Physicochemical characteristics of different pulp and paper mill waste streams for hydrothermal conversion

Abstract

The pulp and paper industry generates significant amounts of waste from various processes consisting of
\norganic and inorganic matter. Due to its composition, the management of pulp and paper mill sludge presents
\nan economic burden for wastewater treatment plants. In South Africa, paper mill sludge is mainly incinerated,
\nlandfilled or used for land application. These practices cause environmental and health hazards. In this study,
\na process of stabilization of paper mill sludge through hydrothermal carbonization is proposed. The quality of
\nbiochar produced and energy yield will depend on the elemental composition, calorific value and ash content
\nof the sludge. Results revealed samples are composed of flat fibrous cellulosic morphology, with high volatile
\nmatter and little fixed carbon percentage. The main decomposition occurred between 220-400 °C. Sludge from
\nprimary clarifier contains the highest ash percentage, hence it was found to be unsuitable for energy recovery
\nthrough hydrothermal carbonization. Sludge from kraft and recycling paper mills exhibited lower ash content
\nand higher caloric values, thus more preferable for coal conversion through hydrothermal carbonization. The
\nsludges have a sulfur composition (2.33%) compared to heavy fuel oils and bituminous coal.

Topics & Concepts