Development of a Continuous Hydrothermal Treatment Process for Efficient Dewatering of Industrial Wastewater Sludge

Abstract

Sludges from the papermaking industry represent a challenging residue stream that is difficult to dewater using conventional processes. The successful development and scale-up of innovative processes from lab- to pilot- to industrial-scale are required to tackle challenges for waste treatment, including paper sludges. Biological paper sludge was treated via a mild hydrothermal carbonization process (TORWASH®) to improve dewaterability of the sludge, including long-duration, continuous testing. Initial lab-scale experiments indicated the optimal treatment temperature for sludge dewatering was 190 °C. Dewaterability improved with increasing temperature, but the obtained solid yield decreased. Scaling-up to a continuous flow pilot plant required a temperature of 200 °C to achieve optimum dewatering. Pilot-scale hydrothermal treatment and dewatering resulted in solid cakes with an average dry matter content of 38% and a solid yield of 39%. This study demonstrates the benefits of hydrothermal carbonization for the dewatering of biological paper sludge without the use of dewatering aids such as fiber sludge or polyelectrolytes. The results also demonstrate the successful adaptation of a lab-scale batch process to a pilot-scale continuous flow process for hydrothermal carbonization of industrial wastewater sludge.

Environmental Assessment of Hydrothermal Treatment of Wet Bio-Residues from Forest-Based and Agro-Industries into Intermediate Bioenergy Carriers

“…The LCA modelling of the system has been based on conceptual process design and modelling study for the systems considered [21], based on experimental work at pilot scale [20,22].…”

“…The project aims to convert wet biogenic residues into intermediate bioenergy carriers (fuel pellets) via hydrothermal treatment. The concept consists of an integrated process for mild hydrothermal carbonization (i.e., TORWASH ® , manufactured at TNO, Petten, The Netherlands) with low-temperature conversion of the biomass and full utilization of both the solids stream and the liquids stream, as well as compares three feedstocks using direct input from experiments and process modelling [20][21][22]. The F-CUBED production system includes the integration of the hydrothermal pretreatment with densification of the solid fraction, i.e., pelletization, to improve the logistics and sustainability aspects of the supply chain [9,23] and the anaerobic digestion of the liquid fraction.…”

Continuous Hydrothermal Carbonization of Olive Pomace and Orange Peels for the Production of Pellets as an Intermediate Energy Carrier

“…The pilot-scale equipment has a maximum capacity of 50 kg/h throughput. A detailed description of the pilot reactor has been previously reported [48].…”

“…As preparation for the hydrothermal carbonization experiments in a continuous-flow reactor for a prolonged time, the effect of feed concentration was tested. Previous experience with sludges has shown that feed concentrations up to 5 wt% can be processed without issues in a continuous-flow reactor [48]. The main effects analyzed in these tests were the pumpability of the feedstock and the effect of the feed concentration on the flow and temperature profile in the reactor.…”

“…One of the factors that is currently limiting the implementation of the HTC technology is the lack of knowledge on continuous pilot-scale operation. We have previously reported the successful hydrothermal treatment of biosludge from a paper mill in a continuous flow-through (TORWASH ® ) reactor [48] and a process model which showed a much more efficient feedstock utilization for the production of energy [49]. An overall block diagram of the continuous treatment of wet organic residue streams to solid hydrochar is shown in Figure 1.…”