Nano-black carbon (BC) is one of the most active fractions in the pyrogenic carbonaceous matter continuum. The majority of recent studies mainly focus on the role of nano-BC in the global carbon cycle. However, based on literature and our recent studies, we suggest that nano-BC may also serve as a super suspending agent, carrier, and redox mediator for sorbates during its migration from terrestrial to water bodies due to its unique properties such as high colloidal stability, strong sorption capacity, and high surface reactivity. The full implications of nano-BC in water/soil environments are far more than we expected. Thus, we call for more detailed investigations on the activity and reactivity of nano-BC in water/soil environments.
Rapid expansion of cultivated bamboo negatively impacts on biodiversity and soil microbial community. As such, it is important to properly manage and use bamboo to prevent and control such issues. This study focuses on optimizing pyrolysis conditions to produce bamboo biochar for agricultural soil amendment, particularly soil potassium (K) and water holding capacity. Bamboo chips were pyrolyzed under nitrogen gas at 400, 600, and 800 °C for 1 and 2 h of retention. A total of six biochar products were created: 400-1 (i.e., 400 °C in 1 h), 400-2, 600-1, 600-2, 800-1, and 800-2. The 600 °C bamboo biochar products were observed to have the greatest potential in increasing soil K and water holding capacity. The 600-1 product had the highest potassium content (4.87%), with a water holding capacity of 3.73 g g−1, while the 600-2 product had the second-highest potassium content (4.13%) and the highest water holding capacity (4.21 g g−1) and cation exchange capacity. The K release in 600 °C products was larger and slower than that of the 400 °C and 800 °C products, respectively. The results also indicated that the physicochemical characteristics of bamboo biochar, such as yield, pH, surface area, water holding capacity, and K content, were significantly impacted by temperature, retention time, or a combination of these parameters. The outcomes from this study are a valuable reference for bamboo biochar production targeting agricultural soil amendment, particularly when it is directed at increasing soil K and water holding capacity.
Biochar can enhance crop production and sequester carbon, but there have been few studies with tree crops. Rubber plantations cover more than 8 million hectares in Southeast Asia, so we assessed the feasibility of biochar application in these plantations with a pot trial. Rubber seedlings were planted in soil with four concentrations (0, 1.25%, 2.5% and 5%, w/w) of biochar combined with two concentrations of compound fertilizer (0 kg/ha and 300 kg/ha). Soil properties and seedling growth were measured, and a leaching experiment was conducted in the rainy season. Our results show that biochar increased pH, water content (27.4–65.1%), total carbon (25.4–53.6%), nitrate nitrogen, and available phosphorus in the soil, and decreased bulk density (3.2–23.9%). Biochar treatment reduced leaching of ammonium nitrogen and ortho-P. Biochar increased seedling nutrient uptake (C, N, P and K), with 2.5% and 5% biochar showing the largest effects, but seedling biomass was the highest with 1.25%, and declined in 2.5% and 5%. Our results suggest that biochar addition is an effective way to improve rubber plantation soils, sequester more carbon and decrease nutrient leaching, but the optimum application rate under field conditions needs further research.
Irrigation water quality plays a vital role in sustaining crop productivity and feeding a growing world population. In many countries, continued agricultural water reuse can lead to greater water-soluble salt concentrations, and in particular Na; finding means by which irrigation water Na, and thus sodium adsorption ratios (SAR), can be reduced would reduce the rate at which soil sodification occurs. Four biochars, containing a variety of organic functional groups and electrochemistries, were examined for their potential to sorb and remove Na from simulated irrigation water, and subsequently reduce water SAR. Two batch experiments examined the role that wheat straw biochar, lodgepole pine biochar, Kentucky bluegrass biochar, and hemp biochar played in terms of sorbing sodium over time or application rate. Of the four biochars examined, hemp biochar had the lowest oxidation–reduction potential (ORP; ~ 0–100 mV), sorbed the greatest Na amount (up to 923 mg kg−1), and released Ca and Mg (up to 115 and 63 mg kg−1, respectively) into solution, all of which led to a significant reduction in water SAR (from 8.8 to 7.3; 17% decrease). Sodium sorption onto hemp biochar better fit a Langmuir versus a Freundlich isotherm, yet followed a pseudo-second-order model better than a pseudo-first-order kinetic model. The data suggest that Na ions formed a monolayer on the hemp biochar surface, influenced by associations with π electrons, but given time the Na ions may diffuse into biochar pores or more slowly interact with biochar-borne π electrons. Hemp biochar shows promise in reducing the SAR of Na-impacted waters. Future investigations should focus on additional laboratory, greenhouse, and field trials with hemp biochar and other biochars designed to have similar or superior properties for sorbing excess irrigation water Na and improving crop growth.
Biochars produced from cotton gin waste (CG) and guayule bagasse (GB) were characterized and explored as potential adsorbents for the removal of pharmaceuticals (sulfapyridine-SPY, docusate-DCT and erythromycin-ETM) from aqueous solution. An increase in biochar pyrolysis temperature from 350 οC to 700 οC led to an increase in pH, specific surface area, and surface hydrophobicity. The electronegative surface of all tested biochars indicated that non-Coulombic mechanisms were involved in adsorption of the anionic or uncharged pharmaceuticals under experimental conditions. The adsorption capacities of Sulfapyridine (SPY), Docusate (DCT) and Erythromycin (ETM) on biochar were influenced by the contact time and solution pH, as well as biochar specific surface area and functional groups. Adsorption of these pharmaceutical compounds was dominated by a complex interplay of three mechanisms: hydrophobic partitioning, hydrogen bonding and π–π electron donor–acceptor (EDA) interactions. Despite weaker π–π EDA interactions, reduced hydrophobicity of SPY− and increased electrostatic repulsion between anionic SPY− and the electronegative CG biochar surface at higher pH, the adsorption of SPY unexpectedly increased from 40% to 70% with an increase in pH from 7 to 10. Under alkaline conditions, adsorption was dominated by the formation of strong negative charge-assisted H-bonding between the sulfonamide moiety of SPY and surface carboxylic groups. There seemed to be no appreciable and consistent differences in the extent of DCT and ETM adsorption as the pH changed. Results suggest the CG and GB biochars could act as effective adsorbents for the removal of pharmaceuticals from reclaimed water prior to irrigation. High surface area biochars with physico-chemical properties (e.g., presence of functional groups, high cation and anion exchange capacities) conducive to strong interactions with polar-nonpolar functionality of pharmaceuticals could be used to achieve significant contaminant removal from water.