# 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 chemical analysis results gave the compost material a pH of 6.73, water content of 10.79%, total N of 1.72%, organic C of 46%, K of 0.45%, P\({}_{2}\)O\({}_{5}\) of 0.04%, a C:N ratio of 27, 0.06 mg/L of Cr, 0.10 mg/L of Pb, and 0.003 mg/L of Cd. The results of the proximate analysis of compost showed volatile matter of 82.23% and ash content of 82.34%. Humic and fulvic acid contents derived from compost were 1.84% and 6.63%, respectively. Biochar had a pH of 9, water content of 3.29%, Cr levels of 0.11 mg/L, a Pb level of 0.13 mg/L, and Cd levels of 0.008 mg/L. The nitrogen level was 2.07%, with 0.09% P and Organic C of 30.12%. The ash content was 54.93%, and the volatile matter was 49.98%, according to the proximate analysis. Humic acids had 14.38% water content, 4.04% nitrogen content and 55.06% organic C content. The Humification Rate (HR) from compost was 18.41%. The humification process can be understood as a process of synthesis or resynthesis of organic compounds, which is influenced by various factors, such as the climate, quantity and quality of plant material, and soil management [29]. The HR value shows the ratio of the organic acid content in the material. For the HR analysis, a higher HR value indicates that the formation of humic and fulvic acid content in the soil is greater than the input of fresh organic matter in the soil [22]. The general features of compost, biochar and humic acids at various pH levels in relation to heavy metal adsorption are shown above (Figure 3). Humic acid, compost and biochar exhibited various adsorption behaviors at each acidity level. Figure 3 shows that humic acid a lower adsorption capacity than both compost and biochar. This was related to humic acid's adsorption mechanism, which was affected by pH. This can also be shown in [30], which suggested that the acidity of the solution altered the mechanism of metal adsorption. As a result of the extraction with NaOH or KOH, the \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Component**} & \multicolumn{3}{c}{**Content (wt\%)**} \\ \cline{2-4}  & **Compost** & **Biochar** & **Humic Acid** \\ \hline C & 54.21 & 57.24 & 65.00 \\ O & 35.57 & 33.18 & 26.90 \\ Si & 3.97 & 4.69 & 0.41 \\ Ca & 2.02 & 1.93 & 0.46 \\ Mg & 0.91 & 0.85 & - \\ Al & 0.82 & 0.79 & 0.58 \\ K & 0.86 & 0.76 & - \\ Cl & 1.07 & - & 0.48 \\ S & - & - & 0.16 \\ Fe & - & 0.31 & - \\ Na & - & 0.24 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Material composition based on SEM-EDX analysis. negative charge of humic acids might be saturated by Na or K ions. The acids achieved optimum solubility and stability in suspension as the pH increased [31]. This mechanism is consistent with humic acid's behavior, which was dissolved in base circumstances and separated in acidic conditions [31]. Figure 3 shows that the biochar had a relatively constant adsorption capacity compared with other adsorbents. The morphological characteristics of the adsorbent material (Figure 2) could also affect the adsorption capacity of heavy metals, where materials with more pores had a greater capability of adsorbing the heavy metals than others. This is in line with [32], which showed that carbonization and calcination produced a more porous adsorbent material. This condition was different from that of humic acid, which produced the same path. In general, the mechanism of the adsorption process was influenced by the surface charge of the adsorbent, the degree of ionization and the speciation of the adsorbate [24]. In general, the behavior of heavy metal Pb in relation to adsorbent humic acid produced a consistent path. The rate of heavy metal adsorption increased when the pH of the solution rose, with the optimum adsorption at a pH of 8. This is in line with [30], which showed that the adsorption behavior of lignin at various pH levels provides a consistent pattern of Pb adsorption.