2.4. Statistical analyses
Before conducting any statistical analysis, normality of the data
was checked with Kolmogorov–Sminov (K–S) test. A three way
analysis of variance (ANOVA) was conducted to evaluate the influence of heavy metal concentration, retention time and plant species on the removal of heavy metals. Post hoc test, Duncan
multiple range test (DMRT at alpha¼0.05) was conducted to
identify the differences among means. Relationship between retention time and heavy metal concentrations was determined by
Spearman rank order correlation. Spearman rank coefficient has
been conducted because the two criteria: (1) the variables should
be interval or ratio and (2) monotonic relationship exists between
them; are fulfilled. Retention time and concentration of heavy
metals are interval variables and monotonic relationship exists
between them. Percent removal of the heavy metal was calculated
using the formula: PR (%)¼(Ci-Cf
)x100/Ci
, where, Ci andCf are the
concentration of the heavy metal before and after treatment. The
concentration of heavy metals in the wastewater was described as
mg L1
, while those in plants were reported as mg kg
1
of dry weight and is mean of thefive replicates