Fern Dicranopteris linearis-derived biochars: Adjusting surface properties by direct processing of the silica phase

Potential of local plant leaves as natural coagulant for turbidity removal

The performance of local plants was tested using synthetic turbid water resembling real wastewater by measuring their ability to remove turbidity. The selected plants were A. indica, S. palustris, D. linearis, S. polyanthum, M. esculenta, P. sarmentosum, and M. malabathricum which can easily be found locally. The experiment was run based on coagulant dosages varied from 0 to 10 g/L for each plant with a rapid mixing speed at 180 rpm for 3 min, slow mixing speed at 10 rpm for 20 min, and settling time for 30 min. The results demonstrated that each plant has been capable of reducing turbidity by different amounts, with an increase in the coagulant dosage. The optimum coagulant dosages achieved for A. indica, S. palustris, S. polyanthum, and D. linearis were 10 g/L with turbidity removal at 26.9%, 24.9%, 24.9%, and 17.5%, respectively. P. sarmentosum and M. esculenta attained optimum coagulant dosages at 5 g/L with turbidity removal at 24.2% and 22.2%, and lastly M. malabathricum at 0.1 g/L (12.2%). P. sarmentosum was suggested to the best natural coagulant which achieved the highest removal of turbidity with a low dosage used.

Effects of CO2 and temperature on phytolith dissolution

Phytoliths, silica structures derived from plant residues in silicon (Si)-accumulating plant species, have recently been recognized as a sink and source of nutrients and a hosting phase for carbon sequestration in soil. While the solubility of phytoliths in relation to their respective nature and solution chemistry has been intensively studied, the combined effects of CO₂ and temperature, two highly variable parameters in soil, have not been fully understood. We hypothesized that changes in CO₂ and temperature may affect the dissolution rate, thereby resizing the soil phytolith pool. Rice straw phytoliths were obtained from either open burning or controlled heating of straw from 300 to 900 °C and used to determine their batch incubation kinetics in a closed chamber at CO₂ concentrations of 0 to 15% vol. and a temperature range of 20 to 50 °C for six days. The results revealed a contrasting effect in which temperature and CO₂ were correspondingly found to accelerate or decelerate the dissolution rate of phytoliths. Under the most dissimilar conditions, i.e., 0% vol. CO₂ and 50 °C and 15% vol. CO₂ and 20 °C, the discrepancy in solubility was approximately six-fold, indicating a high vulnerability of phytoliths to CO₂ and temperature changes. This finding also suggests that the soil phytolith pool can be diminished in the case of either increasing soil temperature or decreasing CO₂ flux. Calculations based on these data revealed that the dissolution rate of phytoliths could be increased by an average of 4.5 to 7.3% for each 1 °C increase in temperature. This finding suggests a possible impact of current global warming on the global biogenic silica pool, and more insight into the relationship between this pool and climate change is, therefore, necessary to maintain the function of the phytolith phase in soil.

Carbonization and H3PO4 activation of fern Dicranopteris linearis and electrochemical properties for electric double layer capacitor electrode

Today, the world’s climate change is a growing problem, plant carbon sequestration is one of the effective ways to mitigate climate change by reducing greenhouse gases, mostly carbon gases. Dicranopteris linearis (D. linearis), a common fern species in the tropic or subtropic ecoregions, has been recently recognized as a potential feedstock to produce highly porous biochar. This study aims to enhance the specific surface area (SSA) and pore volumes of biochars derived from the D. linearis by H₃PO₄ activation and examine electrical properties of the activated biochars and their possible usage for the electric double-layer capacitor (EDLC) electrode. The treated raw fern was activated with H₃PO₄ 85% by the three different mixing ratios 1:0, 1:1, and 1:3 (w/w) and then pyrolysis under N₂ flow maintained at 500 °C for 1 h. The performance as the electrode for an EDLC was evaluated in 1 mol L⁻¹ H₂SO₄ solution for the H₃PO₄-activated samples. The SSA and pore volumes were drastically increased after activation. The maximum SSA and pore volume were 1212 m² g⁻¹ and 1.43 cm³ g⁻¹, respectively for the biochar activated at 400 °C with a weight mixing ratio 1:3 (w/w) between the fern and H₃PO₄ acid while these values of the biochar at 400 °C were 12 m² g⁻¹ and 0.02 cm³ g⁻¹, respectively. The biochar activated at 600 °C with the mixing ratio 1:1 (w/w) showed the maximum capacitance value, ca. 108 F g⁻¹ at 1 mV s⁻¹. The activation using H₃PO₄ showed a positive tendency to enhance electrochemical properties and it could be a premise toward a higher performance of EDLC from the D. linearis derived activated biochar.

Colloidal interactions of micro-sized biochar and a kaolinitic soil clay

Fine-sized biochars and clay minerals co-present in various circumstances, e.g., agricultural land and water treatment. Because both of these materials are scavengers for nutrients, agrochemicals and other toxicants, their dispersibility and transportability have received much attention. However, little is documented about their colloidal interactions and to what extent biochar particles can stimulate the dispersion of clay minerals. Here, the effect of engineered micro-sized biochar amendment on the surface charge (SC) and colloidal dynamics of the clay fraction of a kaolinite-rich soil was determined. The engineered biochars showed distinctive SC and colloidal properties depending on their pyrolysis conditions (e.g., oxygen level and temperature) and solution chemistry (i.e., pH and cation type). Two types of biochars prepared under non-biochar-oriented pyrolysis (open heating, 'O-biochar') and biochar-oriented pyrolysis (N₂-supported heating, 'N₂-biochar') showed contrasting effects on the colloidal dynamics of clay. The O-biochars provoked aggregation due to their higher content of soluble salts, which increased ionic strength and provided multivalent cations, inducing bridging between negatively charged colloids. In contrast, the N₂ biochars low in soluble salts and rich in negatively charged burned organic matter compounds favoured the dispersion of clay. The adjustment of biochar production methods can therefore be highlighted as the way to customize biochar for specific uses or to reduce the risk of clay loss from soils in the short term. In the long term, when soluble salts are removed by leaching, it is likely that dispersion is facilitated and the risk for erosion increases.

Straw phytolith for less hazardous open burning of paddy straw

Rice production helps feed at least half of the world’s population but generates approximately one billion tonnes of straw residue per annum. On-site open burning of rice straw after harvesting is common in recent times because there has been less demand for rice straw to use as fuel and fodder. Due to health and climate change concerns, open burning, which results in biomass losses, smog and emissions of green house gases, e.g., CO₂, has been widely criticized and banned in many countries. Little is known about the positive benefits of straw burning, such as field care (eradication of biotic diseases) or nutrient cycling. Herein, we propose a new viewpoint in which the burning of rice straw followed by cycling of the burned materials, including silica material (so-called phytolith), into soil is demonstrated as a CO₂-sequestration strategy via buffering the soil CO₂ flux and coupling CO₂ with the silicon cycle.