The treatment of post-processing liquid from the hydrothermal carbonization of sewage sludge

The liquid phase, being a major product of the hydrothermal carbonization of sewage sludge, is highly problematic due to numerous toxic compounds that make it impossible to dispose of without adequate purification. Therefore, this study is focused on the two groups of selected advanced methods of post-processing water derived from the hydrothermal carbonization process of sewage sludge. The first group included membrane processes, namely ultrafiltration, nanofiltration and double nanofiltration. The second included coagulation, ultrasonication and chlorination. Chemical and physical indicators were determined to confirm the validity of these treatment methods. The highest reduction values were found for double nanofiltration, which showed a spectacular decrease in the Chemical Oxygen Demand by 84.9 %, specific conductivity by 71.3 %, nitrate nitrogen by 92.4 %, phosphate phosphorus by 97.1 %, total organic carbon by 83.3 %, total carbon by 83.6 %, and inorganic carbon by 88.5 %, as compared to the liquid phase after hydrothermal carbonization. In the second group, for the largest number of parameters, the greatest reduction was achieved when 10 cm³/L of iron coagulant was added to the permeate from ultrafiltration. Additionally, COD decreased by 41 %, P-PO₄^3- content by 78 %, phenol content by 34 %, TOC content by 97 %, TC content by 95 % and IC content by 40 %.