## 4 Conclusions  
Two novel neutralization methods for lime-treated CS were developed for biomethane production: (1) LD-neutralization and (2) CO\({}_{2}\)-neutralization. Compared to other processes, they do not require a washing step, and both the LD and CO\({}_{2}\) are by-products of AD. This saves the cost of additional chemical agents. They all succeeded in reducing the pH to the fermentable range and CN was quicker. Moreover, LDN facilitated AD performance in terms of gas production rate, particularly in L-AD. However, it had a significant reduction in total biomethane yield compared to CN, resulting in a negative net profit, which has entirely counterbalanced its advantage of the production rate. Furthermore, CN exhibited the highest gas production and net profit not only in L-AD but also in SS-AD, but with the disadvantage of the longest stagnation phase. Overall, this study provided references for adjusting the initial pH of lime-treated CS before AD, and CO\({}_{2}\)-neutralization is recommended as a more efficient and affordable method. The following are available online at [[https://www.mdpi.com/article/10.390/app112210884/s1](https://www.mdpi.com/article/10.390/app112210884/s1)]([https://www.mdpi.com/article/10.390/app112210884/s1](https://www.mdpi.com/article/10.390/app112210884/s1)), Figure S1: Changes in pH during liquid digestate (LD) neutralization at different ratios (\(v/w\)) of LD to lime-treated corn stover (wet mass). Data are shown as mean \(\pm\) standard deviation (SD), \(n=3\). Figure S2: Effect of I/S ratio on BMP test of microcrystalline cellulose. Data are shown as mean \(\pm\) standard deviation (SD), \(n=3\). Figure S3: Effect of temperature on BMP test of microcrystalline cellulose. Data are shown as mean \(\pm\) standard deviation (SD), \(n=3\). Figure S4: Effect of different S/I ratios on L-AD. Data are shown as mean \(\pm\) standard deviation (SD), \(n=3\). Figure S5: Effect of different pH endpoints neutralized by LD on the cumulative/daily methane yield during BMP tests of lime-treated corn stover. Data are shown as mean \(\pm\) SD, \(n=3\). Table S1: Characteristics of CS after performing different neutralization before AD. Conceptualization, L.X. and Y.L. ; methodology, L.X. and Y.L. ; formal analysis, L.X. ; investigation, L.X. and M.Y. ; resources, S.Z. ; data curation, L.X. and M.Y. ; writing-original draft preparation, L.X. and Y.L. ; writing-review and editing, L.X. and Y.L. ; visualization, L.X. and D.H.; supervision, Y.M. ; project administration, Y.L. ; funding acquisition, Y.L. and Y.M. All authors have read and agreed to the published version of the manuscript. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Items**} & \multicolumn{2}{c}{**Lime**} & \multirow{2}{*}{**Nastewater**} & \multirow{2}{*}{**Methane**} & \multirow{2}{*}{**Neth**} \\  & **Pretreatment** & & & & **Treatment** \\  & **R Reagent and** & & **Cost** & & **Profits** \\  & **Water Cost** & (**RMB/t TS a)** & & **(RMB/t TS a)** & & **(RMB/t TS a)** \\  & **(RMB/t TS a)** & & & & \\ \hline LDN-L b  & 87.41 & 0.00 & 0.00 & \(-9.33\) & \(-96.74\) \\ CN-L b  & 87.41 & 0.00 & 0.00 & \(188.30\) & \(100.89\) \\ WW-L b  & 87.41 & 82.00 & 40.00 & \(94.37\) & \(-126.89\) \\ RM-L b  & - & - & - & - \\ LDN-SS c  & 87.41 & 0.00 & 0.00 & \(24.72\) & \(-62.69\) \\ CN-SS c  & 87.41 & 0.00 & 0.00 & \(186.15\) & \(98.74\) \\ WW-SS c  & 87.41 & 82.00 & 40.00 & \(-835.10\) & \(-1056.36\) \\ RM-SS c  & - & - & - & - & - \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Economic evaluation of different neutralization methods for lime-pretreated corn stover. FundingThis work was supported by the Key Research and Development Program of Hubei Province, China (Grant No. 2020 BAB095) and Fundamental Research Funds for the Central Universities of China (Grant No. 2662021 FW006). Institutional Review Board StatementNot applicable. Informed Consent StatementNot applicable. Data Availability StatementNot applicable.