## 3 Results and Discussion
### Substrates and Their Characteristics
#### 3.1.2 Substrates and Their Characteristics in CN BGPs  
In the CN BGPs, substrates (only manure) were transported to plants each day, but no storage silos were present. CN1 fed CSM (about 1101 t/a) together with digestate for dilution (about 36 m\({}^{3}\)/d according to the operator, instead of using fresh water). CN2 fed 995 t/a of CSM and 1109 t/a of CM into four identical digesters. CN3 fed 898 t/a of pig manure.  
\begin{table}
\begin{tabular}{l l l l l l l} \hline \hline
**Types** & **Indicators** & **DE1** & **DE2** & **DE3** & **CN1** & **CN2** & **CN3** \\ \hline \multirow{4}{*}{CSM} & FM (t/a) & & & 411 & 1101 & 995 & \\  & DM (\%) & & & 53.9 \(\pm\) 7.5 & 26.3 \(\pm\) 0.9 & 25.7 \(\pm\) 2.7 & \\  & ODM (\%) & & & 46.3 \(\pm\) 6.3 & 19.3 \(\pm\) 2.0 & 19.5 \(\pm\) 3.0 & \\  & FM amount & 313 & 4616 & 272 & & 1109 & \\ CM & DM (\%) & 23.3 \(\pm\) 3.0 & 25.9 \(\pm\) 3.5 & 24.7 \(\pm\) 4.6 & & 31.4 \(\pm\) 2.5 & \\  & ODM (\% FM) & 18.5 \(\pm\) 2.1 & 21.5 \(\pm\) 2.7 & 19.0 \(\pm\) 3.7 & & 23.9 \(\pm\) 0.8 & \\  & FM amount & & & & & 898 \\ PM & DM (\%) & & & & & 26.2 \(\pm\) 2.1 \\  & ODM (\% FM) & & & & & 20.2 \(\pm\) 1.8 \\  & FM amount & 2683 & 7300 & 3043 & & & \\ LM & DM (\%) & 6.9 \(\pm\) 1.9 & 4.5 \(\pm\) 2.2 & 10.2 \(\pm\) 3.4 & & \\  & ODM (\% FM) & 5.2 \(\pm\) 1.6 & 3.5 \(\pm\) 1.9 & 7.8 \(\pm\) 2.6 & & \\  & FM amount & & 10,468 & 215 & & \\ MS & DM (\%) & & 37.7 \(\pm\) 3.2 & 34.1 \(\pm\) 2.9 & & \\  & ODM (\% FM) & & 36.3 \(\pm\) 3.2 & 32.9 \(\pm\) 2.8 & & \\  & FM amount & 3755 & & 591 & & \\ GS & DM (\%) & 32.3 \(\pm\) 4.9 & & 27.1 \(\pm\) 10.8 & & \\  & ODM (\% FM) & 28.5 \(\pm\) 4.3 & & 23.5 \(\pm\) 10.3 & & \\  & FM amount & & 627 & & & \\ CL & DM (\%) & & 83.3 \(\pm\) 6.7 & & & \\  & ODM (\% FM) & & 81.0 \(\pm\) 6.5 & & & \\  & FM amount & & & 13,140 & & \\ DS 1 & DM (\%) & & & & 3.1 \(\pm\) 1.6 & \\  & ODM (\% FM) & & & 1.4 \(\pm\) 0.6 & & \\ Total energy crops FM (t/a) & 3755 & 11,695 & 806 & & & \\ Total manure FM (t/a) & 2996 & 11,916 & 3726 & 14,241 & 2103 & 898 \\ Total FM (t/a) & 6751 & 23,611 & 4532 & 14,241 & 2103 & 898 \\ Total substrate cost (\(\xi\)/a) & 0 (Self-supply) & 277,843.2 & 0 (Self-supply) & 14,101.6 & 19,420.7 & 9475.6 \\ \hline \hline \end{tabular}  
* assumption based on the CN1 operator. CSM = chicken solid manure, CM = cow manure, PM = pig manure, LM = liquid manure, MS = maize silage, GS = grass silage, CL = cereal leftover, DM = dry matter, ODM = organic dry matter, DS = digestate slurry.  
\end{table}
Table 2: Annual substrate input and characteristics in German (DE) and Chinese (CN) biogas plants. Results are averages \(\pm\) SD.  
It was found that the CSM from DE and CN had significantly different compositions. For instance, CSM in CN1 and CN2 had a DM value of 26.3 \(\pm\) 0.9% and 25.7 \(\pm\) 2.7%, respectively, and an ODM value of 19.3 \(\pm\) 2.0% FM and 19.5 \(\pm\) 3.0% FM, respectively. However, in DE3, CSM had a DM value of 53.9 \(\pm\) 7.5% and an ODM value of 46.3 \(\pm\) 6.3% FM. This can be caused by different types of chicken reared, as well as different farming systems used. This result is supported by the research carried out by [PERSON] et al. (2020) for seven CSM samples collected in Lithuania, in which the DM ranged between 27.71 \(\pm\) 1.13% and 81.80 \(\pm\) 1.75%, and the ODM ranged between 45.90 \(\pm\) 2.05% DM and 85.88 \(\pm\) 0.88% DM [40]. Furthermore, CN BGPs used only livestock manure as substrates while DE BGPs used both livestock manure and energy crops as substrates, which can lead to a significant difference in productivity (Table 3).