Effective remediation of agricultural drainage at three influent strengths by bioaugmented constructed wetlands filled with mixture of iron­carbon and organic solid substrates: Performance and mechanisms.

Agricultural drainage containing a large quantity of nutrients can cause quality deterioration and algal blooming of receiving water bodies, thus needs to be effectively remediated. In this study, iron­carbon (FeC) composite-filled constructed wetlands (Fe-C-CWs) were employed to treat farmland drainage at three pollution levels, and organic solid substrates (walnut shells) and phosphate-accumulating denitrifying bacteria (Pseudomonas sp. DWP1) were supplemented to enhance the treatment performance. The results showed that the Fe-C-CWs exhibited notably superior removal efficiency for total nitrogen (TN, 52.0-58.2 %), total phosphorus (TP, 67.8-70.2 %) and chemical oxygen demand (COD, 56.7-70.4 %) than the control systems filled solely with gravel (28.5-32.5 % for TN, 33.2-40.5 % for TP and 30.2-55.0 % for COD) at all influent strengths, through driving autotrophic denitrification, Fe-based dephosphorization, and organic degradation processes. The addition of organic substrates and functional bacteria markedly enhanced pollutant removal in the Fe-C-CWs. Furthermore, use of FeC and organic substrates and denitrifier inoculation decreased CO2 and CH4 emissions from the CWs, and reduced global warming potential of the CWs at low influent strength. Pollutant removal efficiencies in the CWs were only marginally impacted by the increasing influent loads except for NO3--N, and pollutant removal mass was largely increased with the increase of influent strengths. The microbial community in the FeC composite-filled CWs exhibited distinct distribution patterns compared to the gravel-filled CWs regardless of the influent strengths, with obviously higher proportions of dominant genera Trichococcus, Geobacter and Ferritrophicum. Keystone taxa associated with pollutant removal in the Fe-C-filled CWs were identified to be Pseudomonas, Geobacter, Ferritrophicum, Denitratisoma and Sediminibacterium. The developed augmented Fe-C-filled CWs show great promises for remediating agricultural drainage with varied pollutant loads.

Application of microbially induced calcium carbonate precipitation (MICP) process in concrete self-healing and environmental restoration to facilitate carbon neutrality: a critical review.

Soil contamination, land desertification and concrete cracking can have significant adverse impacts on sustainable human economic and societal development. Cost-effective and environmentally friendly approaches are recommended to resolve these issues. Microbially induced carbonate precipitation (MICP) is an innovative, attractive and cost-effective in situ biotechnology with high potential for remediation of polluted or desertified soils/lands and cracked concrete and has attracted widespread attention in recent years. Accordingly, the principles of MICP technology and its applications in the remediation of heavy metal-contaminated and desertified soils and self-healing of concrete were reviewed in this study. The production of carbonate mineral precipitates during the MICP process can effectively reduce the mobility of heavy metals in soils, improve the cohesion of dispersed sands and realize self-healing of cracks in concrete. Moreover, CO2 can be fixed during MICP, which can facilitate carbon neutrality and contribute to global warming mitigation. Overall, MICP technology exhibits great promise in environmental restoration and construction engineering applications, despite some challenges remaining in its large-scale implementation, such as the substantial impacts of fluctuating environmental factors on microbial activity and MICP efficacy. Several methods, such as the use of natural materials or wastes as nutrient and calcium sources and isolation of bacterial strains with strong resistance to harsh environmental conditions, are employed to improve the remediation performance of MICP. However, more studies on the efficiency enhancement, mechanism exploration and field-scale applications of MICP are needed.

Seasonal purification efficiency, greenhouse gas emissions and microbial community characteristics of a field-scale surface-flow constructed wetland treating agricultural runoff.

Controlling nonpoint source pollution (NPSP) is very important for protecting the water environment, and surface-flow constructed wetlands (SFCWs) have been widely established to mitigate NPSP loads. In this study, the pollutant removal efficiencies, greenhouse gas (GHG) emissions, and chemical and microbial community properties of the sediment in a large-scale SFCW established beside a plateau lake (Qilu Lake) in southwestern China to treat agricultural runoff were evaluated over a year. The SFCW performed best in terms of nitrogen removal in autumn (average efficiency of 63.5% at influent concentrations of 9.3-35.4 mg L-1) and demonstrated comparable efficiency in other seasons (23.7-40.0%). The removal rates of total phosphorus (TP) and chemical oxygen demand (COD) were limited (18.6% and 12.4% at influent concentrations of 1.1 and 45.5 mg L-1 on average, respectively). The SFCW was a hotspot of CH4 emissions, with an average flux of 31.6 mg m-2·h-1; moreover, CH4 emissions contributed the most to the global warming potential (GWP) of the SFCW. Higher CH4 and N2O fluxes were detected in winter and in the front-end section of the SFCW with high pollutant concentrations, and plant presence increased CH4 emissions. Significant positive relationships between nutrient and heavy metal contents in the SFCW sediment were detected. The microbial community compositions were similar in autumn and winter, with Thiobacillus, Lysobacter, Acinetobacter and Pseudomonas dominating, and this distribution pattern was clearly distinct from those in spring and summer, with high proportions of Spirochaeta_2 and Denitratisoma. The microbial co-occurrence network in spring was more complex with stronger positive correlations than those in winter and autumn, while it was more stable in autumn with more keystone taxa. Optimization of the construction, operation and management of SFCWs treating NPSP in lake watersheds is necessary to promote their environmental benefits.

Land use regulates the spectroscopic properties and sources of dissolved organic matter in the inflowing rivers of a large plateau lake in southwestern China: implication for organic pollution control.

Dissolved organic matter (DOM) transported by inflowing rivers can considerably contribute to the organic loadings of lakes. The current study characterized the DOM properties and source apportionment in the inflowing rivers of Dianchi Lake, the sixth largest freshwater lake in China suffering from organic pollution, during the rainy season by using spectroscopic and carbon stable isotope techniques, and the regulation role of land use was assessed. The results showed that land use (urbanized, agricultural, or mixed) largely affected DOM properties. Greater concentrations and fluorescence intensities of DOM with low aromaticity and dominant autochthonous sources were observed in the urban rivers than in the agricultural rivers. The proportion of humic-like substances increased, while that of tryptophan-like matter decreased from upstream to downstream of two main urban rivers. DOM in the agricultural rivers was characterized by more amounts of aromatic humic-like substances with dominant allochthonous sources compared to that in the urban rivers. Stable isotope analysis showed that the decomposition of macrophytes and input of terrestrial sources from C3 plant-dominated soil and sewage were the major DOM origins in the rivers. The positive linear relationship between the chemical oxygen demand (COD) concentration and fluorescence intensities of terrigenous DOM components implied the necessity of controlling exogenous inputs to alleviate organic pollution in the Dianchi Lake.

Efficient treatment of mercury(â ¡)-containing wastewater in aerated constructed wetland microcosms packed with biochar.

Effective removal of mercury (Hg) pollutants from contaminated water/wastewater to prevent severe environmental pollution is of great significance due to the extremely high toxicity of Hg. In this study, granular biochar and gravel (control) were packed into intermittently aerated constructed wetland (CW) microcosms to treat Hg(Ⅱ)-containing wastewater over 100 d. The results showed that the biochar-filled CWs exhibited notably better Hg(Ⅱ) removal than the gravel systems by facilitating chemical and microbial Hg(Ⅱ) reduction and volatilization and promoting plant growth and Hg assimilation. More than ten times more Hg was absorbed by the plants (L. salicaria) in biochar CWs than in the gravel systems, with the roots acting as the major sink. In contrast, substrate binding in a predominantly oxidizable fraction was the dominant pathway for Hg removal in the gravel CWs. Biochar substrates also exhibited higher levels of COD, N and P removal, and Hg(Ⅱ) import impacted the removal of these pollutants only slightly. Filling material played a more crucial role than Hg input in shaping the microbial communities in the CWs. The proportions of some dominant genera, including Arenimonas, Lysobacter, Micropruina and Hydrogenophaga, increased in the presence of Hg, implying their tolerance to Hg toxicity and potential roles in Hg detoxification in the CWs. Granular biochar-based CW has high potential for treating Hg(Ⅱ)-contaminated wastewater.

Removal of multiple heavy metals from mining-impacted water by biochar-filled constructed wetlands: Adsorption and biotic removal routes.

Granular biochar made from walnut shells was layered into sand-based constructed wetlands (CWs) to treat simulated mining-impacted water (MIW). The results showed that the biochar media exhibited markedly high capacities for metal binding and acidity neutralization, supported notably better plant growth and mitigated metal transfer from the plant roots to the shoots. The addition of organic liquid wastes (domestic sewage and plant straw hydrolysation broth) stimulated biogenic sulfate reduction after 40 d of adaptation to effectively remove multiple heavy metals in the MIW. The microbial community compositions were prominently regulated by organic carbon, with desirable communities dominated by Cellulomonas and Desulfobulbus formed in the CWs for MIW biotreatment. The role of macrophytes in the CWs in MIW treatment was insignificant and was dependent on operation conditions and metal species. A biochar-packed CW system with liquid organic waste supplementation was effective in metal removal and acidity neutralization of MIW.

Promotion of bioremediation performance in constructed wetland microcosms for acid mine drainage treatment by using organic substrates and supplementing domestic wastewater and plant litter broth.

Gravel-based subsurface-flow constructed wetlands (CWs) amended with a walnut shell (WS) substrate were established to treat synthetic acid mine drainage (AMD) in this study, and artificial domestic wastewater (DW) and plant litter broth (PLB) were supplemented to enhance the performance. The CW media rapidly reached adsorption saturation with respect to metals (except Fe and Cr) without an external carbon source, while the addition of DW and PLB stimulated sulfate reduction activity and achieved efficient biogenic metal removal, primarily by the formation of hydroxide and sulfide precipitates and concomitant co-precipitation. The WS-amended CWs performed notably better than the control systems, not only in sequestering more metals and rapidly establishing favourable environments for biogenic metal abatement but also in supporting better growth of plants and functional microbes. The external organic carbon input greatly shaped the bacterial community compositions in the CWs, with substantial increases in the proportions of core functional populations involved in AMD biotreatment. Cooperation among Cellulomonas, Propioniciclava and sulfate-reducing bacteria (SRB), dominated by Desulfobulbus and Desulfatirhabdium, was the primary biogenic mechanism of AMD remediation in the CWs. Cellulosic waste-amended CWs with DW and PLB addition offer a promising eco-technology for AMD remediation.

Cr(VI) removal performance from aqueous solution by Pseudomonas sp. strain DC-B3 isolated from mine soil: characterization of both Cr(VI) bioreduction and total Cr biosorption processes.

Microbial methods are promising and environmentally friendly methods for remediating heavy metal contamination. In this study, a Cr(VI)-resistant bacterial strain, DC-B3, which was identified as Pseudomonas sp. by 16S rDNA gene sequencing, was isolated from heavy metal-contaminated mine soil, and its performance in Cr(VI) removal from wastewater in terms of Cr(VI) reduction and total Cr adsorption was assessed. This strain exhibited a high capability to reduce Cr(VI) to less toxic Cr(III) without the addition of an external electron donor at low pH (2.0). The Cr(VI) reduction capacity and rate both increased linearly with increasing Cr(VI) concentration, with a reduction capacity of 32.0 mg Cr(VI)·g-1 achieved at an initial concentration of 135.0 mg L-1 over 75 h. In addition, 41.0% of the total Cr was removed from the solution by biosorption, and equilibrium was reached within approximately 5 h. The total Cr sorption process was well described by the pseudo-second-order kinetic and Langmuir isotherm models. Desorption assays indicated that NaOH was the most efficient agent for total Cr desorption, and Cr(VI) and generated Cr(III) were both loaded on the DC-B3 biomass. The bacterial cells after Cr treatment were characterized by scanning electron microscopy-energy dispersive X-ray spectrometer and Fourier transform infrared spectroscopy analyses. Strain DC-B3 showed high potential for possible application in the remediation of Cr(VI) contamination in mine areas.