## 4 Discussion
### Improvement in AD Performance through Bioaugmentation, Comparison with Recent Research  
The accumulation of VFAs caused by impact loadings often leads to the acidification and failure of AD systems. Bioaugmentation is considered to be an effective method to alleviate the VFA inhibition of AD. The most recent research mainly reports the improvement of the mesophilic AD process through bioaugmentation with acetate and propionate-degrading consortiums (Table 3). [PERSON] et al. used the sludge previously acclimated with VFAs for the bioaugmentation of an acidified mesophilic anaerobic digestion system and increased the methane yield by 8.03-9.59 times. Acetoclastic methanogens from the acclimated sludge acted as the main contributors to pH neutralization and methane production during the early phase of bioaugmentation [63]. The bioaugmentation of mesophilic and thermophilic AD under ammonia inhibition with syntrophic acetate and propionate oxidizing consortia was investigated by [PERSON] et al. [61]. Their results showed that the bioaugmented reactors recovered \begin{table}
\begin{tabular}{p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt}} \hline \hline \multirow{2}{*}{**Feedstock**} & **Temperature/ Operation Mode** & \multicolumn{2}{c}{**Enrichment (Bioaugmentation) Culture**} & \multirow{2}{*}{**Improvements**} & \multirow{2}{*}{**Reference**} \\ \cline{3-3} \cline{5-6}  & & & **Bacteria** & & \\ \hline \multirow{8}{*}{Municipal sludge} & \multirow{8}{*}{37\({}^{\circ}\)C/fed-batch} & Mesophilic acetate and propionate-oxidizing consortia & & & \\ \cline{3-3} \cline{5-6}  & & Carbohydrates fermenter (_Latininiculum_), syntrophic & Acetoclastic and hydrogenotropic methanogens (_Methanosata_, _Methanosata_, _Syntrophic_) & Increased biogas yield by 175\% \\  & & VFAs-oxidizing bacteria (_Rikenallacac_, DMER64, _Syntrophic_) & _Methanosata_, _Methanosirillum_) & & \\ \cline{3-3} \cline{5-6}  & & Thermophilic acetate and propionate oxidizing consortia & & & \\ \cline{3-3} \cline{5-6}  & & Protcolytic bacteria (_Kratnikenchant_, and _Tepidiniumulum_), syntrophic VFAs-oxidizing bacteria (_Syntrophic_) & & & \\ \hline \multirow{8}{*}{Sewage sludge} & \multirow{8}{*}{35\({}^{\circ}\)C/semi-flow} & _Exiguchoterium_, _Acinetobacter_, _Acinetobacter_, _Syntrophicomons_ & & & \\ \cline{3-3} \cline{5-6}  & & Culture from propionate-degrading bioreactor & Organic loading rate, methane percentage, volumetric methane production and volatile solid methane production and higher 10 g L//d, 24%, 0.22 & & \\ \cline{3-3} \cline{5-6}  & & & Methanogenic, aero-tolerant propionate enrichment culture & & \\ \cline{3-3} \cline{5-6}  & & & _Syntrophicductance_ (20\%) and _Thernopause_ (12\%) & & & \\ \cline{3-3} \cline{5-6}  & & & & & \\ \cline{3-3} \cline{5-6}  & & & & & \\ \cline{3-3} \cline{5-6}  & & & & & \\ \hline \multirow{8}{*}{Simulated headily biodegradable waste (dog food)} & \multirow{8}{*}{50\({}^{\circ}\)C/batch} & Syntrophic butyrate-degrading consortiums & & & \\ \cline{3-3} \cline{5-6}  & & & _Syntrophicatrics_ (42.9\%), _Methanosacillin_ (25\%), _Methanosallisicocus_ & More than 35, 62 and 29 times higher methane production rate, methane yield, and VS removal, respectively & \\ \cline{3-3} \cline{5-6}  & & & & & \\ \cline{3-3} \cline{5-6}  & & & & & \\ \cline{3-3} \cline{5-6}  & & & & & \\ \cline{3-3} \cline{5-6}  & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Improvements in AD performance through bioaugmentation with syntrophic enrichment cultures. earlier than control reactors at 20 and 8 days, respectively, in mesophilic and thermophilic operation mode. Different bioaugmentation mechanism occurred in mesophilic and thermophilic AD, which are derived from the synergetic effects of ammonia tolerance and microbial interactions [61]. Bioaugmentation with a mixture of microorganisms (Bacteria and Archaea) was applied to improve the anaerobic digestion of sewage sludge.