This article examines the process of pressure agglomeration of garden waste compost mixed with sewage sludge ash (SSA) to produce granulated fertilizer material, using a flat die rotating compaction roller system. The study evaluated the effects of adding SSA at mass fractions of 0%, 10%, 20%, 30%, 40%, and 50% on the process of pelleting and the quality of pellets. Increasing the SSA content from 0% to 50% reduced the power demand of the pellet mill by 13.5% (from 4.92 kW to 4.25 kW), decreased the kinetic strength of the pellets by 0.7% (from 98.21% to 97.56%), and slightly increased the pellet density, by 2.6% (from 1641.17 kg·m⁻³ to 1684.09 kg·m⁻³). The high density of the pellets, i.e., over 1600 kg·m⁻³, indicates that they are of market quality. A chemical analysis revealed that SSA addition positively influenced fertilizer properties. A higher SSA content (up to 50%) decreased the nitrogen content (1.4% to 0.73%) but significantly increased the phosphorus content (0.32% to 2.67%). The potassium content remained stable, at approximately 1.3%. The process of co-pelleting also diluted the heavy metals present in SSA, reducing the final product’s lead and cadmium levels to meet the standards set for fertilizers. Although the SSA contained high levels of heavy metals (lead: 93.89 mg·kg_d.m.⁻¹, cadmium: 11.28 mg·kg_d.m.⁻¹), these elements were not detected in the compost. Co-pelleting of compost and SSA produces high-density, high-quality fertilizer pellets with favorable nutrient profiles and heavy metal contents, complying with regulatory standards. Moreover, by converting garden waste and SSA into valuable agricultural products, the process supports sustainable waste management. This study evaluated the impact of SSA additives on the composition and water absorption of the granulate, providing insights into its suitability as an eco-friendly fertilizer alternative and its potential implications for sustainable agricultural practices.

This paper presents the findings of a study of the pelleting process of pine sawdust with the addition of waste in the form of potato pulp (as a natural binder), in the context of producing fuel pellets. The process of pelleting was carried out for sawdust and for a mixture of sawdust and potato pulp (10, 15, 20, and 25%). The highest moisture content was obtained in the case of pellets produced from a mixture of straw with a 25% potato pulp content, i.e., 26.54% (with a potato pulp moisture content of 85.08%). Increasing the potato pulp content in a mixture with sawdust from 10 to 25% reduced the power demand of the pelletizer by approx. 20% (from 7.35 to 5.92 kW). The obtained density values for pellets made from a mixture of sawdust and potato pulp (over 1000 kg∙m⁻³) with a potato pulp content of 10% make it possible to conclude that the obtained pellets meet the requirements of the ISO 17225-2:2021-11 standard. Increasing the potato pulp content from 0 to 25% caused a slight decrease in the heat of combustion, i.e., from 20.45 to 20.32 MJ∙kg⁻¹, as well as in the calorific value, from 19.02 to 18.83 MJ∙kg⁻¹ (both for dry sawdust matter and the mixture). The results of the laboratory tests were used to verify the densification process of mixtures of sawdust and potato pulp under industrial conditions at the PANBAH plant, using pelleting mixtures with a 5%, 10%, and 25% content of potato pulp. Industrial research also confirmed that the use of the addition of potato pulp in a mixture with sawdust significantly reduces the power demand of the pelletizer, and it also increases the kinetic strength of the obtained pellets.

The paper presents the results of a study on the effects of the addition of bread bakery waste (stale bread, sometimes infected with mold, from store returns) to agricultural waste consisting of triticale straw on the process of solid biofuel pelleting and the physical and fuel properties of the obtained pellets. The pelleting process was conducted in a pelletizer equipped with a flat matrix, with holes 6 mm in diameter, and two pelleting rollers (for straw alone and for a mixture of straw and bread waste with mass fractions of 5, 10, and 15%). The addition of bread waste during the process of pelleting resulted in reduced power demand for the pelletizer in each of the analyzed cases. The largest decrease in the power demand (by approximately 18%, i.e., from 1.27 to 1.04 kW) was recorded for a 15% addition of sunflower seed bread to the mixture with straw. Moreover, the addition of bread waste also caused a significant increase in the kinetic strength of pellets compared to pellets produced from straw alone. The highest kinetic strength was obtained in the case of pellets produced from a mixture of straw with a 15% white bread content, i.e., 99.43%. For all of the analyzed types of additives, kinetic strength increased with increasing additive content. In each of the analyzed cases, the obtained values of density of pellets produced from a mixture of straw and bread waste, as well as the kinetic strength, allow for the conclusion that the obtained pellets, in this respect, meet the requirements of ISO 17225-2:2021 and ENplus standards for Class A1 pellets.

This paper presents research findings on the pelleting process of pine sawdust using bakery waste in a pelletizer. The addition of bakery waste (white wheat–rye bread, whole-grain rye bread, and pumpkin bread) to pine sawdust had a beneficial effect on the kinetic strength of the pellets obtained, an increase of up to approximately three percentage points. The density of pellets with the addition of bakery waste also increased, while the bulk density of the pellets decreased. The addition of bakery waste also had a positive effect on the power demand of the pelletizer. It was reduced from 3.08% (at a 10% addition of white wheat–rye bread) to 22.18% (at a 20% addition of pumpkin bread), compared to the process of compacting pure pine sawdust. In addition, all the pellets containing bakery waste had a lower energy yield (EY) determined based on lower heating value and energy inputs. This index was lower by 53 Wh·kg⁻¹ for pine sawdust pellets with a 10% addition of pumpkin bread. The greatest reduction, on the other hand, was by 173 Wh·kg⁻¹ for pellets, with a 20% addition of white wheat–rye bread. In each case, an increase in the share of bakery additives resulted in a decrease in the energy yield from the pellets obtained. The smallest reduction in EY was found when pumpkin bread was used as an additive (from 53 to 133 Wh·kg⁻¹). Considering all the parameters analyzed characterizing the pellets obtained, it was concluded that the addition of bakery residues to pelletized pine sawdust should not exceed 10%. Further increases in the proportion of bakery waste did not yield relative benefits, due to the deterioration of the energy characteristics of the pellets obtained.

The safe management of waste from biomass combustion is a global problem, as the use of biomass for energy purposes is increasing around the world. Many rapidly developing countries in Asia, Africa, and South America have weak legal regulations regarding the composition of biomass combustion waste, such as ashes. As a result of the improper management of ashes, some of the pollutants may enter agricultural soils and pose a long-term risk to human health through the accumulation of harmful compounds in food. For this reason, research was carried out on the possibility of reducing harmful contaminants contained in ash in the composting process. The work presents the results of the content of 16 polycyclic aromatic hydrocarbons (PAHs) in the created composts, followed by an analysis of the toxicity, mutagenicity, and carcinogenicity of the created fertilisers. Based on the results obtained, a positive impact of the composting process on the reduction in PAHs contained in ash was found. Composting the mixture at 20 °C resulted in a slight decrease in the ΣPAH₁₆ content from 2185.46 µg∙kg⁻¹ to 2063.48 µg∙kg⁻¹. A greater reduction in ΣPAH₁₆ was obtained in the mixture incubated at 40 °C, where an overall decrease in the ΣPAH₁₆ content was recorded from 2185.46 µg∙kg⁻¹ to 1372.38 µg∙kg⁻¹. The composting process also had a positive impact on the TEQ = CEQ, MEQ, and TCDD-TEQ coefficients, causing their decrease.

This paper presents the results of a study on the process of the pelletization of pine sawdust with the addition of herbaceous waste from elderberry, in the working system of a pellet press with a flat matrix, in the context of producing fuel pellets. Based on the research, the impact of the addition of herbal waste in the form of elderberry waste on the granulation process of pine sawdust and the assessment of the quality of the obtained pellets were determined. The addition of herbaceous waste from elderberry to pine sawdust had a beneficial effect on the kinetic durability of the obtained fuel pellets, with an increase of up to approximately 1.3% (from 98.03 to 99.31%). Based on the obtained results, it can be concluded that the mechanical strength of all the tested pellets is higher than 97.5%, which is consistent with the ISO 17225-1:2021-11 standard. The bulk density of pellets with the addition of herbaceous waste from elderberry increased (from 649.34 to 658.50 kg∙m⁻³) as did their density (from 1231.38 to 1263.90 kg∙m⁻³). The addition of herbaceous waste from elderberry in amounts ranging from 10% to 20% did not have a significant effect on the power requirements of the pelletizer, which decreased compared to the pelletization process of pure pine sawdust. The percentage of this decrease compared to the pelleting process with pure pine sawdust was approximately 10%. The addition of herbaceous waste from elderberry to pine sawdust slightly reduces the energy value (i.e., the heat of combustion and the calorific value) of the obtained pellets. The addition of 30% elderberry waste resulted in a decrease in the heat of combustion from 20.27 to 19.96 MJ·kg_d.m.⁻¹, while the calorific value of the pellets decreased from 19.98 to 18.69 MJ·kg_d.m.⁻¹ compared to pine sawdust pellets. Hence, adding herbaceous waste from elderberry seems to be a good way of managing large amounts of waste of this kind generated in herbal processing plants. This method of waste management opens new perspectives towards more sustainable and economically effective energy production.