(199c) Hydrothermal Treatment of Paper Mill Sludge: Nutrient Characterization

Each year the pulp and paper industry generates large amounts of effluent treatment sludge. The sludge is made up of three different fractions namely, primary, secondary, and tertiary sludge. Depending on the layout of the sludge handling in the individual mill, these three sludges can either be extracted separately or mixed into a stream called mixed sludge. Usually secondary and tertiary sludge are mixed together. Paper mill sludges contain several plant nutrients including P, K, N, Ca, and Mg. However, the nutrient, heavy metal, and organic composition of sludges is determined by the fiber source and treatment process, and is quite varied.

Hydrothermal carbonization (HTC) has received considerable attention during the last several years as a prominent alternative for extracting nutrient from different biomass feedstock like forest residues and industrial or municipal wastes. One of the main advantages of HTC is the use of aqueous solutions under high temperature (180-260 °C) and autogenously generated pressure (5-50 bar). As a result, moist and wet feedstocks are favorable for HTC.

This goal of this study was to determine the effects of HTC conditions on the nutrient contents in paper mill sludge. A 600 ml Parr batch reactor was used for HTC. Reaction temperature was varied from 180-260 °C, while reaction time was varied from 5-30 min. The nutrient content in solid hydrochars were assessed by evaluating ultimate analysis, FTIR, and NMR. Meanwhile, the process liquid is characterized with GCMS, HPLC, UV-VIS, NMR, and pH. The results suggested that the nutrient content of hydrochar and process liquid increased with reaction temperature. However, residence time has insignificant effect on it.