# What Advanced Treatments Can Be Used to Minimize the Production of Sewage Sludge in WWTPs?
## 5 Discussion  
The proposed treatments (Table 5) lead to a reduction in sludge production, not only in agricultural but also in urban and industrial areas. Assuming the application of proposed processes, for example, on the urban WWTPs with a capacity higher than 100,000 population equivalent (PE), this would cover more than 50% of the total load (expressed in PE) treated in EU28 [135]. In Table 7, the SS disposal options and costs in Europe are reported.  
As reported by [PERSON] et al. [25], the transport is indicated as 100% because all the disposal options require the SS transport from the WWTP where it is produced. Currently in Europe, about 9.7 million MgDM year\({}^{-1}\) of SS are produced [14]. As previously reported (e.g., Sections 3.1 and 3.2), interventions in the wastewater line present greater risks of the balance alteration in the biological reactor (i.e., CAS) and partial inhibition of biomass. Considering minimization technologies only in the sludge line, a precautionary minimization yield of 50% can be assumed. Therefore, by adopting these criteria only in the WWTPs with over 100,000 PE (i.e., about 50% of the total SS produced in Europe) makes it possible to reduce the SS produced each year to around 7.28 million MgDM year\({}^{-1}\). This would significantly reduce the costs related to the different disposal options currently adopted in Europe, as shown in Figure 5.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{2}{c}{**Process**} & \multirow{2}{*}{**Patent Name**} & \multirow{2}{*}{**Description**} \\ \cline{1-1} \cline{3-4}
**Type** & & & \\ \hline \multirow{4}{*}{Biological} & \multirow{2}{*}{TMBR} & \multirow{2}{*}{Biorime\({}^{\circledR}\)} & Biorime consists of a Thermophilic Aerobic Membrane Reactor (TAMR). TAMR works at temperatures around 54 °C. Pure oxygen is insufflated inside the reactor. \\ \cline{3-4}  & & & It allows a reduction in secondary sludge production. \\ \cline{3-4}  & \multirow{2}{*}{BP} & \multirow{2}{*}{Cannibal\({}^{\circledR}\)} & The technology is applicable both to new plants and to up-grade existing plants. The technology is based on the retention of a part of recirculating sludge in a tank subject to micro-aeration. \\ \hline \multirow{4}{*}{Thermal} & \multirow{2}{*}{Combustion} & \multirow{2}{*}{HELIOSOLIDS\({}^{\circledR}\)} & It can be applied to: (i) municipal and industrial SS, (ii) oily sludge and slurry, (iii) spent grains, (iv) paint and paint sludge, (v) shredded wood and pellets, (vi) meat and bone meal, (vii) acid oils and (viii) soap stock. \\ \cline{3-4}  & \multirow{2}{*}{Pyrolysis} & \multirow{2}{*}{PyroBoiler\({}^{\circledR}\)} & By combining the pyrolysis treatment with the drying treatment, it allows a reduction in the output flow up to 80% in weight and 60% in volume. \\ \cline{3-4}  & & & DM: Dry matter; WW: Wastewater; COD: Chemical oxygen demand. \\ \hline \hline \end{tabular}
\end{table}
Table 6: _Cont._  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Type of Disposal**} & \multirow{2}{*}{**SS Disposal [\%]****(a)**} & \multicolumn{2}{c}{**Disposal Costs [\(\text{c MgDM}^{-1}\)]****(b)**} \\ \cline{3-4}  & & **min** & **max** \\ \hline Agriculture & 28.3 & 150 & 400 \\ \multicolumn{1}{c}{Compost} & 14.8 & 250 & 600 \\ \multicolumn{1}{c}{Incineration} & 37.7 & 450 & 800 \\ \multicolumn{1}{c}{Landfill} & 7.1 & 200 & 600 \\ \multicolumn{1}{c}{Other} & 12.1 & 90 & 260 \\ \hline Transport & 100 & 50 & 160 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Sewage sludge (SS) disposal options and costs in Europe.  
Furthermore, as reported by [PERSON] et al. [136], costs vary. Minimizing the production of SS has the disadvantage of the costs of implementing the WWTPs (not subject to analysis here) but it would allow reducing the costs of disposal of the SS and would eliminate the variable given by the SS disposal price fluctuation.