Biochar surface properties and chemical composition determine the rhizobial survival rate

Biochar as a sustainable sorbent for the removal of lanthanides from acid mine drainage

The extraction and processing of ores containing lanthanides (Ln) generate significant amounts of waste that may lead to Ln-rich leachates and acid mine drainage (AMD). AMD is characterised by an acidic pH and high iron (Fe) concentrations. Due to the environmental risk of these leachates, there is a need to apply effective remediation strategies to decrease Ln concentrations in leachate-affected waters. In this scenario, biochar was investigated as a sustainable and cost-effective alternative for the treatment of these waters. This study explored the viability of two biochar materials (derived from pine branches (PB) and garden wastes (GaW)) for the removal of Ln (La, Sm and Lu) from contaminated waters, including AMD. A continuous-flow sorption technique was used to simulate a real scenario of water filtration using a biochar barrier. Initially, two Sm-spiked water matrices, double-deionised water (DD) and river freshwater (FW) were tested, revealing no statistically significant differences in the biochar sorption capacities obtained (220 and 216 meq kg-1 for PB, 459 and 392 meq kg-1 for GaW in DD vs. FW scenarios, respectively), despite the slight differences in pH, dissolved organic matter, and water-soluble cation concentrations between the matrices. For mixed Ln contamination (La + Sm + Lu), Ln appeared to be equally distributed at the biochar sorption sites, whereas the biochar showed a similar overall sorption capacity when comparing mixed Ln contamination to only Sm contamination. After the initial tests, the efficiency of the biochar materials to sorb Ln from AMD was tested in a simulated AMD matrix. Biochar materials with high buffering capacity, such as those tested in this work, were considered a suitable option for the treatment of Ln-contaminated AMD, provided that the operation times are adapted so as not to exceed the acid neutralising capacity of the material.

Biopolymer as an additive for effective biochar-based rhizobial inoculant

Biochar is an efficient and inexpensive carrier for bacteria that stimulate plant development and growth. In this study, different biopolymer additives (cellulose, xanthan gum, chitin and tryptone) were tested with different addition ratios (1:0.1, 1:0.5 and 1:1) on further enhancing biochar capacity for supporting the growth and activity of Bradyrhizobium japonicum (CB1809). We utilized pine wood biochar (PWBC) pyrolyzed at 400 °C as the base inoculum carrier. The shelf life and survival rate of CB1809 were counted using the colony-forming unit (CFU) method for up to 120 days. Peat served as a standard reference material against which all treatments were compared. Subsequent experiments evaluated the ability of carrier inoculants to promote Glycine max L. (soybean) plant growth and nodulation under different watering regimes, i.e., 55 % water holding capacity (WHC) (D0), 30 % WHC (D1) and, 15 % WHC (D2) using sandy loam soil. Results revealed that among different additives; xanthan gum with 1:0.5 to PWBC [PWBC-xanthan gum(1:0.5)] was observed as a superior formulation in supporting rhizobial shelf life and survival rate of CB1809. In pot experiments, plants with PWBC-xanthan gum(1:0.5) formulation showed significant increase in various physiological characteristics (nitrogenase activity, chlorophyll pigments, membrane stability index, and relative water content), root architecture (root surface area, root average diameter, root volume, root tips, root forks and root crossings), and plant growth attributes (shoot/root dry biomass, shoot/root length, and number of nodules). Additionally, a reduced enrichment of isotopic signatures (δ13C, δ15N) was observed in plants treated with PWBC-xanthan gum(1:0.5), less enrichment of δ15N indicates an inverse link to nodulation and nitrogenase activity, while lower δ13C values indicates effective water use efficiency by plants during drought stress. These results suggest that biopolymers supplementation of the PWBC is useful in promoting shelf life or survival rate of CB1809.

More effective application of biochar-based immobilization technology in the environment: Understanding the role of biochar

In recent years, biochar-based immobilization technology (BIT) has been widely used to treat different environmental issues because of its cost-effectiveness and high removal performance. However, the complexity of the real environment is always ignored, which hinders the transfer of the BIT from lab-scale to commercial applications. Therefore, in this review, the analysis is performed separately on the internal side of the BIT (microbial fixation and growth) and on the external side of the BIT (function) to achieve effective BIT performance. Importantly, the internal two stages of BIT have been discussed concisely. Further, the usage of BIT in different areas is summarized precisely. Notably, the key impacts were systemically analyzed during BIT applications including environmental conditions and biochar types. Finally, the suggestions and perspectives are elucidated to solve current issues regarding BIT.