Biochar cation exchange capacity (CEC) is a key property central to better retention of soil nutrients and reduction of fertilizer runoff. This paper reports a breakthrough process to improve biochar CEC value by a factor of nearly 10 through biochar surface oxygenation by ozonization. The CEC value of the untreated biochar was measured to be anywhere between 14 and 17 cmol/kg. A 90 min dry ozonization treatment resulted in an increased biochar CEC value of 109−152 cmol/kg. Simultaneously, the biochar ozonization process resulted in a reduction of biochar pH from 9.82 to as low as 3.07, indicating the formation of oxygen-functional groups including carboxylic acids on biochar surfaces. Using the technique of X-ray photoelectron spectroscopy (XPS), the formation of oxygen-functional groups including carboxylic acids on biochar surfaces have been observed at a nanometer molecular scale following the ozonization treatment. The molar O/C ratio (0.31:1) on ozonized biochar surface as analyzed by XPS was indeed significantly higher than that (0.16:1) of the control biochar surface. The molar O/C ratio from the elemental analysis data also showed an increase from the nonozonized sample (0.077:1) to the dry-ozonized sample (0.193:1). Fourier-transform infrared (FTIR) spectroscopy analysis also showed an increase in the content of oxygen-functional groups in the form of carbonyl groups on biochar surfaces upon ozonization, which can also produce certain amount of oxygenated biochar molecular fragments that may be solubilized by liquid water, potentially leading to greater effects upon application of biochar in soil.

A large increase in phosphorus (P) solubilization from hydroxyapatite using ozonized biochar has been experimentally demonstrated here for the first time. Briefly, incubation of insoluble phosphate material hydroxyapatite with wet-ozonized biochar, including its filtrate liquid, for 2 days, resulted in a much higher concentration of solubilized phosphate (569.9 mg/L) than that (0.145 mg/L) of the control in which hydroxyapatite was incubated with the nonozonized biochar and its filtrate. The associated calcium solubilization pattern was also observed in the experiment. 31 Phosphorus NMR analysis confirmed the solubilized phosphorus to be mostly in the form of HPO 4 2− . Excitation emission matrix spectroscopy showed the prevalence of humic-like substances in ozonized biochar filtrate, which resulted in stronger P solubilization. This study indicated that the P solubilization may be accomplished through at least one of the following molecular mechanisms: (a) protonic effect, (b) cation exchange, and (c) anion exchange. This green chemistry with ozonized biochar may lead to a new approach to unlock P from "insoluble" phosphate mineral phases.

Introduction: Thermosynechococcus elongatus BP1 is a thermophilic strain of cyanobacteria that has an optimum growth at 57°C, and according to previous analysis by Yamaoka et al, T elongatus BP1 cannot survive at a temperature below 30°C. This suggests that the thermophilic property of this strain may be used as a natural biosafety feature to limit the spread of genetically engineered (GE) organisms in the environment if physical containment fails. Objective: To further explore the growth and survivability range of T elongatus BP1, we report a growth and survivability assay of wild-type and GE T elongatus BP1 strains under different conditions. Methods: Wild-type and GE T elongatus BP1 cultures were prepared and incubated in the laboratory (high temperatures and constant light source) and greenhouse conditions (lower/varied temperatures and sunlight) for 4 weeks. The cell density was monitored weekly by measuring the optical density at 730 nm (OD730). To assess the survivability, a sample of each culture was added to fresh media, placed in laboratory conditions (42.2°C and 30 µE m–2 s–1) in multi-well plates and observed for growth for up to three weeks. Lastly, the number of viable cells were determined by plating a diluted sample of the culture on solid media and counting colony-forming units (CFU) after 1 day, 2 weeks and 4 weeks of incubation in laboratory or greenhouse conditions. Results: Our experimental results demonstrated that growth was hindered but that the cells did not entirely die within 2 to 4 weeks at warm temperatures (31.42°C-36.27°C). The study also showed that 2 weeks of exposure to cool temperature conditions (15.44°C-25.30°C) was enough to cause complete death of GE T elongatus BP1. However, it took 2 to 4 weeks for the wild-type T elongatus BP1 cells to die. Conclusion: This study revealed that the thermophilic feature of the T elongatus BP1 may be used as an effective biosafety mechanism at a cool temperature between 15.44°C and 25.30°C but may not be able to serve as a biosafety mechanism at warmer temperatures.

A dramatic enhancement by a factor of 15 for the production of ozonized biochar molecular products measured as dissolved organic carbon (DOC) was achieved by an innovative biochar ozonization process. The filtrate of the ozonized biochar molecular products contained substantially more carboxyl groups than that of the nonozonized biochar. The ozonized biochar molecules are now identified to be highly potent, even at a ppm DOC concentration level, to "unlock" phosphorus (P) from insoluble phosphate material hydroxyapatite (HA). At a DOC concentration of 600 ppm, the filtrates from the wet-ozonized pine 400 biochar and the dry-ozonized rogue biochar substances were both able to solubilize HA, resulting in a concentration of solubilized phosphorus up to 396.8 ± 28.8 and 339.6 ± 8.5 mg HPO 4 2− /L, respectively. Even at a DOC concentration as low as 10 ppm, the ozonized biochar molecules solubilized up to 8.3 ± 1.1 mg/L of phosphate. At neutralized pH 7, the efficiency in solubilizing phosphate decreased, indicating the importance of the protonic effect. The ozonized biochar organic acids solubilized more phosphate than a hydrochloric acid solution with the same pH, thus showing the applicability of this green chemistry with ozonized biochar molecules to unlock P from insoluble phosphate rock materials. The discovery of ozonized biochar molecules capable of unlocking P is highly relevant to agricultural phosphorus and environmental sustainability on the Earth.

Background Biochar ozonization was previously shown to dramatically increase its cation exchange capacity, thus improving its nutrient retention capacity. The potential soil application of ozonized biochar warrants the need for a toxicity study that investigates its effects on microorganisms. Results In the study presented here, we found that the filtrates collected from ozonized pine 400 biochar and ozonized rogue biochar did not have any inhibitory effects on the soil environmental bacteria Pseudomonas putida, even at high dissolved organic carbon (DOC) concentrations of 300 ppm. However, the growth of Synechococcus elongatus PCC 7942 was inhibited by the ozonized biochar filtrates at DOC concentrations greater than 75 ppm. Further tests showed the presence of some potential inhibitory compounds (terephthalic acid and p-toluic acid) in the filtrate of non-ozonized pine 400 biochar; these compounds were greatly reduced upon wet-ozonization of the biochar material. Nutrient detection tests also showed that dry-ozonization of rogue biochar enhanced the availability of nitrate and phosphate in its filtrate, a property that may be desirable for soil application. Conclusion Ozonized biochar substances can support soil environmental bacterium Pseudomonas putida growth, since ozonization detoxifies the potential inhibitory aromatic molecules. Graphical Abstract