Pyrolysis for exploitation of biomasses selected for soil phytoremediation: Characterization of gaseous and solid products

Combining biochar and grass-legume mixture to improve the phytoremediation of soils contaminated with potentially toxic elements (PTEs)

The combination of soil amendments with plants can be a viable option for restoring the functionality of PTEs-contaminated soils. Soil recovery could be further optimized through the mixed cropping of plant species (e.g. legumes and grasses) with different physiological characteristics. The aim of this study was to assess the phytoremediation ability of Vicia villosa Roth. And Lolium rigidum Gaud. Grown alone or in mixture in a soil contaminated with PTEs (C), i.e. Cd (23 mg kg-1), Pb (4473 mg kg-1) and Zn (3147 mg kg-1), and amended with 3% biochar (C + B). Biochar improved soil fertility and changed PTEs distribution, reducing soluble fractions and increasing the more stable ones. The addition of biochar increased the plant biomass of hairy vetch and annual ryegrass, both in monoculture and when in mixture. For example, shoot and root biomass of the C + B intercropped hairy vetch and annual ryegrass increased 9- and 7-fold, and ∼3-fold respectively, compared to the respective C plants. The biochar addition decreased PTE-uptake by both plants, while mixed cropping increased the uptake of PTEs by shoots of hairy vetch grown in C and C + B. The bioaccumulation, translocation factors, and mineralomass showed that hairy vetch and annual ryegrass behaved as phytostabilising plants. PTE mineralomasses proved that mixed cropping in C + B increased the overall capacity of PTE accumulation by plant tissues, particularly the root system. Therefore, the combination of biochar and legumes/grasses mixed cropping could be an effective solution for the recovery of PTEs-contaminated soils and the mitigation of their environmental hazard.

Microwave assisted carbonization and activation of biochar for energy-environment nexus: A review

Conventional thermochemical conversion techniques for biofuel production from lignocellulosic biomass is often non-selective and energy inefficient. Microwave assisted pyrolysis (MAP) is cost and energy-efficient technology aimed for value-added bioproducts recovery from biomass with less environmental impacts. The present review emphasizes the performance of MAP in terms of product yield, characteristics and energy consumption and further it compares it with conventional pyrolysis. The significant role of biochar as catalyst in microwave pyrolysis for enhancing the product selectivity and quality, and the influence of microwave activation on product composition identified through sophisticated techniques has been highlighted. Besides, the application of MAP based biochar as soil conditioner and heavy metal immobilization has been illustrated. MAP accomplished at low temperature creates uniform thermal gradient than conventional mode, thereby producing engineered char with hotspots that could be used as catalysts for gasification, energy storage, etc. The stability, nutrient content, surface properties and adsorption capacity of biochar was enhanced by microwave activation, thus facilitating its use as soil conditioner. Many reviews until now on MAP mostly dealt with operational conditions and product yield with limited focus on comparative energy consumption with conventional mode, analytical techniques for product characterization and end application especially concerning agriculture. Thus, the present review adds on to the current state of art on microwave assisted pyrolysis covering all-round aspects of production followed by characterization and applications as soil amendment for increasing crop productivity in addition to the production of value-added chemicals, thus promoting process sustainability in energy and environment nexus.

Effect of oil palm biomass cellulosic content on nanopore structure and adsorption capacity of biochar

The influence of biomass cellulosic content on biochar nanopore structure and adsorption capacity in aqueous phase was scarcely reported. Commercial cellulose (100% cellulose), oil palm frond (39.5% cellulose), and palm kernel shell (20.5% cellulose) were pyrolyzed AT 630 °C, characterized and tested for the adsorption of iodine and organic contaminants. The external surface area and average pore size increased with cellulosic content, where commercial cellulose formed biochar with external surface area of 95.4 m²/g and average pore size of 4.1 nm. The biochar from commercial cellulose had the largest adsorption capacities: 371.40 mg/g for iodine, 86.7 mg/L for tannic acid, 17.89 mg/g for COD and 60.35 mg/g for colour, while biochar from palm kernel shell had the least adsorption capacities. The cellulosic content reflected the differences in biochar nanopore structure and adsorption capacities, signifying the suitability of highly cellulosic biomass for producing biochar to effectively treat wastewater.

The Effect of Biodegradable Waste Pyrolysis Temperatures on Selected Biochar Properties

Biochars produced during biodegradable waste pyrolysis are products with a wide range of environmental applications. The effect of impact biochars depends on their properties which determine the course of specific processes. The main aim of the study was to investigate the effect of pyrolysis temperature on selected properties of biochar produced from various plant wastes (beech wood chips, walnut shells, wheat-rye straw), the valorization of which is of key importance for the implementation of the circular economy. Biochars were produced at temperatures of: 400 °C, 500 °C, 600 °C and 700 °C in a nitrogen atmosphere. An increase in the pyrolysis temperature caused a drop in the biochar production yield. As the temperature increased, higher carbon content and lower hydrogen content could be seen in the products obtained. An increase in the pH and total organic carbon (TOC) values also found. The influence of temperature on ash content, observed in the case of BWS (biochar from walnut shell) and BWRS (biochar from wheat and rye straw), did not occur in the case of BWC (biochar from beech wood chips). Another parameter that demonstrated a growing tendency with increasing temperature was the BET specific surface area (except for biochars from wheat and rye straw). An increase in pyrolysis temperature caused a decrease in the diversity and density of the surface functional groups of biochars. The influence of the type of precursor used in the production of biochar on the presence of surface functional groups was demonstrated. The presence of intense stretching vibrations of C-O bonds, having a potential impact on the sorption capacity of biochars, was determined in the FTIR spectra of BWC600 and BWC700 biochars, this feature, combined with the large BET surface area, may affect the sorption potential of these biochars. The presence of this type of high-intensity vibrations was also observed in the spectra of biochar BWRS600 and BWRS700. This can compensate for the low BET surface value and play an important role when using these biochars in sorption processes for organic and inorganic compounds.

Management of poultry manure in Poland - Current state and future perspectives

This review aimed to analyse the current state of management practices for poultry manure in Poland and present future perspectives in terms of technologies allowing closing the loops for circular economy, and thus recovery of nutrients and energy. The scope of the review focused primarily on: (1) the analysis of poultry production and generation of poultry manure with special references to quantities, properties (e.g. fertilizing properties), seasonality, etc.; (2) the overview of current practices and methods for managing poultry manure including advantages and limitations; (3) the analysis of potential and realistic threats and risk related to managing poultry manure, and also (4) the analysis of promising technologies for converting poultry manure into added value products and energy. The review addressed the following technologies: composting of poultry manure to obtain fertilizers and soil improvers, anaerobic digestion of poultry manure for energy recovery, and also pyrolysis of poultry manure into different types of biochar that can be applied in agriculture, horticulture and industry. Poultry manure is rich in macro- and micronutrients but also can contain various contaminants such as antibiotics or pesticides, and thus posing a realistic threat to soil and living organisms when applied to soil directly or after biological treatment. The main challenge in poultry manure processing is to assure sufficient closing of carbon, nitrogen and phosphorous loops and safe application to soil.

Pyrolysis of various phytoremediation residues for biochars: Chemical forms and environmental risk of Cd in biochar

Various phytoremediation residues (PMRs), including Brassica napus L. (BN), Pennisetum sinese (PS) and Lolium perenne L.(LP), were pyrolyzed at 400, 500, 600 and 700 °C, respectively. A series of sequential and single extractions were employed to analyze the chemical speciation and potential environmental risk of Cadmium (Cd) in different phytoremediation residues-derived biochars (PMBs). The results showed that the exchangeable Cd fraction decreased but the residual Cd fraction increased, indicating the inhibition of bioavailability of Cd and low potential ecological risk index of PMBs. When the temperature was over 600 °C, the Cd in biochar was acceptable to the environment and the leaching concentration of Cd extracted by the three extraction methods (distilled water, SPLP and TCLP) were all under the standard limit. Findings from this study illustrated that the treatment of pyrolysis was feasible for the three kinds of PMRs at 600 °C with acceptable environment risk.

Enhancements in phytoremediation technology: Environmental assessment including different options of biomass disposal and comparison with a consolidated approach

Phytoremediation represents a solution for treating soils contaminated by heavy metals, provided that appropriate plant species are selected and the proper strategy chosen. When dealing with soil contaminated with arsenic and/or lead, which are non-essential elements for plants but also among the most toxic metals, this task is particularly difficult to achieve. In a previous contribution we showed that metals accumulation by Lupinus albus, Brassica juncea and Helianthus annuus can be improved by dosing suitable chemicals (i.e. phosphate and EDTA), leading to a quicker and cheaper intervention. This study discusses the assisted phytoremediation of a real site contaminated by several metals, presenting an environmental assessment realized by using the GaBi LCA software. The environmental sustainability of the reclamation technology was analyzed in terms of Global Warming Potential (GWP-100 years), considering different destinations for the harvested biomass, and comparing its ecological footprint with the outcomes of a conventional treatment of excavation and landfill disposal. The comparison clearly shows the great advantage of the phytoremediation, in terms of environmental impact, highlighting the importance of correctly handling the disposal of contaminated biomass produced. In fact, its incineration (aimed at reducing the volumes to be disposed of) could be more onerous than a direct landfilling, but re-qualify as a more sustainable choice if combined with energy recovery. The same applies to fast pyrolysis, which seems to be the most sustainable approach to date, at least in terms of technological maturity, although this requires technical-economic considerations on the quality and use of biofuels produced.

Steam assisted slow pyrolysis of contaminated biomasses: Effect of plant parts and process temperature on heavy metals fate

The post-treatment of biomass from phytoremediation is not yet a well-established practice due to the risk induced by the presence of Potentially Toxic Elements (PTEs). Pyrolysis is a thermochemical treatment that reduces the volume and weight of contaminated matter producing a combustible vapor phase and a solid residue (char). A key factor enhancing the economic and the environmental sustainability of biomass valorization through pyrolysis is the production of a market value char. A proper choice of the pyrolysis operating conditions should take into account the effect of final temperature on PTEs release, on the char physicochemical properties as well as on the mobility of retained PTEs. In particular, in this work the influence of both the temperature and the plant parts is discussed (branches and leaves of Populus Nigra L. and rhizomes and culms of Arundo donax L.) on the release of Cd, Pb, Cu, and Zn in the temperature range 653-873 K under steam assisted slow pyrolysis conditions. The mobility of the heavy metals retained in the chars was also studied as well as the product yields, the gas composition and char porosity. The results suggested that in presence of Cd it is necessary to operate at low-temperature (lower than 703 K) to obtain a heavy metals free vapor phase fuel, whereas in presence of one or more metals among Pb, Cu, and Zn, it is possible to conduct a pyrolytic treatment at higher temperatures, thus obtaining a char with high BET surface area and lower metals mobility.

Thermal conversion of a promising phytoremediation plant (Symphytum officinale L.) into biochar: Dynamic of potentially toxic elements and environmental acceptability assessment of the biochar

Symphytum officinale L., as a hyperaccumulator, was pyrolyzed into biochar at 350, 550, and 750 °C, respectively. PTEs could be enriched in biochars except Cd volatilized greatly at 750 °C. In order to evaluate the environmental acceptability of biochars, a series of sequential and single extractions and biochar oxidation procedures were performed for simulating different environmental conditions. There was a sharp decline in PTEs release under various conditions when the temperature above 550 °C, indicating PTEs might transform into more stable forms at higher temperature. Thus, increasing the pyrolysis temperature is helpful for reducing biochar phytotoxicity, suppressing biochar leaching and improving biochar environmental safety. Moreover, the economic feasibility analysis of the biochar confirmed the practicability of it. Findings from this work illustrated that biochars pyrolyzed from Symphytum officinale L. at the temperature higher than 550 °C might be environmental acceptable, which is beneficial for biochar application.

Assessing the Potential of Biochars Prepared by Steam-Assisted Slow Pyrolysis for CO2 Adsorption and Separation

The potentialities in the use of biochars prepared by steam-assisted slow pyrolysis as adsorbents of gases of strategic interest (N₂, CO₂, and CH₄) and their mixtures were explored. The biochars prepared from Populus nigra wood and cellulose fibers exhibited a narrow microporosity, with average pore sizes ranging between 0.55 and 0.6 nm. The micropore volume increased with the pyrolysis temperature, allowing CO₂ and CH₄ uptakes at room temperature between 1.5 and 2.5 mmol/g and between 0.1 and 0.5 mmol/g, respectively. These values are in line with those from the literature on biomass-derived carbon-based materials, exhibiting much higher porous features than those reported herein. As for the separation of CO₂/N₂ and CO₂/CH₄ gas mixtures, data showed that the prepared biochars exhibited good selectivities for CO₂ over both N₂ and CH₄: between ca. 34 and 119 for a CO₂/N₂ mixture in typical post-combustion conditions (15:85, v/v) and between 14 and 34 for a CO₂/CH₄ mixture typical of natural gas upgrading (30:70, v/v).

Supporting local farming communities and crop production resilience to climate change through giant reed (Arundo donax L.) cultivation: An Italian case study

Bioenergy crops are well known for their ability to reduce greenhouse gas emissions and increase the soil carbon stock. Although such crops are often held to be in competition with food crops and thus raise the question of current and future food security, at the same time mitigation measures are required to tackle climate change and sustain local farming communities and crop production. However, in some cases the actions envisaged for specific pedo-climatic conditions are not always economically sustainable by farmers. In this frame, energy crops with high environmental adaptability and yields, such as giant reed (Arundo donax L.), may represent an opportunity to improve farm incomes, making marginal areas not suitable for food production once again productive. In so doing, three of the 17 Sustainable Development Goals (SDGs) of the United Nations would be met, namely SDG 2 on food security and sustainable agriculture, SDG 7 on reliable, sustainable and modern energy, and SDG 13 on action to combat climate change and its impacts. In this work, the response of giant reed in the marginal areas of an agricultural district of southern Italy (Destra Sele) and expected farm incomes under climate change (2021-2050) are evaluated. The normalized water productivity index of giant reed was determined (WP; 30.1gm^-2) by means of a SWAP agro-hydrological model, calibrated and validated on two years of a long-term field experiment. The model was used to estimate giant reed response (biomass yield) in marginal areas under climate change, and economic evaluation was performed to determine expected farm incomes (woodchips and chopped forage). The results show that woodchip production represents the most profitable option for farmers, yielding a gross margin 50% lower than ordinary high-input maize cultivation across the study area.