Soil application potential of post-sorbents produced by co-sorption of humic substances and nutrients from sludge anaerobic digestion reject water.

This study introduces a novel soil conditioning approach using humic substances (HSs) and nutrients co-recovered from reject water from sewage sludge anaerobic digestion. For the first time, HSs and nutrients were simultaneously recovered through sorption on low-cost, environmentally inert materials: natural rock opoka (OP) and waste autoclaved aerated concrete (WAAC). This innovative application of OP and WAAC as carriers and delivery agents for soil-relevant substances offers potential for resource recovery and soil conditioning. Results indicate that the post-sorption opoka (PS-OP) and post-sorption waste autoclaved aerated concrete (PS-WAAC) effectively release retained HSs at 350-480 µg g⁻1 d⁻1, respectively. These materials also show potential as NPK fertilizers, releasing 280-430 µg g⁻1 d⁻1 N-NH4⁺, 80-150 µg g⁻1 d⁻1 P-PO4³â», and 270-350 µg g⁻1 d⁻1 K⁺. Additionally, PS-OP demonstrated promising fungicide properties, reducing P. diachenii growth by 31% at a concentration of 1 g L⁻1. A two-way ANOVA indicated that the effects of PS-OP and PS-WAAC on soil physicochemical and biological parameters varied with plant species. Both post-sorbents improved the quality of soil collected from sand mining area, increasing cation exchange capacity by 7%-85% and organic matter content by 10%-58%. They also enhanced the functional potential of soil microbial communities, increasing their metabolic activities by 23%-36% in soils sown with clover and by 33%-39% in soils sown with rapeseed. An opposite effect was observed in soils sown with sorghum, suggesting these amendments may not universally act as plant biostimulants. The effectiveness of these post-sorbents in enhancing plant growth varied depending on plant species and the mineral base of the post-sorbent. PS-OP increased the total length of clover and sorghum by 41% and 36%, and their fresh biomass by 82% and 80%, respectively. In turn, PS-WAAC increased the total length of clover and sorghum by 76% and 17%, and their fresh biomass by 29% and 15%, respectively. It was notably more effective than PS-OP for rapeseed. This study proposes a strategy to decrease reliance on non-renewable resources and costly sorbents while minimizing environmental impact. It shows that PS-OP and PS-WAAC can enhance soil quality, microbial activity, and plant growth. Given their origins, these amendments are recommended for soil remediation, particularly in degraded areas. Future research should focus on optimizing their application across various plant species to maximize effectiveness.

Humic substances sorption from wastewater on the biochar produced from the waste materials.

In recent years, increasing attention has been paid to the possibility of converting waste materials, e.g. manure, bio-waste, green waste, waste from the water and sewage industries (e.g. post-fermentation sludge), and agri-food waste into biochars (BCs) by pyrolysis. The ability of biochar to improve soil health and fertility is driving growing interest in its use as a soil amendment. A high soil stability of BCs and their excellent nutrient sorption properties are the main reasons for the superiority of such materials over other organic soil amendments. In addition, BCs can retain soil-relevant compounds, including humic substances (HSs). Since most of the resources used to produce humic fertilisers are non-renewable, the effluent from anaerobic digestion of sewage sludge (reject water, RW), which contains high levels of HSs, is considered a promising target for their recovery. In this study, the potential of ten BCs derived from pine, oak, straw, sunflower, and digestate at different pyrolysis temperatures for the recovery of HSs from RW was evaluated. The sorption of HSs on the applied BCs was conducted using contact method for 24 h and then determined spectrophotometrically. The most effective sorbents for HSs from RW were BCs obtained from straw in the low and high temperatures with the sorption capacity of 3.10 mg g-1 and 5.31 mg g-1, respectively. It was observed that the BCs produced from the same biomass at different pyrolysis temperatures had different sorption capacities for FA, HA, and a mixture of these compounds. The results indicated that BCs obtained from sunflower at different temperatures and oak at high temperature were the most promising sorbents for the recovery of HSs from RW. Such materials have the potential to be applied to soil and were selected for further evaluation due to their ability to enhance soil quality and immobilize pollutants. Further studies will assess their effectiveness in different soil conditions, their stability and persistence, and their impact on plant health and growth.

Increased oxygen content in biochar lowered bioavailability of polycyclic aromatic hydrocarbons-related toxicity to various organisms.

Agricultural or environmental application of biochar (BC) is connected with the introduction of biochar-derived components among which polycyclic aromatic hydrocarbons (PAHs) and heavy metals are the most toxic. Their presence and bioavailability are crucial considering biochar toxicity. The effect of feedstock and pyrolysis temperature on the physicochemical properties of produced biochar and contaminant content was established and combined with toxicity to a broad range of living organisms. The obtained data revealed that predicting the bioavailability of PAHs using the total content is misleading. The toxicity was influenced by factors in the following way: the bioavailable PAHs > ash > total PAHs content in BC stressing the role of BC physicochemical characteristics. Among tested BC properties, surface functionalization, e.g. presence of oxygen-containing functional groups was crucial in revealing the toxicity. The data clearly indicate that additional research is required to determine BC's impact on various organisms and performing one ecotoxicity test is not sufficient.

Plant-Waste-Derived Sorbents for Nitazoxanide Adsorption.

The increased application of drugs during the COVID-19 pandemic has resulted in their increased concentration in wastewater. Conventional wastewater treatment plants do not remove such pollutants effectively. Adsorption is a cheap, effective, and environmentally friendly method that can accomplish this. On the other hand, maintaining organic waste is required. Thus, in this study, plant waste-derived pelletized biochar obtained from different feedstock and pyrolyzed at 600 °C was applied for the adsorption of nitazoxanide, an antiparasitic drug used for the treatment of SARS-CoV-2. The adsorption was fast and enables one to remove the drug in one hour. The highest adsorption capacity was noted for biochar obtained from biogas production (14 mg/g). The process of NTZ adsorption was governed by chemisorption (k2 = 0.2371 g/mg min). The presence of inorganic ions had a detrimental effect on adsorption (Cl-, NO3- in 20-30%) and carbonates were the most effective in hindering the process (60%). The environmentally relevant concentration of DOM (10 mg/L) did not affect the process. The model studies were supported by the results with a real wastewater effluent (15% reduction). Depending on the applied feedstock, various models described nitazoxanide adsorption onto tested biochars. In summary, the application of carbonaceous adsorbents in the pelletized form is effective in nitazoxanide adsorption.

Effect of the Application of Sunflower Biochar and Leafy Trees Biochar on Soil Hydrological Properties of Fallow Soils and under Soybean Cultivation.

Soils enriched with biochar are recommended as a cultivation grounds, especially in case they contain significant amount of sand. However, the interactions between biochar and plants, as well as the influence of the biochar on water retention, cultivation and air properties of soils, are still not obvious. The present study aimed to determine the impact of various biochar doses on soils used for soya cultivation, in comparison to soils maintained as black fallow soil, on their water retention and productivity, for the period of two years. Sunflower husk biochar (BC1) and biochar of leafy trees (BC2), in doses of 0, 40, 60, 80 t·ha-1, were used for field experiments. The water retention was investigated with porous boards in pressure chambers by a drying method. No differences in the hydrological properties of the soils that were differently managed (black fallow soil, crop) were observed following biochar application. Addition of BC1, in the amounts of 40, 60, and 80 t·ha-1, caused an increase in the plant available water capacity (AWC) by 15.3%, 18.7%, and 13.3%, respectively, whereas the field capacity (FC) increased by 7.4%, 9.4%, and 8.6% for soils without biochar. Application of BC2 analogously resulted in higher AWC, by 8.97, 17.2%, and 33.1%, respectively, and higher FC by 3.75, 7.5%, and 18.3%, respectively. Increasing the doses of BC1 and BC2, both on black fallow soils and soils enriched with soya, caused a rise in total porosity (TP) and drainage porosity (DP), and a decrease in soil bulk density (SBD). Biochar with a higher total area and higher porosity (BC1) applied to soils with soya cultivation resulted in lower reductions in AW and FC than BC2 in the second year of investigation.

Long-term physical and chemical aging of biochar affected the amount and bioavailability of PAHs and their derivatives.

Biochar applied into the soil is recommended as an effective tool for increasing its properties and crop productivity. However, biochar can contain some potentially toxic compounds such as polycyclic aromatic hydrocarbons (PAHs). Moreover, during biochar production or environmental application (e.g. as soil fertilizer), more toxic PAHs derivatives containing nitrogen, oxygen or sulfur can be formed. There is a lack of information on how the environmental factors affect the bioavailability of such compounds during the long-term application of BC into the soil. In the presented studies the effects of physical (freeze-thaw cycles) and chemical aging (temperatures 60 °C and 90 °C) on the total and bioavailable content of PAHs and their derivatives were estimated. The results indicate that long-term (6 months) aging affected the physicochemical characteristic of biochars promoting the formation of new C and O-containing species on the BC surface increasing their polarity and hydrophilicity. Physical and chemical aging promoted the formation of compounds with higher molecular weight and a significant (up to 550 %) increase in the bioavailability of PAHs and their derivatives. The results of this study highlight the importance of the bioavailable fraction of PAHs and their derivatives for evaluation of the toxicity of aged biochar.

Acidity of rainfall samples in close vicinity of coal-fired power plant with wet cooling tower with flue gas injection.

The paper presents measurement data concerning the degree of acidification of precipitation collected during a 6-month measurement campaign carried out in an immediate vicinity of a power plant, where the cooling tower was used for discharging flue gases as a product of coal combustion. As reference, data obtained from parallel measurements carried out at a monitoring station considered as city background station were used. High acidity of precipitation was anticipated due to reactions of acid gases contained in the combustion gases with water, which already occur inside the cooling tower. The results have not confirmed this assumption. The pH value of the precipitation samples was significantly higher than the pH of rainwater at the background station located 18 km away from the power plant.

Effect of Fine Size-Fractionated Sunflower Husk Biochar on Water Retention Properties of Arable Sandy Soil.

Biochar application has been reported to improve the physical, chemical, and hydrological properties of soil. However, the information about the size fraction composition of the applied biochar as a factor that may have an impact on the properties of soil-biochar mixtures is often underappreciated. Our research shows how sunflower husk biochar (pyrolyzed at 650 °C) can modify the water retention characteristics of arable sandy soil depending on the biochar dose (up to 9.52 wt.%) and particle size (<50 µm, 50-100 µm, 100-250 µm). For comparison, we used soil samples mixed with biochar passed through 2 mm sieve and an unamended reference. The addition of sieved biochar to the soil caused a 30% increase in the available water content (AWC) in comparing to the soil without biochar. However, the most notable improvement (doubling the reference AWC value from 0.078 m3 m-3 to 0.157 m3 m-3) was observed at the lowest doses of biochar (0.95 and 2.24 wt.%) and for the finest size fractions (below 100 µm). The water retention effects on sandy soil are explained as the interplay between the dose, the size of biochar particles, and the porous properties of biochar fractions.

Numerical Analysis of the Combustion of Gases Generated during Biomass Carbonization.

The paper deals with the analysis of the combustion of volatiles evolved during thermolysis (thermal treatment) of biomass feedstock. The process is tailored to produce charcoal (biochar), heat and electricity and the whole system consists of a carbonizer, afterburning chamber and steam recovery boiler. In order to maintain safe operation of the carbonizer the process temperature has to be maintained at an acceptable level and thus the majority of gases evolved during biomass processing have to be combusted outside in the afterburning chamber. In this paper the combustion of those gases in a specially-designed combustion chamber was investigated numerically. The calculation results indicated that the production of the biochar has to be carried out with tight integration and management of the heat produced from the combustion of the volatiles and the emission of CO and methane may be maintained at a low level by optimization of the combustion process. The most promising effects were achieved in cases C4 and C5 where the gas was fed tangentially into the afterburning chamber. The calculation results were then used for the design and manufacture of a pilot reactor-from which the parameters and operational data will be presented and discussed in a separate paper.