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Aims A paper by Araújo et al. (2018) claims that a variety of compounds present in pyroligneous acid (guaiacol, phenols and furfural) are responsible for the observed antimicrobial activity. We show, on the other hand, that the low pH due to acetic acid present in pyroligneous acid is the real cause of the activity. Methods and Results Pyroligneous acid (PA) was synthesized according to a previous method (Medeiros et al. 2019) with its inhibition activity tested on Escherichia coli and Staphylococcus aureus via the agar diffusion method. The activity of acetic acid at different concentrations was also evaluated for comparison. As expected, crude PA (pH 3.0) and acetic acid produced inhibition halos whose diameters varied according to their employed concentration. However, any PA inhibitory activity completely vanished upon neutralization (pH 7.0), a behaviour also observed for neutralized acetic acid. Conclusions The claim that guaiacol, phenols and furfural are responsible for any inhibitory activity is unsubstantiated. The authors should have neutralized the pyroligneous acid if any activity was to be discovered. Significance and Impact of Study To increase awareness that interfering species may play a detrimental role on the interpretation of results. In this case, the action of acetic acid is vastly more important for the inhibitory activity than any other compound present in PA.

Carbon dioxide (CO2) is a primary greenhouse gas and the main cause of global warming. Respiration from plant cells and microorganisms enables CO2 to be produced during ensiling, a method of moist forage preservation applied worldwide. However, limited information is available regarding CO2 emissions and mitigation during ensiling. Pyroligneous acid, a by-product of plant biomass pyrolysis, has a strong antibacterial capacity. To investigate CO2 production and the influence of pyroligneous acid, fresh stylo, and rice straw were ensiled with or without 1% or 2% pyroligneous acid. Dynamics of the fermentation characteristics, CO2 production, and bacterial communities during ensiling were analyzed. Pyroligneous acid increased the lactic acid content and decreased the weight losses, pH, ammonia-N content, butyric acid content, and coliform bacterial numbers (all P < 0.05). It also increased the relative abundance of Lactobacillus and decreased the relative abundances of harmful bacteria such as Enterobacter and Lachnoclostridium. Adding pyrolytic acids reduced the gas production, especially of CO2. It also increased the relative abundances of CO2-producing bacterial genera and of genera with the potential for CO2 fixation. In conclusion, adding pyroligneous acid improved the fermentation quality of the two silages. During ensiling, CO2 production was correlated with bacterial community alterations. Using pyroligneous acid altered the bacterial community to reduce CO2 production during ensiling. Given the large production and demand for silage worldwide, application of pyroligneous acid may be an effective method of mitigating global warming via CO2 emissions.

Huge volumes of lignocellulosic biomass residues generated from agricultural activities such as oil palm biomass pose great environmental threats if improperly treated. In this study, pyroligneous acid (PA) obtained from slow pyrolysis of palm kernel shell (PKS) were evaluated for its antioxidant activity via chemical assays, toxicity, and potential as anti-inflammatory agent based on nitric oxide (NO) inhibition activity. The PA was extracted using ethyl acetate (EA) and fractionated using column chromatography. Fractions 13–17 that contain highest total phenolic contents (866.84 ± 54.28 µg GAE/mg) were chosen for subsequent studies. Results obtained were as follows; DPPH—75.34 ± 3.40%, TEAC—1346.48 ± 5.29 μg Trolox/mg, FRAP—11.80 ± 0.41 mmol Fe(II)/mg, hydroxyl radical scavenging—IC50 270.34 ± 4.88 µg/mL, superoxide radical scavenging—IC50 472.32 ± 1.87 µg/mL, cytotoxicity after 24 h at less than 50 µg/mL—cell viability of ≥ 93.08% for RAW 264.7 macrophage cell and anti-inflammatory activity with NO production of 6.55% after 24 h at sample concentration of 25 µg/mL. From the GC–MS analysis, phenols and derivatives were identified as major compound (83.24%) followed by esters (11.23%), and ketones (5.53%). The present of phenolic compounds namely benzene-1,2-diol, catechol (35.01%), 1,3-dimethoxy-2-hydroxybenzene, syringol (23.81%), and other catechol derivatives can be attributed to the antioxidant and anti-inflammatory activities determined. This study has successfully demonstrated the potential use of PA obtained from PKS as alternative antioxidant and anti-inflammatory agent.

Los grandes volúmenes de biomasa generados en el mantenimiento de áreas verdes se los considera un punto focal de producción de desechos orgánicos. En el presente trabajo, se propone la obtención del ácido piroleñoso a partir del precursor Pennisetum Clandestinum L (kikuyo), residuo muy común producto de las podas y de adecentamiento de jardines; se describe todo el proceso termoquímico de validación de la tecnología para obtención del producto y subproductos aprovechables (carbón, alquitrán) y la evaluación de los macro elementos y los componentes estructurales de la sustancia mediante el método de Espectrometría Infrarroja con Transformada de Fourier (FTIR del inglés Fourier transform infrared spectroscopy), por una comparativa directa, se demuestra que sus propiedades son similares al producto proveniente del Bambú (Phyllostachys pubescens f) el cual posee características que pueden incrementar el crecimiento radicular en vegetales, en animales de granja mejora la digestibilidad de los nutrientes y reduce los coliformes intestinales perjudiciales. Los resultados obtenidos describen un rendimiento de entre 20 y 30 % para los gases con una energía máxima entregada que oscila entre 150 y 1000 kcal., The large volumes of biomass generated in the maintenance of green areas are considered a focal point for the production of organic waste. In the present work, it is proposed to obtain piroleñoso acid from the precursor Pennisetum Clandestinum L (kikuyo), a very common waste product of pruning and gardening; Describes the thermochemical process for the validation of the technology for the production of the product and utilizable byproducts (coal and tar) and the evaluation of the macro elements and the structural components of the substance by means of the Fourier Transform Infrared Spectrometry (FTIR) method. (Fourier transform infrared spectroscopy), by a direct comparison, it is shown that its properties are similar to the product from Bamboo (Phyllostachys pubescense f) which has characteristics that can increase root growth in vegetables, in farm animals improves the digestibility of Nutrients and reduces harmful intestinal coliforms. The results obtained describe a yield of between 20 and 30% for the gases with a maximum delivered energy that oscillates between 150 and 1000 kcal.

A novel technology was developed to obtain a high amount of pyroligneous acid (PA) rich in organics. PA was obtained by atmospheric pyrolysis of a mixture of pine, spruce and fir wood particles, analyzed by gas chromatography-mass spectrometry (GC–MS) and evaluated for in vitro antibacterial and antifungal activity. Several microbial inhibitory compounds were observed in PA. Antimicrobial activity of PA was studied at both acidic pH (3.7) and neutral pH (7.0) of the liquid. Neutralized PA showed higher antibacterial activity than acidic PA against 5 pathogenic bacterial strains, and Minimum Inhibitory Concentration (MIC) obtained with neutralized PA were 0.3125% (v/v), 0.3125% (v/v), 0.625% (v/v), 0.3125% (v/v), 0.3125% (v/v) for Escherichia coli, Enterobacter aerogenes, Pseudomonas aeruginosa, Listeria monocytogenes and Enterococcus faecalis, respectively. For fungal strains, acidic PA was found to be more effective than neutralized PA. The highest activity was against Trametes versicolor, followed by Aspergillus niger and Aspergillus fumigatus. The MIC of acidic PA with which fungal inhibition was seen was 0.125% (v/v) for T. versicolor and A. fumigatus, and 0.25% (v/v) for A. niger. Hence, the novel technology was found to be effective to produce a high yield of PA (40–45 wt% of dry biomass), rich in antimicrobial compounds, and the PA is proposed as a potential alternative to antibiotics, preservatives and/or chemical disinfectants that are currently in use. Keywords: Pyroligneous acid, Pyrolysis, Antibacterial, MIC, Antifungal

Twelve tropical timbers indigenous to the south-east of Nigeria were analysed for their physical properties with results as follows: pH 4.26-6.72, specific gravity (0.16-0.49), charring temperature (64 -116oC) and porosity index (1.08 - 2.24%). Results of quantitative and proximate analysis of the constituent of woods studied includes; tannin (760 mg/100 g - 1240 mg/100 g), alkaloids (4.0-14.6%), flavonoids (2.0 -10.5%), saponin (2.0 - 11%), oxalate (0.28 - 2.92 g/100 g), total acidity (0.09 -0.54 g/100 cm3), cyanogenic glucoside (324-891 mg/100g), moisture content (13-31%), lipid (0.8-7.6%) and ash content (1.0-3.5%,). The qualitative screening was carried out to determine the presence of metabolites in the wood sample. Also, the destructive distillations of the timbers were studied. Results revealed their compositions as follows; wood charcoal (1.50 to 5.00 g), pyroligneous acid (2.0 -3.0 cm3), wood tar (0.1- 0.3 cm3) and wood gas (512 cm3 - 998 cm3). Thus, from the qualitative and quantitative analysis, it was observed that the timbers have medicinal properties which could be harnessed by pharmaceutical industries in drug formation or production while the products obtain from the destructive distillation of the wood can be utilized by other industries for industrial process.

Dissolved organic matter (DOM) greatly influences the transformation of nutrients and pollutants in the environment. To investigate the effects of pyrolysis temperatures on the composition and evolution of pyroligneous acid (PA)-derived DOM, DOM solutions extracted from a series of PA derived from eucalyptus at five pyrolysis temperature ranges (240–420 °C) were analysed with Fourier transform infrared spectroscopy, gas chromatography–mass spectroscopy, and fluorescence spectroscopy. Results showed that the dissolved organic carbon content sharply increased (p &lt, 0.05) with an increase in pyrolysis temperature. Analysis of the dissolved organic matter composition showed that humic-acid-like substances (71.34–100%) dominated and other fluorescent components (i.e., fulvic-acid-like, soluble microbial by-products, and proteinlike substances) disappeared at high temperatures (&gt, 370 °C). The results of two-dimensional correlation spectroscopic analysis suggested that with increasing pyrolysis temperatures, the humic-acid-like substances became more sensitive than other fluorescent components. This study provides valuable information on the characteristic evolution of PA-derived DOM.

Surface sterilization is a vital step in preparation of healthy and viable explants in tissue culture. Most surface contaminants can be eliminated by surface sterilization with a suitable sterilizing agent. The study aimed to present an effective disinfection method for Clinacanthus nutans shoot regeneration using nodal segments. A total of four different sterilization approaches were conducted by treating nodal explants with various concentrations of sterilizing agent. Sterilizing agents used were Rhizophora apiculata Pyroligneous acid (PA), sodium hypochlorite (Clorox) thiophanate-methyl (fungicide), and Mercuric chloride (HgCl2). Nodal explant then was cultured on plant growth regulator-free Murashige and Skoog (MS) basal medium. This study sterilizing agents revealed that PA showed strong bactericidal activity. However, it led to a high number of fungal contaminations. The pyroligneous acid did not exhibit a strong potential as a disinfectant for C. nutans nodal explant. Overall, HgCl2 exhibits the best reduction in fungal contamination and gives a significant result with thiophanate-methyl fungicide. Surface sterilization with mercuric chloride (0.2%) for 1 hour was the optimum concentration and duration, which resulted in the highest percentage of nodal explant survival and viability. All viable nodal segments developed into shoots. It had been concluded that the best surface sterilization agent was HgCl2.

The antibacterial properties of a wood distillate obtained from residual virgin chestnut biomass were investigated by means of quantitative MIC (minimum inhibitory concentration) test and a whole-cell assay that specifically responds to different classes of antimicrobials on the basis of the mode of action. Results indicate that wood distillate is active against gram-positive and gram-negative bacteria related to human and/or fish diseases with a mechanism, which could mainly affect wall components and plasma membrane of the bacterial cells. These findings highlight the possible sustainable use of chestnut residues as a source of bioactive natural compounds with antibacterial properties.

Aims To evaluate the applicability of the Mimosa tenuiflora and Eucalyptus urograndis pyroligneous acids (PAs) as alternative antiseptics in dairy goats. Methods and results Cytotoxicity was evaluated in vitro using bacteria, as well as in vivo using goats, and the influence of PAs on the physicochemical parameters of fresh milk were examined. The cytotoxicity of PAs was evaluated in terms of morphology, cell viability, and metabolic activity of goat tegumentary cells. The PA of M. tenuiflora had results similar to those of 2% iodine. For the in vitro tests, strains of Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa were used with the well technique, demonstrating inhibition halos greater than 9 mm. In the in vivo test, 15 animals were used per phase of the experiment, and the plate counting technique showed that there was antiseptic action of both extracts, with emphasis on the M. tenuiflora PA. Physicochemical analysis of the milk showed that neither PAs interfered with its physical-chemical parameters. Conclusions The PA of M. tenuiflora presented potential as an alternative antiseptic in dairy goats. Significance and impact of the study This study demonstrates the use of PA as an antimicrobial agent in animals.

Replacement of synthetic pesticides with biochemical alternatives and other biological and mechanical control methods represents a future need in plant protection. We investigated if slow pyrolysis liquids (PL) originating from hardwoods, which contain a wide range of organic compounds, can be used to control giant hogweed (Heracleum mantegazzianum) either by (i) spraying directly on the seeds (Carum carvi seeds used as substitute) and seedlings or by (ii) covering seedlings with PL-containing mulching material (PLM). The effectiveness of the methods was evaluated in laboratory and greenhouse experiments using seedlings of various ages, PLs produced from aspen (Populus sp.), birch (Betula sp.) and willow (Salix sp.) and various PL/PLM application doses. In addition, the biodegradation of birch-derived PL was investigated. All tested liquids inhibited C. carvi seed germination effectively when used at > 20% concentrations and only slight differences existed among PLs produced from different biomasses. Direct spraying of PL on H. mantegazzianum seedlings was ineffective. PLM (containing 7.5%-40% of PL) inhibited seedling development effectively. Birch PL was readily biodegradable. Further product development is needed because the chemical composition of the PLs in PLM and their modes of action are poorly understood. The weed-inhibiting effect of PLM likely results from the PL and the mechanical barrier constituted by PL-bound peat fibers. (C) 2020 The Author(s). Published by Elsevier B.V.

Treatments of crops with additives to increase their productivity may pose environmental risks and induce negative effects also on non-target organisms. In this study, we investigated the potential effect of chestnut wood distillate (pyroligneous acid) used in agriculture, on the accumulation of trace elements in aquatic plants. As a model species, the common water fern Azolla filiculoides Lam. was selected, being often used also in phytoremediation processes. The content of selected elements of toxicological concern (As, Ba, Cd, Cu, Fe, Mn, Ni, Pb, Zn) was assessed in the fern after short-term treatments (1&ndash, 3 days) over a range of wood distillate concentrations 1:300 (3.33 mL/L), 1:500 (2.00 mL/L), 1:700 (1.43 mL/L). A statistically significant accumulation of Cd, Cu, Mn, Pb, Zn (1:700) and Pb (1:300) was recorded after three days of incubation, despite the concentrations remained overall low. Using treatment vs. control ratios, a trend of increasing temporal uptake was detected for As, Ba, Fe, Mn, Pb (1:700), Mn, Pb (1:500), and only Pb at 1:300. The results suggested that, under the experimental conditions, element uptake is positively influenced by time and negatively by increasing concentrations of wood distillate, likely due to the acidification of the medium. On the whole, the element concentrations measured in A. filiculoides were low and did not pose any toxicological concern.

Bio-oil is a promising fuel as one of the main products from biomass fast pyrolysis for improving energy density and reducing transportation cost, but high acidity and low calorific value limit its direct application. It can be used to prepare coal bio-oil slurry as partial green fuels for potential feeds for synthesis gas production via gasification with the advantages over traditional coal-water slurries of calorific values and being additives-free. In the present work, three bio-oils were blended with lignite to prepare slurry fuels for the investigation of the effect of bio-oil species on rheological behaviors and gasification characteristics of coal bio-oil slurry fuels. Results show that slurry prepared with bio-oil from fruit tree pyrolysis is highly viscous and has higher activation energy in gasification. Slurries prepared with bio-oils from straw pyrolysis and pyroligneous acid from wood pyrolysis exhibited an acceptably lower viscosity, and the gasification temperatures were lower than for coal. The activation energy decreased by 15.98 KJ/mol and 2.77 KJ/mol, respectively, which indicates these bio-oils are more suitable with lignite for slurries preparation.

Pyroligneous acid (PA) was evaluated as a potential alternative to therapeutic antibiotics in poultry. Antimicrobial activity of PA was studied at acidic pH (2.0) and neutral pH (7.0) of the liquid against Salmonella enterica and Lactobacillus acidophilus. Acidic PA gave a MIC value of 0.8% (v/v) and 1.6% (v/v), and neutralized PA gave a MIC value of 1.6% (v/v) and 3.2% (v/v) against S. enterica and L. acidophilus respectively. Acidic PA was evaluated at different concentrations in a simulated poultry digestive tract and cecal fermentation to study its effect on the cecal microflora and fermentation profile. PA at a concentration of 1.6% (v/v) completely inhibited S. enterica and was also found to have a similar effect on lactobacilli count as compared with the control (p = 0.17). Additionally, PA at this concentration was found not to have a significant effect on acetic acid production after 24 h of cecal fermentation (p = 0.20). Graphical abstract.

Cyanobacteria blooms are crucial environmental issues by threatening both aquatic ecosystem and human health. A biomass by-product with antimicrobial activity, pyroligneous acid (PA) was tested for its suitability for removal of the cyanobacteria Microcystis aeruginosa (M. aeruginosa) in this work. Results show that the removal efficiency could reach up to 90% in the presence of 0.45% of PA and the inhibition to M. aeruginosa growth could extend to at least 40 days. The removal mechanism was studied. Both organic acids and phenols are functional content in M. aeruginosa removal and acetic acid is the most important one. Zeta potential analysis and morphology study show that the damage of cells dominates the flocculation and sedimentation of M. aeruginosa under low PA concentration (0.7%), and increasing PA (≥0.7%) resulted in a trend of zeta potential to zero, thus removing any "shield" and triggering flocculation. Finally, study on the phenols residual after M. aeruginosa treatment shows that it could be close to 0 in 70 h. Therefore, this work proposes a possible method for world-wide treatment of cyanobacteria bloom and a new way for further utilization of PA.

Strategies to mitigate the spread of antibiotic resistance genes (ARGs) in soils are urgently needed. Therefore, a pristine pyroligneous acid (PA) from pyrolyzing blended woody waste at 450 °C and its three fractions distilled at 98, 130, and 220 °C (F1, F2, and F3) were used to evaluate their feasibility of reducing ARGs in soil. Application of PA, F2, and F3 effectively decreased the relative ARG abundance by 22.4–75.4% and 39.7–66.7% in the rhizosphere and bulk soil relative to control, respectively, and the removal efficiency followed an order of F3 > PA > F2. Contrarily, F1 increased the abundance of ARGs. The decreased abundance of two mobile genetic elements and impaired conjugative transfer of RP4 plasmid in the presence of PA, F2 and F3 demonstrated that the weakened horizontal gene transfer (HGT) contributed to the reduced ARG level. Variation partitioning analysis and structural equation models confirmed that ARG reduction was primarily driven by the weakened HGT, followed by the decreased co-selection of heavy metals and shifted bacterial community (e.g., reduced potential host bacteria of ARGs). Our findings provide practical and technical support for developing PA-based technology in remediating ARG-contaminated soil to ensure food safety and protect human health.

Pyroligneous acid (PA) obtained from slow pyrolysis of palm kernel shell (PKS) has high total phenolic contents and exhibits various biological activities including antioxidant, antibacterial and antifungal. In this study, PA obtained using slow pyrolysis method and fractionated using column chromatography was characterized (chemical and antioxidative properties) and investigated for its cyclooxygenase-2 (COX-2) and 5-lipoxygenase (5-LOX) inhibition activities using the in vitro and in silico approaches. The F9 PA fraction exhibited highest total phenolic content of 181.75 ± 17.0 μg/mL. Fraction F21–25 showed ferric reducing antioxidant power (FRAP) (331.80 ± 4.60 mg TE/g) and IC50 of 18.56 ± 0.01 μg/mL towards COX-2 and 5.25 ± 0.03 μg/mL towards the 5-LOX enzymes, respectively. Molecular docking analysis suggested favourable binding energy for all chemical compounds present in fraction F21–25, notably 1-(2,4,6-trihydroxyphenyl)-2-pentanone, towards both COX-2 (− 6.9 kcal/mol) and 5-LOX (− 6.4 kcal/mol) enzymes. As a conclusion, PA from PKS has the potential to be used as an alternative antioxidant and antiinflammatory agents which is biodegradable and a more sustainable supply of raw materials.

Wood distillate (pyroligneous acid) can be successfully applied in agriculture to increase crop quality and productivity with a lower risk for the environment respect to synthetic chemical herbicides, pesticides or fertilizers. However, the effects of wood distillate on the environment and biota are still under investigation, depending on biological attributes of potentially influenced organisms. The potential toxicological effects of wood distillate on sensitive non-target organisms, lichens and mosses, are studied for the first time. The physiological parameters (chlorophyll a fluorescence emission FV/FM and PI(ABS), chlorophyll content, spectral reflectance, antioxidant power, and dehydrogenase activity) and eventual bioaccumulation of selected elements (As, Ba, Cd, Cr, Cu, Fe, Ni, Pb, Zn) were investigated in the lichen Xanthoria parietina and the moss Hypnum cupressiforme after short-term treatments over a range of wood distillate solutions (1:300, 1:500, 1:700) to detect potential early stress responses. Overall, the lichen did not show changes after the treatments, while in the moss wood distillate caused only modest alterations in FV/FM and PI(ABS) and progressive increasing of antioxidant activity according to the dose supplied. The bioaccumulation of toxic elements was low and did not show any pattern of uptake with increasing concentrations of wood distillate.

Polluted land in marginalized regions, such as tropical low-income countries and sparsely populated regions in industrialised countries, demand special remediation strategies that are energy-efficient, locally adapted, economically viable. Strategies for appropriate bioremediation technology under such circumstances can be based on locally available resources in combination with in situ bioremediation technologies to keep energy and material costs down. A pilot scale experiment was set up to test the application of three organic by-products from the local industry (whey, pyroligneous acid and compost tea) to enhance the natural biodegradation of diesel in ultisol. Biweekly applications of 6 mL whey kg−1 soil significantly increased the degradation rate but no positive effect on degradation was found with any of the other amendments. Tropical climate is favourable for biodegradation but many tropical soils are rich in clay which can inhibit the bioavailability of the pollutant which in turn may be decisive for biodegradation kinetics. If low cost is a crucial factor, our results indicate that whey treatment has the potential to be an appropriate technology for treating petroleum-contaminated soils in tropical regions.

Pyrolysis of plant biomass is a promising way to produce charcoal (solid), tar and pyroligneous acid, and other gaseous products. These products are of great import as they are alternative to traditional fuels and inorganic chemicals. In this review, main emphasis has been given to properties of pyroligneous acid and its potential benefits in agriculture. Pyroligneous acid is a crude condensed, highly oxygenated organic liquid which is a by-product of pyrolysis of plant biomass. It mainly consisted of aliphatic, aromatic, and naphthenic hydrocarbons and other oxygenated compounds such as alcohols, aldehydes, ketones, furans, acids, phenols and ethers. Pyroligneous acid exhibits antioxidant and scavenger properties and has been used in agriculture as antimicrobial agent, insecticide, and for the promotion of seed germination and plant growth. This review takes a critical look at some of the production principles, roles of pyroligneous acid in plant growth, development and defense, and the prospects and broader application of pyroligneous acid in agriculture. It is envisaged that this review will generate global discussion and create awareness for the numerous opportunities in pyroligneous acid research and global use.

Physicochemical characteristics and in vitro antioxidant activities of four pyroligneous acids carbonized from the wastes of wood species including Mangosteen (Garcinia mangostana Linn.), Durian (Durio zibethinus L.), Rambutan (Nephelium lappaceum L.), and Langsat (Lansium domesticum Serr.) were assessed. Appearing as transparent liquors with pH 3.9–4.2, the pyroligneous acid samples under test possessed acetic acid (23.22–25.46%) as the dominant component. The total soluble tar, total acid, and water content were 0.15 − 0.28 wt%, 99–192 mg KOH/g and 84.5–93.5 wt%, respectively. Phenolic compounds namely: 2,6-dimethoxyphenol (6.88–9.69%), phenol (2.97–5.88%), 4-methylsyringol (3.10–3.56%), guaiacol (2.36–3.55%), and 2-methoxy-4-methylphenol (1.08–1.28%) were found. All had in vitro antioxidant activities especially mangosteen pyroligneous acid, which showed activity roughly similar to BHT (P > 0.05) against anti-lipid peroxidation. Nitric oxide scavenging capacities of all pyroligneous acids were significantly higher than BHT (P

Upon the processing of different agricultural products, considerable amounts of by-products and bio-wastes are produced and discarded or burnt as fuel, which are a potential source of valuable compounds. Over the past several decades, plant by-products have been recognized as a source of nutraceutical components, including dietary fibers, phenolics, and many other useful compounds. The walnut is known as an important tree nut. The shell of a walnut is the middle part of the fruit and it is a waste product of walnut processing industries. Recently, pyroligneous acids from the walnut shell have been receiving much-increasing interest because of their excellent antimicrobial and antioxidant activities. Hence, this review deals with the recent scientific literature on walnut shell pyroligneous acids and their chemical composition as well as their functional applications.

Urea is one of the most commonly used nitrogen fertilizers in agricultural soil and is easily decomposed by soil urease resulting in ammonium release. The produced ammonium can be volatilized or converted to nitrate, which is susceptible to leaching, leading to groundwater contamination unless used by plants. Hence, it is important to control the release of nitrogen from the urea. Pyroligneous acid inhibited the urease activity and decreased ammonium release up to 80% compared to the control. Amidase including asparaginase and glutaminase is an enzyme that catalyzes hydrolysis of amide group, similar to urease. Therefore, the effect of pyroligneous acid on the inhibition of soil amidase was also tested and the results showed that pyroligneous acid competitively inhibited asparaginase while glutaminase was not inhibited. However, inhibitory effect of pyroligneous acid on asparaginase was negligible compared to the urease. The application of pyroligneous acid with a smaller amount of urea for controlled nitrogen release during Chinese cabbage growth showed that dry biomass and nutrient contents of Chinese cabbage were similar to the case of the conventional urea application. The nitrogen utilization efficiency (NUE) was highest for 33% less amount of urea supply with pyroligneous acid (2.21) compared to conventional treatment (1.81). Consequently, the use of pyroligneous acid with urea enhances nitrogen use efficiency while also protecting environments from non-point source contamination.

Remediation of agricultural soils polluted with antibiotic resistance genes (ARGs) is important for protecting food safety and human health. However, the feasibility of co-application of biochar and pyroligneous acid, two multifunctional soil amendments, for mitigating dissemination of soil ARGs is unknown. Thus, a woody biochar (BC450) and its by-product, pyroligneous acid (PA450) simultaneously produced at 450 °C from blended wood wastes, were used to compare their individual and combined effects on soil ARG abundance using a 65-day pot experiment planted with leafy vegetable Brassica chinensis L. The individual and combined applications of PA450 and BC450 significantly reduced the absolute abundance of ARGs by 65.7–81.4% and 47.5–72.9% in the corresponding rhizosphere and bulk soil. However, the co-application showed little synergistic effect, probably due to the counteractive effect of BC450 on the PA450-mitigated soil ARG proliferation, resulted from the promoted soil bacterial growth and/or adsorption of antimicrobial components of PA450 by BC450. The decreased abundances of mobile genetic element intI1 and Tn916/1545 in the PA450 treatments demonstrated the potential of PA450 for weakening horizontal gene transfer (HGT). Furthermore, weakened HGT by individual PA450, lowered availability of heavy metals by individual BC450, and different bacterial community (e.g., reduced ARGs bacterial host) together with improved soil properties from co-application of PA450 and BC450 all contributed to the reduced ARG level. This study highlighted the feasibility of co-applications of biochar and pyroligneous acid amendment for mitigating soil ARG pollution. These findings provide important information for developing eco-friendly technologies using biochar and pyroligneous acid in remediating ARG-contaminated soils.

The biochar (BC), pyroligneous acid (PA), and gas were collected from cotton stalks based on a polygeneration process, and this study was systematically focused to develop and process biochar and its byproducts obtained with various pyrolysis temperatures (300, 350, 400, 450, 500, and 550 °C). The results showed that the yield of biochar decreased from 46.71 % to 30.26 % as the pyrolysis temperature was increased from 300 to 550 °C, and this was accompanied by an increase in carbon content from 71.32–78.02%. Heatmap analysis on the correlation among pyrolysis temperature of biochar and elements illustrated that the content of C, H, and O were highly correlated with pyrolysis temperature of biochar. The ketones, phenols, alcohols, acids, and alkyl phenyl ethers were the major chemical constituents. The maximum total content of amino acids reached 647.1 mg/kg when the pyroligneous acids were collected at 450 °C. Moreover, the volume fractions of gas (CO and CH4) content increased with increasing pyrolysis temperature, leading to an increase in the gas heating value. Overall, the outcomes presented above indicated that the polygeneration system would be environmentally benign and effective in producing biochar, pyroligneous acids, and gas, which provides economic benefits and suggests a potential industrial application for cotton stalk.