# What Advanced Treatments Can Be Used to Minimize the Production of Sewage Sludge in WWTPs?
## 3 Advanced Treatments and Technologies
### Thermal Treatments  
The thermal treatments (i.e., combustion, pyrolysis and gasification) intervene with the production of SS, reducing the water content and the fraction of volatile solids. In recent years, the applications of these processes within the WWTPs, at the end of the sludge line usually after thermal drying (Figure 3), are increasing. The advantages in this case consist not only of the minimization of the SS, limiting  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Process** & **Application** & **Operative Conditions** & **Sludge Reduction/Production** & **Other Results** & **Ref.** \\ \hline \multirow{4}{*}{**MMBR**} & \multirow{2}{*}{Water line} & HRT = 6 h; & SP = 0.23-0.32 kgMLSS kg & \multirow{2}{*}{n.a.} & [99] \\  & & SRT = 20–40 d & CODownwood\({}^{-1}\) & & \\ \cline{2-5}  & \multirow{2}{*}{Water line} & T = 22 \({}^{\circ}\)C & SP = 0.22 kgMLSS kg CODownwood\({}^{-1}\) & & \\ \cline{2-5}  & & Water line & Anaerobic; & & \\  & & T = 17–33 °C & SP = 0.16 kgms kg CODownwood\({}^{-1}\) & & \\ \hline \multirow{4}{*}{**TMBR**} & \multirow{4}{*}{Sludge line} & Intermittent aeration; & & & \\  & & PH = 8;5; & & & \\  & & T = 55 \({}^{\circ}\)C; & & & \\  & & HRT = 12–31 d & & & \\ \cline{2-5}  & \multirow{2}{*}{Sludge line} & Aerobic; pH = 7; & & & \\  & & T = 55 \({}^{\circ}\)C & & & \\ \cline{2-5}  & & Aerobic; & & & \\  & & T = 55 \({}^{\circ}\)C & & & \\ \cline{2-5}  & \multirow{2}{*}{Water line} & Aerobic; & & & \\  & & SRR; & & & \\  & & Municipal wastewater; & & & \\  & & T = 12–28 °C & & & \\ \cline{2-5}  & \multirow{2}{*}{Water line} & Aerobic; & & & \\  & & & & & \\  & & & & & \\  & & & & & \\ \cline{2-5}  & \multirow{2}{*}{Water line} & Aerobic; & & & \\  & & SRR; & & & TSS removal \(>\) 90\% & [92] \\  & & Municipal wastewater; & & & & \\  & & T = 12–28 °C & & & \\ \cline{2-5}  & \multirow{2}{*}{Water line} & Aerobic; & & & & \\  & & SRR; & & lower than commonly reported for & & \\  & & Municipal wastewater & conventional treatment plants & & \\ \cline{2-5}  & \multirow{2}{*}{Water line} & Aerobic; & & & & \\  & & SRR; & & & \\  & & Municipal wastewater & & the existing plant & & \\ \cline{2-5}  & \multirow{2}{*}{Water line} & Aerobic; & & & & \\  & & SRR; & & & \\  & & Primary effluent from a tamey & & & & \\  & & WWTP & & & & \\ \hline \multirow{4}{*}{**BP**} & \multirow{4}{*}{Water line} & Protozoa; & & & & \\  & & Two-stage system; & & & \\  & Treating different pulp and & & & & \\  & paper industry wastewater & & & & \\ \cline{2-5}  & \multirow{2}{*}{Water line} & Protozoa; & & & & \\  & & Two-stage system; & & & \\  & treating synthetic wastewater & & & & \\ \cline{2-5}  & \multirow{2}{*}{Sludge line} & Metazoa _(Electronic Illinois);_ & & & \\  & HRT = 13 d & & & & \\ \cline{2-5}  & \multirow{2}{*}{Sludge line} & Metazoa _(Electronic Florida);_ & & & \\  & & HRT = 21 d & & & \\ \hline \multicolumn{5}{c}{HRT: Hydraulic retention time; SRT: Ludge retention time; SP: Sludge production; MLSS: Mixed liquor suspended solids; COD: Chemical oxygen demand; VS: Volatile solid; TOC: Total organic carbon; SRR: Sequencing batch reactor; TKN: Total kjeldahl nitrogen; SR: Sludge reduction; TSS: Total suspended solids; n.a.: Not available.} \\ \end{tabular}
\end{table}
Table 2: Several applications of biological treatments.  
the amount of generated SS exiting the WWTP, but also in the possibility of recovering the energy produced directly inside the WWTP.