## 3 Results and Discussion
### Physical Activation of Manure
#### 3.2.2 Structural Characteristics and Chemical Functional Groups under Different Atmosphere  
The structural characteristics of manure biochar produced after pyrolysis with nitrogen or combined pyrolysis-gasification with steam or carbon dioxide are summarized in Table 2. As can be seen, a rise in pyrolysis temperature from 700 to 800 \({}^{\circ}\)C, associated with a greater decomposition and release of volatile products, elevated pore volume and size and increased the surface area by 45%. Nevertheless, the value of 69 m\({}^{2}\)/g was quite low, most probably due to the high ash content of manure biochar, which can hinder the access of nitrogen to the pores. Previous investigations have reported [19; 22; 24; 41; 42] even lower surface areas of 2.4-17 m\({}^{2}\)/g at 500 \({}^{\circ}\)C and 8.3 m\({}^{2}\)/g at 700 \({}^{\circ}\)C.  
When manure biochar was further activated with steam at 700 \({}^{\circ}\)C, it is clearly shown that micropore volume and surface area were greatly enhanced 4.9-fold, reaching a value of 231.4 m\({}^{2}\)/g. At the higher temperature of 800 \({}^{\circ}\)C, micropporosity increased, in addition to the size of the pores, which are characterized as mesopores. By comparison, upon activation of manure biochar with carbon dioxide at 800 \({}^{\circ}\)C, micropporosity was developed, the average pore size was smaller and specific surface area was elevated 3.4-fold, reaching a value of 233.3 m\({}^{2}\)/g. Some authors reported [24] a further increase in micropporosity and specific surface area at a higher temperature, 900 \({}^{\circ}\)C, enabling a value of 700 m\({}^{2}\)/g to be attained. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Temperature** (\({}^{\circ}\)C) & **Activation Gas** & \begin{tabular}{c} **Specific** \\ **Surface Area (m\({}^{2}\)/g)** \\ \end{tabular} & \
\begin{tabular}{c} **Micropore** \\ **Volume \(\times\) 10\({}^{2}\) (cm\({}^{3}\)/g)** \\ \end{tabular} &
\begin{tabular}{c} **Average** \\ **Pore Size (Å)** \\ \end{tabular} \\ \hline
700 &
\begin{tabular}{c} N\({}_{2}\) \\ H\({}_{2}\)O\({}_{\mathrm{v}}\) \\ \end{tabular} & 47.6 & 4.4 & 37.0 \\ \hline
800 &
\begin{tabular}{c} N\({}_{2}\) \\ H\({}_{2}\)O\({}_{\mathrm{v}}\) \\ CO\({}_{2}\) \\ \end{tabular} & 231.4 & 15.9 & 33.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Structural characteristics of manure biochar produced after pyrolysis/gasification. Figure 3: Yield of biochar under N\({}_{2}\), H\({}_{2}\)O\({}_{\mathrm{v}}\) or CO\({}_{2}\) atmosphere as a function of temperature. From the above results, taking into consideration the yield and surface area of manure biochar activated by either steam or carbon dioxide at 700 and 800 \({}^{\circ}\)C, it can be inferred that this material presents a significant potential for adsorption of various inorganic or organic contaminants and it is promising for further investigation. Table 3 compares the chemical functional groups identified [43] from the FTIR spectra of the manure sample produced under nitrogen, steam and carbon dioxide activation at 800 \({}^{\circ}\)C. The Pyrolyzed material represented C=C alkene groups at 666 cm\({}^{-1}\), whereas C-O sharp peaks in the range 1000-1400 cm\({}^{-1}\) are associated with alcohols and ethers. Peaks at 1454, 1650 and 1714 cm\({}^{-1}\) are characteristic of C-H, C=C and C=O stretching vibration bands from alkanes, alkenes and carboxylic acids, respectively, and were also identified in a previous study [24]. Smaller bands in the range 2000-2400 cm\({}^{-1}\) correspond to O=C=O stretching, whereas those in the range 2500-3000 cm\({}^{-1}\) are assigned to C-H deforming vibration from aldehydes or alkanes. Finally, the broad band between 3000 and 4000 cm\({}^{-1}\) indicates the presence of -OH stretching groups from alcohols or carboxylic acids. FTIR spectra are generally in agreement with those obtained for different manure biochar samples [22; 41].