https://doi.org/10.3390/agriculture13020336
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2.9. Carbon, Hydrogen, and Nitrogen Analysis
Carbon, hydrogen, and nitrogen analysis was carried out to quantify elemental composition in the treated POME samples from heterotrophic and mixotrophic growth modes at day 1 and day 14. The analysis was conducted using a CHN Elemental Analyzer (Perkin Elmer 2400 Series II, Waltham, MA, USA). Approximately 1.5 mg of the dried sample was placed inside the instrument, with helium gas pressure set at 20 psi, oxygen pressure set at 20 psi, and compressed air set at 60 psi. Acetanilide was used as the standard sample in this experiment [22,23].
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3.6. Carbon, Hydrogen, and Nitrogen (CHN) Analysis
Table 2 delineates carbon (C), hydrogen (H), and nitrogen (N) content, as well as oil and grease composition, for cultivation samples of both S. parvus and C. dispar in the heterotrophic and mixotrophic modes. The highest C and H content was observed in the mixotrophic mode with S. parvus (63.45% and 11.16%, respectively).
Table 2. Oil and grease residue together with oil reduction at day 1 and day 14 under the heterotrophic and mixotrophic modes for both S. parvus and C. dispar with the optimum 20% cell concentration.
Table 2. Oil and grease residue together with oil reduction at day 1 and day 14 under the heterotrophic and mixotrophic modes for both S. parvus and C. dispar with the optimum 20% cell concentration.
| Compositions | S. parvus | C. dispar | ||
|---|---|---|---|---|
| Heterothropic | Mixotrophic | Heterothropic | Mixotrophic | |
| Elemental analysis at day 14 (wt%) | ||||
| Carbon, C | 57.04 | 63.45 | 57.59 | 55.04 |
| Hydrogen, H | 8.49 | 11.16 | 9.90 | 8.68 |
| Nitrogen, N | 2.72 | 1.17 | 1.76 | 2.08 |
| Oil and grease residue (wt%) | ||||
| Day 1 | 66.28 | 61.13 | 58.03 | 61.47 |
| Day 14 | 61.85 | 44.72 | 56.85 | 53.37 |
| Reduction | 6.69 | 26.85 | 2.02 | 13.18 |
S. parvus cultivated in the mixotrophic mode achieved higher C and H content due to the availability of light for photosynthesis, and thus exhibited the highest CEV. This trend is in agreement with the CEV results and increasingly shows that there is a strong correlation between C and H content and CEV. In addition, researchers have validated that high C content simultaneously leads to a high CEV [25]. Thus, the result shows positive validation of the former studies conducted on energy produced from biomass fuels, whereby high CEVs were obtained with increases in C and H content [26,27]. Only 1.17% nitrogen content was observed in the mixotrophic mode with S. parvus. The low nitrogen content will be beneficial to the formation of POME biomass fuel as low nitrogen content will produce less nitrogen oxide from biomass fuel combustion; thus, this would result in a lower risk of undesirable negative impacts to the environment [27].
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