**3.8. Analysis of wastewater samples**

**Metal Langmuir Freundlich Comment** *R***<sup>2</sup> Adsorption capacity** *R***<sup>2</sup>** *KF***/mg g−1**

Unmodified 0.974 0.059 0.605 0.948 Langmuir Modified 0.512 0.001 0.502 – Langmuir

Unmodified 0.043 0.060 0.251 1.137 Freundlich Modified 0.941 0.276 0.993 2.843 Freundlich

Unmodified 0.570 0.021 0.929 0.791 Freundlich Modified 0.560 0.112 0.906 1.695 Freundlich

the unmodified and modified adsorbent materials in the same order.

**Metal Lagergren Ho Comment** *R* **<sup>2</sup>** *R* **<sup>2</sup>**

Modified 0.936 0.954 Pseudo-second order Unmodified 0.846 0.849 Pseudo-second order

Modified 0.574 0.584 Pseudo-second order Unmodified 0.765 0.770 Pseudo-second order

Modified 0.512 0.502 Pseudo-first order Unmodified 0.583 0.573 Pseudo-first order

**Table 2.** The Lagergren first-order and Ho et al. second-order data.

increases showing that an equilibrium has been reached.

Copper on the other hand fitted well with the Langmuir model with *R*<sup>2</sup> values of 0.974 for the unmodified and 0.512 for the modified algal material. These values show that the data has a strong correlation and therefore the sorption mechanism can be prescribed to the Langmuir model. The adsorption capacities were found to be 0.059 and 0.001 mg g−1 for copper, by the unmodified and modified materials, respectively. Sorption of cadmium and lead prescribed to the Freundlich model with a sorption of 1.137 and 2.843 and 0.791 and 1.695, respectively, by

Lagergren's first-order and Ho's second-order kinetics were applied to the data that was obtained [17, 18]. This was used to determine the molecularity of the adsorption and the rate controlling step. A summary of the results that were obtained for all the three metals is

For all metals the adsorption rates are very fast initially and become almost constant as time

**Copper**

260 Water Quality

**Cadmium**

**Table 1.** Results for Langmuir and Freundlich models.

**3.7. Kinetics of adsorption of the metal ions**

shown in **Table 2**.

**Lead**

**Cadmium**

**Copper**

**Lead**

Fifty millilitre samples of water from Turi River were placed into plastic bottles and spiked with known concentrations of lead, cadmium and copper. The solution was agitated in a shaker for 30 min and then filtered, and the filtrate was analyzed for lead, cadmium and copper samples using AAS. The percentage of the metal recovered from the water samples was then recorded. Results from this analysis are shown in **Table 3**.


**Table 3.** The percentage recovery of metals from real water samples.

From the results, the percentage recovery is high at low concentrations but decreased as the concentration of the metal in the water sample increased. The adsorption of copper by the unmodified sample was found to be the best and cadmium the least. For the modified sample, the adsorption of lead was the most and cadmium was the least. This can be explained by the fact that copper ions unlike lead and cadmium have relatively high affinity for ligands containing the nitrogen atom [44]. Such ligands which are smaller than the adsorbent have high affinity for the metal ion due to their high basicity [45]. These results show that the algal biomass has shown good potential to be used in water resource management.
