# Agricultural Residue Management for Sustainable Power Generation: The Poland Case Study
## 4 Results
### Biogas Production  
Since 1999 animal population has decreased from 9.24 to 8.90 million LSU (Figure 3) [82]. It has resulted in changing the spatial distribution of livestock unit. Greater Poland and Podlaskie vovodships have 104.02 and 93.4 LSU per km\({}^{2}\). It means that animal concentration has been increased in separate regions.  
Biogas production potential is calculated by the Equation (4). In 2018 the energy potential of biogas production was 104.45 PJ. The potential power generation is determined at 11.61 TWh (the Equation (5) is used) or 6.83% of the national electricity generation. It is lower compared to straw based power generation.  
Maize silage is the most popular feedstock for biogas production in the EU including Germany and Poland. For example, in Germany over 10% of arable land is used to cultivate maize silage [68].  
Over the last decade a number of countries of the EU have introduced limitations for cultivation of energy crops. Moreover, maize silage prices are growing. This feedstock has rather a high price. This phenomenon results in worsening the economic indicators of biogas plants. This fact forces potential investors to look for alternative substrates [5]. That is why agricultural crop residues are in the spotlight for biogas production. Corn straw is half the cost of maize silage [83; 84]. Moreover, this crop residue is not currently widely used by industry in Poland [85]. The cost of methane produced from corn straw (only at the cost of raw materials) ranges from EUR 1.61/GJ to EUR 2.78/GJ. It is much less compared to maize silage (EUR 6.42/GJ). The efficiency of corn straw-based biogas plants has been confirmed by Chinese experiences [86; 87]. The pretreatment of lignocellulosic substrate (corn straw) before anaerobic digestion results in the increase of biogas yield [88].  
The use of corn straw can increase the biogas production up to 115.64 PJ. The average increment is 10.71%. The best result can be achieved in Lower Silesian vovodship--57.68% (Figure 4). Opole and Subcarpathian vovodships have high results too. Therefore, the above three regions may be recommended to use the corn straw for co-digestion to produce biogas.  
Figure 3: Animal population history.  
Spatial agricultural residue (crop and livestock) distribution is presented in Figure 5.  
Figure 4: Increment of biogas production: DS—Lower Silesian; KP—Kuyavian-Pomeranian; LU—Lublin; LB—Lubusz; LD—Lódz; MP—Lesser Poland; MA—Masovian; OP—Opole; PK—Subcarpatian; PD—Podlaskie; PM—Pomeranian; SL—Silesian; SW—Holy Cross; WM—Warnian-Masurian; WP—Greater Poland; ZP—West Pomeranian.  
Figure 5: Dendrogram of crop and livestock residues energy potential distribution (2018).  
Six clusters emerged. The total agricultural residues have the energy potential of 273.23 PJ (Table 2) and they can generate up to 26.60 TWh or 15.65% of the national electricity production. Lublin voivodship maintains a leading position.  
Some crop residues, for example, sugar beet leaves, cannot be directly burnt for power generation. However, they can be feedstock for biogas production. Poland farmers produce sugar beet over 12 Mts per year [82]. Thus, biogas production from sugar beet leaves should be studied.