Chen, Yanbo (2015)

Theme

Lab-scale investigations of hydro-thermal carbonization of municipal wastewater treatment sludges

Subject

Several different sludges consisting of biosolids and mineralic compounds are produced in wastewater treatment plants (i.e. primary sludge, waste activated sludge, digested sludge). Hydrothermal carbonization (HTC) has been proposed as a means to produce fuels from biosolids. The subject of this study is the lab-scale investigation of process parameters (e.g. time, pH) and reaction products of HTC of the different wastewater treatment sludges.

The graduating student is assigned to the task of designing the experimental setup, executing the experiments and evaluating the results. This includes a preliminary estimation of the required materials for the experiments as well as an estimation of reaction products derived from a literature research. Evaluation of experimental data has to be focused on process feasibility, comparison of nutrient and energy balances to regular anaerobic digestion of wastewater treatment sludges and quantity and quality of secondary by-products. Chemical analyses have to be planned accordingly. Additionally, removal of excess water by lab-scale means (e.g. centrifuge, paper filters) has to be addressed by respective investigations.

Abstract

Hydrothermal carbonization (HTC) is a process which can convert various biomass into carbonized coal-like solids. HTC is typically conducted at 150-250 °C under an autogenic pressure. The HTC process can be utilized in a variety of fields such as fuel production, carbon sequestration, catalyst and absorbent production, soil enrichment, nanomaterials and biomass pre-treatment. The HTC of sewage sludge results in a significant reduction of sludge volume as well as a considerable enhancement of sludge dewaterability. Considering the additional increase of the heating value of the solids, the HTC process provides various potential benefits to conventional sludge treatment, especially as an alternative or supplementary measure to anaerobic digestion. However, the reaction pathways in HTC process are still largely unknown and the application of HTC to the treatment of different types of sludge has not been well investigated in previous researches. Particularly the produced process liquids including their influence on wastewater treatment operations and the overall energy balance are of interest, when considering the use of HTC within the frame of municipal wastewater treatment. In this study, HTC experiments with sucrose, egg solutions and different types of sewage sludge were conducted in a lab-scale high pressure reactor. The main focus was put onto the investigation of the behavior of nitrogen, phosphorous, chemical oxygen demand and solids with regards to their distribution in solid and liquid residues of the HTC. From the results advantages of HTC and anaerobic digestion were evaluated, and the feasibility of applying HTC in sludge treatment process was discussed.
 

Supervisors