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).
Sewage sludge (SS) recycling is an important part of the proposed 'circular economy' concept. SS can be valorized via torrefaction (also known as 'low-temperature pyrolysis' or 'roasting'). SS can, ...therefore, be considered a low-quality fuel or a source of nutrients essential for plant growth. Biochar produced by torrefaction of SS is a form of carbonized fuel or fertilizer. In this research, for the first time, we tested the feasibility of torrefaction of SS with high ash content for either fuel or organic fertilizer production. The research was conducted in 18 variants (six torrefaction temperatures between 200~300 °C, and three process residence times of 20, 40, 60 min) in 5 repetitions. Fuel and fertilizer properties and multiple regression analysis of produced biochar were conducted. The higher heating value (HHV) of raw SS was 21.2 MJ·kg
. Produced biochar was characterized by HHV up to 12.85 MJ·kg
and lower H/C and O/C molar ratio. Therefore, torrefaction of SS with high ash content should not be considered as a method for improving the fuel properties. Instead, the production of fertilizer appears to be favorable. The torrefaction increased C, N, Mg, Ca, K, Na concentration in relation to raw SS. No significant (
< 0.05) influence of the increase of temperature and residence time on the increase of biogenic elements in biochar was found, however the highest biogenic element content, were found in biochar produced for 60 min, under the temperature ranging from 200 to 240 °C. Obtained biochars met the Polish regulatory criteria for mineral-organic fertilizer. Therefore SS torrefaction may be considered a feasible waste recycling technology. The calculation of torrefaction energy and the mass balance shows energy demand <2.5 GJ∙Mg
w.m., and the expected mass yield of the product, organic fertilizer, is ~178 kg∙Mg
w.m of SS. Further investigation should consider the scaling-up of the SS torrefaction process, with the application of other types of SSs.
The aim of the work was to analyze the impact of biochar produced under various production conditions on the course of the dark (hydrogen) fermentation process. A series of experiments were planned, ...in which the starting material was digestate from a functioning agricultural biogas plant. Changes in the physicochemical properties and microstructure of biochar obtained in the manufacturing process with different parameters were also analyzed. Another issue analyzed was the size and dynamics of the gas production during dark fermentation with the use of various types of auxiliary material. This work showed that increasing the temperature and holding time during the production of biochar from digestion pulp improved the dynamics of biohydrogen production during the process of dark fermentation. The results of this research can be used in industrial research to optimize the process of biohydrogen production using biochar.
Energy production from renewable sources is one of the main ways to fight against global warming. Anaerobic digestion process can be used to produce biogas containing methane. In the light of the ...growing demand for substrates, a variety of raw materials are required. These substrates should be suitable for anaerobic digestion, and processing them need to provide the desired amount of energy. This paper aims to discuss the agricultural biogas market in Poland, its current state, and the possibility of development during energy transformation, in particular in terms of using waste as a substrate for energy production. In February 2022, there were 130 agricultural biogas plants registered in Poland. On the other hand, in 2020, 4,409,054.898 Mg of raw materials were used to produce agricultural biogas in Poland. Among all the substrates used, waste played a special role. With the right amount of raw materials and proper management of a biogas plant, it is possible to produce electricity and provide stable and predictable heat supply. Bearing in mind the development of the Polish and European biogas markets, attention should be paid to ensure access to raw materials from which chemical energy in the form of biogas can be generated. Due to limited access to farmland and the increasing demand for food production, one should expect that waste will be increasingly often used for biogas production, especially that with high energy potential, such as waste related to animal production and the meat industry.
Improved technologies are needed for sustainable management of sewage sludge (SS). The torrefaction (also known as biomass “roasting”) is considered a pretreatment of SS before use in agriculture. ...However, it is not known whether the torrefaction has the potential to decrease heavy metals’ (HMs) leachability and the SS toxicity. Thus, the aim of the study was to evaluate the influences of the SS torrefaction parameters (temperature and process time) on HM contents in biochar, HM leachability, and biochar toxicity, and compare them with raw SS. The experiments were designed in 18 combinations (six temperatures, 200, 220, 240, 260, 280, and 300 °C; and three process times—20, 40, 60 min). Standard tests were used to determine HMs content, leachability, and toxicity. Results indicated that the torrefaction did not increase (p < 0.05) the HM content in comparison to the raw SS. The leachability of Zn, Ni, Cu, Cr, and Mn from SS biochars was similar to raw SS. However, the degree of leachability varied significantly (p < 0.05) from as low as 0.1% for Cu to high as 16.7% for Cd. The leachability of Cd (<16.7%) and Pb (<11.9%) from biochars was higher than from raw SS (<6.1% and <2.4%, respectively). The leachability of Cd from SS biochar, in five torrefaction combinations, was higher than the threshold value for hazardous waste. It is recommended that site-specific decisions are made for torrefaction of SS with respect to its HM content, as the resulting biochar could be considered as hazardous waste, depending on the feedstock. Moreover, the biochar produced under the whole range of temperatures during 20 min retention time significantly (p < 0.05) increased the Daphnia magna Straus mobility inhibition by up to 100% in comparison to the biochar obtained during 40 and 60 min torrefaction. Taking into account the increased leachability of specific HMs and D. magna Straus mobility inhibition, biochar should be considered a potentially hazardous material. Future research should focus on biochar dosage as a fertilizer in relation to its toxicity. Additional research is warranted to focus on the optimization of SS torrefaction process parameters affecting the toxicity.
Digestate from a biogas plant can be a valuable organic and mineral fertilizer. Quantitative proportions of co-substrates used in three agricultural biogas plants in Poland were analyzed. The ...composition of digestates was examined and large differences in the content of macronutrients were found, especially N and K. On the basis of the factors used to calculate emissions from the production and use of artificial fertilizers, the GHG reduction resulting from replacing mineral fertilizers with digestate was calculated. In terms of 1 Mg of fresh digestate, this reduction may not seem large, as it amounts to 27.9-61.6 kg of CO2 eq, but it should be taken into account that digestate contains little dry matter. The annual amount of digestate used on an area of 1 ha allows avoiding GHG emissions of 25.8-44.5 Mg CO2 eq.
In modern agricultural biogas plants, the biowaste are increasingly used for biogas production. Food waste are also widely used in larvae breeding. This is important because, based on biowaste, its ...proper management and green energy production is possible. This study aims to determine the biogas and methane efficiency of Hermetia illucens larvae that were fed using food waste. In the research on biogas and methane efficiency, Hermetia illucens larvae were used. The total solids (TS) of the substrate equals 30.35%, and volatile solids (VS) content was 92.31% of TS. The larvae were fed only by plant origin food waste. The obtained substrates were homogeneous. The experiment was carried out under mesophilic anaerobic digestion conditions – 39°C in the 21-chamber biofermentor set in the Institute of Biosystems Engineering in Poznań University of Life Sciences. The anaerobic digestion process in the batch reactor ran correctly. Fermentation inhibition was not detected. Biogas efficiency for larvae amounted to 198.75 m3∙Mg-1 fresh mass (FM). On the other hand, methane efficiency, amounted to 127.73 m3∙Mg-1, at methane concentration of 64.27%. Based on the research, it was found that the larvae feeding food waste can be used directly as anaerobic digestion in the bioconversion process.
The influence of sewage sludge torrefaction temperature on fuel properties was investigated. Non-lignocellulosic waste thermal treatment experiment was conducted within 1 h residence time, under the ...following temperatures: 200, 220, 240, 260, 280 and 300°C. Sawdust was used as lignocellulosic reference material. The following parameters of biochar have been measured: moisture, higher heating value, ash content, volatile compounds and sulfur content. Sawdust biochar has been confirmed to be a good quality solid fuel. High ash and sulfur content may be an obstacle for biochar energy reuse. The best temperature profile for sawdust torrefaction and fuel production for 1 h residence time was 220°C. At this temperature the product contained 84% of initial energy while decreased the mass by 25%. The best temperature profile for sewage sludge was 240°C. The energy residue was 91% and the mass residue was 85%. Higher temperatures in both cases caused excessive mass and energy losses.
Diary production is steadily increasing worldwide, as evidenced by a 1.6% increase in milk production. Cattle headcount in Europe amounts to 75.6 mln, with Poland heaving more than 10% of the EU ...population. Such a significant production is yielding massive waste and animal by products, mainly cow manure. Storage and utilization of these byproducts may result in unwanted emissions of greenhouse gasses such as methane, carbon dioxide, and other potentially dangerous compounds like ammonia. Proper manure management and utilization of animal by-products and carcasses could successfully mitigate GHG emissions. One of the main means of utilization that could be implemented in Poland is the fermentation process and biogas production. Such an approach is beneficial not only due to energy production but also because of fertilizer production in form of digestate. To allow and maximize this process deep investigation is necessary, because of the different properties of a vast type of products, for example, the biogas yield of by-products ranges from 20 to more than 500 m3 of biogas per Mg. Because of that, the fermentation process of the above-mentioned materials must be properly conducted. Mainly substrate mix and process prosperities must be carefully assessed. In this paper, the steps necessary to implement mentioned solution will be presented as well as projected outcomes.
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