# Evaluation of Eco-Efficiency of Two Alternative Agricultural Biogas Plants
## 3 Results  
### Life Cycle Assessment  
The results of the computations are presented in relation to the defined functional unit in the following order: (1) the total environmental impact of examined biogas plants; and (2) the impact of individual operational stages of the examined biogas plants, with special emphasis on stages with the highest values of cumulative eco-indicator. A positive value of the eco-indicator means a negative environmental impact (environmental burden), while a negative value means an environmental benefit the higher the positive result of the eco-indicator, the higher the negative environmental impact, and the higher the negative result of the eco-indicator, the higher the environmental benefit. The analysis of the results of the conducted studies demonstrated that Biogas Plant A generates a negative environmental impact. The value of the eco-indicator for this type of installation amounts to 2.02 Pt. On the other hand, Biogas Plant B demonstrates a negative eco-indicator value of \(-0.25\) Pt, which means that it generates favourable environmental effects during its operation (Table 2). The environmental benefit gained in the Biogas Plant B results from the fact that the positive environmental impact associated with its operation exceeds appearing related burdens. It is associated not only with the organisation of waste-to-energy stage in this installation but also with a significant limitation of wheeled transport of raw materials. In the case of Biogas Plant A, the highest impact was recorded for the damage category associated with human health. At the same time, for Biogas Plant B, the environmental impact on all damage categories is expressed in negative values of the eco-indicator (Table 2). Thus, Biogas Plant A generates environmental burden in all the analysed damage categories, whereas Biogas Plant B fully balances the environmental damages under consideration. The largest change within the value of the eco-indicator was observed for the _depletion of natural resources_ category, which means that avoiding the extraction of fossil fuels as a result of waste-to-energy in Biogas Plant B is the most favourable environmental effect associated with this installation as compared to the operation of Biogas Plant A. Results at a level of the so-called damage category may be further specified through their breakdown into fifteen impact categories (Figure 2). While comparing individual impact categories, it was recognised that Biogas Plant A is responsible for almost all negative environmental impacts considered within these categories. In the scope of the _terrestrial acid_ subcategory (_ecosystem quality \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Damage Category**} & \multicolumn{2}{c}{**Eco-Indicator Value [Pt/1 MWh]**} \\ \cline{2-3}  & **A** & **B** \\ \hline Human health & \(0.66\) & \(-0.04\) \\ Ecosystem quality & \(0.17\) & \(-0.00\) \\ Climate changes & \(0.57\) & \(-0.1312\) \\ Resources & \(0.62\) & \(-0.09\) \\ \hline TOTAL VALUE & \(2.02\) & \(-0.25\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Negative and positive environmental impact of the examined biogas plants expressed as weighted results of damage category indicators. category) 12% of negative impacts occur for Biogas Plant B, and it is actually the only category in which an adverse environmental impact for this biogas plant was demonstrated. For the other three categories, _respiratory organics_, _land occupation_ and _mineral extraction_, the negative impact is marginal and represents around 1% for each. This is mainly the result of the fact that the digestate in Biogas Plant B is stored in an open lagoon, which generates ambient air emissions of ammonia and residual methane. The value of the eco-indicator for the digestate storage stage for Biogas Plant B amounts to 59.65 mPt/1 MWh (Table 3). Moreover, Biogas Plant B potentially results in avoiding many environmental damages generated by Biogas Plant A.