Biofiltration of toluene in the presence of ethyl acetate or n-hexane: Performance and microbial community.

This study describes the operation of two independent parallel laboratory-scale biotrickling filters (BTFs) to degrade different types of binary volatile organic compound (VOC) mixtures. Comparison experiments were conducted to evaluate the effects of two typical VOCs, i.e., ethyl acetate (a hydrophilic VOC) and n-hexane (a hydrophobic VOC) on the removal performance of toluene (a moderately hydrophobic VOC) in BTFs ''A" and ''B", respectively. Experiments were carried out by stabilizing the toluene concentration at 1.64 g m-3 and varying the concentrations of gas-phase ethyl acetate (0.85-2.8 g m-3) and n-hexane (0.85-2.8 g m-3) at an empty bed residence time (EBRT) of 30 s. In the presence of ethyl acetate (850 ± 55 mg m-3), toluene exhibited the highest removal efficiency (95.4 ± 2.2%) in BTF "A". However, the removal rate of toluene varied from 48.1 ± 6.9% to 70.1 ± 6.8% when 850 ± 123 mg m-3 to 2800 ± 136 mg m-3 of n-hexane was introduced into BTF "B". The high-throughput sequencing data revealed that the genera Pseudomonas and Comamonadaceae_unclassified are the core microorganisms responsible for the degradation of toluene. The intensity of the inhibitory or synergistic effects on toluene removal was influenced by the type and concentration of the introduced VOC, as well as the number and activity of the genera Pseudomonas and Comamonadaceae_unclassified. It provides insights into the interaction between binary VOCs during biofiltration from a microscopic perspective.

Effects of dairy manure biochar on adsorption of sulfate onto light sierozem and its mechanisms.

The adsorption of nitrogen and phosphorous nutrients on biochar and even biochar-soil mixtures was investigated. However, the situation of sulfur was not very clear. Here, sulfate (SO4 2-) adsorption onto dairy manure biochar obtained at 700 °C (DMBC700), soil (light sierozem) and a 1 : 9 (w/w) biochar-soil mixture (DMBC700-soil) was investigated using batch experiments. The contact time, sulfate concentration, and solution pH value were chosen as the main factors; their effects on sulfate adsorption were tested, and the kinetics and isotherms were also investigated. Fourier transform infrared (FTIR) and X-ray diffraction (XRD) spectroscopies were used to characterize DMBC700 and soil before and after adsorbing sulfate, respectively, and to analyze the mechanisms of adsorption. The results showed that the adsorption kinetics were well described by the pseudo-second-order model, whereas the Langmuir and Freundlich models fitted well with the equilibrium data. DMBC700 modification did not increase the adsorption capacity of light sierozem for sulfate. When the pH values of the initial solution were increased, all the adsorption capacities of sulfate onto DMBC700, light sierozem and light sierozem with DMBC700 decreased. The electrostatic interaction was the main force for the adsorption of sulfate onto DMBC700, whereas both electrostatic interaction and formation of poorly soluble CaSO4 were the main forces for adsorption of sulfate onto light sierozem. DMBC700 was found to have negative effect on sulfate adsorption onto light sierozem.

Effect of pyrolysis temperature on sulfur content, extractable fraction and release of sulfate in corn straw biochar.

The contents and release of the nutrient elements N, P and K in biochars have been investigated. Sulfur is an indispensable element for plants, but its content and release in biochar are still unclear. The effect of pyrolysis temperature (300, 500 and 700 °C) on the sulfur content, extractable fraction and release of sulfate in corn straw biochars (CS300, CS500 and CS700) was investigated. The biochars were characterized using element analysis, BET, FTIR, and XRD. It was shown that the contents of sulfur in biochars decreased significantly with increasing pyrolysis temperature. The extraction results indicated that the percentages of water extractable-sulfate (W-SO4 2-) and organosulfur in biochars decreased while those of HCl- and NaH2PO4-extractable sulfate (HCl-SO4 2-, NaH2PO4-SO4 2-) increased with pyrolysis temperature. Batch release experiments were conducted to test the effect of contact time and addition of Hoagland nutrient solution (HNS) on the release of sulfate from biochars. The release kinetics fitted well with a pseudo-second-order model. Approximately 10.7 mg g-1 of sulfate was released from CS300 during the initial 2 h, whereas 6.32 and 3.93 mg g-1 were released from CS500 and CS700, respectively. Increasing the amounts of HNS led to negative effects on sulfate release. The results indicate that low-temperatures might be optimal for producing biochar from corn straw to improve the sulfur fertilization.

Sulfate sorption on rape (Brassica campestris L.) straw biochar, loess soil and a biochar-soil mixture.

The effects of biochar amendment on sulfur behavior in soils are unknown. In this paper, sulfate (SO42-) sorption on rape (Brassica campestris L.) straw biochar produced at 600 °C (BC), loess soil (soil) and a 1:9 (w/w) biochar-soil mixture (BC-soil) was investigated by batch experiments. The effects of contact time, initial SO42- concentration, temperature and solution pH value on sorption were tested. Kinetics, isotherms and thermodynamics for sorption were investigated. Pre- and post-sorption characterizations of BC and soil were respectively studied using Fourier transform infrared (FTIR) and X-ray diffraction (XRD) spectroscopy, respectively. It has been shown that SO42- sorption on three sorbents was well described by pseudo-second-order kinetic model. The sorption isotherms could be fitted using Langmuir and Freundlich models. BC amendment did not increase the sorption capacity of soil for SO42-. The values of ΔG0, ΔH0 and ΔS0 indicated that the nature of sorption was spontaneous, endothermic and feasible. Increasing solution pH value led to a slight reduction in the sorption amount of SO42-. Sulfate was mainly sorbed onto BC through electrostatic interaction, whereas onto the soil via electrostatic interaction and formation of poorly soluble CaSO4.

[Migration and transformation of nitrogen in urban stream located in plain river-net area based on water resources regulation].

To study hydrological features and physical and chemical characteristics of urban stream located in the plain river network area in the process of water resources regulation, and to discuss the forming and composition of nitrogen in urban stream based on water resources regulation. Effects of water regulation on the ammonium release from sediments in urban stream were studied under the condition of experimental simulation. The results showed that diurnal variation of water depth under the action of water resources regulation was significant. The value of DO in the overlying water along the water resources regulation path tended to decrease, while the concentration of permanganate index tended to increase. The concentration of nitrate in overlying water along the water resources regulation path gradually decreased, while the concentration of ammonium significantly increased. DO and permanganate index were the main factors influencing the concentrations of nitrate and ammonium in overlying water. Ammonium released from the sediments was an important source of ammonium in overlying water. Water resources regulation had a significant influence (P < 0. 05) on the concentration of ammonium in overlying water, but had no significant influence on the amount of cumulative ammonium released from sediments (P > 0. 05).