Recovery of chemical energy from retentates from cascade membrane filtration of hydrothermal carbonisation effluent

Organic fraction of municipal solid waste is a type of biomass that is attractive due to its marginal cost and suitability for biogas production. The residual product of organic waste digestion is digestate, the high moisture content of which is a problem, even after mechanical dewatering, due to the significant heat requirement for drying. Hydrothermal carbonisation is a process that can potentially offer great benefits by improved mechanical dewatering and valorisation of the digestate into a better-quality solid fuel. However, such valorisation produces liquid by-product effluent rich in organic compounds. Membrane separation could be used to treat such effluent and increase the concentration of the organic compounds while at the same time facilitating the recovery of clean water in the permeate. This work presents the results of the investigation performed using polymeric membranes. The study showed that membrane separation keeps a significant fraction of organics in the retentate. Such concentration significantly increases the biomethane potential of such effluent as well as the energy that could be theoretically used for the generation of process heat using the concentrated retentate in the wet oxidation process.Web of Science284art. no. 12852

Hydrothermal Carbonisation as Treatment for Effective Moisture Removal from Digestate—Mechanical Dewatering, Flashing-Off, and Condensates’ Processing

One of the processes that can serve to valorise low-quality biomass and organic waste is hydrothermal carbonization (HTC). It is a thermochemical process that transpires in the presence of water and uses heat to convert wet feedstocks into hydrochar (the solid product of hydrothermal carbonization). In the present experimental study, an improvement consisting of an increased hydrophobic character of HTC-treated biomass is demonstrated through the presentation of enhanced mechanical dewatering at different pressures due to HTC valorisation. As part of this work’s scope, flashing-off of low-quality steam is additionally explored, allowing for the recovery of the physical enthalpy of hot hydrochar slurry. The flashing-off vapours, apart from steam, contain condensable hydrocarbons. Accordingly, a membrane system that purifies such effluent and the subsequent recovery of chemical energy from the retentate are taken into account. Moreover, the biomethane potential is calculated for the condensates, presenting the possibility for the chemical energy recovery of the condensates.Web of Science1613art. no. 510

Estimating the NEMA characteristics of the J-PET tomograph using the GATE package

The novel whole-body PET system based on plastic scintillators is developed by the {J-PET} Collaboration. It consists of plastic scintillator strips arranged axially in the form of a cylinder, allowing the cost-effective construction of the total-body PET. In order to determine properties of the scanner prototype and optimize its geometry, advanced computer simulations using the GATE software were performed. The spatial resolution, the sensitivity, the scatter fraction and the noise equivalent count rate were estimated according to the NEMA norm as a function of the length of the tomograph, number of the detection layers, diameter of the tomographic chamber and for various types of the applied readout. For the single-layer geometry with the diameter of 85 cm, strip length of 100 cm, cross-section of 4 mm x 20 mm and silicon photomultipliers with the additional layer of wavelength shifter as the readout, the spatial resolution (FWHM) in the centre of the scanner is equal to 3 mm (radial, tangential) and 6 mm (axial). For the analogous double-layer geometry with the same readout, diameter and scintillator length, with the strip cross-section of 7 mm x 20 mm, the NECR peak of 300 kcps was reached at 40 kBq/cc activity concentration, the scatter fraction is estimated to about 35% and the sensitivity at the centre amounts to 14.9 cps/kBq. Sensitivity profiles were also determined

Multiphase analysis of hydrochars obtained by anaerobic digestion of municipal solid waste organic fraction

Digestate is a nutrient-rich substance produced by anaerobic digestion that contains organic, inorganic, and biological matter. The European Nitrates Directive (91/676/EEC) provides regulations regarding the wider implementation of the digestate. Owing to a significant amount of organic matter in the digestate, it can be utilised as a solid biofuel, soil amendment substance, or substrate for activated carbon production. However, the solid by-products of the anaerobic digestion of the municipal solid waste wet fraction cannot be used for such applications because it is still considered a waste. Hydrothermal carbonisation (HTC) was investigated as a pre-treatment method for the digestate obtained by anaerobic digestion of the municipal solid waste wet fraction. HTC was carried out at temperatures of 180, 200 and 230 °C and residence times of 30, 60 and 120 min. The value of pressure was determined based on water temperature and partial pressure of the gaseous by-products. The HTC process resulted in changes in the physical and chemical properties of the hydrochars compared to those of the raw materials. A temperature of 200 °C and residence time of 60 min during HTC were optimal for energy consumption; this hydrochar exhibited the best combustion parameters and physical properties (specific surface area)

Cascade Membrane System for Separation of Water and Organics from Liquid By-Products of HTC of the Agricultural Digestate—Evaluation of Performance

New regulations aimed at curbing the problem of eutrophication introduce limitations for traditional ways to use the by-product of anaerobic digestion—the digestate. Hydrothermal carbonisation (HTC) can be a viable way to valorise the digestate in an energy-efficient manner and at the same time maximise the synergy in terms of recovery of water, nutrients, followed by more efficient use of the remaining carbon. Additionally, hydrothermal treatment is a feasible way to recirculate recalcitrant process residues. Recirculation to anaerobic digestion enables recovery of a significant part of chemical energy lost in HTC by organics dissolved in the liquid effluent. Recirculating back to the HTC process can enhance nutrient recovery by making process water more acidic. However, such an effect of synergy can be exploited to its full extent only when viable separation techniques are applied to separate organic by-products of HTC and water. The results presented in this study show that using cascade membrane systems (microfiltration (MF) → ultrafiltration (UF) → nanofiltration (NF)), using polymeric membranes, can facilitate such separation. The best results were obtained by conducting sequential treatment of the liquid by-product of HTC in the following membrane sequence: MF 0.2 µm → UF PES 10 → NF NPO30P, which allowed reaching COD removal efficiency of almost 60%