# The Various Forms of Cow Manure Waste as Adsorbents of Heavy Metals
## 3 Results and Discussion
### Heavy Metal Adsorption of Cr, Pb and Cd
The percent removal for all the treatments can be seen in Figure 7.  
The percent removal of three types of adsorbents from cow manure followed a varied path, as shown in Figure 7, although in general, the percent removal of heavy metals rose with the addition of adsorbent. The percent removal was a significant indicator in determining an adsorbent's success in decreasing pollutants, as it refers to a material's maximal ability to reduce the existing pollutant content. Heavy metals were among the chemicals most commonly found in industrial waste that are harmful to humans. Heavy metals were found in the soil naturally and could not be degraded; they can stay in the soil and water for long periods of time, and rise over time [36]. Heavy metals enter animals and humans through intravascular or extravascular systems (systemic circulation) and disperse throughout the body. Minerals and heavy metals that are not essential for the body's physiological functioning accumulate in the body as toxins that are hazardous to health [37]. Figure 7: Percent removal of biochar (**a**), compost (**b**) and humic acid (**c**). The results of the isotherm model study are shown in Tables 2 and 3. The three varieties of cow manure used for the adsorption of heavy metals Cr, Cd and Pb showed R\({}^{2}\) values ranging from 0.60 to 0.96, according to the Langmuir model study (Table 2). The relationship pattern for each material can be described using the calculation from Tables 2 and 3. This equation was based on R\({}^{2}\) and was derived from the calculation of both equations. For the biochar Cr adsorption, the model fit the Langmuir model (0.96) rather than the Freundlich model (0.62). This was different for the adsorption of Cd and Pb, which fit the [PERSON] model better than the Langmuir model. The adsorption model for Cr in compost fit better with the [PERSON] model (0.60) than the [PERSON] model (0.55). However, the [PERSON] model (0.99) outperformed the Langmuir model for Cd (0.98); similarly, the [PERSON] model (0.84) exceeded the [PERSON] model for Pb (0.83). Furthermore, the [PERSON] model (0.84) fit the data better than the [PERSON] model in the case of Cr adsorption by the humic acid adsorbent (0.81). The [PERSON] model (0.92) fit better than the [PERSON] model in the case of humic acid and Pb (0.91). Despite the fact that both models were extremely far from 1, the [PERSON] model (0.18) matched Cd in humic acid better than the [PERSON] model (0.15), necessitating another study that was more precise in predicting adsorption. More than one surface was assumed for systems of adsorption that fit the [PERSON] model. This refers to the several surface layers (multilayers) and the fact that the sides were heterogeneous for mechanisms that suited the [PERSON] model. When the adsorption process followed the Langmuir isotherm, there was a different behavior in binding energy on each side. Adsorption processes that fit the Langmuir model suggest one-layer adsorption (monolayer). In general, the mobility of heavy metals varied depending on the metal type and the adsorption mechanism that occurred [38]. The adsorption process was influenced by the organic chemical functional groups and surface structures of materials that were altered during the raw material process. In terms of metal adsorption, raw \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Type** & **Criteria** & **Cr** & **Cd** & **Pb** \\ \hline Biochar & a & 0.0002 & 0.0012 & 0.0052 \\  & b & 0.0001 & 0.00008 & 0.00006 \\  & R\({}^{2}\) & 0.9604 & 0.7747 & 0.4350 \\ Compost & a & 0.0011 & 0.0035 & 0.0013 \\  & b & 0.0046 & 0.0011 & 0.0010 \\  & R\({}^{2}\) & 0.6016 & 0.9866 & 0.8327 \\ Humic Acid & a & 7.6264 & 0.1003 & 0.0093 \\  & b & 22.877 & 0.0979 & 0.0182 \\  & R\({}^{2}\) & 0.8424 & 0.1502 & 0.9258 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The result of the isotherm Langmuir model.