Element content (%)

Mean value ± SD

Carbon (C)

39.4 ± 1.6

Oxygen (O)

48.46 ± 3.10

Calcium (Ca)

4.85 ± 0.13

Potassium (K)

3.84 ± 1.22

Magnesium (Mg)

0.88 ± 0.05

Sulfur (S)

0.27 ± 0.03

Phosphorus (P)

0.22 ± 0.03