# Biochar as a Multifunctional Component of the Environment--A Review
## 2 Biochar and its Properties  
Biochar may be produced from numerous materials of varied origins, e.g., energy crops, forest residues as well as agricultural residues [25; 26; 27; 28; 29; 30]. Other materials used for biochar production include sewage sludge, waste from the food processing industries, e.g., oats previously subjected to fermentation, as well as poultry litter and cattle manure (Table 1) [31; 32]. Importantly, the choice of feedstock for biochar production depends on e.g., economic and logistic factors as well as the parameters of the pyrolysis process itself and the types and properties of the applied substrates, e.g., water contents [21]. The most important properties of biochars include their chemical composition, stability, specific surface and porosity. Importantly, the chemical composition of biochars mainly depends on the chemical composition of the substrates used in biochar production. Biochars contain stable organic carbon, aromatic compounds, aliphatic compounds and ash [33]. Taking into account the type of biomass and parameters of thermal processing applied, the content of carbon in biochar may be in the range of 50-90%, water 1-15%, volatile substances up to 40% and mineral substances up to 5%. Carbonization products have a neutral or alkaline pH and are highly resistant to microbiological degradation and decomposition; applied in the soil they are stable in terms of their chemical composition [21]. Their porous structure on the other hand contributes to improved sorption capacity of soils (Figure 1) [34]. \begin{table}
\begin{tabular}{c c} \hline
**Origin of Feedstocks** & **Type** \\ \hline Agriculture & Energy crops, corncob, rice husk, sunflower husk, post-fermentation oats, bamboo, \\  & bagasse, waste from olive oil production, straw, wheat husk, cattle manure, poultry litter \\ Forest & Conifer bark, pellets from sawdust, peat, moss, beech timber, \\ Waste & Waste from tea factories, paper, sewage sludge, municipal organic waste \\ \hline \end{tabular}
\end{table} 
Table 1: Selected feedstocks used in biochar production [25; 26; 27; 28; 29; 30]. Figure 1: The porous structure of biochar [35]. Biomass pyrolysis conducted at higher temperatures may lead to an increased pH of the biochar. At lower temperatures it is possible to obtain biochar with higher ion-exchange capacity. Because of their physicochemical properties, biochars can be used for such purposes as soil carbon sequestration, the production of soil conditioner, as well as soil rehabilitation [21]. Table 2 presents some selected properties of biochars in relation to the feedstocks used and pyrolysis temperature applied. Different types of fuel, including waste, can be used for pyrolysis. The types of raw materials for pyrolysis can generally be divided into three groups: mine fuels, e.g., coal, biomass, e.g., wood, sewage sludge and plastics, e.g., tires. Each of these raw materials has different chemical composition and physical properties, which affect the quality of the pyrolysis products obtained. Biomass is a very universal raw material in its morphology and physical characteristics. Biomass material can be partially wet or dry, homogeneous or heterogeneous, of high density or of a loose structure, low or high ash content, high or low fragmentation [45]. This variety of properties of raw materials for biofuel production in gasification reactors is difficult and it is necessary to apply other processing measures focusing on the properties in question. Hence there is a large diversity of bioreactors used in biomass processing as well as a wide range of final products diversified in terms of properties determined by the conditions of the pyrolysis process and the type of bioreactor. Knowledge of the chemical structure and their behavior during the process of pyrolysis is extremely important from the point of view of application of optimal technological solutions, selection of appropriate parameters (temperature, process duration), process efficiency and environmental nuisance.