We propose a 'Waste to Carbon' thermal transformation of sewage sludge (SS) via torrefaction to a valuable product (fuel) with a high content of carbon. One important, technological aspect to develop this concept is the determination of activation energy needed for torrefaction. Thus, this research aimed to evaluate the kinetics of SS torrefaction and determine the effects of process temperature on fuel properties of torrefied products (biochars). Torrefaction was performed using high ash content SS at six (200~300 • C) temperatures and 60 min residence (process) time. Mass loss during torrefaction ranged from 10~20%. The resulting activation energy for SS torrefaction was 12.007 kJ·mol −1 . Initial (unprocessed) SS higher heating value (HHV) was 13.5 MJ·kg −1 . However, the increase of torrefaction temperature decreased HHV from 13.4 to 3.8 MJ·kg −1 . Elemental analysis showed a significant decrease of the H/C ratio that occurred during torrefaction, while the O/C ratio fluctuated with much smaller differences. Although the activation energy was significantly lower compared with lignocellulosic materials, low-temperature SS torrefaction technology could be explored for further SS stabilization and utilization (e.g., dewatering and hygienization). Energies 2019, 12, 565 2 of 10 J.A.K.; validation, J.P., A.B., J.A.K.; investigation, J.P.; resources, J.P., A.B., P.M.; data curation, A.B., J.A.K.; writing-original draft preparation, J.P., A.B.; writing-review and editing, A.B., P.M., J.A.K.; visualization, J.P., A.B., J.A.K.; supervision, A.B., P.M., J.A.K.

Biochar (BC) addition is a novel and promising method for biogas yield increase. Brewer’s spent grain (BSG) is an abundant organic waste with a large potential for biogas production. In this research, for the first time, we test the feasibility of increasing biogas yield and rate from BSG digestion by adding BC, which was produced from BSG via torrefaction (low-temperature pyrolysis). Furthermore, we explore the digestion of BSG with the presence BCs produced from BSG via torrefaction (low-temperature pyrolysis). The proposed approach creates two alternative waste-to-energy and waste-to-carbon type utilization pathways for BSG: (1) digestion of BSG waste to produce biogas and (2) torrefaction of BSG to produce BC used for digestion. Torrefaction extended the short utility lifetime of BSG waste turned into BC. BSG was digested in the presence of BC with BC to BSG + BC weight ratio from 0 to 50%. The study was conducted during 21 days under mesophilic conditions in n = 3 trials. The content of dry mass 17.6% in all variants was constant. The kinetics results for pure BSG (0% BC) were: reaction rate constant (k) 1.535 d−1, maximum production of biogas (B0) 92.3 dm3∙kg−1d.o.m. (d.o.m. = dry organic matter), and biogas production rate (r), 103.1 dm3∙kg−1d.o.m.∙d−1. his preliminary research showed that the highest (p < 0.05) r, 227 dm3∙kg−1d.o.m.∙d−1 was due to the 5% BC addition. This production rate was significantly higher (p < 0.05) compared with all other treatments (0, 1, 3, 8, 10, 20, 30, and 50% BC dose). Due to the high variability observed between replicates, no significant differences could be detected between all the assays amended with BC and the variant 0% BC. However, a significant decrease of B0 from 85.1 to 61.0 dm3∙kg−1d.o.m. in variants with the high biochar addition (20–50% BC) was observed in relation to 5% BC (122 dm3∙kg−1d.o.m.), suggesting that BC overdose inhibits biogas production from the BSG + BC mixture. The reaction rate constant (k) was not improved by BC, and the addition of 10% and 20% BC even decreased k relatively to the 0% variant. A significant decrease of k was also observed for the doses of 10%, 20%, and 30% when compared with the 5% BC (1.89 d−1) assays.

In this work, for the first time, the feasibility of obtaining carbonized refuse-derived fuel (CRDF) pelletization from municipal solid waste (MSW) was shown. Production of CRDF by torrefaction of MSW could be the future of recycling technology. The objective was to determine the applied pressure needed to produce CRDF pellets with compressive strength (CS) comparable to conventional biomass pellets. Also, the hypothesis that a binder (water glass (WG)) applied to CRDF as a coating can improve CS was tested. The pelletizing was based on the lab-scale production of CRDF pellets with pressure ranging from 8.5 MPa to 76.2 MPa. The resulting CS pellets increased from 0.06 MPa to 3.44 MPa with applied pelletizing pressure up to the threshold of 50.8 MPa, above which it did not significantly improve (p < 0.05). It was found that the addition of 10% WG to 50.8 MPa CRDF pellets or coating them with WG did not significantly improve the CS (p < 0.05). It was possible to produce durable pellets from CRDF. The CS was comparable to pine pellets. This research advances the concept of energy recovery from MSW, particularly by providing practical information on densification of CRDF originating from the torrefaction of the flammable fraction of MSW-refuse-derived fuel. Modification of CRDF through pelletization is proposed as preparation of lower volume fuel with projected lower costs of its storage and transportation and for a wider adoption of this technology.Energies 2018, 11, 3233 2 of 20 that can be a renewable low-emission fuel. Its fuel properties, such as the lower heating value (LHV) ranging from 19.6 MJ·kg −1 to 25.3 MJ·kg −1 , compete with conventional energy generation solutions [4]. In addition, the higher heating value (HHV) of biochar, including CRDF, depending on the substrate used, can reach up to 35 MJ·kg −1 [5]. This HHV is comparable with energy content in different types of coal, such as hard coal (HHV > 23.9 MJ·kg −1 ), non-agglomerating highly volatile coals (17.4 < HHV < 23.9 MJ·kg −1 ), or lignite (HHV < 17.4 MJ·kg −1 ) [6]. Also, biochar is characterized by high energy density, hydrophobicity, improved abrasiveness and low ash content [7].The transformation of MSW into CRDF allows for solving the problem of waste storage and disposal, and the CRDF produced can be a fully-fledged renewable fuel [8][9][10]. Initial economic evaluation of MSW torrefaction has been published by Stępień et al. [11] where some basic calculations of heat demand for the process were determined. Authors concluded that the heat demand for drying and torrefaction of MSW is~1.27 GJ·Mg −1 . Assuming the heat utilization rate of 90%, the chemical energy introduced with fuel into a boiler is~1.41 GJ·Mg −1 . Assuming the use of natural gas (~$3/GJ; U.S. pricing), the total cost of drying and torrefaction is~$4.21·Mg −1 of MSW. Obviously, that cost will differ for other markets due to fuel prices and fuel type. Additional operation costs were not included [11], but despite this, the comparison of MSW torrefaction costs with other MSW t...

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Composting is generally accepted as the sustainable recycling of biowaste into a useful and beneficial product for soil. However, composting processes can produce gases that are considered air pollutants. In this dataset, we summarized the spatial and temporal distribution of process gases (including rarely reported carbon monoxide, CO) generated inside full-scale composting piles. In total 1375 cross-sections were made and presented in 230 figures. The research aimed to investigate the phenomenon of gas evolution during the composting of biowaste depending on the pile turning regime (no turning, turning once a week, and turning twice a week) and pile location (outdoors, and indoors in a composting hall). The analyzed biowaste (a mixture of tree leaves and branches, grass clippings, and sewage sludge) were composted in six piles with passive aeration including additional turning at a municipal composting plant. The chemical composition and temperature of process gases within each pile were analyzed weekly for ~49–56 days. The variations in the degree of pile aeration (O2 content), temperature, and the spatial distribution of CO, CO2 and NO concentration during the subsequent measurement cycles were summarized and visualized. The lowest O2 concentrations were associated with the central (core) part of the pile. Similarly, an increase in CO content in the pile core sections was found, which may indicate that CO is oxidized in the upper layer of composting piles. Higher CO and CO2 concentrations and temperature were also observed in the summer season, especially on the south side of piles located outdoors. The most varied results were for the NO concentrations that occurred in all conditions. The dataset was used by the composting plant operator for more sustainable management. Specifically, the dataset allowed us to make recommendations to minimize the environmental impact of composting operations and to lower the risk of worker exposure to CO. The new procedure is as follows: turning of biowaste twice a week for the first two weeks, followed by turning once a week for the next two weeks. Turning is not necessary after four weeks of the process. The recommended surface-to-volume ratio of a compost pile should not exceed 2.5. Compost piles should be constructed with a surface-to-volume ratio of less than 2 in autumn and early spring when low ambient temperatures are common.