# Agricultural Residue Management for Sustainable Power Generation: The Poland Case Study
## 4 Results
### Sugar Beet Leaf Based Biogas Production  
Maize silage is a valuable substrate for biogas production, but despite this, its acceptance in society is declining. The amendment to the German Renewable Energy Act has restricted its application [89]. Similar documents have been introduced in Poland [37]. Animal manure has high water content and its organic matter is not easily digestible. To improve this anaerobic process, easily digestible feedstock (organic matter) should be added [90; 91; 92]. Therefore, alternative substrates are currently being sought. According to studies, sugar beet and its by-product (leaves) are an acceptable co-substrate [93; 94].  
Fibre-rich feedstock like straw and silage have low biogas yields [95]. Their co-digestion with sugar beet or its leaves makes the digestion process easy. Moreover, this co-digestion process has advantages in terms of positive synergetic effects (increasing in a methane yield) [96; 97].  
In Poland sugar beet yield is increasing. It results in an increase in the gross harvest of sugar beet and its by-product (leaf) (Figure 6) [82]. Therefore, biogas industry can get from 2 to 3 Mt of leaves to be used as substrate. The use of this by-product can allow biogas plants to produce additionally from 87.8 to 158.5 million cubic meters of biomethane or from 3.16 to 5.71 PJ. It constitutes from 3.02 to 5.46% of the manure biogas energy potential. Thus, the total energy potential increases up to 279.94 PJ.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Group** & **Voivodship** & **Sum** & \begin{tabular}{c} **Share of** \\ **Biomass,\%** \\ \end{tabular} & **Average** & **Minimum** & **Maximum** \\ \hline A & Lublin & 42.15 & - & 42.15 & 42.15 & 42.15 \\ \hline B & \
\begin{tabular}{c} Kuyavian-Pomeranian, \\ Masovian, Greater Poland \\ \end{tabular} & 84.53 & - & 28.18 & 26.97 & 29.48 \\ \hline C & Lód�, Opole, Pomeranian & 58.63 & - & 19.54 & 18.17 & 21.02 \\ \hline D &
\begin{tabular}{c} Lower Silesian, \\ Subcarpathian, West \\ Pomeranian, Lesser Poland, \\ Warmin-Masurian, \\ Silesian, Holy Cross \\ \end{tabular} & 86.18 & - & 12.31 & 8.51 & 15.95 \\ \hline E & Lubusz & 4.52 & - & 4.52 & 4.52 & 4.52 \\ \hline F & Podlaskie & \(-2.77\) & - & \(-2.77\) & \(-2.77\) & \(-2.77\) \\ \hline Total & & 273.23 & 61.77 & 17.08 & \(-2.77\) & 42.15 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Energy potential by clusters (crop residues and manure biogas), PJ (2018).  
The total bioenergy potential (crop residues and manure) of voivodships is depicted in Figure 7. Greater Poland, Masovian, Lublin, and Kuyavian-Pomeranian are the top four voivodships, whose collectible biomass potential totaled 46.68% of national biomass resource potential. The demand of farmers in Podlaskie Voivodeship for straw (soil conservation, bedding and feed consumption for livestock) exceeds its production. As a result, the voivodeship has negative energy potential and is forced to import straw. The share of crop residues is the highest and constitutes 60.62%. Sugar beet leaves have the lowest value of 1.87% (Figure 8).  
Figure 6: Sugar beet and its leaf yield and production history.  
Figure 7: Voivodship bioenergy potential in 2018.  
The use of agricultural residues for power and heat generation results in a reduction of carbon dioxide emissions. Its value is determined in the following subsection.