## 2 Biogas Production in AnMBRs
### Process Yield
#### 2.2.2 Impact of Temperature  
It is apparent that temperature plays a key role in biogas production in AnMBR technology. Indeed, it mainly affects the structure and composition of the microbial community, the thermodynamic equilibrium of biochemical conversion, and the stoichiometry of the final products [126,127]. More precisely, the process temperature allows the thermodynamically feasible reactions and microorganisms able to grow [128]. In general, municipal wastewater has a temperature below 20 \({}^{\circ}\)C, which limits the hydrolysis process and the dissolution of complex organic constituents (Table 1) [125]. It should be pointed out that the microbial community is sensitive to temperature fluctuations, which may lead to changes in the rate of maximum specific growth and substrate utilization [129]. Moreover, the decreasing temperature may result in a decrease in both the production rate of volatile fatty acids and ammonia concentration [40]. Furthermore, the temperature has a significant impact on the hydrogen partial pressure in a rector; hence, it affects the kinetics of the syntrophic metabolism [130]. Due to the aforementioned reasons, it is of crucial importance to investigate the impact of temperature on the biogas yield in AnMBR technology. From a technological point of view, the important fact is that temperature may have an impact on methane distribution between the gas and liquid phases. Indeed, a decrease in temperature leads to an increase in the fraction of methane dissolved in a permeate [131,132]. Surprisingly, according to the data presented in Table 2, it can be indicated that although many attempts have been made to examine the biogas production in AnMBRs, the influence of temperature on the process performance has only been reported in a limited number of studies for both laboratory-scale [95] and pilot-scale [74,76,80] installations. Figure 5: Impact of temperature HRT of the average methane yield in submerged AnMBRs used for the treatment of municipal and domestic wastewater. Data from [70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 87, 89, 90, 92, 95, 96]. \begin{table}
\begin{tabular}{l l l l l l l l l l l l l l l l} \hline \multicolumn{1}{c}{**AABAR**} & \multicolumn{3}{c}{**Montenance Concentration**} & \multicolumn{3}{c}{**Process Conditions**} & \multicolumn{3}{c}{**Rigorous Membrane**} \\ \multicolumn{1}{c}{**Scale**} & \multicolumn{1}{c}{**Configuration**} & \multicolumn{1}{c}{**Volume (\(\lambda\))**} & \multicolumn{1}{c}{**Type**} & \multicolumn{1}{c}{**Fore Value**} & \multicolumn{1}{c}{**Montial Condition**} & \multicolumn{1}{c}{**Configuration**} & \multicolumn{1}{c}{**Area (\(\mu\))**} & \multicolumn{1}{c}{**Temperature**} & \multicolumn{1}{c}{**size (\(\mu\))**} & \multicolumn{1}{c}{**Net**} & \multicolumn{1}{c}{**\#H**} & \multicolumn{1}{c}{**Performance (\(\mu\))**} & \multicolumn{1}{c}{**Ref. **} \\ \cline{2-17}  & & & & & & &  
[PERSON] et al. [95] investigated the application of a laboratory-scale submerged anaerobic membrane bioreactor for the treatment of municipal wastewater under constant HRT equal to 6 h and temperatures of 15 \({}^{\circ}\)C; 20 \({}^{\circ}\)C; and 25 \({}^{\circ}\)C. For this purpose, a PVDF microfiltration membrane was used. In the above-mentioned study, it was demonstrated that temperature has a remarkable effect on biogas production. Indeed, for 20 \({}^{\circ}\)C and 25 \({}^{\circ}\)C, the obtained biogas yield was equal to 0.18 L/g COD and 0.22 L/g COD, respectively. In turn, for a temperature of 15 \({}^{\circ}\)C, the value of 0.09 \(\pm\) 0.02 L/g COD was obtained. These results demonstrated that at low operation temperatures, the activity of anaerobic microorganisms is significantly lower. The same range of temperature values was applied by [PERSON] et al. [80] wherein a pilot-scale AnMBR system equipped with a PVDF microfiltration membrane was used. Likewise, it was shown that temperature is a key factor affecting methane production.