Chemical stabilization of Cd contaminated soil using fresh and aged wheat straw biochar

Soil pollution can adversely affect the ecosystem services provided by the soil. Polluted soils reduce land productivity by reducing crop yields and polluting groundwater. Also, both crops and water in polluted lands may unsafe for the consumption by animals or humans. Release of chemicals or toxic substance can happen through industrial and agricultural activities. Metal mining and smelting to separate minerals is one such of activity which can introduce large quantities of heavy metals into the environment which persist in the soil for long periods even after those activities are ended. The Campine area on the border of Belgium and the Netherlands contains Cd contaminated sites due to historic metal smelting activities. A soil collected in that region containing 11±0.5 ppm Cd exceeding soil remediation standards was taken in consideration for this soil remediation study. Biochar is increasingly getting attention as a remediation tool to immobilizing heavy metals in contaminated soils. However, long-term provisioning of such service is mainly depends on the biochar carbon stability. Biochar carbon stability is mainly depending on the biochar production conditions, nature of the feedstock material and the biotic and abiotic environmental conditions that biochar is being used. Also, the heavy metal immobilization process heavily depends on the soil and biochar pH and the nature of the functional groups present on biochar surfaces such as carbonates and phosphates. Within this context, three types of wheat straw biochar were produced using a screw reactor at 400 °C, 500 °C, and 600 °C. To age the biochar samples, biochar samples were subjected to accelerated aging using a method suggested by Cross and Sohi, 2013 [1]. This method can be used as proxy for environmental aging of biochar approximately 100 years under temperate conditions. Then these six biochar samples (BC400F, BC500F, BC600F, BC400A, BC500A, BC600A) were characterized for elemental analysis, ash content, volatile matter content and fixed carbon content, pH, EC, phosphate and carbonate content and FT-IR analysis. The soil used in this study was characterized for the soil texture, elemental contents, organic matter content, pH and EC. Six months of laboratory incubation study was conducted with contaminated soil amended with each type of biochar at 2 % rate (w/w). Rhizon extractions were collected at the end of each month to quantify the Cd concentration, pH and total organic carbon content in the soil pore water. At the end of the six months of incubation time, Cd concentration in the pore water ranged from 100.36 ppb in BC600A to 249.85 ppb BC400A. The Cd concentration in each treatment was BC600A\u3c BC400F\u3c BC600F\u3c BC500F\u3c Soil only (control) \u3c BC500A\u3c BC400A. According to the FT-IR analysis of the six biochar samples, more carboxylic-C and carbonate- C functional groups were present in aged biochar samples compared to the freshly produced wheat straw biochar samples. Also, biochar produced at lower temperatures were characterized by lower pH and a lower amount of stable C compounds compared to the biochar produced freshly and in higher production temperatures. These results suggest that the stability of biochar carbon and pH of both biochar and soil have a significant impact on the stabilization of heavy metals in the soil environment. Therefore, the selection of biochar with desired qualities thus choosing of suitable biochar production conditions is essential in decision-making processes to keeping the biochar services in the long run. References: [1]. Cross, A., & Sohi, S. P. (2013). A method for screening the relative long‐term stability of biochar. Gcb Bioenergy, 5(2), 215-220

Characterization of tree bark biochar and evaluation of its potential to use in horticultural growing mediums

Peat is popular in horticulture industry as a main constituent in the horticultural growing medium due to its high water holding capacity, improve aeration in the medium, ability to adjust the pH and fertility level in the substrate as required and pathogen freeness. However, the use of peat in growing mediums cause for the environmental problems such as greenhouse gas emissions due to excavating and drainage of natural peatlands. As a sustainable approach and an alternative to peat, biochar is getting attention due to its stable nature. As a byproduct of pyrolysis, biochar has high porosity, high pH, high cation exchange capacity (CEC) and high water holding capacity. These properties make biochar as an appropriate constitute in growing medium applications with long term plant productivity. Within this context, the aim of this study was to examine the potential of biochar produced from bark as an alternative to peat use in growing mediums. Biochar was characterized for elemental, proximate, organic matter content, pH, EC, Py GC-MS and FT-IR. Then, five growing medium substrates including peat only, biochar only, biochar and peat in 1:1, 1:3, 3:1 (V/V) ratios were analyzed for pH, electrical conductivity (EC), CEC, bulk density, porosity, water holding capacity, aeration, and particle size distribution parameters. Germination test was carried out to assess the phytotoxicity of the formulated substrates. Preliminary plant growth test was carried out to determine the tomato seedling growth up to four weeks. Additionally, one month of laboratory incubation was conducted to determine the pore water nutrient dynamics. For that, nitrate-N, phosphate-P and sulphate-S in rhizone extractions in each growing medium formulations were collected weekly up to one month of period. Addition of biochar into peat increased the pH, EC, and CEC of all peat and biochar mixed treatments. According to the germination test results for the cress, lettuce and tomato seeds, the addition of biochar into peat had significantly increased the germination percentage, shoot and root length of the germinated seeds compared to the peat only treatment. Addition of bark biochar into peat significantly increased the plant growth parameters compared to peat only and biochar only treatments. Nitrate-N, sulphate-S and phosphate-P content in pore water of each substrate were significantly high in biochar added treatments compared to the peat only treatment. These results indicate that bark biochar could use to partially replace peat use in horticultural growing mediums

Biochar from sawmill residues: Characterization and evaluation for its potential use in the horticultural growing media

Peat remains the primary constituent of horticultural growing media in professional use. However, use of peat in horticultural growing media results in greenhouse gas emissions and biodiversity loss due to excavation of natural peatlands. Biochar is gaining attention as a sustainable alternative to peat use in horticulture. This study examined the potential of biochar produced from a particular type of sawmill residue, as a partial replacement for peat in horticultural growing media. Five treatments including peat only, biochar only, biochar and peat in 1:1, 1:3, and 3:1 (V/V) ratios were assessed. The addition of biochar into growing media increased the pH and EC of the medium. However, physical properties (air-filled porosity and water holding capacity) were negatively affected with the increase in biochar content in the medium. According to the germination test results, biochar significantly improved germination and the shoot and root length of germinated seeds of cress, lettuce and tomato when compared to peat-only and biochar-only treatments. The inclusion of biochar in 25–50% volume ratio improved plant growth parameters compared to peat-only and biochar-only media. Results obtained from this study suggest that sawmill residue offers great potential as a feedstock for biochar production and inclusion of biochar has positive effects on seed germination and plant growth that might compete with modified pea

Metal sorption by biochars : a trade-off between phosphate and carbonate concentration as governed by pyrolysis conditions

Three feedstocks, pine wood, grass and cow manure, were pyrolyzed under various conditions and tested on their ability to sorb metals in aquatic systems. The feedstocks were pyrolyzed at 2 different temperatures (350 degrees C and 550 degrees C) and 2 different residence times (10 and 60 min) and resulting biochars were assessed on their capability to immobilize Pb, Cu, Cd and Zn. Manure-based chars, and to a lesser extent grass-based chars, featured high concentrations of phosphates and carbonates, These anions play an important role in metal sorption because they form insoluble complexes with the metals. Washing reduced the concentration of these anions, leading to a reduced sorption of metals by the biochar. The carbonate concentration on the biochars' surface increased at higher reactor temperature and longer residence times. The opposite trend was observed for the phosphate concentration and the cation exchange capacity. Accordingly, the optimal temperature-residence time combination for sorption was a trade-off between these properties. Biochar produced from cow manure and pyrolyzed at 550 degrees C for 10 min showed the best sorption for all metals considered

Chemical stabilization of Cd-contaminated soil using fresh and aged wheat straw biochar

Metal mining and smelting activities can introduce a substantial amount of potentially toxic elements (PTE) into the environment that can persist for an extended period. That can limit the productivity of the land and creates dangerous effects on ecosystem services. The effectiveness of wheat straw biochar to immobilize Cd in contaminated soil due to metal smelting activities was investigated in this study. The biochar carbon stability and long-term provisioning of services depend on the biochar production conditions, nature of the feedstock, and the biotic and abiotic environmental conditions in which the biochar is being used. Within this context, three types of wheat straw biochar were produced using a screw reactor at 400 °C, 500 °C, and 600 °C and tested in a laboratory incubation study. Soil was amended with 2 wt% of biochar. Both fresh and aged forms of biochar were used. Biochars produced at lower temperatures were characterized by lower pH, a lower amount of stable C, and higher amounts of acidic surface functional groups than the freshly produced biochars at higher production temperatures. At the end of the 6 months of incubation time, compared to the soil only treatment, fresh and aged forms of wheat straw biochar produced at 600 °C reduced the Cd concentration in soil pore water by 22% and 15%, respectively. Our results showed that the aged forms of biochar produced at higher production temperatures (500 °C and 600 °C) immobilized Cd more efficiently than the aged forms of lower temperature biochar (400 °C). The findings of this study provide insights to choose the production parameters in wheat straw biochar production while considering their aging effect to achieve successful stabilization of Cd in contaminated soils