Sulfate reduction behavior in response to landfill dynamic pressure changes.

During the long-term stabilization process of landfills, the pressure field undergoes constant changes. This study constructed dynamic pressure changes scenarios of high-pressure differentials (0.6 MPa) and low-pressure differentials (0.2 MPa) in the landfill pressure field at 25 °C and 50 °C, and investigated the sulfate reduction behavior in response to landfill dynamic pressure changes. The results showed that the pressurization or depressurization of high-pressure differentials caused more significant differences in sulfate reduction behavior than that of low-pressure differentials. The lowest hydrogen sulfide (H2S) release peak concentration under pressurization was only 29.67% of that under initial pressure condition; under depressurization, the highest peak concentration of H2S was up to 21,828 mg m-3, posing a serious risk of H2S pollution. Microbial community and correlation analysis showed that pressure had a negative impact on the sulfate-reducing bacteria (SRB) community, and the SRB community adjusted its structure to adapt to pressure changes. Specific SRBs were further enriched with pressure changes. Differential H2S release behavior under pressure changes in the 25 °C pressure environments were mediated by Desulfofarcimen (ASV343) and Desulfosporosinus (ASV1336), while Candidatus Desulforudis (ASV24) and Desulfohalotomaculum (ASV94) played a key role at 50 °C. This study is helpful in the formulation of control strategies for the source of odor pollution in landfills.

Sulfate reduction behavior in response to changing of pressure coupling with temperature inside landfill.

The behavior of sulfate reduction, which was the source of hydrogen sulfide (H2S) odor, was investigated under changing pressure and temperature conditions inside landfills. The results showed that the release of H2S and methyl mercaptan (MM) was significantly inhibited at 25 °C and 50 °C under pressure, and the highest H2S and MM concentrations released were only 0.82 %-1.30 % and 1.87 %-4.32 % of atmospheric pressure, respectively. Analysis of the microbial community structure and identification of sulfate-reducing bacteria (SRB) revealed that temperature significantly altered the microbial community in the landfill environment, while pressure inhibited some bacteria and induced the growth and reproduction of specific bacteria. Key SRB (Desulfosporosinus-ASV212, Desulfitibacter-ASV1744) mediated differentiated sulfate reduction behavior in the pressure-bearing environment at 25 °C, while key SRB (Dethiobacter-ASV177, Desulfitibacter-ASV2355 and ASV316) were involved at 50 °C. This study provides a theoretical basis for the formulation of landfill gas management and control strategies.

A simulation-driven supervised learning framework to estimate brain microstructure using diffusion MRI.

We propose a framework to train supervised learning models on synthetic data to estimate brain microstructure parameters using diffusion magnetic resonance imaging (dMRI). Although further validation is necessary, the proposed framework aims to seamlessly incorporate realistic simulations into dMRI microstructure estimation. Synthetic data were generated from over 1,000 neuron meshes converted from digital neuronal reconstructions and linked to their neuroanatomical parameters (such as soma volume and neurite length) using an optimized diffusion MRI simulator that produces intracellular dMRI signals from the solution of the Bloch-Torrey partial differential equation. By combining random subsets of simulated neuron signals with a free diffusion compartment signal, we constructed a synthetic dataset containing dMRI signals and 40 tissue microstructure parameters of 1.45 million artificial brain voxels. To implement supervised learning models we chose multilayer perceptrons (MLPs) and trained them on a subset of the synthetic dataset to estimate some microstructure parameters, namely, the volume fractions of soma, neurites, and the free diffusion compartment, as well as the area fractions of soma and neurites. The trained MLPs perform satisfactorily on the synthetic test sets and give promising in-vivo parameter maps on the MGH Connectome Diffusion Microstructure Dataset (CDMD). Most importantly, the estimated volume fractions showed low dependence on the diffusion time, the diffusion time independence of the estimated parameters being a desired property of quantitative microstructure imaging. The synthetic dataset we generated will be valuable for the validation of models that map between the dMRI signals and microstructure parameters. The surface meshes and microstructures parameters of the aforementioned neurons have been made publicly available.

Microplastics enrichment characteristics of antibiotic resistance genes and pathogens in landfill leachate.

Microplastics (MPs) pollution is a pressing environmental issue for aquatic ecosystems. Landfill leachate is an important contributor of MPs and antibiotic resistant genes (ARGs). However, there are few studies on the colonization of ARGs and pathogens on MPs in leachate. This study conducted incubation experiments with polyethylene terephthalate (PET) and polypropylene (PP) MPs in landfill leachate which were about 3-5 years old (PL) and 5-10 years old (AL). After incubation, the bacterial cells colonized and grew on the surface of MPs, inducing the increase of oxygenated oxygen functional groups (e.g., hydroxyl, carbonyl) on the MPs surface. Real-time PCR indicated that MPs selectively enriched ARGs, such as genes tetM, tetC, mcr-1, aac(6')-Ib-cr, blaTEM and blaSHV in leachate. The diversity of bacterial communities on MPs was significantly increased in AL leachate, but decreased in PL leachate. The differences in bacterial communities in MPs biofilms were related to the type of MPs. Compared with AL leachate, the abundance of Chloroflexi increased by 15.7% on the PET, and the abundance of Acidobacteriota increased by 6.23 fold on the PP. The abundance of Firmicutes increased from 20.7% in PL leachate to 65.8% and 60.7% on PET and PP, respectively. Additionally, pathogens were observed to be more abundant on MPs compared to leachate. In particular, pathogens (Staphylococcus, Streptococcus, Enterobacter and Rhodococcus) associated with sul1 and sul2 were generally present at higher levels on MPs than in the surrounding leachate. These results provide significant implications for understanding the health risk of MPs in the environment.

Stress response mechanism of wastewater biological nitrogen removal systems to environmentally realistic concentrations of tire wear particles: Contribution of leachable additives.

The study quantified the biological nitrogen removal performance, microbial metabolism, microbial community structure, and antioxidant system in a sequencing batch reactor under long-term exposure to 0.1 and 1 mg/L tire wear particles (TWPs), and determined the contribution of leachable additives to the biotoxicity of TWPs. The results showed that long-term exposure to 0.1 and 1 mg/L TWPs inhibited both the nitrification and denitrification processes, reducing ammonia nitrogen (NH4+-N) and total nitrogen (TN) removal efficiency. The TWP leachate (TWPL) primarily contributed to the denitrification inhibition by TWPs, potentially due to the high concentration of zinc ions in the leachable additive. Furthermore, both TWP and TWPL inhibit nitrogen conversion, with TWP inhibiting the generation and transfer of electrons, while TWPL only negatively affects the electron transfer process. This study presents novel insights into the impact of TWPs on biological nitrogen removal, underscoring its broader implications for the geochemical nitrogen cycle.

Incorporating interface permeability into the diffusion MRI signal representation while using impermeable Laplace eigenfunctions.

Objective. The complex-valued transverse magnetization due to diffusion-encoding magnetic field gradients acting on a permeable medium can be modeled by the Bloch-Torrey partial differential equation. The diffusion magnetic resonance imaging (MRI) signal has a representation in the basis of the Laplace eigenfunctions of the medium. However, in order to estimate the permeability coefficient from diffusion MRI data, it is desirable that the forward solution can be calculated efficiently for many values of permeability.Approach. In this paper we propose a new formulation of the permeable diffusion MRI signal representation in the basis of the Laplace eigenfunctions of the same medium where the interfaces are made impermeable.Main results.We proved the theoretical equivalence between our new formulation and the original formulation in the case that the full eigendecomposition is used. We validated our method numerically and showed promising numerical results when a partial eigendecomposition is used. Two diffusion MRI sequences were used to illustrate the numerical validity of our new method.Significance.Our approach means that the same basis (the impermeable set) can be used for all permeability values, which reduces the computational time significantly, enabling the study of the effects of the permeability coefficient on the diffusion MRI signal in the future.

Mechanism of antibiotic resistance development in an activated sludge system under tetracycline pressure.

The mechanism of antibiotic resistance (AR) development in an activated sludge system under tetracycline (TC) pressure was discussed and analyzed. According to the variation of macro-factors, including TC, COD, TN, TP, NH3-N, pH, heavy metals, and reactor settings, the tet genes respond accordingly. Consequently, the enrichment sites of tet genes form an invisible AR selection zone, where AR microorganisms thrive, gather, reproduce, and spread. The efflux pump genes tetA and tetB prefer anaerobic environment, while ribosome protective protein genes tetM, tetO, tetQ, tetT, and tetW were more concentrated in aerobic situations. As a corresponding micro-effect, different types of tet genes selected the corresponding dominant bacteria such as Thauera and Arthrobacter, suggesting the intrinsic relationship between tet genes and potential hosts. In summary, the macro-response and micro-effect of tet genes constitute an interactive mechanism with tet genes as the core, which is the crucial cause for the continuous development of AR. This study provides an executable strategy to control the development of AR in actual wastewater treatment plants from the perspective of macro-factors and micro-effects.

Alteration of the migration trajectory of antibiotic resistance genes by microplastics in a leachate activated sludge system.

The environmental behavior of emerging contaminants of microplastics (MPs), antibiotics and antibiotic resistance genes (ARGs) in the leachate activated sludge system has been monitored and analyzed comprehensively. The results suggested that MPs could effectively alter the migration trajectory of tetracycline resistance genes (tet genes) in the leachate activated sludge system under intermittent and continuous influent conditions. After adding MPs, the total average abundance of tet genes in leachate increased from 0.74 ± 0.07 to 0.78 ± 0.07 (log10tet genes/log10 16S rRNA) and that in sludge increased from 0.65 ± 0.08 to 0.70 ± 0.06 (log10tet genes/log10 16S rRNA). Except for tetA, the abundance of tetB, tetO, tetM and tetQ on MPs increased with increasing TC concentration under both aerobic and anaerobic conditions. MPs not only significantly affect the abundance level and migration trajectory of ARGs in the leachate activated sludge system, but also remarkably improve the level of heavy metals in the ambient environment, indirectly promoting the selective effect of antibiotic-resistant bacteria (ARB) and promoting the development of antibiotic resistance (AR). In addition, MPs changed their physicochemical properties and released hazardous substances with aging to force tet genes to migrate from the leachate activated sludge system to the MPs, making AR more difficult to eliminate and persisted in wastewater treatment plants. Meanwhile, microorganisms played a driving role, making MPs serve as a niche for ARGs and ARB colonization. The co-occurrence network analysis indicated the specific distribution pattern of tet genes and microorganisms in different media, and the potential host was speculated. This study improves the understanding of the environmental behavior of emerging contaminants in leachate activated sludge system and lays a theoretical for protecting the ecological environment.

The effects of microplastics and nanoplastics on nitrogen removal, extracellular polymeric substances and microbial community in sequencing batch reactor.

Wastewater treatment plants can be nanoplastics (NPs) and microplastics (MPs) sinks and sources. The effects of NPs and MPs on nitrogen removal and extracellular polymeric substances (EPS) during activated sludge process need further investigation. Results showed that polystyrene NPs (NPS) and 100 mg/L polystyrene MPs (MPS) decreased the specific nitrate reduction rate, resulting in nitrate accumulation. The negative effects on functional genes involved in denitrification (narG, napA, nirS and nosZ) were the main mechanism. NPS stimulated EPS secretion, but MPS inhibited it. NPS and MPS increased the ratio of protein to polysaccharide except for 10 mg/L MPS and changed the secondary structure of protein in EPS, affecting flocculation ability of activated sludge. The changes of microbial abundance in activated sludge could be the main factor to the alterations of EPS and nitrogen removal. These results may facilitate understanding the impacts of NPs and MPs on wastewater treatment processes.

Effect of hydraulic parameters of leachate treatment process on di(2-ethylhexyl) phthalate removal from aged leachate.

The effect of hydraulic parameters of an anaerobic/anoxic/oxic leachate treatment reactor on the removal of di(2-ethylhexyl) phthalate (DEHP) from aged landfill leachate was studied. The mean DEHP removal efficiencies were 79.5%, 87.1%, 89.7% and 87.8% at hydraulic retention times of 6, 4.5, 3 and 2 d, respectively. The removal efficiency of DEHP was significantly higher when the internal reflux ratio was 200% than others. There was no significant difference among the DEHP removal efficiencies at different external reflux ratios of the reactor. Due to the overall efficiency of the reactor, hydraulic retention time 3 d, internal reflux ratio 200% and external reflux ratio 60%, were considered the optimal hydraulic parameters for DEHP removal from aged leachate. The removal efficiency of DEHP was significantly improved (from 75.7% to 89.1%) after the optimization of hydraulic parameters of the reactor. The removal percentages of DEHP in the anaerobic, anoxic, and oxic units of the reactor were 42.8%, 17.6%, and 15.3%, respectively. The oxic microcosms in the reactor had little effect on DEHP removal. The correlation between DEHP and leachate pollutants indicated that DEHP removal was strongly correlated with leachate COD and NH4+-N.

Effect of antibiotic exposure on the characteristics of activated sludge in a landfill leachate biological treatment system.

Changes in the activated sludge performance in an anaerobic/aerobic biological treatment system for leachate was discussed under the condition of tetracycline (TC) exposure. The results show that a low concentration of TC did not have an obvious effect on the removal of chemical oxygen demand (COD) while a high concentration of TC had a certain promoting effect. Under the stimulation of TC, the particle size distribution of anaerobic/aerobic sludge tended to be more uniform, the particle size of anaerobic sludge decreased while the settleability increased; however, the particle size of aerobic sludge increased due to bulking. With the addition of TC, the concentration of most heavy metal ions in sludge samples increased.TC exposure results in the release of a large amount of extracellular polymeric substances (EPS), thus leading to a smoother surface of anaerobic sludge and a rougher surface of aerobic sludge. The high removal efficiency of COD under the high concentration of TC was also presumed to be due to EPS promoting the microbial absorption of anaerobic substances in the leachate. The results clearly showed that TC had a bacteriostatic effect. After antibiotic exposure, the abundance and diversity index of bacteria in each reactor decreased obviously, the microbial community evolved, and the dominant species at the genus and phylum levels of anaerobic/aerobic reactors changed. This study provides a better understanding the effect of TC on activated sludge and has reference value for the management of antibiotic exposure in leachate treatment facilities.

Adsorption characteristics of antibiotics on microplastics: The effect of surface contamination with an anionic surfactant.

Microplastics and antibiotics are common, typical pollutants, and they can cause compound pollution where they coexist in the environment. Surfactants in the environment can change the interface characteristics of pollutants, and then drive the change of environmental behavior of pollutants. In this paper, we studied the physicochemical properties of complexes of polystyrene (PS) and polyethylene (PE) contaminated with sodium dodecyl benzene sulfonate (SDBS); the complexes are referred to as SPS and SPE, respectively. Taking oxytetracycline (OTC) and norfloxacin (NOR) as representatives of broad-spectrum antibiotics, the effects of SDBS on the adsorption behavior of PS and PE were analyzed and possible mechanisms were proposed. The results showed that SDBS could effectively combine with PS and PE to enhance the surface electronegativity and reduce the Brunner-Emmett-Teller (BET) specific surface area and porosity. The crystal structure remained basically unchanged, and the surface functional groups changed slightly. SDBS greatly enhanced the saturated adsorption capacities of PS and PE for OTC and NOR, and made adsorption easier, which reduced the Gibbs free energy of the adsorption system. The adsorption behaviors of SPS and SPE for the two antibiotics were consistent with the Elovich kinetic model and Sips isothermal model. SDBS enhanced the hydrophilicity of the microplastics, which facilitated their adsorption of antibiotics dissolved in water. SDBS could directly combine with antibiotics to form a complex, further increasing the adsorption capacity of the microplastics for antibiotics. The -SO3H in SDBS could combine with oxygen-containing functional groups and -NH2 in OTC and NOR. Non-ionic covalent bonds, electrostatic interactions, and hydrophobic attraction between the alkyl chain and benzene ring also played a role in adsorption. SDBS made it possible for MPs to load more types and quantities of pollutants and change their preferential adsorption selectivity, which significantly aggravated the environmental hazards.

Adsorption of tetracycline and Cd(II) on polystyrene and polyethylene terephthalate microplastics with ultraviolet and hydrogen peroxide aging treatment.

Microplastics (MPs) could serve as vectors of antibiotics and heavy metals through sorption and desorption. However, the combined adsorption process of antibiotics and heavy metals on aged MPs has rarely been studied. In this study, combined adsorption/desorption of tetracycline (TC) and Cd(II) on/from polystyrene (PS) and polyethylene terephthalate (PET) MPs, as well as ultraviolet (UV) and H2O2 aged MPs, was investigated. The specific surface areas of the MPs increased after UV and H2O2 aging. Adsorption experiments showed that the pseudo-second-order kinetic model and Freundlich model fitted adsorption of TC and Cd(II) on all of the MPs. The adsorption capacities of TC and Cd(II) were higher on aged MPs than on the pristine MPs, especially on H2O2 treated MPs. TC adsorption on the MPs was hardly affected by Cd(II), and Cd(II) adsorption was not significantly affected by TC when the solution pH value was below 8.0. Cd(II) slightly enhanced TC adsorption on the MPs at pH 8.0, especially on the aged MPs. The TC adsorption capacities increased with increasing pH, reaching a maximum at pH 5.0 or 6.0, and they then decreased, while the largest level of Cd(II) adsorption was at approximately pH 6.0. Adsorption of TC and Cd(II) on the pristine and aged MPs was thermodynamically favorable and spontaneous. The trend of the desorption rates of TC and Cd(II) from the MPs in different background solutions was ultrapure water < surface water < simulated gastric fluid. The desorption rates of TC and Cd(II) from the aged MPs were lower than those from the pristine MPs. The results revealed the mechanism of the TC and Cd(II) combined adsorption process on aged MPs, which will provide insight for understanding the aging process and its potential effects on sorption and desorption of antibiotics and heavy metals in the real environment.

Vertical distribution of antibiotics and antibiotic resistance genes in a representative municipal solid waste landfill, China.

The vertical distribution of sulfonamides (SAs), tetracyclines (TCs), macrolides (MLs), and their related antibiotic resistance genes (ARGs) were comprehensively investigated and characterized in a representative municipal solid waste (MSW) landfill in China. The total concentrations of target antibiotics in the MSW landfill were SAs > TCs > MLs. The abundances of mexF (10.78 ± 0.65 log10copies/g) and sul genes (9.15 ± 0.54 log10copies/g) were relatively high, while the tet genes (7.19 ± 0.77 log10copies/g) were the lowest. Both the abundance of antibiotics and genes fluctuated with landfill depth, and the ARGs of the same antibiotics were consistent with depth change. Intl1 and sul genes (sul1, sul2) were tightly connected, and a close relationship also existed between tet genes (tetM, tetQ) and MLs resistance genes (ermB, mefA). High-throughput sequencing showed the dominant genera were Sporosarcina (38%) and Thiobacillus (17%) at sampling points A and C, while the microbial community varied with depth increase at point B were Brevundimonas (20%), Sporosarcina (20%), Pseudomonas (24%), Lysobacter (28%), and Thioalkalimicrobium (14%), respectively. Network analysis further visualized the relationship among antibiotics, genes, and microbial communities and the results indicated the non-random connection among them and the possible host of the target gene. Even at 12.0 m below the landfill surface, the pollution of antibiotics resistance was still serious, which posed difficulties for subsequent landfill remediation and pollution control.

The panorama of antibiotics and the related antibiotic resistance genes (ARGs) in landfill leachate.

Landfill leachate is an important source and sink of antibiotics and antibiotic resistance genes (ARGs), which poses a potential threat to human health and ecological environment. Ten antibiotics and 8 ARGs in leachates collected from Zhejiang Province, China, were systematically investigated. The effects of multiple factors were considered: leachate age, season when the leachate was sampled (dry or rainy), heavy metal concentrations, and leachate quality parameters. Leachate age was crucial to the profile of the detectable antibiotics and ARGs. The total concentration of antibiotics were in the order of macrolides > sulfonamides > tetracyclines and they decreased significantly with leachate age. Similarly, fewer ARGs were harbored in aged leachate; the order of abundance of the ARGs was mexF (11.92 ± 0.22 log10 gene copies/L) > sul2 > Intl1 > sul1 > ermB > mefA > tetM > tetQ (9.57 ± 1.32 log10 gene copies/L). The extreme abundances (i.e., the maxima and minima) of ARGs relating to the same class of antibiotic were always surprisingly similar and appeared in leachate of the same age. Seasonal variation greatly affected the concentrations of antibiotics in the leachate-the concentration difference between the dry and rainy seasons could reach two orders of magnitude. Heavy metal concentrations and leachate quality parameters also had important effects on the distribution of antibiotics and ARGs. Overall, the profile of antibiotics and ARGs in leachates was influenced by numerous factors, and the pollution of antibiotics and ARGs may be reduced and controlled by adjusting the environmental factors.

Evolution of sulfate reduction behavior in leachate saturated zones in landfills.

The sulfate reduction behavior of the landfill leachate saturated zone under different temperatures was investigated. The results showed that temperature had significant effects on sulfate reduction behavior. The sulfate reduction efficiency was the highest at high temperatures (55 °C and 45 °C), followed by mesophilic temperature (35 °C). Normal temperature 25 °C was far less effective than 55 °C, 45 °C and 35 °C. High abundances of aprA and dsrA genes were distributed under high temperatures. Through indicator species analysis and functional comparison, some key taxa were identified as putative key genera for sulfate reduction. Under high temperature, Paenibacillus could effectively degrade dimethyl sulfide. DsrAB is present in the genome of Tissierella. Gordonia, Syntrophomonas, and Lysinibacillus under mesophilic temperature indicates the potential of these organisms to degrade heterogenous biomass, environmental pollutants or other natural polymers with slow biodegradation. This microbial function is similar to that of the putative key genera under normal (25 °C) temperature. Most of the putative key genera belong to Firmicutes, Proteobacteria and Myxococcota. This study provides theoretical support for the control of hydrogen sulfide release from landfills.

Sulfate-reduction behavior in waste-leachate transition zones of landfill sites.

The sulfate reduction behavior of the waste-leachate transition zone of landfill was investigated at different temperatures and moisture contents. Marked differences in the sulfate reduction behavior were observed in the waste-leachate transition zone. The highest H2S concentration was observed when the solid-to-liquid ratio was 1:3 at both temperatures. Although more leachate led to higher H2S concentrations, the solid-to-liquid ratio was likely of subordinate significance compared with temperature. The microbial community was more unstable at 50 °C and more extensive mutualistic interactions among bacteria were observed, resulting in SRB showing a more violent response to changes in the solid-to-liquid ratio. At 25 °C, it's the opposite. A temperature of 25 °C was suitable for most SRB (such as Desulfomicrobium and Desulfobulbus), while some specific SRB that did not contain the functional genes (such as Dethiobacter and Anaerolinea) played a pivotal role in the significant differences in sulfate reduction behavior observed at 50 °C. This study provides a theoretical basis for controlling the release of H2S from landfill.

Microbes drive changes in arsenic species distribution during the landfill process.

Landfills are considered an anthropogenic source of arsenic (As). The As species mediated by microbes in landfills vary significantly in toxicity. Based on random matrix theory, 16S rRNA genes were used to construct four microbial networks associated with different stages over 12 years of landfill ages. The results indicated that network size and microbial structure varied with landfill age. According to the network scores, about 208 taxa were identified as putative keystones for the whole landfill; the majority of them were Firmicutes, which accounted for 66.8% of all specialists. Random Forest analysis was performed to predict the keystone taxa most responsible for As species distribution under different landfill conditions; 17, 10 and 14 keystone taxa were identified as drivers affecting As species distribution at early, middle, and later landfill stages, respectively.

Effect of air and water on the release of chlorine from semi-aerobic landfill.

Landfill leachate has a high chloride (Cl-) content. Because it is highly mobile, and cannot be sorbed or transformed bio-chemically, it is important to have detailed information about how it migrates in landfill sites. In this study, we set up four lab-scale simulated landfills, including an anaerobic landfill (AL), an anaerobic landfill with leachate recirculation (RAL), an anaerobic/semi-anaerobic landfill with leachate recirculation (RASL), and an anaerobic/semi-aerobic landfill (ASL), to explore how, when regulated, moisture and air affected the migration of chlorine. We found that water and air had a strong influence on the release of Cl-. Leachate obviously promoted Cl- dissolution in refuse when recirculated. When air was introduced into landfill, thereby changing it from anaerobic to semi-aerobic, the leachate Cl- concentration increased sharply from around 4-9 g L-1 (RASL) and 18 g L-1 (ASL), respectively. In principle, Cl- is released continuously when leachate is recirculated in landfills (RAL and RASL), but it can also be found a terminal when the leachate recirculation stops (AL and ASL). Cumulative amounts of 64, 66, 27, and 53 g of Cl- were released from the AL, RAL, RASL, and ASL, respectively. Lower COD/Cl and NH4+-N/Cl ratios in ASL and RASL after day 175 indicated that lower Cl- pollution risk than that in AL and RAL.

Drivers and ecological consequences of arsenite detoxification in aged semi-aerobic landfill.

Microbial populations responsible for arsenite [As(III)] detoxification were examined in aged refuse treated with 75 µM As(III) under semi-aerobic conditions. As(III) was rapidly oxidized to As(V) via microbial activity, and substantial As was fixed in the solid phase. The abundance of arsenite oxidase genes (aioA) was about four times higher in the moderate As(III) stressed treatment than in the untreated control. Network analysis of microbial community 16S rRNA genes based on MRT (random matrix theory) further illuminated details about microbe-microbe interactions, and showed six ecological clusters. A total of 166 "core" taxa were identified by within-module connectivity and among-module connectivity values. When compared with the control treatment without As(III), 12 putative keystone operational taxonomic units were positively correlated with As(III) oxidation, of which 10 of these were annotated to genera level. Eight genera were associated with As(III) detoxification: Pseudomonas, Paenalcaligenes, Proteiniphilum, Moheibacter, Mobilitalea, Anaerosporobacter, Syntrophomonas and Pusillimonas. Most of those putative keystone taxa were rare species in landfill, which suggests that low-abundance taxa might significantly contribute to As(III) oxidation.