, required nitrogen gas and electricity as the major inputs. At the laboratory scale, researchers used the same style of furnace; however, the quartz tube had a 60 mm diameter. The load limit for a 60 mm tube was small, only allowing for 0.030 kg of dried, ground BSG in each run. Instead, this CFA assumes that a 200 mm diameter quartz tube could host 0.299 kg of dried, ground BSG, which is equivalent to the functional unit of 1 kg of unprocessed BSG. The nitrogen gas flow rate was set to 500 mL/min and was active for 3 h and 40 min, thereby requiring 170 L per run. It is known that 1 L nitrogen is equivalent to 0.808 kg [24]. Furnace electricity usage was determined based on wattage and time. There were three major outputs of pyrolysis: syngas, bio-oil, and biochar; yield data for bio-oil and syngas were not collected at the laboratory scale. Another study considered the greenhouse gas impact of the pyrolysis of switchgrass for biochar production [25]. The functional unit of the study was 1 Mg of BSG. Yields of syngas and bio-oil were reported on a percentage dry basis, and, therefore, did not need to be converted. The biochar yield was 29% on a dry basis; the bio-oil yield was 64.1% on a dry basis; and the syngas yield was 6.1% on a dry basis [26]. This aligned with the present study's yields, as biochar recovery averaged 27.6% or 0.0825 kg.