Characteristics of Hydrochar and Liquid Products Obtained by Hydrothermal Carbonization and Wet Torrefaction of Poultry Litter in Mixture with Wood Sawdust

Changes in Selected Organic and Inorganic Compounds in the Hydrothermal Carbonization Process Liquid While in Storage

Although many studies have investigated the hydrothermal transformation of feedstock biomass, little is known about the stability of the compounds present in the process liquid after the carbonization process is completed. The physicochemical characteristics of hydrothermal carbonization (HTC) liquid products may change over storage time, diminishing the amount of desired products or producing unwanted contaminants. These changes may restrict the use of HTC liquid products. Here, we investigate the effect of storage temperature (20, 4, and -18 °C) and time (weeks 1-12) on structural and compositional changes of selected organic compounds and physicochemical characteristics of the process liquid from the HTC of digested cow manure. ANOVA showed that the storage time has a significant effect on the concentrations of almost all of the selected organic compounds, except acetic acid. Considerable changes in the composition of the process liquid took place at all studied temperatures, including deep freezing at -18 °C. Prominent is the polymerization of aromatic compounds with the formation of precipitates, which settle over time. This, in turn, influences the inorganic compounds present in the liquid phase by chelating or selectively adsorbing them. The implications of these results on the further processing of the process liquid for various applications are discussed.

Study on the Effect of Hydrothermal Carbonization Parameters on Fuel Properties of Chicken Manure Hydrochar

Economic development and population growth lead to the increased production of chicken manure, which is a problematic organic waste in terms of its amount, environmental threats, and moisture content. In this study, hydrothermal carbonization, an emerging way of waste disposal, was performed on chicken manure to produce an energy-rich material called hydrochar. The effects of hydrothermal carbonization temperature (180, 240, 300 °C) and process time (30, 90, 180 min) were summarized. Proximate and ultimate analysis, as well as low and high heating values were applied both on raw material and derived hydrochars. Additionally, the performance of the process was examined. The obtained results show that hydrothermal carbonization is a feasible method for chicken manure disposal and valorization. Although the process time did not influence the fuel properties of chicken manure considerably, a higher temperature led to a significantly higher heating value, reaching 23,880.67 ± 34.56 J × g^-1 at 300 °C and 180 min with an improvement of ~8329 J × g^-1 compared with raw chicken manure (15,551.67 J × g^-1). Considering the energy gain value, the hydrochar derived at 240 °C in 30 min had the best result. Moreover, the energy consumption for this process was relatively low (124.34 ± 8.29 kJ × g^-1). With its still feasible fuel properties and high heating value of 20,267.00 ± 617.83 kJ × g^-1, it was concluded that these parameters of chicken manure hydrochar are the most beneficial and present a potential alternative for conventional fuel.

Some Results of Poultry Litter Processing into a Fertilizer by the Wet Torrefaction Method in a Fluidized Bed

Poultry litter mass is formed in large quantities at poultry farms producing poultry meat (1–3 kg of litter mass per 1 kg of produced meat). These wastes represent a threat to the environment because of the presence of pathogenic microflora in them and the greenhouse gas emitted during the storage of these wastes. The procedure of poultry litter mass processing by wet torrefaction in a superheated water vapor environment at a temperature of 150–260 °C is studied. It is shown that after torrefaction at a temperature of 150 °C, the poultry litter mass retains high humidity, i.e., it represents an environment suitable for the re-development of pathogenic microflora. Only after wet torrefaction at a temperature of 260 °C does the humidity of the poultry litter mass decreases to 4%, and the risk of re-infection with pathogenic microflora decreases sharply. The absence of nitrates in the samples after torrefaction at a temperature of 260 °C indicates the termination of the activity of nitrifying bacteria. After torrefaction at a temperature of 260 °C, the poultry litter mass has a pH close to 7. This increases the mobility and availability of microelements for plants. Torrefaction at a temperature of 260 °C increases the content of ash, phosphorus and potassium by 30–40% and nitrogen by 15–20%, which makes the fertilizer more concentrated and optimizes the ratio of nitrogen, phosphorus and potassium. After wet torrefaction, due to the burning of the most easily degradable nitrogen-containing organic compounds and the destruction of some organophosphorus compounds, the mobility of nitrogen decreases, and the mobility of phosphorus increases. As a result of the research, it was found that the treatment of poultry manure by wet torrefaction in an environment of superheated water vapor at a temperature not lower than 260 °C makes it possible to obtain organic fertilizer with the most optimal nutrient content.

Superheated Steam Torrefaction of Biomass Residues with Valorisation of Platform Chemicals—Part 1: Ecological Assessment

Within the last decade, research on torrefaction has gained increasing attention due to its ability to improve the physical properties and chemical composition of biomass residues for further energetic utilisation. While most of the research works focused on improving the energy density of the solid fraction to offer an ecological alternative to coal for energy applications, little attention was paid to the valorisation of the condensable gases as platform chemicals and its ecological relevance when compared to conventional production processes. Therefore, the present study focuses on the ecological evaluation of an innovative biorefinery concept that includes superheated steam drying and the torrefaction of biomass residues at ambient pressure, the recovery of volatiles and the valorisation/separation of several valuable platform chemicals. For a reference case and an alternative system design scenario, the ecological footprint was assessed, considering the use of different biomass residues. The results show that the newly developed process can compete with established bio-based and conventional production processes for furfural, 5-HMF and acetic acid in terms of the assessed environmental performance indicators. The requirements for further research on the synthesis of other promising platform chemicals and the necessary economic evaluation of the process were elaborated.