New insights into the production, characterization and potential uses of vineyard pruning waste biochars.

Vineyard pruning waste (VP) can be converted into a useful char using pyrolysis as part of a valorization strategy. This study analyzed the effect of temperature (300 and 600 °C) and residence time (1 and 3 h) on an ample number of properties of VP derived biochars, including potential negative environmental impacts. The results showed a clear influence of temperature on biochar's properties and a weaker effect of residence time. Increasing temperature raised soil pH, electrical conductivity (EC), ash and C contents, aromaticity, specific surface area, solid density, mesoporosity and partial graphitization. However, higher pyrolysis temperature reduced O/C and N/C ratios, total N, P and Mg, and polycyclic aromatic hydrocarbons (PAHs). Particularly, the concentration of water extractable organic carbon (WEOC) decreased dramatically with pyrolysis temperature. Moreover, the WEOC fraction of biochars pyrolyzed at 300 °C exhibited a larger aromaticity than those pyrolyzed at 600 °C. Prolonged residence time increased ash content and fixed carbon (FC) and decreased H/C and O/C ratios; however, most frequently this parameter affected biochar properties following opposite trends for the two pyrolysis temperatures. Hydrophysical properties were adequate to consider VP derived biochars as growing media component. PAH concentration was much lower than thresholds following international standards. The germination index increased with temperature and decreased with residence time, so that phytotoxicity was observed in VP and in biochars pyrolyzed for 3 h. Our research demonstrates that, besides temperature, residence time can be useful to modulate the properties of biochars and that prolonged time effect is temperature-dependent.

Long-term effects of gasification biochar application on soil functions in a Mediterranean agroecosystem: Higher addition rates sequester more carbon but pose a risk to soil faunal communities.

Biochar applications can have important implications for many of the soil functions upon which agroecosystems rely, particularly regarding organic carbon storage. This study evaluated the impacts of adding a highly aromatic gasification biochar at different rates (0, 12 and 50 t ha-1) to a barley crop on the provision of crucial soil functions (carbon sequestration, water content, greenhouse gas emissions, nutrient cycling, soil food web functioning, and food production). After natural ageing in the field for six years, a wide range of soil properties representative of the studied soil functions were measured and integrated into a soil quality index. Results showed that C sequestration increased with biochar rate (23 and 68% higher than in the control for the 12 and 50 t biochar ha-1 treatments, respectively). Water content was enhanced at the 50 t ha-1 treatment depending on the sampling date. Despite biochar additions neither abating nor increasing CO2 equivalent emissions (carbon dioxide plus nitrous oxide and methane), the system shifted from being a methane sink (-0.017 ± 0.01 mg CH4-C m-2 h-1 at the 12 t ha-1 treatment), to a net source (0.025 ± 0.02 mg CH4-C m-2 h-1 at the 50 t ha-1 treatment). In addition, biochar ageing provoked a loss of nitrate mitigation potential, and indeed ammonium production was stimulated at the 50 t ha-1 rate. The 50 t ha-1 treatment also adversely affected nematode and collembolan functional diversity. Lastly, biochar did not affect barley yield. The results of the soil quality index indicated that no biochar treatment provided more benefits to our agricultural soil, and, although the 50 t ha-1 treatment increased C sequestration, this was potentially offset by its harmful effects on soil faunal communities. Therefore, application of this biochar at high rates should be avoided to prevent risks to soil biological communities.

New insights into the efficient removal of emerging contaminants by biochars and hydrochars derived from olive oil wastes.

The removal of emerging contaminants (ECs) for water source reclamation, minimizing energy and chemical use, is an environmental concern worldwide. In this study, we used the technologically cleaner pyrolysis and hydrothermal carbonization (HTC) processes to convert olive oil production wastes into chars in order to simultaneously remove triclosan (TCS), ibuprofen (IBP) and diclofenac (DCF) from water. The chars prepared from olive stone (S), olive tree pruning (P) and pitted and reprocessed wet olive mill waste (H), as well as commercial biochars and a commercial active carbon (CAC), were characterized using different techniques and assayed as adsorbents. Pyrolysis temperatures had only a slight effect on the adsorption capacity of chars. The pseudo second-order reaction kinetic and the Freundlich equation provided the best fit for experimental data. The pH values of char suspensions were negatively correlated with their maximum adsorption capacities. The hydrochars synthetized at the lowest temperatures (≤ 240 °C), which had an acidic pH and were rich in oxygenated functional groups, recorded the highest adsorption rates (64% for DCF, 43% for IBP) and especially for TCS, with a rate of 98%, despite of a low surface area of 7.5 m2/ g. This study demonstrates for the first time that unmodified hydrochars from pitted and reprocessed wet olive mill waste are inexpensive, sustainable and environmentally friendly adsorbents which can be used to remove ECs and other similar compounds in water treatments.

Fresh biochar application provokes a reduction of nitrate which is unexplained by conventional mechanisms.

Soil-applied biochar has been reported to possess the potential to mitigate nitrate leaching and thus, exert beneficial effects beyond carbon sequestration. The main objective of the present study is to confirm if a pine gasification biochar that has proven able to decrease soil-soluble nitrate in previous research can indeed exert such an effect and to determine by which mechanism. For this purpose, lysimeters containing soil-biochar mixtures at 0, 12 and 50 t biochar ha-1 were investigated in two different scenarios: a fresh biochar scenario consisting of fresh biochar and a fallow-managed soil, and an aged biochar scenario with a 6-yr naturally aged biochar in a crop-managed soil. Soil columns were assessed under a mimicked Mediterranean ambient within a greenhouse setting during an 8-mo period which included a barley crop cycle. A set of parameters related to nitrogen cycling, and particularly to mechanisms that could directly or indirectly explain nitrate content reduction (i.e., sorption, leaching, microbially-mediated processes, volatilisation, plant uptake, and ecotoxicological effects), were assessed. Specific measurements included soil solution and leachate ionic composition, microbial biomass and activity, greenhouse gas (GHG) emissions, N and O isotopic composition of nitrate, crop yield and quality, and ecotoxicological endpoints, among others. Nitrate content reduction in soil solution was verified for the fresh biochar scenario in both 12 and 50 t ha-1 treatments and was coupled to a significant reduction of chloride, sodium, calcium and magnesium. This effect was noticed only after eight months of biochar application thus suggesting a time-dependent process. All other mechanisms tested being discarded, the formation of an organo-mineral coating emerges as a plausible explanation for the ionic content decrease.

Biochar sorption of PFOS, PFOA, PFHxS and PFHxA in two soils with contrasting texture.

The ability to immobilise PFAS in soil may be an essential interim tool while technologies are developed for effective long-term treatment of PFAS contaminated soils. Serial sorption experiments were undertaken using a pine derived biochar produced at 750 °C (P750). All experiments were carried out either in individual mode (solution with one PFAS at 5 µg/L) or mix mode (solution with 5 µg/L of each: PFOS, PFOA, PFHxS and PFHxA), and carried out in 2:1 water to soil solutions. Soils had biochar added in the range 0-5% w/w. Kinetic data were fitted to the pseudo-second order model for both amended soils, with equilibrium times ranging 0.5-96 h for all congeners. PFOS sorption was 11.1 ± 4.5% in the loamy sand compared to 69.8 ± 4.9% in the sandy clay loam. While total sorption was higher in the unamended loamy sand than sandy clay loam for PFHxA, PFOA and PFOS, the effect of biochar amendment for each compound was found to be significantly higher in amended sandy clay loam than in amended loamy sand. Application of biochar reduced the desorbed PFAS fraction of all soils. Soil type and experimental mode played a significant role in influencing desorption. Overall, the relationship between sorbent and congener was demonstrated to be highly impacted by soil type, however the unique physiochemical properties of each PFAS congener greatly influenced its unique equilibrium, sorption and desorption behaviour for each amended soil and mode tested.

Phosphorus-Rich Biochars Can Transform Lead in an Urban Contaminated Soil.

Transformation of soil Pb to pyromorphites and phosphates has the potential to be an effective strategy to immobilize this contaminant in situ. Soil treatment using monocalcium phosphate, a commercial fertilizer (NTS Soft Rock) and biochars prepared from poultry litter and from biosolids at three different temperatures (300, 400, and 500°C) and two doses (1 and 3%) were evaluated. Lead bioaccesibility, mobility, and solid speciation were measured. Leachable Pb (determined with the toxicity characterized leaching procedure) was not significantly ( > 0.05) changed after biochar addition, but a significant decrease in bioaccesible Pb was found for several treatments ( < 0.05). This was particularly notable for treatments receiving biosolids prepared at 400 and at 500°C or monocalcium phosphate at the 3% dose. The decrease in bioaccesible Pb concentration in the biochar treatments was similar to traditional phosphate amendments. Our research found transformation of Pb species to the more stable pyromorphite and Pb-phosphate to be partially responsible for the observed changes, although other mechanisms, including pH changes, might also play an important role. Overall, pyrolysis was an effective method to upgrade waste streams and facilitate Pb immobilization, although key pyrolysis parameters need to be selected carefully.

Soil resources and element stocks in drylands to face global issues.

Drylands (hyperarid, arid, semiarid, and dry subhumid ecosystems) cover almost half of Earth's land surface and are highly vulnerable to environmental pressures. Here we provide an inventory of soil properties including carbon (C), nitrogen (N), and phosphorus (P) stocks within the current boundaries of drylands, aimed at serving as a benchmark in the face of future challenges including increased population, food security, desertification, and climate change. Aridity limits plant production and results in poorly developed soils, with coarse texture, low C:N and C:P, scarce organic matter, and high vulnerability to erosion. Dryland soils store 646 Pg of organic C to 2 m, the equivalent of 32% of the global soil organic C pool. The magnitude of the historic loss of C from dryland soils due to human land use and cover change and their typically low C:N and C:P suggest high potential to build up soil organic matter, but coarse soil textures may limit protection and stabilization processes. Restoring, preserving, and increasing soil organic matter in drylands may help slow down rising levels of atmospheric carbon dioxide by sequestering C, and is strongly needed to enhance food security and reduce the risk of land degradation and desertification.

Valorization of biochars from pinewood gasification and municipal solid waste torrefaction as peat substitutes.

Gasification and torrefaction have both gained significant interest as bioenergy techniques. During biomass gasification together with fuel gas, carbon-rich solid substances are produced, whereas torrefaction process is mainly used to prepare a final product with higher calorific value and carbon content than the feedstock, through a low temperature pyrolysis. Both materials (carbon wastes from gasification and torrefied product) could be classified as alternatives to biochar obtained from slow pyrolysis of biomass. The use of biochar, typically from the slow pyrolysis of biomass, as soil amendment and, more recently, as growing media components has been widely researched. However, to our knowledge, no studies have compared the use of biochar from gasification and torrefaction as growing media component for growing media formulation. The objective of this work was to study the effect of two biochars on peat-based growing media: a pinewood gasification biochar (BG) and a biochar (BT) obtained by torrefaction of the organic fraction of municipal solid waste. Growing media mixing PT (peat) with 50%vol of BG or BT were prepared and characterized according to their chemical, thermal and hydrophysical properties. Phytotoxic experiments and growth of Lolium perenne were also performed. Results indicated that peat substitution in growing media by BG and BT at a 50%vol ratio improved their hydrophysical properties. Specifically, bulk density increased more than 50%, air space increased by 43%, the increment of the total porosity was 20%, and, finally, the water holding capacity increased by 18.3%. Significantly, a positive effect on plant biomass production (yield increment: 274%) was observed after addition of BT, whereas no significant differences were observed after addition of BG biochar. Therefore, it can be concluded that both BT and BG could be used as peat substitutes in growing media formulation.

Biochar from Biosolids Pyrolysis: A Review.

Ever increasing volumes of biosolids (treated sewage sludge) are being produced by municipal wastewater facilities. This is a consequence of the continued expansion of urban areas, which in turn require the commissioning of new treatment plants or upgrades to existing facilities. Biosolids contain nutrients and energy which can be used in agriculture or waste-to-energy processes. Biosolids have been disposed of in landfills, but there is an increasing pressure from regulators to phase out landfilling. This article performs a critical review on options for the management of biosolids with a focus on pyrolysis and the application of the solid fraction of pyrolysis (biochar) into soil.

The effect of biochar and its interaction with the earthworm Pontoscolex corethrurus on soil microbial community structure in tropical soils.

Biochar effects on soil microbial abundance and community structure are keys for understanding the biogeochemical cycling of nutrients and organic matter turnover, but are poorly understood, in particular in tropical areas. We conducted a greenhouse experiment in which we added biochars produced from four different feedstocks [sewage sludge (B1), deinking sewage sludge (B2), Miscanthus (B3) and pine wood (B4)] at a rate of 3% (w/w) to two tropical soils (an Acrisol and a Ferralsol) planted with proso millet (Panicum milliaceum L.). The interactive effect of the addition of earthworms was also addressed. For this purpose we utilized soil samples from pots with or without the earthworm Pontoscolex corethrurus, which is a ubiquitous earthworm in tropical soils. Phospholipid fatty acid (PLFA) measurements showed that biochar type, soil type and the presence of earthworms significantly affected soil microbial community size and structure. In general, biochar addition affected fungal but not bacterial populations. Overall, biochars rich in ash (B1 and B2) resulted in a marked increase in the fungi to bacteria ratio, while this ratio was unaltered after addition of biochars with a high fixed carbon content (B3 and B4). Our study remarked the contrasting effect that both, biochar prepared from different materials and macrofauna, can have on soil microbial community. Such changes might end up with ecosystem-level effects.

Combining phytoextraction and biochar addition improves soil biochemical properties in a soil contaminated with Cd.

The main goal of phytoremediation is to improve ecosystem functioning. Soil biochemical properties are considered as effective indicators of soil quality and are sensitive to various environmental stresses, including heavy metal contamination. The biochemical response in a soil contaminated with cadmium was tested after several treatments aimed to reduce heavy metal availability including liming, biochar addition and phytoextraction using Amaranthus tricolor L. Two biochars were added to the soil: eucalyptus pyrolysed at 600 °C (EB) and poultry litter at 400 °C (PLB). Two liming treatments were chosen with the aim of bringing soil pH to the same values as in the treatments EB and PLB. The properties studied included soil microbial biomass C, soil respiration and the activities of invertase, ß-glucosidase, ß-glucosaminidase, urease and phosphomonoesterase. Both phytoremediation and biochar addition improved soil biochemical properties, although results were enzyme specific. For biochar addition these changes were partly, but not exclusively, mediated by alterations in soil pH. A careful choice of biochar must be undertaken to optimize the remediation process from the point of view of metal phytoextraction and soil biological activity.

Can biochar and phytoextractors be jointly used for cadmium remediation?

Phytoremediation of soils contaminated with cadmium was tested after liming (CaO) or biochar addition, using red amaranth (Amaranthus tricolor L.) as test plant species. Two biochars with contrasting characteristics were prepared from two feedstocks and added to the soil at a rate of 3% (w:w): Eucalyptus pyrolysed at 600°C (EB) and poultry litter at 400°C (PLB). Liming was carried out in two treatments (CaO1) and (CaO2) to the same pH as the treatments EB and PLB respectively. Total plant mass increased in soils amended with PLB and with a mixture of PLB and EB; however this was not sufficient to increase the efficiency of phytoextraction. Bioavailable and mobile fractions of Cd diminished after liming or biochar addition. Our study infers that, both the amount of Cd immobilized and the main mechanism responsible for this immobilization varies according to biochar properties.

Carbon dioxide emissions from semi-arid soils amended with biochar alone or combined with mineral and organic fertilizers.

Semi-arid soils cover a significant area of Earth's land surface and typically contain large amounts of inorganic C. Determining the effects of biochar additions on CO2 emissions from semi-arid soils is therefore essential for evaluating the potential of biochar as a climate change mitigation strategy. Here, we measured the CO2 that evolved from semi-arid calcareous soils amended with biochar at rates of 0 and 20tha(-1) in a full factorial combination with three different fertilizers (mineral fertilizer, municipal solid waste compost, and sewage sludge) applied at four rates (equivalent to 0, 75, 150, and 225kg potentially available Nha(-1)) during 182 days of aerobic incubation. A double exponential model, which describes cumulative CO2 emissions from two active soil C compartments with different turnover rates (one relatively stable and the other more labile), was found to fit very well all the experimental datasets. In general, the organic fertilizers increased the size and decomposition rate of the stable and labile soil C pools. In contrast, biochar addition had no effects on any of the double exponential model parameters and did not interact with the effects ascribed to the type and rate of fertilizer. After 182 days of incubation, soil organic and microbial biomass C contents tended to increase with increasing the application rates of organic fertilizer, especially of compost, whereas increasing the rate of mineral fertilizer tended to suppress microbial biomass. Biochar was found to increase both organic and inorganic C contents in soil and not to interact with the effects of type and rate of fertilizer on C fractions. As a whole, our results suggest that the use of biochar as enhancer of semi-arid soils, either alone or combined with mineral and organic fertilizers, is unlikely to increase abiotic and biotic soil CO2 emissions.

Solubility and toxicity of antimony trioxide (Sb2O3) in soil.

Antimony trioxide (Sb2O3) is a widely used chemical that can be emitted to soil. The fate and toxicity of this poorly soluble compound in soil is insufficiently known. A silt-loam soil (pH 7.0, background 0.005 mmol Sb kg(-1)) was amended with Sb2O3 at various concentrations. More than 70% of Sb in soil solution was present as Sb(V) (antimonate) within 2 days. The soil solution Sb concentrations gradually increased between 2 and 35 days after Sb2O3 amendment but were always below that of soils amended with the more soluble SbCl3 at the lower Sb concentrations. The soil solution Sb concentrations in freshly amended SbCl3 soils (7 days equilibration) were equivalent to those in Sb2O3-amended soils equilibrated for 5 years at equivalent total soil Sb. Our data indicate that the Sb solubility in this soil was controlled by a combination of sorption on the soil surface, Sb precipitation at the higher doses, and slow dissolution of Sb2O3, the latter being modeled with a half-life ranging between 50 and 250 days. Toxicity of Sb to plant growth (root elongation of barley, shoot biomass of lettuce) or to nitrification was found in soil equilibrated with Sb2O3 (up to 82 mmol Sb kg(-1)) for 31 weeks with 10% inhibition values at soil solution Sb concentrations of 110 microM Sb or above. These concentrations are equivalent to 4.2 mmol Sb per kg soil (510 mg Sb kg(-1)) at complete dissolution of Sb2O3 in this soil. No toxicity to plant growth or nitrification was evident in toxicity tests starting one week after soil amendment with Sb2O3, whereas clear toxicity was found in a similar test using SbCl3. However, these effects were confounded by a decrease in pH and an increase in salinity. It is concluded that the Sb(V) toxicity thresholds are over 100-fold larger than background concentrations in soil and that care must be taken to interpret toxicity data of soluble Sb(III) forms due to confounding factors.

Application of a physical input-output table to evaluate the development and sustainability of continental water resources in Spain.

Continental waters are complex resources in terms of a measurable physical quantity, and measuring them requires a good knowledge of total water availability. In this research, an accounting physical input-output table (PIOT) was applied to evaluate total water resources and gross annual availabilities at each stage of the natural-artificial water cycle. These stages are considered subsystems of a continental water resource system describing water transfers for an average year within 13 administrative basins of Spain. Water transfers between various subsystems are characterized by internal flows decreasing the water resource availabilities. The PIOT analysis establishes these internal flows, and the origins and final uses of the total resources for each subsystem. The input-output balance registered an unsustainable negative net accumulation in eight water basins. The PIOT analysis also allowed the calculation of significant indicators such as water resource developments (RDI) and their sustainable use (SUI). RDI and SUI demonstrate that groundwater is a critical resource affecting the environment (e.g., wetlands in the upper Guadiana) and the water supply (e.g., irrigation in the Segura basin). The results of this model suggest that above-/below-ground hydrological links are important when decisions have to be made in order to provide a satisfactory supply of water in Spain. The model integrates the different water basins under territorial criteria, and therefore it may be useful for the Spanish National Hydrological Plan.