Ammonium (NH) is a common form of reactive nitrogen in wastewater, and its discharge to water bodies can lead to eutrophication. This study was conducted to understand NH adsorption mechanisms of pine sawdust and wheat straw biochars in aqueous solutions and the factors affecting NH removal. Biochars were produced by pyrolysing pine sawdust at 300 °C (PS300) and 550 °C (PS550) and wheat straw at 550 °C (WS550). Pseudo-second-order and Redlich-Peterson models best fitted the adsorption data. The PS300 showed the highest NH adsorption capacity (5.38 mg g), followed by PS550 (3.37 mg g) and WS550 (2.08 mg g). Higher H/C and O/C ratios of PS300 (0.78 and 0.32, respectively) indicated the greater presence of functional groups on the biochar's surface as compared to PS550 (0.35 and 0.10, respectively) and WS550 (0.36 and 0.08, respectively), resulting in different NH adsorption through electrostatic interactions. The dominant mechanism for NH adsorption by the biochars was likely chemical bonding and electrostatic interaction of NH with the surface functional groups. Lower pyrolysis temperature resulted in a higher NH adsorption capacity by the pine sawdust biochar. At the same pyrolysis temperature (550 °C), the biochar made with pine sawdust as the feedstock had a higher NH adsorption capacity than biochar made from wheat straw. We conclude that biochars can be efficient absorbents for NH removal from wastewater, and the removal efficiency can be optimised by selecting different feedstocks or the pyrolysis condition for biochar production.

Biochar can be used as an adsorbent for phosphate removal in aquatic environments to treat eutrophication problems. Designing biochars that have large phosphate adsorption capacity through altering pyrolysis conditions and applying activation techniques will improve phosphate removal efficiency. In this study, four pine sawdust biochars were produced at 300 and 550 °C with and without steam activation. Batch sorption experiments including isotherm and kinetic studies were conducted to understand how phosphate removal capabilities and adsorption mechanisms of biochars were affected by pyrolysis temperature and steam activation. Our results showed that the steam activation and pyrolysis temperature did not affect phosphate adsorption by the biochars. The four biochars removed <4% of phosphate from the aqueous solution, which were not affected by the pH of the solution and biochar application rate. The repulsion forces between biochar surfaces and phosphate ions were likely the cause of the low adsorption.

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We employed capacitance to evaluate the kinship and interspecific variation of homoploid hybrid conifer Pinus densata, P. tabuliformis, P. yunnanensis and artificial hybrids of P. tabuliformis (maternal parent) and P. yunnanensis (paternal parent) which were cultivated and selected in the common garden experiment.  By measuring capacitance spectra under different voltage frequencies, we could differentiate different germplasms based on the electrical response. We aims to demonstrate that P. densata as the hybrid of P. tabuliformis and P. yunnanensis based on the capacitance values of the species, and to provide new evidence to the previously known biological evidence, as well as and the parental effect on the hybrids. Our results revealed that capacitance values between the species are significantly different in the spectra where P. yunnanensis positioned at the lowest and P. densata was much higher than all other species, indicating that P. densata had possessed a great capacity to store electrical energy. The capacitance spectra of P. densata and the artificial hybrid are not similar, which rejected our hypothesis. Both of the capacitance values of P. densata and the hybrids were closer to P. tabuliformis than to P. yunnanensis, which shows that the maternal influence was stronger than the paternal influence. Correlation analysis on the relationship between capacitance and fitness-related characteristics showed that capacitance is negatively correlated to mortality rate, and positively correlated with second-year survival rate. High capacitance values of P. densata and some of the hybrids reveal their superior adaptability to harsh environment in the Tibet Plateau. We concluded that capacitance as a new indicator for plant fitness and evolution evidence of homoploid hybrid conifers.