# Recent Advances in Hydrothermal Oxidation Technology for Sludge Treatment
## 2 Results and Discussion
### Comparison of Sludge Before and After HTO Treatment  
In order to study the changes before and after the reaction of sludge treated by hydrothermal oxidation technology, including its treatment efficiency of organic pollutants and dewatering performance of sludge and product composition, the following summary was made, as shown in Table 8:  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Original Sludge Type** & **Treatment Process** & **Before Treatment** & **After Treatment** & **Reference** \\ \hline Pharmaceutical Sludge & CWO & COD: 15,000–16,000 & COD and VSS removal rates: 81.2\%, 93.8\% & [15] \\ \hline Municipal Sludge & HTO-Alkaline Hydrolysis & TCOD: 12,000, COD: 285–320, TP: 25.52, pH: 6.52 & COD: 69,500, TP: 1145, pH: 11.8, TN: 2150 (NH\({}_{3}\)-N: 1080, NO\({}_{3}\)-N: 693) & [11] \\ \hline  & & Soluble TOC and COD: 65, 164; total TOC and COD: 3880, 13,000 \(\pm\) 260; TSS, VSS: 14,448 \(\pm\) 28.3, 9310 \(\pm\) 12.5, and 93.8\% & Total COD and VSS removal rate & [11] \\ \hline Municipal Sludge & HTO & Soluble TOC and COD: 65, 164; total TOC and COD: 3880, 13,000 \(\pm\) 260; TSS, VSS: 960, 13,000 \(\pm\) 260; TSS, VSS: 93.8\% & Total COD and VSS removal rate & [11] \\ \hline  & & Soluble TOC and COD: 65, 164; total TOC and COD: 3880, 13,000 \(\pm\) 260; TSS, VSS: 980, 13,000 \(\pm\) 260; TSS, VSS: 93.8\% & Total COD and VSS removal rates: 78.6\%, 89.3\%, acetic acid, formic acid, and 900, 100, 100 \\ \hline  & & & & \\  & & & & \\  & & & & \\  & & & & \\  & & & & \\  & & & & \\  & & & & \\ \hline Coal Chemical Sludge & HTO & Total COD: 20,000–25,000, & 89.3\%, acetic acid, formic acid, and 900, 100, 100 & [35] \\  & & pH: 7.42–8.56 & oxalic acid concentrations: 7000, & 350 \\ \hline  & & & & about 1500 \\ \hline Mechanical Processing & CWO & Initial sludge with particle size 100–200 μm, moisture content 76.30\% & Sludge particle size significantly reduced, moisture content 51.72\% & [20] \\ \hline Coal Chemical Sludge & CWO & COD: 16,500–17,500, VSS/SS 81.3\%, pH: 8.47 & COD, VSS, and SCOD removal rates: 78.3\%, pH: 8.47 & [38] \\ \hline Municipal Sludge & CWPO & Moisture content: 95.5\%, TN: 12.5, NH\({}_{4}\)\({}^{*}\): 10.3, CST: 163.5 & Moisture content: 38.5\%, SCST: 8.74, 16.5\%, TN: 153.4, 16.5\% & Total COD, VSS, and NH\({}_{4}\)\({}^{*}\): 52.3 & Total COD, VSS, and SCOD removal rates: 78.3\%, pH: 8.47 & Total COD, VSS, and SCOD removal rates: 78.3\%, pH: 8.3\%, acetic acid concentrations: 4000, 4750 \\ \hline  & & & & \\  & & & & \\ \hline Municipal Sludge & CWPO & No: 4.24\%, volatile: 45\%, & \multirow{2}{*}{Dentification rate: 76.2\%, protein:} & \multirow{2}{*}{[64]} \\  & & fixed carbon: 99\% & & 4184 \\ \hline Municipal Sludge & CWPO & Ammonia nitrogen: 1230, & \multirow{2}{*}{Acetic acid: 2923.41, moisture content: 46.41\%} & Acetic acid: 2923.41, moisture content: 45.70\%, ammonia Nitrogen: & [44] \\ \hline  & & & & SCFA: 6070, acetic acid accounts for 28.2\%, 2830 \(\pm\) 80, non-volatile lactic acid: 750 \(\pm\) 20, lactic acid bacteria, & \multirow{2}{*}{[41]} \\ Urban Sludge & HTO & TCOD: 22,030 \(\pm\) 40, SCOD: 350 \(\pm\) 150, TOC: 6100 \(\pm\) 800, TSS: 33,000 \(\pm\) 1000, VSS: 26,800 \(\pm\) 400 & & \\  & & & & \\  & & & & \\  & & & & \\ \hline Municipal Sludge & HTO/HT & Ni, Cu, Hg, Cr, Zn: 28, 150, 0.6, 19, 340 mg/g & Ni, Cu, Hg, Cr, Zn removal rates: 86.7\%, 56.1\%, 35.7\%, 14\%, 11.2\% & [30] \\ \hline  & & & & 98\% phosphorus recovery in liquid 2000 200 2000 2000 2000 2000 2000 2000 2000 2000 2000 2000 2000 2000 2000 2000 20000 2000 2000 2000 2000 2000 2000 2000 2000 2000 2000 20000 2000 2000 2000 20000 2000 20000 2000 20000 20000 20000 2000 20000 2000 20000 20000 20000 20000 20000 20000 200000 20000  
From Table 8, it is evident that sludge undergoes significant changes after treatment with hydrothermal oxidation technology, which is reflected in several key aspects: first, the dewatering performance of the sludge improves, leading to a reduction in moisture content.