## 3 Rice Industry By-Products
### Properties of Rice Straws  
Rice straw is the vegetative part of the rice plant (_Oryza sativa_ L.) and it is generated after cut at grain harvest. It consists of the stem of the paddy plant, leaves, and spikelet. Typically, rice straw is used for animal feed, composting process, cattle house bedding, the paper industry, to make handmade items, as an energy source in some industries, and covering material for agricultural fields [70]. In addition, the remaining part of the rice straw is burned in the paddy fields before the next ploughing process to prepare the field. The chemical composition of any biomass is highly dependent on variety, cultivated area, seasons, nitrogen fertilization, plant maturity, plant health, and many other environmental and human factors [71; 72]. Variation of chemical and physical factors affect the yield and the quality of the end product. Rice straws consist of cellulose, hemicellulose, lignin, and a considerable amount of other components that are represented in Table 4[73]. Table 5 lists the elemental composition of dried rice straw as determined by EDX [74]: it is well evident that the amount of Si is strongly lower than for rice husk. [PERSON] [75] has revealed that rice plant leaves consist of more silica than their stem. Due to the higher amount of oxalate (1-2% dry matter) in rice straw, the Ca concentration is decreased and therefore, it is necessary to make Ca supplementation when it is used as animal feed [43]. Figure 4: ATR-FTIR spectra of rice husk (own source) acquired at room temperature by a Nicolet FTIR iS10 spectrometer (Nicolet, Madison, WI, USA) equipped with Smart iTR with diamond plate on organic Carnaroli rice husk. Husk was dried at 45 \({}^{\circ}\)C, milled and sieved with a 1000 \(\upmu\)m mesh sieve before analysis. Thirty-two scans in the 4000–600 cm\({}^{-1}\) range at 4 cm\({}^{-1}\) resolution were coadded. The peaks are indexed by the tool “Find Peaks” in the Ommic Spectra software Nicolet, Madison, WI, USA. adsorption on Rice Straw  
Rice straw is rich in cellulose, hemicellulose, silica, and lignin, which provide binding sites for various contaminants like heavy metals and dyes, in water and wastewater [76; 77]. Therefore, straw has a large potential for use as a low-cost adsorbent material in water treatment. [PERSON] et al. [78] have emphasized that the surface of this type of biomass adsorbent is activated at lower pH values for removal of heavy metals. Furthermore, Cr adsorption process is more favorable in strong acid conditions [76]. In Figure 5, the ATR-FTIR spectrum of rice straw is reported. In this case, the same peaks outlined for pure husk are evident. In particular, the broad band centered at 3287 cm\({}^{-1}\) is associated with O-H stretching (in cellulose or hemicelluloses), the bands at around 2900 cm\({}^{-1}\) are attributing to C-H stretching, the peaks around 2000 cm\({}^{-1}\) are due to the vibrations of the carbon skeleton bonds (see the table in [79]). Moreover, the OH bending vibration is well evident in the peak at 1606 cm\({}^{-1}\) and the presence of CH\({}_{3}\) and methoxy (-OCH\({}_{3}\)) groups present in lignin is confirmed by the signals between 1320 and 1500 cm\({}^{-1}\)[68; 80]. The bands between 1650 to 1515 cm\({}^{-1}\) can be assigned to aromatic skeleton stretching and to the presence of C=O bonds. Finally, the peaks at 1032 cm\({}^{-1}\) can be due to C-O and C-H bonds' vibrations and the bands at 782 cm\({}^{-1}\) to Si-O bonds deformations, respectively. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Cellulose** & **Hemicellulose** & **Lignin** & **Ash** \\ \hline
**Rice Straw** & 320–386 & 197–357 & 135–223 & 100–170 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Major components of rice straw (mg/g) (modified from [73]). Figure 5: FTIR spectra of rice straw (own source) acquired at room temperature by a Nicolet FTIR iS10 spectrometer (Nicolet, Madison, WI, USA) equipped with Smart iTR with diamond plate on Luna CL rice straw.