Suitability of marginal biomass-derived biochars for soil amendment.

The term "marginal biomass" is used here to describe materials of little or no economic value, e.g. plants grown on contaminated land, food waste or demolition wood. In this study 10 marginal biomass-derived feedstocks were converted into 19 biochars at different highest treatment temperatures (HTT) using a continuous screw-pyrolysis unit. The aim was to investigate suitability of the resulting biochars for land application, judged on the basis of potentially toxic element (PTE) concentration, nutrient content and basic biochar properties (pH, EC, ash, fixed carbon). It was shown that under typical biochar production conditions the percentage content of several PTEs (As, Al, Zn) and nutrients (Ca, Mg) were reduced to some extent, but also that biochar can be contaminated by Cr and Ni during the pyrolysis process due to erosion of stainless steel reactor parts (average+82.8% Cr, +226.0% Ni). This can occur to such an extent that the resulting biochar is rendered unsuitable for soil application (maximum addition +22.5 mg Cr kg(-1) biochar and +44.4 mg Ni kg(-1) biochar). Biomass grown on land heavily contaminated with PTEs yielded biochars with PTE concentrations above recommended threshold values for soil amendments. Cd and Zn were of particular concern, exceeding the lowest threshold values by 31-fold and 7-fold respectively, despite some losses into the gas phase. However, thermal conversion of plants from less severely contaminated soils, demolition wood and food waste anaerobic digestate (AD) into biochar proved to be promising for land application. In particular, food waste AD biochar contained very high nutrient concentrations, making it interesting for use as fertiliser.

Buss W ，Graham MC ，Shepherd JG ，Mašek O ... -  《-》

Risks and benefits of marginal biomass-derived biochars for plant growth.

In this study, 19 biochars from marginal biomass, representing all major biomass groups (woody materials, grass, an aquatic plant, anthropogenic wastes) were investigated regarding their content of available potentially toxic elements (PTEs) and nutrients (determined by NH4NO3-extractions) and their effects on cress (Lepidium sativum) seedling growth. The objective was to assess the potential and actual effects of biochar with increased PTE content on plant growth in the context of use in soil amendments and growing media. It showed that the percentage of available PTEs was highest for biochars produced at the highest treatment temperature (HTT) of 750°C. On average, however, for all 19 biochars, the percentage availability of Cu, Cr, Ni and Zn (<1.5% for all) was similar to the percentage availability reported in the literature for the same elements in soils at similar pH values which is a highly important finding. Most biochars exceeded German soil threshold values for NH4NO3-extractable PTEs, such as Zn (by up to 25-fold), As and Cd. Despite this, cress seedling growth tests with 5% biochar in sand did not show any correlations between inhibitory effects (observed in 5 of the 19 biochars) and the available PTE concentrations. Instead, the available K concentration and biochar pH were highly significantly, negatively correlated with seedling growth (K: p<0.001, pH: p=0.004). K had the highest available concentration of all elements and the highest percentage availability (47.7±19.7% of the total K was available). Consequently, available K contributed most to the osmotic pressure and high pH which negatively affected the seedlings. Although a potential risk if some of these marginal biomass-derived biochar were applied at high concentrations, e.g. 5% (>100tha(-1)), when applied at agriculturally realistic application rates (1-10tha(-1)), the resulting smaller increases in pH and available K concentration may actually be beneficial for plant growth.

Buss W ，Graham MC ，Shepherd JG ，Mašek O ... -  《-》

Soil application of biochar produced from biomass grown on trace element contaminated land.

Trace element (TE) contamination of soils is a worldwide problem. However, although not considered safe anymore for food production without clean-up, many of these soils may still be used to produce biomass for non-food purposes such as biochar. Exploring the suitability of such biochar for the amendment of low-fertility soil, we investigated growth and metal accumulation of ryegrass (Lolium perenne, var. Calibra) as well as soil microbial abundance on a non-contaminated soil after amendment with biochar from birch (Betula pendula) wood produced on TE contaminated soil in comparison to a treatment with birch wood biochar originating from non-contaminated soil. Biochars were produced from both feedstocks by pyrolysis at two temperatures: 450 and 700 °C. During the pyrolysis, in contrast to Cu, Fe, Mg, K, Mn and P, the elements Cd, Pb, S and Na volatilized. The root biomass of the biochar treated plants was lower than that of the non-amended plants, while that of the shoot was higher. Plant shoot K and Zn concentrations were increased significantly by up to 7- and 3.3-fold respectively. For P, Mg, Mn, Fe and Cu no significant increase in shoot concentration could be detected. Neither the TE-contaminated biochar, nor the non-contaminated biochar had adverse effect on the bacterial community of the soil.

Evangelou MWH ，Brem A ，Ugolini F ，Abiven S ，Schulin R ... -  《-》

Bioavailability of phosphorus, other nutrients and potentially toxic elements from marginal biomass-derived biochar assessed in barley (Hordeum vulgare) growth experiments.

Biochars produced from marginal biomass feedstocks are a potential source of recycled nutrients for agriculture, but may also contain potentially toxic elements (PTEs) which can cause phytotoxicity. We assessed the potential for nutrient recycling from such materials against potential environmental risks in 17 biochars containing high concentrations of various PTEs and nutrients. Methods for investigating the risk of biochar-derived PTEs were developed and assessed. Short-term (21days) growth experiments with barley (Hordeum vulgare) in 5% biochar/sand mixtures were used to present the 'worst-case scenario' of high dose and low pH buffering. We compared plant nutrient and PTE concentrations with amounts extracted from the same biochars using 1M NH4NO3 or 0.01M CaCl2 (buffered and unbuffered, respectively) and Mehlich 3 to analyse whether such extractions could be used to predict bioavailability. The yields of barley grown with biochars "EPOCAD550", and "WLB550" were significantly higher than the control (p<0.05). Total phosphorus (P) concentration in above-ground biomass was higher than the control for the EPOCAD550 treatment (p<0.01). Both buffered and unbuffered 0.01M CaCl2 biochar extractions were significantly positively correlated with plant leaf concentration for six of the 18 elements investigated, more than any of the other extractions. CaCl2 extractions provided the most representative assessment of element bioavailability from marginal biochars compared to more resource-intensive growth experiments. Our results provide new insights into the bioavailability of elements in biochar and the standardisation of methods which accurately assess this attribute, which is necessary for promoting use of biochars from marginal biomass for recycling nutrients from wastewater and to agricultural production.

Shepherd JG ，Buss W ，Sohi SP ，Heal KV ... -  《-》

Changes in heavy metal bioavailability and speciation from a Pb-Zn mining soil amended with biochars from co-pyrolysis of rice straw and swine manure.

Biochar has been utilized as a good amendment to immobilize heavy metals in contaminated soils. However, the effectiveness of biochar in metal immobilization depends on biochar properties and metal species. In this study, the biochars produced from co-pyrolysis of rice straw with swine manure at 400°C were investigated to evaluate their effects on bioavailability and chemical speciation of four heavy metals (Cd, Cu, Pb and Zn) in a Pb-Zn contaminated soil through incubation experiment. Results showed that co-pyrolysis process significantly change the yield, ash content, pH, and electrical conductivity (EC) of the blended biochars compared with the single straw/manure biochar. The addition of these biochars significantly increased the soil pH, EC, and dissolved organic carbon (DOC) concentrations. The addition of biochars at a rate of 3% significantly reduced the CaCl2-extractable metal concentrations in the order of Pb>Cu>Zn>Cd. The exchangeable heavy metals decreased in all the biochar-amended soils whereas the carbonate-bound metal speciation increased. The increase in soil pH and the decrease in the CaCl2 extractable metals indicated that these amendments can directly transform the highly availability metal speciation to the stable speciation in soils. In conclusion, biochar derived from co-pyrolysis of rice straw with swine manure at a mass ratio of 3:1 could most effectively immobilize the heavy metals in the soil.

Meng J ，Tao M ，Wang L ，Liu X ，Xu J ... -  《-》