## 3 Anaerobic Digestion Plant Technologies
high strength industrial and municipal wastewaters in order to achieve solids free effluents and a high efficiency in pathogen removal. However, further investigations are being conducted to increase the efficiency of anaerobic plants. The main issues to be addressed are module configuration, aeration systems, control systems, surface modifications, low-energy membrane cleaning and fouling mitigation methods [24]. Examples of novel strategies for mechanical cleaning are those based on the use of granular medium, membrane vibration and electric field. \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline \multicolumn{4}{c}{**(a) unstructured reactor versus conventional anaerobic reactor [22]**} \\ \hline \multicolumn{2}{c}{**Description**} & \multicolumn{2}{c}{**Advantages**} & \multicolumn{2}{c}{**Drawbacks**} \\ \hline \hline \multirow{8}{*}{**Unstructured reactor**} & \multirow{8}{*}{\begin{tabular}{} \end{tabular} } & \multirow{8}{*}{\begin{tabular}{} \end{tabular} } & Lowest gas production \\  & & & * Least controlled system \\  & & & Longest HRT \\  & & & Low tech & Cover maintenance and service life \\  & & & Easy to construct & Large footprint \\  & & & & Solids and nutrients accumulation \\ \hline \hline \multirow{8}{*}{**Anaerobic sequence batch reactor—ASBR**} & \multirow{8}{*}{\begin{tabular}{} \end{tabular} } & Better process control \\  & & * & Higher process efficiency \\  & & * & Wide range of influent volumes \\  & & * & Efficient quality control of \\  & & & the effluent \\  & & used for treatment and fermentation \\  & & & Flexibility of use \\  & & & Low input process and \\  & & & mechanical requirements \\  & & & Cost-effectiveness \\  & & & High biogas yield \\ \hline \hline \multirow{8}{*}{**Complete stirred tank reactor—CSTR**} & \multirow{8}{*}{\begin{tabular}{} \end{tabular} } & \multirow{8}{*}{\begin{tabular}{} \end{tabular} } & Reliability for wastewater, high-dense liquid animal manure and organic industrial waste \\  & & & Complete mixing \\  & & & microorganism concentration \\  & & * & Prop-phase/two-stage system \\  & & * & Simplicity of construction \\ \hline \multirow{8}{*}{**Anaerobic plug-flow reactor—APFR**} & \multirow{2}{*}{\
\begin{tabular}{} \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{} \end{tabular} } & Low VFA concentration in the effluent \\  & & & High degree of sludge retention \\  & & * & High degree of sludge retention \\  & & * & Process stability \\  & & * & Low retention time \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison among different digester technologies. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & & **(b) sludge retention reactor[22]** & \\ \hline
**Description** & **Advantages** & **Drawbacks** & **Description** \\ \hline
**Anaerobic contact reactor—ACR** & & \(\bullet\) & Efficient process \\  & & \(\bullet\) & Rapidly achieved steady-state \\  & & \(\bullet\) & times due to mixing \\  & & \(\bullet\) & Sufficiently short hydraulic \\  & & solid settling tank for & retention time \\  & & microorganism & \(\bullet\) & Limited biomass washout \\  & & recycling, generally in & \(\bullet\) & Low change in biogas \\  & & mesophilic condition. & concentration and composition \\  & & \(\bullet\) & Good for OLR higher than \\  & & & 8 kg COD/m\({}^{3}\)/d with COD \\  & & & removal of 78–95\% \\ \hline
**Un-flow anaerobic** & & \(\bullet\) & Compact and inexpensive \\  & & \(\bullet\) & Less reactor volume and space \\  & & \(\bullet\) & Higher flow velocity and \\  & & \(\bullet\) & Bigas production \\  & & \(\bullet\) & Bigas production \\  & & \(\bullet\) & Bigar organic load \\  & & \(\bullet\) & Bigar content time than AF \\  & & \(\bullet\) & Bigar content recycling needed \\  & & \(\bullet\) & Bigar content recycling needed \\  & & \(\bullet\) & Bigar content recycling needed \\  & & & \\ \hline
**Up-flow anaerobic** & & \(\bullet\) & Higher processing efficiency in \\  & & \(\bullet\) & terms of hydrolytic and \\  & & \(\bullet\) & Highenogenic power \\  & & \(\bullet\)