## 3 Results and Discussion
### Effects of Copper Exposure on Ethanol Yield  
The hemicellulose and cellulosic hydrolysates were combined to yield a total sugar concentration of 17.73 \(\pm\) 0.07 g/L (64.7% of theoretical) from the experimental hydrolysates and 16.87 \(\pm\) 0.05 g/L (61.6% of theoretical) for the control hydrolysates. Inhibitor concentrations in the Cu exposed hydrolysate were 0.16 \(\pm\) 0.10 g/L furfural, 0.16 \(\pm\) 0.03 g/L 5-hydroxymethylfurfural, and 5.47 \(\pm\) 0.07 g/L acetic acid. Furfural, 5-hydroxymethylfurfural, and acetic acid concentrations for the control hydrolysate were 0.11 \(\pm\) 0.07 g/L, 0.14 \(\pm\) 0.02 g/L, and 4.56 \(\pm\) 0.07 g/L, respectively. There were no significant differences between the experimental and control furfural and 5-hydroxymethylfurfural concentrations. The differences between the acetic acid (_p_ = \(<\) 0.0001) and total sugar (_p_ = \(<\)0.0001) concentrations were significant in favor of the control. Figure 4 shows comparisons the bioconversion of sugar to ethanol for control and experimental groups over time. Peak ethanol for the Cu exposed treatment group was 15.41 \(\pm\) 1.81 g/L at 23.5 h (110% of theoretical) and 8.71 \(\pm\) 1.08 g/L at 35 h (62.3% of theoretical) for the control. The calculated volumetric productivity for the experimental and control groups were 0.613 g*hr-1 and 0.249 g*hr-1, respectively. There was a significant difference in ethanol yield between the control and experimental hydrolysates (_p_ = \(<\)0.0001) at times of peak ethanol. Fermentation of biomass harvested from Cu contaminated soil produced significantly greater ethanol yield than control biomass. This could be attributed to the presence of Cu ions which act as cofactors during yeast metabolism [74; 75]. In addition, the alternation in the lignocellulosic composition of vetiver biomass when cultivated on Cu loaded soils, as discussed in previously is likely to have played a role in increased ethanol yield. The presence of less lignin and greater sugar content was previously reported to lead to an increased yield of ethanol via yeast fermentation [76]. A preliminary cost analysis of ethanol for the processing of biomass to hydrolysate, and its conversion to ethanol (0.15 g dry weight; 125 mL) was performed based on the total cost of consumables for these sequential processes. Commercially available Fisher brand reagent pricing, found on their website (www.fishersci.com) [77], was used for cost determination; the option for the smallest quantity of each Fisher brand reagent was selected for use in determining cost due to the small-scale quantities used in each fermentation. The optimal quantity of each reagent was factored into the cost determination per bench scale fermentation, and pricing was found to be $31.66. For the experimental ethanol produced from vetiver biomass grown on stamp sand, the cost per gram of ethanol is $2.03 \(\pm\) $0.07, and the cost per gram of ethanol from the control biomass is $3.61 \(\pm\) $0.04. The expenses to produce a gram of ethanol are significantly different (\(p\) = 0.0002) between the two treatment groups of veitvers using [PERSON]'s \(t\)-test with \(\alpha\) = 0.05. Thus, ethanol produced from vetiver biomass harvested from stamp sand is significantly cheaper than ethanol produced from vetiver biomass harvested from control soil. Since our experiments were performed on a bench-scale, no attempt was made to compare the cost to the current market price of ethanol. Increasing interest in the use of biomass grown in marginal, nutrient poor, and contaminated soil has resulted in a few recent reports where various plant species were investigated for phytoremediation of PTM-contaminated soil, followed by bioethanol extraction from the metal-laden biomass. [PERSON] et al. [78] studied the potential use of canola for phytoremediation of Zn and Ni, followed by bioethanol production from the harvested biomass. They reported a saccharification yield of 74% and ethanol yield of 67% using Ni-contaminated biomass. [PERSON] et al.