Properties of Animal-Origin Ash—A Valuable Material for Circular Economy

Sustainable heavy metal (Cr(VI) ion) remediation: Ternary blend approach with chitosan, carboxymethyl cellulose, and bioactive glass

Heavy metal pollution poses a significant environmental challenge to worldwide, especially in developing countries. This study focuses on eliminating the heavy metal chromium (VI) ion from wastewater, employing an eco-friendly and economical ternary blend composed of Chitosan (CS), Carboxymethyl cellulose (CMC), and bioactive glass (BAG). The innovative bioactive glass is crafted from biosilica extracted from biowaste of cow dung ash, calcium oxide from eggshell ash, and phosphorus pentoxide. The CS/CMC/BAG blend is prepared via sol-gel method and characterized using XRD, FT-IR, TGA, BET, TEM and SEM revealing a porous structural morphology during blending. Batch adsorption studies explore various parameters such as pH, adsorbent dose, contact time and initial metal ion concentrations. The results are then evaluated through adsorption kinetics and adsorption isotherms (Langmuir, Freundlich, D-R, and Temkin isotherm modeling). The investigation concludes that the optimal conditions for Cr (VI) removal are pH 3, contact time of 300 min, adsorbent dosage of 0.5 g, and an initial metal ion concentration of 50 ppm. The adsorption isotherm model indicates an excellent fit with the Freundlich isotherm (R2 = 0.9576) and pseudo-second-order kinetics (R2 = 0.981). In summary, the CS/CMC/BAG ternary blend exhibits a remarkable ability to effectively remove heavy metal Cr(VI) ions from industrial wastewater.

Properties of Poultry-Manure-Derived Biochar for Peat Substitution in Growing Media

Peat is considered a contentious input in horticulture. Therefore, there is a search for suitable alternatives with similar properties that can be used for partial or complete peat substitution in growing media. Poultry-manure-derived biochar (PMB) is considered such an alternative. This study aimed at determining the properties of PMBs obtained through pyrolysis at selected temperatures and assessing their potentials to substitute peat in growing media based on the selected properties. The scope included the laboratory-scale pyrolysis of poultry manure at the temperatures of 425-725 °C; the determination of selected physico-chemical and physical properties of the obtained biochars, including the contaminants; and the assessment of the potentials of produced biochars to be used as peat substitutes. PMBs contained less than 36% of total organic carbon (TOC). The contents of P and K were about 2.03-3.91% and 2.74-5.13%, respectively. PMBs did not retain N. They can be safely used as the concentrations of heavy metals, polycyclic aromatic hydrocarbons (PAHs), polychlorinatd biphenyls (PCBs), dioxins, and furans are within the permissible values (except for Cr). Due to high pH (9.24-12.35), they can have a liming effect. High water holding capacity (WHC) in the range of 158-232% w/w could allow for the maintenance of moisture in the growing media. PMBs obtained at 525 °C, 625 °C, and 725 °C showed required stability (H/Corg < 0.7).

The role of additives in improving the flammability and calorific value of leather shavings and the binding of chromium compounds in ash

Leather processing companies are struggling with the problem of increasing costs of post-production waste disposal. Therefore, the issue of thermal waste disposal at the plant and the use of generated heat in the production process is becoming more and more popular. Leather waste on its own does not allow for autothermal combustion despite the sufficient higher heating value (HHV). Therefore the Authors proposed to improve the flammability of the fuel by adding a small amount of wood sawdust to leather waste and produce premixed pellets. Six such samples were incinerated in a laboratory-scale reactor, which enables the simultaneous measurement of characteristic temperatures, exhaust gas analysis and sample mass loss rate. Research has shown that even a small addition of sawdust enables a stable combustion process and does not cause the formation of sinters. In addition, studies of the ash showed that in the case of chromium-containing waste, a large part of it remained in the ash in the form of Cr₂O₃. Nevertheless, very fine ash causes the small fraction chromium to be carried with the flue gas stream, therefore controlled agglomeration of the ash structure would be advisable in the final installation. Emission analysis showed high and moderately high NO_x and SO₂ emissions, decreasing with the increase in the amount of sawdust addition in the sample. Research has shown that leather waste is not a burden, but can be an attractive and safe source of energy for the company, while improving waste management in a circular economy.

Innovative Technological Approach for the Cyclic Nutrients Adsorption by Post-Digestion Sewage Sludge-Based Ash Co-Formed with Some Nanostructural Additives under a Circular Economy Framework

This paper presents a new, innovative technological approach, in line with Circular Economy principles, to the effective management of sludge generated during municipal wastewater treatment processes and subsequently used for biogas production. This approach allows for optimal, functional, and controlled cascade-type biotechnological thermal conversion of carbon compounds present in sewage sludge, later in solid digestate residues (after biogas production), and finally in the ash structure (after incineration, purposefully dosed nanostructural additives make the production of a useful solid product possible, especially for cyclic adsorption and slow release of nutrients (N, P, K) in the soil). The idea is generally targeted at achieving an innovative conversion cycle under a Circular Economy framework. In particular, it is based on an energy carrier (methane biogas) and direct energy production. The functionalized combustion by-products can be advantageous in agriculture. The use of ashes with nanostructural additives (halloysite, kaolinite) from combustion of sewage sludge after the anaerobic fermentation as an adsorbent of selected nutrients important in agriculture (Na+, K+, NO3-, SO42-, PO43-, Cl-) was verified at laboratory scale. The tests were carried out both for pure ash and for the ash derived from combustion with the purposeful addition of kaolinite or halloysite. The equilibrium conditions for nitrate, potassium, sodium, phosphate(V), sulphate(VI), and chloride ions from aqueous solutions with the use of the three adsorbent structures were determined. The obtained innovative results were interpreted theoretically with adsorption isotherm models (Langmuir, Freundlich, Temkin, Jovanović). The most spectacular and clearly favorable results related to the influence of nanostructural additives in the process of sludge combustion, and formation of sorption surfaces under high temperature conditions were identified in the case of sorption-based separation of phosphate(V) ions (an increase from 1.13% to 61.24% with the addition of kaolinite, and even up to 76.19% with addition of halloysite).