# What Advanced Treatments Can Be Used to Minimize the Production of Sewage Sludge in WWTPs?
## 3 Advanced Treatments and Technologies
### Electrochemical Treatments  
Electro-Osmosis  
In this case, the osmosis process is combined with the use of electric current [120]. [PERSON] et al. [123] have recently tested this type of treatment. They obtained up to 40-45% of dry substance content compared to 20-25% obtainable by conventional physical/mechanical processes [123]. This type of process can be applied in the sludge line, before or after the phase of stabilization, with very low energy consumption: 0.12-0.5 kWh kgwater\({}^{-1}\) for activated sludge and 0.14-0.55 kWh kgwater\({}^{-1}\) for digested sludge [124; 125]. Moreover, other advantages, such as the removal of pathogens and reduction of the final transportation cost, can be highlighted [125]. Therefore, the application of an electric field, combined with pressure, tends to increase the dehydration of the sludge. Many experimental factors can influence the reduction of water content and consequently, the process yields: (i) the electric voltage, (ii) the pressure, (iii) the contact time, (iv) the characteristics of the polyelectrolyte dosed, (v) the temperature, etc. The electrode reactions are not only influenced by the material of which the electrode is made but also by the ions contained in the sludge. The process could therefore be hindered by the characteristics of the sludge [123; 126], although the action mechanism has not yet been fully clarified [126]. Other experiments confirmed these results, and 38-45% of dry matter has been obtained [122; 127]. In Table 4, some applications and results of electro-dewatering processes are reported.  
\begin{table}
\begin{tabular}{p{56.9 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Process** & **Temperature [\({}^{\circ}\)C]** & **Results** & **Ref.** \\ \hline Combustion & 800 & The main decomposition during the combustion process is in the 180–580 \({}^{\circ}\)C temperature range. The highest mass loss is caused mainly by the decomposition of carbohydrates and lipids. After this process, c.a. 77\%, of total mass is degraded. & [116] \\ \hline Combustion & n.a. & High reduction of sludge volume by about 90\% and nearly complete elimination of the organic materials. & [110] \\ \hline Pyrolysis & 460–600 & In pyrolysis, the second stage finishes at \(\sim\)540 \({}^{\circ}\)C, with an average 55 wt.\% mass loss. The final decomposition is of inorganic matter. & [116] \\ \hline Pyrolysis & 300 & Pyrolysis temperature was the most important factor affecting the yield of biochars produced. Sewage sludge pyrolysis at 300 \({}^{\circ}\)C maximized biochar yield. & [117] \\ \hline Pyrolysis & 500–900 & Biophysical dried sludge was rapidly pyrozed at temperatures from 500 \({}^{\circ}\)C to 900 \({}^{\circ}\)C. With the temperature rising, the yield of biochars decreased, the ash content and microstructure development of biochars were promoted. & [118] \\ \hline Pyrolysis & n.a. & Volume reduction by as much as 90\% and production of a sterile carbon char high efficiency and energy self-sufficient. & [110] \\ \hline \multirow{2}{*}{
\begin{tabular}{c} Drying + \\ Gasification \\ \end{tabular} } & 120 (Drying) & SS was partially dried in an oven at 120 \({}^{\circ}\)C for 2 h. The drying reduced the moisture content from 43\% to 3.5\%. After gasification, the moisture content in the char was 2.1–2.8\%. & [119] \\ \hline \hline \end{tabular}
\end{table}
Table 3: Several applications of thermal treatments.