Effect of Wet-Dry Cycles on the Mechanical Performances and Microstructure of Pisha Sandstone.

The effects of the wet-dry cycles on the chemical compositions, microstructure, and mechanical properties of Pisha sandstone were experimentally investigated in the current study. A series of uniaxial compression tests were conducted to validate the deterioration of the mechanical property of specimens after wet-dry cycles. In addition, the evolutions of the mineral compositions and microstructure characteristics were confirmed by X-ray diffraction (XRD) and scanning electron microscope (SEM). Experimental results indicated that with the increase of wet-dry cycles, the mechanical properties of Pisha sandstone gradually decrease. After five wet-dry cycles, the uniaxial compressive strength, elastic modulus, and fracture energy of specimens were reduced by 41.06%, 62.39%, and 31.92%, respectively. The failure mode of the specimen changes from inclined shear failure to peel failure. Compared to the initial specimens, the relative content of primary minerals after five wet-dry cycles declined by 5.94%, and the relative content of clay minerals after five wet-dry cycles increased by 54.33%. Additionally, the porosity of samples exhibits a positive correlation with wet-dry cycles. Compared to the initial specimens, the porosity of specimens after five wet-dry cycles increased by 176.32%. Finally, a prediction model of the correlation between uniaxial compressive strength and porosity is proposed and verified.

Removal and kinetics of cadmium and copper ion adsorption in aqueous solution by zeolite NaX synthesized from coal gangue.

Zeolite can remove the heavy metals in wastewater, but the removal efficiency was determined by the types of zeolites and the treatment conditions. In this study, a kind of zeolite NaX synthesized from the coal gangue, a by-product of coal production, was used and the removal efficiency of Cd2+ and Cu2+and the kinetic models were studied. The effects of its dosage, initial pH value of wastewater, and adsorption temperature on its adsorption of heavy metals Cd2+ and Cu2+ in the simulated wastewater were studied through the indoor experiments in laboratory, and the adsorption mechanism was analyzed by the adsorption kinetic model based on its adsorption efficiency and its structures. The results show that the zeolite NaX synthesized from coal gangue has a good adsorption effect on Cd2+ and Cu2+. The adsorption reaches the best effect when the dosage of zeolite is 2 g/L, the initial pH of simulated wastewater is 5, the adsorption temperature is room temperature (25 ℃), and the removal efficiency of Cd2+ and Cu2+ (100 mg/L) is more than 90%. Additionally, the Langmuir, Freundlich, and Temkin isothermal adsorption models were used to compare and analyze the adsorption effects. The equilibrium data was better fitted by the Langmuir model with the maximum adsorption capacities of 100.11 mg/g (Cd2+) and 95.29 mg/g (Cu2+), and both separation coefficients were 0-1, which shows that the process was the favorable adsorption. Weber Morris diffusion model shows that the adsorption process at 120 min was more consistent with the pseudo-second-order kinetics model, and the adsorption efficiency was simultaneously controlled by the liquid diffusion step and intraparticle diffusion step. Moreover, the removal mechanism of Cd2+ and Cu2+ mainly includes physical adsorption and ion exchange. Therefore, the adsorption effect of zeolite synthesized from coal gangue is remarkable, which will provide a feasible and potential alternative for its resource application.

Mixotrophic denitrification processes in basalt fiber bio-carriers drive effective treatment of low carbon/nitrogen lithium slurry wastewater.

Lithium battery slurry wastewater was successfully treatedby using basalt fiber (BF) bio-carriers in a biological contact oxidation reactor. This resulted in a significant reduction of COD (93.3 ± 0.5 %) and total nitrogen (77.4 ± 1.0 %) at 12 h of HRT and dissolved oxygen (DO) of 0-1 mg/L. The modified Stover-Kincannon model indicated that the total nitrogen removal rate was 4.462 kg/m3/d in R-BF while the substrate maximum specific reaction rate (qmax) in the Monod model was 0.323 mg-N/mgVSS/d. A stable internal environment was established within the bio-nest. Metataxonomic analysis revealed the presence of denitrification and decarbonization bacteria, combined heterotrophic nitrification-aerobic denitrification bacteria, nitrite-oxidizing bacteria, and ammonia-oxidizing bacteria. Functional analysis displayed changes related to (aerobic)chemoheterotrophy, nitrogen respiration, nitrate reduction, respiration/denitrification of nitrite, and nitrate in R-BF. The study proposes a novel approach to achieve denitrification for the treatment of lithium slurry wastewater at low C/N conditions.

Organic and inorganic nitrogen removals by an ureolytic heterotrophic nitrification and aerobic denitrification strain Acinetobacter sp. Z1: Elucidating its physiological characteristics and metabolic mechanisms.

Although heterotrophic nitrification-aerobic denitrification (HN-AD) is promising in nitrogen removal, it remains unclear for most HN-AD strains in physiological characteristics and metabolic mechanisms. In this study, a newly isolated strain Acinetobacter sp. Z1 converted not only inorganic nitrogen, but also organic nitrogen to N2. Among them, urea was the preferential nitrogen substrate. Single-factor experiments showed that efficient HN-AD process occurred with acetate as carbon source, C/N ratios of 12 for NH4+-N and 15 for NO3--N, pH 8, 30 °C, DO of ∼5.8 mg/L and salinity less than 1.5 %. Subsequently, response surface analysis was applied to predict the optimal growth conditions. Its complete genome annotation in combination with enzymatic activity assay and nitrogen balance calculation showed that at least four pathways involved in nitrogen metabolism. This work indicates that ureolytic strain Z1 could be prepared as bacterial agents with other HN-AD strains to treat urea-containing wastewater like urine from urban community.

Low carbon-to-nitrogen ratio digestate from high-rate anaerobic baffled reactor facilitates heterotrophic/autotrophic nitrifiers involved in nitrogen removal.

In this study, baffled anaerobic-aerobic reactors (AOBRs) with modified basalt fiber (MBF) carriers and felt were used to treat domestic wastewater (DWW). The influent was first treated in anaerobic compartments, with the NH4+-N containing digestate refluxed into aerobic compartment for nitrification. The nitrified liquid was channeled to the anaerobic compartments for further denitrification. Under optimal conditions, AOBR with MBF carriers could remove 91% chemical oxygen demand (COD) and 81% total nitrogen (TN), with biomass production increased by 7.6%, 4.5% and 8.7% in three successive anaerobic compartments compared to the control. Biological viability analysis showed that live cells outnumbered dead cells in bio-nests. Metagenomics analysis showed that multiple metabolic pathways accounted for nitrogen conversion in anaerobic and aerobic compartments. More importantly, low COD/TN ratio digestate facilitated heterotrophic nitrification-aerobic denitrification (HN-AD) species growth in aerobic compartment. This study provides a promising strategy to source treatment of DWW from urban communities.

Effects of a compound microbial agent and plants on soil properties, enzyme activities, and bacterial composition of Pisha sandstone.

The objective of this study was to investigate the effects of the microbial agent on the improvement of Pisha sandstone soil and find out an effective measure for the control of soil erosion in the Pisha sandstone area. Pisha sandstone containing the microbial agent composed of Bacillus halotolerans P75, Sinorhizobium meliloti D10, Bacillus megaterium H3, Bacillus subtilis HB01, and organic substrate was utilized to be the soil matrix for pot experiment, and then alfalfa, ryegrass, and caragana were planted, respectively. Effects of the microbial agent plus plants on the soil properties of Pisha sandstone were evaluated, and the results showed that the microbial agent plus plants significantly increased the organic matter content, alkali hydrolyzed nitrogen content, available phosphorus content, available potassium content, invertase activity, and urease activity. Meanwhile, inoculation with the microbial agent significantly promoted the growth of alfalfa, ryegrass, and caragana and also influenced the number of soil bacteria and the relative abundance of Proteobacteria, Bacteroidetes, Actinobacteria, and others. However, the effects of the microbial agent plus different plants on the soil properties and bacterial composition of Pisha sandstone were different, while the growth of different plants showed differences, suggesting that there was a different interaction between microbes and different plants in Pisha sandstone soil. In conclusion, the microbial agent plus plants could improve Pisha sandstone soil which could provide some theoretical and experimental references for soil erosion control in the Pisha sandstone area.

Enhancement of nitrogen removal in hybrid wastewater treatment system using ferric citrate modified basalt fiber biocarrier.

Developing biofilm carriers is of great significance for efficient wastewater treatment. In this work, ferric citrate was used to modify inorganic basalt fiber (BF) biocarrier, thus improving its surface properties and the nitrogen removal in hybrid wastewater treatment system. The results showed that the iron element on modified basalt fiber (Fe-MBF) existed in the forms of ferric citrate, Fe(OH)3, Fe2O3, and FeO. The ferric deposition increased the surface roughness, hydrophilicity and reduced the electronegativity of BF. The water contact angle of BF and Fe-MBF was 117.46° and 64.85°, respectively. The surface zeta potential of BF was -17.64 mV, but shifted positively (-8.67 mV) after deposition modification. The microorganism adhesion tests showed that the attached biomass and extracellular polymeric substances (EPS) content on Fe-MBF biocarrier significantly increased and the attached bacteria had also high viability. The Fe-MBF biocarrier showed good nitrogen removal performance in the hybrid bioreactor, with total nitrogen removal efficiency up to 95.35±0.82%, increasing by about 16% compared to that with unmodified BF biocarrier. This work also provided a green modification strategy to enhance biofilm carrier in wastewater treatment.

Improving the consolidation properties of hydrophilic polyurethane for feldspathic sandstone water erosion prevention.

Feldspathic sandstone is a type of sandstone that is severely eroded by wind, rainfall, and gravity forces. The land surface in feldspathic area is degraded and covered with extremely low vegetation coverage. In this study, we propose a type of hydrophilic polyurethane (W-OH) to control its erosion and conduct the experiment to evaluate the consolidation performances. The results showed that the cementing materials (such as montmorillonite) are the main reason for the vulnerability of feldspathic sandstone to erosion, which expands by absorbing water. Additionally, the organic content is extremely low and is not suitable for vegetation growth. However, when the different concentrations of W-OH solution were sprayed on the feldspathic sandstone surface, the solution could penetrate in several minutes and form a flexible and porous consolidation layer. The anti-scourability index (K) of the layer could increase from approximately 0.2 to 1.0 which significantly increased the water resistance. The water retention benefit increased by 50%. In the simulated rainfall test, the sediment yield reduction in the treated slopes sprayed with the W-OH solution could reach 99% compared with that on the control slopes. The SEM images indicated that the W-OH solution enveloped the feldspathic sandstone particles and connected them tightly together. Therefore, the consolidation layer could decrease water erosion rate and reduce evaporation.

Effects of rainfall intensity, slope angle, and vegetation coverage on the erosion characteristics of Pisha sandstone slopes under simulated rainfall conditions.

The water loss and soil erosion in the Pisha sandstone region in the middle reaches of the Yellow River are extremely severe, leading to extremely harmful effects on the ecological environment and safety of the lower reaches. In this paper, the effects of the slope angle (20, 30, and 40°), rainfall intensity (20, 50, and 80 mm/h), and vegetation coverage (10, 30, and 50%) on the erosion characteristics of the Pisha sandstone slopes are studied using indoor-simulated rainfall tests. The results show that the infiltration into the Pisha sandstone is only 10~15%. It is found that rainfall intensity has the most significant effect on runoff, which gradually increases with increasing rainfall intensity. Vegetation significantly affects runoff reduction when the rainfall intensity is low (approximately 20 mm/h), but this effect decreases with increasing rainfall intensity. Rainfall intensity has an extremely significant effect (P < 0.01) on the sediment yield, followed by vegetation coverage, and slope angle. When the vegetation coverage is approximately 50%, the reduction in sediment yield reaches approximately 70%. Additionally, the sediment reduction benefit is more significant than the runoff reduction benefit. The presence of the eroded gullies on slopes with vegetation is less compared to that on the bare slopes. Therefore, relatively high vegetation coverage (≥ 50%) is required for soil and water conservation in Pisha sandstone area. The findings will provide some reference for Pisha sandstone conservation.

Evaluation of modified basalt fiber as biological carrier media for wastewater treatment with the extended DLVO theory model.

In this study, environment-friendly inorganic basalt fiber (BF) was used as bio-carrier for wastewater treatment. To enhance the bio-affinity, raw BF was modified by grafting the diethylamino functional groups to make the surface more hydrophilic and electro-positive. Contact angle and zeta potential of modified basalt fiber (MBF) were characterized. The capacity of MBF bio-carriers was evaluated by microorganism immobilization tests. To explain the mechanism of capacity enhancement by modification, the profiles of total interaction energy barrier between raw BF (or MBF) and bacteria (Escherichia coli, E. coli) were discussed based on the extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The results showed the contact angle of fiber decreased from 89.71° to 63.08° after modification, and zeta potential increased from - 18.53 to +10.58 mV. The microorganism immobilization tests showed that the surface modification accelerated the initial bacterial adhesion on fiber. The total interaction energy barrier between MBF and E. coli disappeared as a result of electrostatic and hydrophilic attractive forces, and enhanced the irreversible adhesion. MBF bio-carrier medium provides a promising alternative to conventional bio-carrier materials for wastewater treatment. Graphical abstract.

Interpretation of adhesion behaviors between bacteria and modified basalt fiber by surface thermodynamics and extended DLVO theory.

Surface properties of carrier are critical for microorganism initial adhesion and biofilm formation in wastewater treatment. Until now, there are few reports on adhesion behaviors between bacteria and inorganic fiber surface. In this study, inorganic basalt fiber (BF) was modified with cationic polyacrylamide (CPAM) to make surface more hydrophilic and positively charged. The initial adhesion behaviors of BF modified with CPAM (CMBF) were interpreted by thermodynamics and extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. According to the total interaction energy calculated by the extended DLVO theory, insurmountable energy barrier between BF and Escherichia coli (E. coli) made irreversible adhesion unachievable due to hydrophobicity and electronegativity of BF, but allowed reversible adhesion at second minimum. By contrast, the energy barrier between CMBF and E. coli could be overcome allowing irreversible bacterial adhesion and thus a huge amount of biomass because of hydrophilicity and electropositivity of CMBF. The results showed the total interaction energies were dominated by Lewis acid-base and electrostatic interactions and coating BF with CPAM could promote initial bacterial adhesion on carrier surface. Overall, the extended DLVO theory provides a comprehensive tool to interpret initial adhesion behaviors between bacteria and inorganic fibers.