Phosphorus adsorption from aqueous solutions using different types of cement: kinetics, isotherms, and mechanisms.

Exploring low-cost and high-performance phosphorus (P) adsorbents is key to controlling P contamination in water. This study evaluated the P adsorption performance of three types of cement: Ordinary Portland cement (OPC), Portland slag cement (PSC), and Portland pozzolana cement (PPC). Furthermore, SEM-EDS, XRD, XPS, and FTIR were employed to reveal the adsorption mechanism. The results showed that the pseudo-second-order model exhibited higher regression coefficients than the pseudo-first-order model, indicating that chemisorption dominated the adsorption process. The Langmuir equation fitted the P adsorption data well, with maximum P adsorption capacities of 245.8, 226.1, and 210.0 mg g-1 for OPC, PSC, and PPC at 25 °C, respectively. P adsorption capacities decreased gradually with increasing initial pH and reached their maximum values at pH 3. The anions of F-, CO32-, and SO42- negatively affected P adsorption due to the competitive adsorption with Ca2+. The results of XPS, XRD, and FTIR confirmed that Ca-P precipitates (i.e., hydroxyapatite) were the main removal mechanism. A real domestic sewage experiment showed that 0.6 g L-1 OPC effectively reduced the P concentration from 2.4 to below 0.2 mg L-1, with a dosage cost of 0.034 $ per ton. This study indicated that cement, as a low-cost and efficient P adsorbent, has great potential for application in removing P from acidic and neutral wastewater.

Enhanced ammonia removal in tidal flow constructed wetland by incorporating steel slag: Performance, microbial community, and heavy metal release.

Utilizing alkaline solid wastes, such as steel slag, as substrates in tidal flow constructed wetlands (TFCWs) can effectively neutralize the acidity generated by nitrification. However, the impacts of steel slag on microbial communities and the potential risk of heavy metal release remain poorly understood. To address these knowledge gaps, this study compared the performance and microbial community structure of TFCWs filled with a mixture of steel slag and zeolite (TFCW-S) to those filled with zeolite alone (TFCW-Z). TFCW-S exhibited a much higher NH4+-N removal efficiency (98.35 %) than TFCW-Z (55.26 %). Additionally, TFCW-S also achieved better TN and TP removal. The steel slag addition helped maintain the TFCW-S effluent pH at around 7.5, while the TFCW-Z effluent pH varied from 3.74 to 6.25. The nitrification and denitrification intensities in TFCW-S substrates were significantly higher than those in TFCW-Z, consistent with the observed removal performance. Moreover, steel slag did not cause excessive heavy metal release, as the effluent concentrations were below the standard limits. Microbial community analysis revealed that ammonia-oxidizing bacteria, ammonia-oxidizing archaea, and complete ammonia-oxidizing bacteria coexisted in both TFCWs, albeit with different compositions. Furthermore, the enrichment of heterotrophic nitrification-aerobic denitrification bacteria in TFCW-S likely contributed to the high NH4+-N removal. In summary, these findings demonstrate that the combined use of steel slag and zeolite in TFCWs creates favorable pH conditions for ammonia-oxidizing microorganisms, leading to efficient ammonia removal in an environmentally friendly manner.

High-Density CuInS2 Quantum Dots for Efficient and Stable CO2 Electroreduction.

Electrochemically converting CO2 back into fuels and chemicals is promising in alleviating the greenhouse effect worldwide. Various high-efficiency catalysts have been achieved, yet the unsatisfied structural stability under CO2 electrolysis conditions restricts their practical application. Herein, a sub-5 nm sized CuInS2 quantum dots (CIS-QDs) based electrocatalyst for converting CO2 into CO are developed. Taking advantage of the stable M─Ch (metal-chalcogenide) covalent bonds, and unique p-block metal properties, the as-prepared catalyst exhibits excellent structural stability under large overpotentials and can achieve a high CO Faradaic efficiency (FE) of 86% (total CO2 reduction FE of 89%) at -0.65 V versus reversible hydrogen electrode with long-term durability of 40 h and outstanding current densities of 10.6 mA cm-2 simultaneously. Furthermore, detailed electrochemical analyses revealed that the excellent performance of the as-prepared catalysts shall be attributed to the high-density active sites and fast charge transfer brought by the ultrasmall size of CIS-QDs. This work provides insights into the design of high-density and stable catalytic sites for developing high-performance electrocatalysts.

Phase evolution and arsenic immobilization of arsenate-bearing amorphous calcium phosphate.

The formation of As(V) substituted hydroxylapatite (HAP) has a vital influence on the fate of As(V) in the environment. However, despite growing evidence showing that HAP crystallizes in vivo and in vitro with amorphous calcium phosphate (ACP) as a precursor, a knowledge gap exists concerning the transformation from arsenate-bearing ACP (AsACP) to arsenate-bearing HAP (AsHAP). Here we synthesized AsACP nano-particles with varied As contents and investigated the arsenic incorporation during their phase evolution. The phase evolution results showed that the transformation process of AsACP to AsHAP could be divided into three Stages. A higher As(V) loading significantly delayed the transformation of AsACP, increased the distortion degree, and decreased the crystallinity of AsHAP. NMR result showed that the PO43- tetrahedral is geometrically preserved when PO43- is substituted by AsO43-. From AsACP to AsHAP, the As-substitution led to the transformation inhibition and As(V) immobilization.

Effects of exogenous calcium on cadmium accumulation in amaranth.

Calcium oxalate (CaOx) crystals in plants act as a sink for excess Ca and play an essential role in detoxifying heavy metals (HMs). However, the mechanism and related influencing factors remain unclear. Amaranth (Amaranthus tricolor L.) is a common edible vegetable rich in CaOx and a potential Cd hyperaccumulation species. In this study, the hydroponic experiment was carried out to investigate the effect of exogenous Ca concentrations on Cd uptake by amaranth. The results showed that either insufficient or excess Ca supply inhibited amaranth growth, while the Cd bioconcentration factor (BCF) increased with Ca concentration. Meanwhile, the sequence extraction results demonstrated that Cd mainly accumulated as pectate and protein-bound species (NaCl extracted) in the root and stem, compared to pectate, protein, and phosphate-bound (acetic acid extractable) species in the leaf. Correlation analysis showed that the concentration of exogenous Ca was positively correlated with amaranth-produced CaOx crystals but negatively correlated with insoluble oxalate-bound Cd in the leaf. However, since the accumulated insoluble oxalate-bound Cd was relatively low, Cd detoxification via the CaOx pathway in amaranth is limited.

The fate of Cd during the replacement of Cd-bearing calcite by calcium phosphate minerals.

Carbonate-bound speciation is a critical sink of potentially toxic elements (PTEs) like cadmium (Cd) in soil and sediment. In a phosphate-rich environment, carbonate minerals could be replaced by phosphate minerals such as dicalcium phosphate dihydrate (DCPD, also known as brushite), octacalcium phosphate (OCP), and hydroxylapatite (HAP). Currently, it is unclear the migration and fate of PTEs during the replacement of PTEs-bearing carbonates by HAP and related intermediate minerals. Therefore, we synthesized Cd-bearing calcite by the coprecipitation method and converted it to DCPD, OCP, and HAP to investigate the redistribution and fate of Cd. The results showed that Cd incorporation in calcite significantly inhibited their replacement by DCPD and OCP, respectively. 1.26% of Cd in calcite was released into the solution when DCPD replaced calcite, and subsequently, most of the released Cd was recaptured by OCP. Significantly, the released Cd was below 0.05‰ when all the solid converted to HAP. These results suggested that with the application of phosphate fertilizer in alkaline soil, the secondary calcium phosphate minerals could control the environmental behavior of Cd.

Effect of phosphate on cadmium immobilized by microbial-induced carbonate precipitation: Mobilization or immobilization?

Microbial-induced carbonate precipitation (MICP) is a promising technology to immobilize/remediate heavy metals (HMs) like cadmium (Cd). However, the long-term stability of MICP-immobilized HMs is unclear, especially in farmland where chemical fertilization is necessary. Therefore, we performed MICP treatment on soils contaminated with various Cd compounds (CdCO3, CdS, and CdCl2) and added diammonium phosphate (DAP) to explore the impact of phosphate on the MICP-immobilized Cd. The results showed that MICP treatment was practical to immobilize the exchangeable Cd but to mobilize the carbonate and Fe/Mn oxide-bound Cd. After applying DAP, soil pH declined due to ammonium nitrification. At high P/Ca molar ratios (1/2 and 1), partial previously immobilized Cd was released due to the carbonate dissolution. Contrarily, exchangeable Cd transformed to less mobilizable Fe/Mn oxide-bound at low P/Ca molar ratios (1/4 and 1/8). Meanwhile, other treatments were also helpful in avoiding the release of immobilized Cd, such as applying non-ammonium phosphate and adding lime material after soil acidification. Our investigation suggested that the long-term stability of HMs in remediated sites should be carefully evaluated, especially in agricultural areas with phosphate and nitrogen fertilizer input.

Effect of steel slag on ammonia removal and ammonia-oxidizing microorganisms in zeolite-based tidal flow constructed wetlands.

The ammonia removal performance of tidal flow constructed wetlands (TFCWs) requires to be improved under high hydraulic loading rates (HLRs). The pH decrease caused by nitrification may adversely affect the NH4+-N removal and ammonia-oxidizing microorganisms (AOMs) of TFCWs. Herein, TFCWs with zeolite (TFCW_Z) and a mixture of zeolite and steel slag (TFCW_S) were built to investigate the influence of steel slag on NH4+-N removal and AOMs. Both TFCWs were operated under short flooding/drying (F/D) cycles and high HLRs (3.13 and 4.69 m3/(m2 d)). The results revealed that a neutral effluent pH (6.98-7.82) was achieved in TFCW_S owing to the CaO dissolution of steel slag. The NH4+-N removal efficiencies in TFCW_S (91.2 ± 5.1%) were much higher than those in TFCW_Z (73.2 ± 7.1%). Total nitrogen (TN) removal was poor in both TFCWs mainly due to the low influent COD/TN. Phosphorus removal in TFCW_S was unsatisfactory because of the short hydraulic retention time. The addition of steel slag stimulated the flourishing AOMs, including Nitrosomonas (ammonia-oxidizing bacteria, AOB), Candidatus_Nitrocosmicus (ammonia-oxidizing archaea, AOA), and comammox Nitrospira, which may be responsible for the better ammonia removal performance in TFCW_S. PICRUSt2 showed that steel slag also enriched the relative abundance of functional genes involved in nitrification (amoCAB, hao, and nxrAB) but inhibited genes related to denitrification (nirK, norB, and nosZ). Quantitative polymerase chain reaction (qPCR) revealed that complete AOB (CAOB) and AOB contributed more to the amoA genes in TFCW_S and TFCW_Z, respectively. Therefore, this study revealed that the dominant AOMs could be significantly changed in zeolite-based TFCW by adding steel slag to regulate the pH in situ, resulting in a more efficient NH4+-N removal performance.

Enhanced immobilization of uranium(VI) during the conversion of microbially induced calcite to hydroxylapatite.

Carbonate-bound uranium (U) is critical in controlling the migration of U in circumneutral to alkaline conditions. The potential release risk of carbonate-bound U should be concerned due to the contribution of mineral replacement. Herein, we explored the fate of U during the conversion process from microbial-induced calcite to hydroxylapatite (HAP) and investigated the phase and morphology evolution of minerals and the immobilization efficiency, distribution, and stability of U. The results showed that most calcite could convert to HAP during the conversion process. The aqueous residual U was below 1.0 mg/L after U-HAP formation, and the U removal efficiencies were enhanced by 20.0-74.4% compared to the calcite precipitation process. XRD and TEM results showed that the products were a mixture of HAP and uramphite. The elemental mapping results showed that most U concentrated on uramphite while a handful of U distributed homogeneously in calcite and HAP matrixes. The stability test verified that U-bearing HAP decreased the U solubility by 98-100% relative to calcite due to the uramphite formation and U incorporation into HAP. Our findings demonstrated that the combinations of microbial-induced calcite precipitation and calcite-HAP conversion could facilitate the U immobilization in treating radioactive wastewater and soil.

Ferric iron incorporation promotes brushite hydrolysis and enhances cadmium immobilization.

Dissolution-precipitation processes on the surface of brushite (dicalcium phosphate dihydrate, DCPD) control the migration and transformation of potentially harmful elements (PHEs). The incorporation of impurities could affect the properties of DCPD and its interactions with PHEs. In this study, we synthesized Fe3+-bearing DCPD via coprecipitation and investigated the influence of Fe3+ incorporation on the crystal structure, hydrolysis process, and Cd removal performance. Fe-bearing DCPD had lattice expansion due to the coupled substitution of Fe3+ and NH4+ for Ca2+. Therefore, the Cd removal performance of Fe-DCPD was enhanced, with a maximum Cd uptake capacity of 431.6 mg/g, which is 1.77 times that of Fe-free DCPD (244.4 mg/g). Furthermore, Fe-DCPD also exhibited a faster hydrolysis rate, which was up to 2.67 times that of Fe-free DCPD and accelerated Cd's transfer to the stable host mineral, hydroxylapatite. Cd was first caught by the DCPD surface in a weakly crystalline form and then incorporated into the hydroxylapatite structure during crystallization. Based on the X-ray photoelectron spectroscopy and thermogravimetric analysis results, we concluded that the decrease in interstitial water due to Fe incorporation was responsible for accelerating hydrolysis and enhancing Cd immobilization. In all, the incorporation of Fe3+ into DCPD could promote its transformation and improve its Cd uptake capacity. Our results suggest that Fe-DCPD could be a promising candidate for environmental remediation.

Immobilization and migration of arsenic during the conversion of microbially induced calcium carbonate to hydroxylapatite.

Coprecipitation with calcium carbonate (CaCO3) could decrease the bioavailability of arsenic (As). However, in a phosphate-rich environment, some CaCO3 will be converted to hydroxylapatite (HAP). Currently, the behavior of carbonate-bound As during conversion is unclear. Therefore, we prepared bio-induced CaCO3 in an As solution and converted it to HAP. The results showed that a high concentration of arsenate promoted vaterite precipitation and the conversion of CaCO3 to HAP. The dissolution data verified the low solubility of As in HAP, though its As-bearing CaCO3 precursor released up to 88.19% As during the conversion. Furthermore, HPLC-ICP-MS data showed partial oxidation of arsenite to arsenate, suggesting that CaCO3 and HAP's structure favored the incorporation of arsenate. Our results demonstrated that the stability of heavy metal-bearing CaCO3 should be considered, and the role of HAP in the immobilization of heavy metals such as As should not be overestimated.

Effects of hydraulic loading rate and substrate on ammonium removal in tidal flow constructed wetlands treating black and odorous water bodies.

The efficient removal of ammonium nitrogen (NH4+-N) is vital to eliminating black and odorous water bodies. In this work, tidal flow constructed wetlands with gravel (TFCW-G) and with a mixture of zeolite and gravel (TFCW-Z) were set up to treat black and odorous water bodies at different hydraulic loading rates (HLRs). Results showed that zeolite significantly enhanced nitrogen removal, and the maximum NH4+-N removal efficiency of 96.69% was achieved in TFCW-Z at HLR of 3 m·d-1 with a flooding and drying cycle of 2 h. Zeolite addition changed the microbial community structure and the abundance of nitrification genes. Comammox Nitrospira was the only enriched strain accounting for NH4+-N removal in TFCW-G, while the co-occurrence of comammox Nitrospira and the canonical and potential ammonia-oxidizing bacteria were identified in TFCW-Z. Summarily, high performance, together with low footprint and low maintenance cost, are characteristics that make the TFCW-Z a promising and competitive alternative.

Divalent heavy metals and uranyl cations incorporated in calcite change its dissolution process.

Due to the high capacity of impurities in its structure, calcite is regarded as one of the most attractive minerals to trap heavy metals (HMs) and radionuclides via substitution during coprecipitation/crystal growth. As a high-reactivity mineral, calcite may release HMs via dissolution. However, the influence of the incorporated HMs and radionuclides in calcite on its dissolution is unclear. Herein, we reported the dissolution behavior of the synthesized calcite incorporated with cadmium (Cd), cobalt (Co), nickel (Ni), zinc (Zn), and uranium (U). Our findings indicated that the HMs and U in calcite could significantly change the dissolution process of calcite. The results demonstrated that the incorporated HMs and U had both inhibiting and enhancing effects on the solubility of calcite, depending on the type of metals and their content. Furthermore, secondary minerals such as smithsonite (ZnCO3), Co-poor aragonite, and U-rich calcite precipitated during dissolution. Thus, the incorporation of metals into calcite can control the behavior of HMs/uranium, calcite, and even carbon dioxide.

Activation of natural halloysite nanotubes by introducing lanthanum oxycarbonate nanoparticles via co-calcination for outstanding phosphate removal.

Halloysite nanotubes were activated via co-calcination of halloysite and the precursors of lanthanum oxycarbonate (LO), generating reactive alumina nanoparticles and uniformly anchoring LO nanoparticles to halloysite surfaces. The resulting LO-alumina combination exhibits record-high phosphate adsorption capacity as well as excellence in adsorption selectivity and sewage phosphate removal.

Immobilization of cadmium by hydroxyapatite converted from microbial precipitated calcite.

As one of the most toxic heavy elements, humans are mainly exposed to cadmium (Cd) via daily diets and smoking. Calcite can be used as an amendment directly or precipitated in situ based on microbial-induced carbonate precipitation (MICP) technology to immobilize Cd in soil with potential release of Cd due to calcite dissolution. Therefore, we converted microbial-induced calcite to less soluble hydroxyapatite and investigated the phase and morphology evolutions of the solids, as well as the immobilized efficiency, distribution and release of Cd. The results showed that the conversion of calcite to hydroxyapatite enhanced Cd removal efficiency up to 1.67% and 33.14% compared to the MICP process and adsorption by calcite, respectively. Accordingly, the released Cd decreased up to 94.10% and 99.96%, respectively. Our findings demonstrated that the conversion of calcite to hydroxyapatite might control the environmental behavior of heavy metals like Cd and can potentially be applied for soil remediation.

Activating 2D nano-kaolinite using hybrid nanoparticles for enhanced phosphate capture.

A synergistic host-guest coupling is exploited to disorder nano-kaolinite unit layers to form Al2O3 nanoparticles, which act as activated adsorptive sites; meanwhile, the coupling enables La-based nanoparticles to anchor homogenously on the nano-kaolinite surfaces, fully utilizing their adsorption ability. The activated hybrid nanostructures exhibit an excellent phosphate adsorption capacity.

Removal of antibiotics from piggery wastewater by biological aerated filter system: Treatment efficiency and biodegradation kinetics.

This study aimed to investigate the removal efficiency and mechanism for antibiotics in swine wastewater by a biological aerated filter system (BAF system) in combination with laboratory aerobic and anaerobic incubation experiments. Nine antibiotics including sulfamonomethoxine, sulfachloropyridazine, sulfamethazine, trimethoprim, norfloxacin, ofloxacin, lincomycin, leucomycin and oxytetracycline were detected in the wastewater with concentrations up to 192,000ng/L. The results from this pilot study showed efficient removals (>82%) of the conventional wastewater pollutants (BOD5, COD, TN and NH3-N) and the detected nine antibiotics by the BAF system. Laboratory simulation experiment showed first-order dissipation kinetics for the nine antibiotics in the wastewater under aerobic and anaerobic conditions. The biodegradation kinetic parameters successfully predicted the fate of the nine antibiotics in the BAF system. This suggests that biodegradation was the dominant process for antibiotic removal in the BAF system.

Nitrogen removal and its relationship with the nitrogen-cycle genes and microorganisms in the horizontal subsurface flow constructed wetlands with different design parameters.

This study aims to investigate nitrogen removal and its relationship with the nitrogen-cycle genes and microorganisms in the horizontal subsurface flow constructed wetlands (CWs) with different design parameters. Twelve mesocosm-scale CWs with four substrates and three hydraulic loading rates were set up in the outdoor. The result showed the CWs with zeolite as substrate and HLR of 20 cm/d were selected as the best choice for the TN and NH3-N removal. It was found that the single-stage mesocosm-scale CWs were incapable to achieve high removals of TN and NH3-N due to inefficient nitrification process in the systems. This was demonstrated by the lower abundance of the nitrification genes (AOA and AOB) than the denitrification genes (nirK and nirS), and the less diverse nitrification microorganisms than the denitrification microorganisms in the CWs. The results also show that microorganism community structure including nitrogen-cycle microorganisms in the constructed wetland systems was affected by the design parameters especially the substrate type. These findings show that nitrification is a limiting factor for the nitrogen removal by CWs.

Removal of antibiotics and antibiotic resistance genes from domestic sewage by constructed wetlands: Effect of flow configuration and plant species.

This study aims to investigate the removal of antibiotics and antibiotic resistance genes (ARGs) in raw domestic wastewater by various mesocosm-scale constructed wetlands (CWs) with different flow configurations or plant species including the constructed wetland with or without plant. Six mesocosm-scale CWs with three flow types (surface flow, horizontal subsurface flow and vertical subsurface flow) and two plant species (Thaliadealbata Fraser and Iris tectorum Maxim) were set up in the outdoor. 8 antibiotics including erythromycin-H2O (ETM-H2O), monensin (MON), clarithromycin (CTM), leucomycin (LCM), sulfamethoxazole (SMX), trimethoprim (TMP), sulfamethazine (SMZ) and sulfapyridine (SPD) and 12 genes including three sulfonamide resistance genes (sul1, sul2 and sul3), four tetracycline resistance genes (tetG, tetM, tetO and tetX), two macrolide resistance genes (ermB and ermC), two chloramphenicol resistance genes (cmlA and floR) and 16S rRNA (bacteria) were determined in different matrices (water, particle, substrate and plant phases) from the mesocosm-scale systems. The aqueous removal efficiencies of total antibiotics ranged from 75.8 to 98.6%, while those of total ARGs varied between 63.9 and 84.0% by the mesocosm-scale CWs. The presence of plants was beneficial to the removal of pollutants, and the subsurface flow CWs had higher pollutant removal than the surface flow CWs, especially for antibiotics. According to the mass balance analysis, the masses of all detected antibiotics during the operation period were 247,000, 4920-10,600, 0.05-0.41 and 3500-60,000µg in influent, substrate, plant and effluent of the mesocosm-scale CWs. In the CWs, biodegradation, substrate adsorption and plant uptake all played certain roles in reducing the loadings of nutrients, antibiotics and ARGs, but biodegradation was the most important process in the removal of these pollutants.

Removal of antibiotics and antibiotic resistance genes from domestic sewage by constructed wetlands: Optimization of wetland substrates and hydraulic loading.

This study aimed to assess removal potential of antibiotics and antibiotic resistance genes (ARGs) in raw domestic wastewater by various mesocosm-scale horizontal subsurface-flow constructed wetlands (CWs) planted Cyperus alternifolius L. with different design parameters. Twelve CWs with three hydraulic loading rates (HLR 10, 20 and 30cm/day) and four substrates (oyster shell, zeolite, medical stone and ceramic) were set up in order to select the best optimized wetland. The result showed that 7 target antibiotics compounds including erythromycin-H2O, lincomycin, monensin, ofloxacin, sulfamerazine, sulfamethazine and novobiocin were detected, and all selected 18 genes (three sulfonamide resistance genes (sul1, sul2 and sul3), four tetracycline resistance genes (tetG, tetM, tetO and tetX), two macrolide resistance genes (ermB and ermC), three quinolone resistance genes (qnrB, qnrD and qnrS) and four chloramphenicol resistance genes (cmlA, fexA, fexB and floR)) and two integrase genes (int1 and int2) were positively detected in the domestic wastewaters. The aqueous removal rates of the total antibiotics ranged from17.9 to 98.5%, while those for the total ARGs varied between 50.0 and 85.8% by the mesocosm-scale CWs. After considering their aqueous removal rates in combination with their mass removals, the CW with zeolite as the substrate and HLR of 20cm/day was selected as the best choice. Combined chemical and biological analyses indicate that both microbial degradation and physical sorption processes were responsible for the fate of antibiotics and ARGs in the wetlands. The findings from this study suggest constructed wetlands could be a promising technology for the removal of emerging contaminants such as antibiotics and ARGs in domestic wastewater.