The continuous advancement of the food industry is accompanied by increased generation of animal waste, including poultry feathers. Composting presents a sustainable alternative to disposal methods such as incineration by converting waste into valuable fertilizer products. This study aimed to evaluate the impact of inoculation with the keratinolytic strain Bacillus subtilis P22 on the quality and maturity of compost produced from feathers combined with organic additives (wood shavings and lignite). The experiment involved evaluation of the keratinolytic potential of the tested strain, and characterization of its proteolytic enzymes, solid-state cultures and composting conducted at semi-technical scale. The B. subtilis P22 strain demonstrated the ability to solubilize 78% of feather material within 7 days of cultivation. The keratinolytic enzyme complex was likely dominated by polycatalytic alkaline serine proteases, i.e., subtilisins. The effectiveness of the inoculum was confirmed in laboratory solid-state cultures, where the dry mass loss in inoculated samples was twice that of the control containing only endogenous microflora. At the semi-technical scale, inoculation with B. subtilis P22 significantly accelerated compost maturation and mineralization (C/N = 10.2; N-NH₄⁺/N-NO₃⁻ = 0.4; Cw/Corg = 0.9) compared to the control. The final compost’s mineral composition indicates its potential for use as an organic soil amendment.

Reprocessing lignocellulosic waste to obtain new products for industrial purposes is a vital part of circular economy. This paper reports the cellulase production by newly isolated Bacillus methylotrophicus cultured on lignocellulosic agro-industrial by-products, out of which brewer’s spent grain (BSG) was selected as most beneficial. Plackett–Burman design was used for screening medium components, while Box–Behnken design was further applied to model the impact of the three most influential variables. The maximum approximated cellulase activity was 0.469 U/mL (1 U = 1 µmol of reducing sugars/1 min), at 48.6 g/L substrate, 5.3 g/L ammonium sulfate, pH 6.1. The partially purified cellulase was characterized, which demonstrated broad range of optimal pH (6.5–9.4), temperature (50–60 °C), and sensitivity to metals. Changes in lignin and pentosans content was demonstrated as a result of BSG hydrolysis with a cell-free cellulase preparation. The produced enzyme was used for hydrolysis of various chemically pretreated (NaOH and H₂SO₄) cellulosic substrates, where for reused alkali-pretreated BSG (after microbial enzyme production) the saccharification efficiency was at a level of 25%. The cellulolytic potential of the bacterial strain, along with its resistance to ethanol, present a beneficial combination, potentially applicable to aid saccharification of lignocellulosic by-products for biofuel production.

Bioleaching, mediated by selected microflora, offers a more environmentally friendly and cost-effective alternative to traditional mining techniques by transforming metals from sulfide ores into water-soluble forms. Pyrite ores often contain valuable rare or noble metals, such as gold (Au), silver (Ag), nickel (Ni), and cobalt (Co), which can be leached through the metabolic activity of specific chemoautotrophic microorganisms. This study investigates the adaptation process of the Acidithiobacillus ferriphilus bacterial strain, originally isolated from acid mine drainage (AMD), for the bioleaching of pyrite. The progress of the bioleaching process was evidenced by the release of iron (3.6 mg/mL) and significant quantities of gold (0.21 mg/L, equivalent to 3 g/t) into the post-culture liquid. The results indicate that the most effective bioleaching was achieved during the final adaptation stage, utilizing a medium with 7% pyrite content and a 0.75% supplement of an easily accessible energy source in the form of iron sulfate. These findings confirm the potential of the A. ferriphilus strain for pyrite bioleaching.

This study addresses degraded post-mining soil reclamation by developing a novel, microbially-inoculated waste-derived feather–straw–lignite organic-mineral compost material. Formulated from chicken feathers (20%), wheat straw (60%), and lignite (20%) to optimize the initial C:N ratio, the substrate was inoculated with a multi-strain complex (MIX) of Bacillus altitudinis 33, Bacillus methylotrophicus Alk, and Streptomyces fulvissimus K59. Testing progressed from laboratory scale to a 200 dm³ dynamic reactor and a 2025 field evaluation with maize (Zea mays L.) on sandy mining soils in Konin (Poland). Inoculation accelerated maturation, yielding a favorable C:N ratio of 12.09 and stabilized NH4-N of 0.03%. Peak dehydrogenase activity reached 16 DU by day 3. Field application enhanced sandy soil properties, increasing urease activity to 3.91 UU and providing 3.4 g/kg P₂O₅. Consequently, maize showed a highly significant 15% increase in average shoot height (30.23 cm vs. 25.88 cm in control; t(645) = 6.63, p < 0.001) and intense green coloration. However, absolute soil enzymatic activity remained low due to early spring moisture limitations and temperature constraints typical of temperate climates. These initial findings suggest that the microbially-enriched compost shows strong potential as a safe functional soil-reclamation material and compliant alternative to synthetic fertilizers.

This study evaluates the potential of fine-grained waste gneiss as a soil improver, with particular emphasis on its chemical and grain composition and its effects on plant growth. The experimental material consisted of mixtures of fine-grained waste gneiss with varying proportions (from 0.38% to 7.5% in the pot) supplemented with varying proportions of dolomite (from 0.14% to 0.22% in the pot). Pot experiments were conducted for 57 days under controlled conditions using selected crops. Plant response was assessed based on growth rate, green mass production, and dry mass. For most tested variants, the results demonstrated a dose-dependent enhancement in plant productivity associated with gneiss supplementation. Compared to the control, experiments containing higher proportions of fine-grained gneiss resulted in an increase in green and dry mass from 8.14% to 78.73% and by 12.5% to 96.88%, respectively. Additionally, strong positive correlations between gneiss content and yield parameters (Pearson’s r > 0.8) were observed. In contrast, the dolomite fraction mainly conceptually affected soil chemical properties, including calcium and magnesium availability and pH stabilization. Overall, the findings suggest that fine-grained waste gneiss acts as a growth-promoting soil conditioner, as evidenced by the marked improvement in plant biomass. The findings confirm the high potential of waste gneiss as a functional soil improver, supporting sustainable resource management and aligning with the principles of the circular economy.