# Recent Advances in Hydrothermal Oxidation Technology for Sludge Treatment
## 2 Results and Discussion
### Research on Influencing Factors of Sludge Treatment by HTO
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**Sludge Type** & **Treatment Process** & **Optimal Temperature (°C)** & **Impact of Temperature (T) Change** & **Change in Efficiency/Yield (mg/L)** & **References** \\ \hline \multirow{4}{*}{Pharmaceutical Sludge} & \multirow{4}{*}{CWO} & \multirow{4}{*}{260} & T increases, the removal rate of COD accelerates obviously, the removal rate of VSS increases little, the concentration of acetic acid increases, and the concentration of formic acid and oxal acid begins to decrease & (T: 180–260 °C) The removal rate of COD: 10–60\%; and VSS: 70–97\% & [47] \\ \cline{1-1} \cline{2-5}  & & & T increases, COD and VSS removal rates significantly improve & (T: 180–260 °C) The removal rate of COD: 43–81.2\%; and VSS: 61–93.8\% & [15] \\ \hline \multirow{4}{*}{Pharmaceutical Sludge} & \multirow{4}{*}{CWO} & \multirow{4}{*}{260} & T increases, the removal rates of TSS and VSS are significantly increased, the removal rates of SOD and TCOD are significantly increased, the concentration of VFAs rises sharply and then plummets & (T: 200–260 °C) The removal rate of TSS: 72.5-90\%; and VSS: 80–98.4\% & [16] \\ \cline{1-1} \cline{2-5}  & & & T increases, the removal rates of TSS and VSS are significantly increased, the removal rates of SOD and TCOD are significantly increased, the concentration of VFAs rises sharply and then plummets & (T: 390–450 °C) The concentration of TOC: 300–2600 and COD: 900–6300, \(\mathrm{w_{co}}\): 20–30\%, and \(\mathrm{w_{sal}}\): 20–15\% & [16] \\ \hline \multirow{4}{*}{Oilfield Sludge} & \multirow{4}{*}{SCWO} & \multirow{4}{*}{450} & T increases, the concentration of TOC and COD decrease first and then became stable, gaseous carbon & (T: 390–450 °C) The concentration of TOC: 3000–2600 and COD: 9000–6300, \(\mathrm{w_{co}}\): 20–30\%, and \(\mathrm{w_{aqueous}}\): 40–30\% & [48] \\ \cline{1-1} \cline{2-5}  & & & T increases, the concentration of TOC and COD decrease first and then became stable, gaseous carbon & (T: 390–450 °C) The concentration of TOC: 3000–2600 and COD: 9000–6300, \(\mathrm{w_{co}}\): 20–30\%, and \(\mathrm{w_{aqueous}}\): 40–30\% & [48] \\ \cline{1-1} \cline{2-5}  & & & T increases, the degradation efficiency of COD, SOD, and TOC is significantly improved, VFA concentration sharply increases & \(\mathrm{w_{sal}}\): 20–15\% & [38] \\ \hline \multirow{4}{*}{C Coal Chemical Sludge} & \multirow{4}{*}{CWO} & \multirow{4}{*}{260} & T increases, COD removal rate significantly increases then decreases, acetic acid concentration increases, while formic acid concentrations decrease & (T: 180–260 °C) The removal rate of COD: 25–78.6\%; and VSS: 68–89.3\% & [35] \\ \cline{1-1} \cline{2-5}  & & & T increases, COD removal rate significantly increases then decreases, acetic acid concentration increases, while formic acid concentrations decrease & (T: 180–260 °C) The removal rate of COD: 25–78.6\%; and VSS: 68–89.3\% & [38] \\ \hline \multirow{4}{*}{C Coal Chemical Sludge} & \multirow{4}{*}{HTO} & \multirow{4}{*}{260} & T increases, COD removal rate significantly increases then decreases, acetic acid concentration increases, while formic acid concentrations decrease & (T: 180–260 °C) The removal rate of COD: 25–78.6\%; and VSS: 68–89.3\% & [38] \\ \cline{1-1} \cline{2-5}  & & & T increases, COD removal rate significantly increases then decreases, acetic acid concentration increases, while formic acid concentrations decrease & (T: 180–260 °C) The removal rate of COD: 25–78.6\%; and VSS: 68–89.3\% & [35] \\ \hline \hline \end{tabular} Note: temperature changes, other things being equal. TSS: total suspended solids, VSS: volatile suspended solids, TOC: total organic carbon, COD: chemical oxygen demand, TCOD: total chemical oxygen demand, EPS: extracellular polymers, SCOD: dissolved organic matter, VFA: volatile fatty acids, thermal hydrolysis, HTO: hydrothermal oxidation technology, CWO: catalytic wet oxidation technology, CWPO: catalytic hydrothermal oxidation technology (different oxidants), SCWO: supercritical water oxidation technology.  
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