# Thermal Hydrolysis of Sewage Sludge: A Case Study of a WWTP in Burgos, Spain
## 3 Results and Discussion
### Total Self-Consumption, Electric Power Balance and Specific Energy Parameters  
Table 8 represents the total self-consumption (details are provided in Tables S3-S5), the electric power balance and the values for energy-specific parameters. For the calculation of these parameters, the inlet of TS and VS are those values set at the incoming section of the control volume established, which, in this case, takes the mixing ring as the starting point where primary and secondary sludge are homogenised. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Parameter** & **Scenario 1** & **Scenario 2** & **Scenario 3** & **Scenario 4** & **Scenario 5** \\ \hline \hline \multicolumn{6}{c}{**Total self-consumption of electric power**} \\ \hline \multicolumn{6}{c}{**\(\text{EP}_{\text{additional}}\), additional self-consumption (\(\text{kW}\))**} & \(\dots\) & 197.3 & 139.4 & 189.2 & 177.2 \\ \multicolumn{6}{c}{\(\text{EP}_{\text{saved}}\), consumption saving (\(\text{kW}\))} & \(\dots\) & 129.8 & 75.1 & 72.2 & 66.1 \\ \multicolumn{6}{c}{Total self-consumption (\(\text{kW}\))} & \(\dots\) & 67.5 & 64.3 & 125 & 111.1 \\ \hline \multicolumn{6}{c}{**Electric power balance**} \\ \hline \hline \multicolumn{6}{c}{**Electric efficiency of engines (\%)**} & 38.3 & 38.2 & 35.3 & 36.2 & 37.8 \\ \multicolumn{6}{c}{\(\text{EP}_{\text{ang.gross electric power (kW)}}\)} & 1048 & 1039 & 1050 & 1183 & 1478 \\ \multicolumn{6}{c}{\(\text{\%SC}\), percentage of self-consumption (\%)} & 0 & 6.5 & 6.1 & 10.6 & 7.5 \\ \multicolumn{6}{c}{\(\text{EP}_{\text{eng.net}}\), net electric power (\(\text{kW}\))} & 1048.0 & 971.5 & 985.7 & 1058.0 & 1366.9 \\ \hline \multicolumn{6}{c}{**Specific energy parameters**} \\ \hline \hline SBP, specific production of biogas (\(\text{m}^{3}/\text{t}\,\text{ST}\)) \({}^{\text{a}}\) & 310 & 406 & 380 & 434 & 484 \\ \multicolumn{6}{c}{\(\text{TP}_{\text{biogas-specific}}\), specific biogas production (\(\text{MWh}/\text{t}\,\text{ST}\))} & 1829 & 2395 & 2238 & 2560 & 2855 \\ \multicolumn{6}{c}{\(\text{EP}_{\text{cross-specific}}\), gross specific electric power (\(\text{MWh}/\text{t}\,\text{ST}\))} & 699 & 693 & 700 & 766 & 986 \\ \multicolumn{6}{c}{\(\text{EP}_{\text{net-specific}}\), net specific electric power (\(\text{MWh}/\text{t}\,\text{ST}\))} & 699 & 648 & 657 & 705 & 911 \\ \multicolumn{6}{c}{\(\text{SPV}_{\text{VS}}\), specific production of biogas by VS removed} & 900 & 900 & 900 & 900 & 900 \\ \multicolumn{6}{c}{\(\text{m}^{3}/\text{t}\,\text{VS}\)} & 31 & 22.4 & 40 & 56.1 \\ \multicolumn{6}{c}{\(\text{Increment of net biogas production (\%)}\)} & \(\dots\) & \(-0.8\) & 8.6 & 19.2 & 42.5 \\ \multicolumn{6}{c}{\(\text{Increment of gross electric power production (\%)}\)} & \(\dots\) & \(-0.9\) & 0.2 & 12.9 & 41 \\ \multicolumn{6}{c}{\(\text{Increment of net electric power production (\%)}\)} & \(\dots\) & \(-7.3\) & \(-6\) & 0.9 & 30.3 \\ \hline \hline \end{tabular}  
* \({}^{\text{a}}\): Specific biogas production was calculated from [10; 13; 22; 23] based on VS removal expected for the different scenarios.  
\end{table} 
Table 8: Total self-consumption, electric power and specific energy parameters obtained from the economic balance under the assumptions of Case I. Scenarios 2 and 3 report a value of 64 kW as electricity self-consumption, whilst Scenarios 4 and 5 report a value of 102 kW, 59.4% higher. However, the demand for electricity expressed in terms of percentage is about the same (6%, with this value being calculated using the total electrical energy consumed by the plant and that globally produced as a base) for all scenarios; however, for Scenario 4, a value of 8.7% was reached. The gross production of biogas in Scenario 2 is 31% higher than that of Scenario 1, reporting a higher production thanks to the sludge pretreatment. However, the use of biogas by the recovery mixed boiler leads to a decrease in biogas available for the engines.