# Recent Advancements in Anaerobic Digestion and Gasification Technology
## 5 Intensification of the Anaerobic Digestion Process  
As stated by [PERSON] et al. [8], the need to improve anaerobic digestion has been of great interest in recent years. The use of different types of additives or accelerants has been explored in several synergies, thereby enhancing the methane yield and quality of digestate, which are products of anaerobic digestion. It is important to know that the use of the additive in enhancing the performance of anaerobic digestion reduces the challenges associated with slow start-up, substrate-induced inhibition, and low energy output [8]. Some of these additives include microbes, enzymes, microelements, biological metabolites, adsorbents, deforming agents, and chelating agents. Therefore, Table 1 presents these additives, their substances, and the effects from various studies.  
Some of these additives are cost-effective and have been widely studied to test their efficacy. In this case, their findings and results were successful in enhancing gas production, favourable digestion condition, and superior organic degradation [21,33].  
Carbon-based materials intensify the process of anaerobic digestion by promoting the growth of microorganisms, providing required nutrients to microorganisms and improving the activities of enzymes. These results in quick methane production and content as well as improved quality digestate [31]. Previous studies conducted by [PERSON] et al. [29], [PERSON] et al. [30], [PERSON] et al. [31], and [PERSON] et al. [32] revealed that carbon material is necessary for anaerobic digestion because it enhances its efficiency and stability, thereby increasing the methane yield.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Types of Additives** & **Functions** & **References** \\ \hline Enzymes (Cellulose, Amylase, Lipase, etc.) & Facilitate the activities of hydrolysis of the particulate compounds & [19] \\ \hline Nutrients (Nitrogen, Phosphorus, Potassium, etc.) & Essential for the growth of biogas fermentation microorganisms & [20] \\ \hline Microelements (Iron, Cobalt, Nickel, etc.) & Essential for methanogens activities & [21] \\ \hline Inhibitors (Heavy-metal ions) & Promote the biological activity of the system at a low concentration & [22] \\ \hline Forming agent (Polyester deformer) & Help to eliminate formation during anaerobic digestion & [23] \\ \hline Absorbent (Aluminium powder) & Help to increase biogas content and methane content to a different degree; decrease BOD and COD content & [24] \\ \hline Chelating agent & Increase the growth rate of methanogens and gas production of anaerobic digestion & [25] \\ \hline Accelerants & Increase biogas yield or production, COD, and buffer capacity as well as degradation rate & [20,21,26,27] \\ \hline Carbon-based materials (Carbon nanotube, Graphene, and Carbon cloth) & Promote microbial growth and microbial immobilization; provide nutrients to microbes, resulting in faster methane production; stimulate the mechanism of methanogens as well as improve the efficiency and stability of the anaerobic process, thereby increasing methane yield & [28, 29, 30, 31, 32] \\ \hline \hline \end{tabular}
\end{table}
Table 1: Additives used in anaerobic digestion enhancement.  
The properties of graphene in relation to anaerobic digestion include electric conductivity, high mechanical strength, and large surface area. To improve the stability and efficiency of biogas digester through anaerobic digestion, graphene is required and recommended. The introduction of graphene during anaerobic digestion improves the methanogens, which is the microorganism responsible for methane production in the low-temperature range of 10-20 \({}^{\circ}\)C [27,34]. Furthermore, graphene results in the change in syntrophic microbes between methane production archaea and acidogenic microbes, which increases the rate of methane production by 28% to be specified through 71.1% _Methanobacterium_ and _Methanosarcina_ (11.3%). Graphene indeed intensifies and influences microbial community dynamics during anaerobic digestion.