## 3 Results
### Scenario 3  
The thermal hydrolysis of the whole incoming stream of manure may improve the degradability of the substrate, mainly given by the high lignocellulosic content of this type of material. There are several reports regarding the treatment of different substrates under thermal hydrolysis [20; 101; 102]. Alkaline pre-treatment seems to guarantee better solubilization performance at lower temperatures [103]. However, operational constraints associated with the handling of this type of stream and the subsequent stage for neutralizing the final material do not make this alternative an attractive technology. Different authors have reported enhancements in methane yield from 10 to 30% when evaluating thermal hydrolysis of cow manure [104; 105; 106], however, better values were obtained for swing manure, doubling the methane yield attributable to the application of thermal pre-treatment [31; 107]. If a conservative value is selected for evaluating the thermal hydrolysis of cattle manure in the present scenario, then a 20% enhancement in methane yield can be considered. The mass flow of the manure stream to be treated will account for 21,700 kg/d if the system is run at 15% TS content. Two thermal hydrolysis reactors with a working volume of 5.1 m\({}^{3}\) operating under batch conditions (3 cycles each) would be needed. Based on technical data reported by [PERSON] et al. [27], a steam injection time of 15 min was assumed with a 20 min duration for the hydrolysis process. Using these assumptions, the steam flow needed would account for 3750 kg/h for a total period of 1.5 h (derived from the summation of the six operating cycles). The energy to produce this steam flow is 22,700 MJ, with a boiler efficiency of 85.7%. However, the energy needed for heating the hydrolysis reactor should also be added (4920 MJ). Thus, it is clear that the energy necessary for running this type of system is excessive. Table 4 shows results obtained from Scenario 3. The enhancement considered 20% increase in methane yield, which translates into 3230 MJ/d. The additional energy obtained from the digestion of hydrolyzed manure is much lower than the amount needed to run the whole process (see Figure 5). A deficit of 24,350 MJ is the result of installing such a technology (value estimated considering the treatment of manure as a single substrate). Even if a higher biogas enhancement is assumed, then the extra energy obtained will be consumed in running the thermal pre-treatment. [PERSON] et al. [31] came to the same conclusion when evaluating thermal pre-treatment of different wastes (food wastes, swine manure and sewage sludge). These authors tested mesophilic and thermophilic digestion of the hydrolyzed wastes indicating that the increased energy benefits by thermal hydrolysis did not cover the energy demand of the pre-treatment. \begin{table}
\begin{tabular}{c c} \hline Plant Characteristics & Scenario 1 \\ \hline Substrate & Hydrolyzed manure + cheese \\  & whey (25\% \(\
u/w\)) \\ TS content of feed to thermal hydrolysis process & 15\% \\ TS of the feed after adding cheese whey to hydrolyzed manure & 10\% \\ Organic loading rate (based on reactor working volume) & 2.5 kg/m\({}^{3}\) d \\ Digester inlet (volumetric flow) & 34.6 m\({}^{3}\)/d \\ Digester thermal demand 1  & – \\ Biogas production from hydrolyzed manure and cheese whey & 902 m\({}^{3}\) \\ Energy in biogas & 21,450 MJ/d \\ Mass flow of dewarted digestate (30\% TS content) & 7700 kg/d \\ TS mass flow of digested material & 2309 kg/d \\ Thermal hydrolysis energy demand & 27,580 MJ/d \\ Thermal energy recovery (from flash steam) & 6840 MJ/d \\ Energy demand for digestate drying & 14,726 MJ/d \\ Energy from digestate combustion (85\% energy recovery) & 22,374 MJ/d \\ \hline \end{tabular}
\end{table} 
Table 4: Main calculated parameters of the integrated system: thermal hydrolysis and anaerobic digestion, Scenario 3. Hydrolyzed manure and cheese whey (25% \(\
u/w\)) used as substrate.