## 9 Conclusions  
This review can be summarised through the following statements. There is a lack of literature regarding the usage of sugar wastewater as a substrate for biogas production compared with municipal solid waste. It is, therefore, necessary to explore the potential of this substrate and its co-digestion compatibility, particularly in South Africa, as the country is a big sugar producer, making it a hub generating volumes of sugar wastewater in the production process. Anaerobic digestion of single substrates does not lead to maximum biogas generation; hence, two or more substrates need to be co-digested for better biogas yield and high methane content. Efficient biogas production can be achieved only if there is an excellent synergistic effect between the co-digested substrates. This means an excellent overall balance of nutrients from each substrate, leading to the correct \begin{table}
\begin{tabular}{c c c c c} \hline
**Biodigester Type** & **Feedstocks** & **Advantages** & **Shortcomings** & **Ref** \\ \hline \multirow{4}{*}{Batch} & & simple and flexible in & & \\  & & configuration and & & \\  & & operation, low & & \\  & & installation and & & \\  & & operation cost, higher & & \\  & & biomass retention & & \\ \hline \multirow{4}{*}{Upflow Anaerobic Sludge Blanket (UASB)} & Recycled and synthetic wastewater containing methanol & no need for temperature & & & \\  & & control as heat is released & & & \\  & & during methanogenesis & & & \\  & & & & \\  & & & & & \\ \hline \multirow{4}{*}{Anaerobic Sequencing Batch Reactor (ASBR)} & & relatively cheap, their & & & \\  & & stepwise nature allows & & & \\  & & observation of dynamic, & & & \\  & & repeatable behavior & & & \\  & & & & & \\ \hline \multirow{4}{*}{Covered lagoon} & & & needs hydraulic & & \\  & & easy to build, operate, & & maintenance from 20 to & \\  & & and maintain & & 90 days and wide areas, & \\ \cline{1-1}  & & & easy to leak out & & \\ \hline \end{tabular}
\end{table} 
Table 2: _Cont._microbial community and aiding an enhanced AD process. Different parameters affect biogas production differently; therefore, special attention must be paid to such parameters for thorough parametric analysis. For example, when exploring the hydraulic retention time on biogas generation, analysis must be conducted periodically in 3-5 day intervals to investigate if the AD process is affected thoroughly. Regarding temperature studies, it can be concluded that the thermophilic range leads to higher biogas yields than the psychrophilic and mesophilic ranges. However, the mesophilic range is deemed the best since the thermophilic microorganisms are sensitive to environmental changes. Biogas production is favored by pH in a range of 6.0-8.5, meaning that there should be continuous monitoring of this parameter throughout the process. This study also found that a good balance of OLR may help avoid reactor failures. The type of reactor/digester employed for biogas production depends mainly on the type of substrates treated. Finally, sugar wastewater and the municipal solid waste can be considered as good substrates for biogas production in SA due to their enormous availability and the potential to turn their negative impacts into value addition. Biogas production is a viable alternative, among others, to boost the country from its current energy issues. The study was limited regarding available literature in the South African context, which shows that there is a huge gap in the area of waste valorisation in South Africa, even though the country is struggling with waste management. This opens up space for more research to be conducted in this area using two of the country's most abundant feedstocks, sugarcane wastewater and municipal solid waste. The specific parameters to be considered for this waste valorisation are highlighted in this review as a foundation. Conceptualization, L.Z.L., M.C. and N.D.; Methodology, Z.T. and L.Z.L. ; Investigation, Z.T. ; writing--original draft preparation, Z.T. ; writing--review and editing, L.Z.L., M.C., Z.T.