(663c) Hydrothermal Treatment of Paper Mill Sludge

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. The primary sludge, often rich in fiber material and easy to dewater, can easily be used as fuel source. However, water is difficult to remove from mixed sludge.^1-2 Moreover, a low fuel heating value of mixed sludge results against economical combustion. Therefore, a new technology that converts mixed sludge to viable solid fuel may be required for mixed sludge valorization.

Hydrothermal carbonization (HTC) has received considerable attention during the last several years as a prominent alternative for upgrading biomass feedstock ranging from wood and algae to agricultural and 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).³ As a result, moist and wet feedstocks are favorable for HTC.⁴

This goal of this study was to determine the effects of HTC conditions on paper mill sludge dewaterbility and fuel value. A 100 ml Parr batch reactor was be used for HTC. Reaction temperature was varied from 180-260 °C, while reaction time was varied from 30 min-1h. The solid hydrochars were analyzed for energy content, ultimate analysis, FTIR, and NMR. Meanwhile, the process liquid is characterized with GCMS, HPLC, UV-VIS, NMR, and pH. The energy content of the hydrochar was increased with reaction temperature and longer reaction time as a result of the decrease in oxygen content. The resulted hydrochar is more hydrophobic than the feedstock. Therefore, dewaterbility is enhanced with the hydrothermal treatment of paper mill sludge.

References

1. Makela, M.; Benavente, V.; Fullana, A., Hydrothermal carbonization of industrial mixed sludge from a pulp and paper mill. Bioresource Technol 2016, 200, 444-450.

2. Makela, M.; Yoshikawa, K., Simulating hydrothermal treatment of sludge within a pulp and paper mill. Appl Energ 2016, 173, 177-183.

3. Reza, M. T.; Andert, J.; Wirth, B.; Busch, D.; Pielert, J.; Lynam, J. G.; Mumme, J., Hydrothermal Carbonization of Biomass for Energy and Crop Production. Applied Bioenergy 2014, 1 (1).

4. Reza, M. T.; Coronella, C.; Holtman, K. M.; Franqui-Villanueva, D.; Poulson, S. R., Hydrothermal Carbonization of Autoclaved Municipal Solid Waste Pulp and Anaerobically Treated Pulp Digestate. Acs Sustain Chem Eng 2016, 4 (7), 3649-3658.