Changes and release risk of typical pharmaceuticals and personal care products in sewage sludge during hydrothermal carbonization process

Hydrochars were obtained by hydrothermal carbonization treatment of municipal sewage sludge. Effects of reaction temperature (180-300 degrees C) and reaction time (2-15 h) on structural characteristics of the hydrochars, and changes and release risk of typical pharmaceuticals and personal care products (PPCPs) in the hydrochars were investigated. Reaction temperature played a more important role than reaction time on hydrochar prop-erties and decarboxylation reaction was the primary process during the converting of sludge to hydrochars. The sludge hydrochars had higher yields, carbon recovery rates, polarity and less aromaticity than biochars. Hy-drothermal process reduced PPCPs' load in sludge hydrochars effectively except caffeine and acetaminophen. The hydrochars prepared at intermediate and high temperatures (240 and 300 degrees C) had higher caffeine con-centrations than the original sludge, which can be ascribed to the transformation of N-containing precursors. The highest CaCl2 extracted caffeine concentration occurred at intermediate temperature of 240 degrees C (48.1 mu g/kg) due to the stronger affinity of caffeine in the high-temperature hydrochars. Caffeine was not detected in hydrox-ypropyl-beta-cyclodextrin (HPCD) extract. Hydrochars prepared at low temperature (180 degrees C) had a higher acet-aminophen concentration than the original sludge, which was attributed to the high thermal stability temperature of acetaminophen. Low-and intermediate-temperature hydrochars had higher CaCl2 extracted acetaminophen concentrations. The HPCD extracted acetaminophen was low with a range of nd to 6.72 mu g/kg. In conclusion, PPCPs are less likely to constitute a limiting factor on the farm application of sludge hydrochar. This study provides theoretical support for the safe application of sludge hydrochar in the farmland.

Automated summary

Hydrochars were prepared from municipal sewage sludge by hydrothermal carbonization treatment. The study found that reaction temperature had a greater impact on the properties of hydrochars and the presence of PPCPs than reaction time. The hydrothermal process effectively reduced the load of PPCPs in hydrochars, except for caffeine and acetaminophen, with their concentrations being affected by the reaction temperature.