Variation on leaching behavior of caustic compounds in bauxite residue during dealkalization process

Bauxite residue, a byproduct of alumina manufacture, is a serious environmental pollutant due to its high leaching contents of metals and caustic compounds. Four typical anions of CO₃^2?, HCO₃^?, Al(OH)₄^? and OH^? (represented caustic compounds) and metal ions (As, B, Mo and V) were selected to assess their leaching behavior under dealkalization process with different conditions including liquid/solid ratio (L/S ratio), temperature and leaching time. The results revealed that washing process could remove the soluble composition in bauxite residue effectively. The leaching concentrations of typical anions in bauxite residue decreased as follows: c(CO₃^2?) > c(HCO₃^?) > c[Al(OH)₄^?] > c(OH^?). L/S ratio had a more significant effect on leaching behavior of OH^?, whilst the leaching concentration of Al(OH)₄^? varied larger underleaching temperature and time treatment. Under the optimal leaching, the total alkaline, soluble Na concentrations, exchangeable Ca concentrations were 79.52, 68.93, and 136.0 mmol/L, respectively, whilst the soluble and exchangeable content of As, B, Mo and V in bauxite residue changed slightly. However, it should be noted that water leaching has released metal ions such as As, B, Mo and V in bauxite residue to the surrounding environment. The semiquantitative analysis of XRD revealed that water leaching increased the content of gismondine from 2.4% to 6.4%. The SEM images demonstrated the dissolution of caustic compounds on bauxite residue surface. The correlation analysis indicated that CO₃^2? and HCO₃^? could effectively reflect the alkalinity of bauxite residue, and may be regarded as critical dealkalization indicators to evaluate alkalinity removal in bauxite residue.     

Changes in distribution and microstructure of bauxite residue aggregates following amendments addition

Bauxite residue is a highly alkaline byproduct which is routinely discarded at residue disposal areas. Improving soil formation process to revegetate the special degraded lands is a promising strategy for sustainable management of the refining industry. A laboratory incubation experiment was used to evaluate the effects of gypsum and vermicompost on stable aggregate formation of bauxite residue. Aggregate size distribution was quantified by fractal theory, whilst residue microstructure was determined by scanning electron microscopy and synchrotron-based X-ray micro-computed tomography. Amendments addition increased the content of macro-aggregates( 250 μm) and enhanced aggregate stability of bauxite residue. Following gypsum and vermicompost addition, fractal dimension decreased from 2.84 to 2.77, which indicated a more homogeneous distribution of aggregate particles. Images from scanning electron microscopy and three-dimensional microstructure demonstrated that amendments stimulate the formation of improved structure in residue aggregates. Pore parameters including porosity, pore throat surface area, path length, and path tortuosity increased under amendment additions. Changes in aggregate size distribution and microstructure of bauxite residue indicated that additions of gypsum and vermicompost were beneficial to physical condition of bauxite residue which may enhance the ease of vegetation.     

Rapid conversion of alkaline bauxite residue through co-pyrolysis with waste biomass and its revegetation potential

The extreme alkalinity of bauxite residue(BR) leads to difficulty with its reuse. Alkaline leachate and dust generation during the stacking process can pollute surrounding soil, air and water. In this work, co-pyrolysis of bauxite residue and sawdust was applied to rapidly produce a soil-like matrix that met the conditions for plant growth as demonstrated by ryegrass pot experiments. The present study aimed to characterize the detailed changes in physicochemical, mineral weathering, and microbia...     

Ca~(2+) and OH~- release of ceramsites containing anorthite and gehlenite prepared from waste lime mud

Lime mud is a kind of solid waste in the papermaking industry,which has been a source of serious environmental pollution.Ceramsites containing anorthite and gehlenite were prepared from lime mud and fly ash through the solid state reaction method at 1050°C.The objective of this study was to explore the efficiency of Ca~(2+) and OH-release and assess the phosphorus and copper ion removal performance of the ceramsites via batch experiments,X-ray diffraction(XRD) and scanning electron microscopy(SEM).The results show that Ca~(2+) and OH-were released from the ceramsites due to the dissolution of anorthite,gehlenite and available lime.It is also concluded that gehlenite had stronger capacity for Ca~(2+) and OH-release compared with anorthite.The Ca~(2+) release could be fit well by the Avrami kinetic model.Increases of porosity,dosage and temperature were associated with increases in the concentrations of Ca~(2+) and OH-released.Under different conditions,the ceramsites could maintain aqueous solutions in alkaline conditions(p H = 9.3–10.9) and the release of Ca~(2+) was not affected.The removal rates of phosphorus and copper ions were as high as 96.88% and 96.81%,respectively.The final p H values of both phosphorus and copper ions solutions changed slightly.The reuse of lime mud in the form of ceramsites is an effective strategy.     

Immobilization of Cu~(2+) and Cd~(2+) by earthworm manure derived biochar in acidic circumstance

Earthworm manure, the by-product obtained from the disposing of biowastes by earthworm breeding, is largely produced and employed as a feedstock for biochar preparation through pyrolysis. For repairing acidic soil or acidic electroplating effluent,biochar physicochemical properties would suffer from some changes like an acidic washing process, which hence affected its application functions. Pristine biochar(UBC)from pyrolysis of earthworm manure at 700°C and biochar treated by HCl(WBC) were comparatively investigated regarding their physicochemical properties, adsorption capability and adsorption mechanism of Cu~(2+) and Cd~(2+) from aqueous solution to explore the immobilization characteristics of biochar in acidic environment. After HCl treatment,the soluble ash content and phenolic-OH in the WBC sample was notably decreased against the increase of the carboxyl C_O, aromatic C_C and Si–O–Si, compared to that of UBC. All adsorption processes can be well described by Langmuir isotherm model. The calculated maximum adsorption capacity of Cu~(2+) and Cd~(2+) adsorption on UBC were 36.56 and 29.31 mg/g, respectively, which were higher than that of WBC(8.64 and 12.81 mg/g,respectively), indicating that HCl treatment significantly decreased biochar adsorption ability. Mechanism analysis revealed that alkali and alkaline earth metallic, salts(carbonates, phosphates and silicates), and surface functional groups were responsible for UBC adsorption, corresponding to ion exchange, precipitation and complexation,respectively. However, ion exchange made little contributions to WBC adsorption due to the great loss of soluble ash content. WBC adsorption was mainly attributed to the abundant exposure of silicates and surface functional groups(carboxyl C_O and aromatic C_C).     

Reduction behaviors of permanganate by microbial cells and concomitant accumulation of divalent cations of Mg2+, Zn2+, and Co2+

Permanganate treatment is widely used for disinfection of bacteria in surface-contaminated water. In this paper, the fate of the dissolved permanganate in aqueous solution after contact with cells of Pseudomonas fluorescens was studied. Concomitant accumulation of divalent cations of Mg~(2+), Zn~(2+), and Co~(2+) during precipitation of Mn oxides was also studied. The time course of the Mn concentration in solution showed an abrupt decrease after contact of Mn(VII) with microbial cells, followed by an increase after ～ 24 hr.XRD analysis of the precipitated Mn oxides, called biomass Mn oxides, showed the formation of low-crystalline birnessite. Visible spectroscopy and X-ray absorption near edge structure(XANES) analyses indicated that dissolved Mn(VII) was reduced to form biomass Mn oxides involving Mn(IV) and Mn(III), followed by reduction to soluble Mn(II).The numbers of electron transferred from microbial cells to permanganate and to biomass Mn oxides for 24 hr after the contact indicated that the numbers of electron transfer from microbial cell was approximately 50 times higher to dissolved permanganate than to the biomass Mn oxides in present experimental conditions. The 24 hr accumulation of divalent cations during formation of biomass Mn oxides was in the order of Co~(2+) Zn~(2+) Mg~(2+).XANES analysis of Co showed that oxidation of Co~(2+) to Co~(3+) resulted in higher accumulation of Co than Zn and Mg. Thus, treatment of surface water by KMnO_4 solution is effective not only for disinfection of microorganisms, but also for the elimination of metal cations from surface water.     

Adsorption of Ca2+ on single layer graphene oxide

Graphene oxide(GO) holds great promise for a broad array of applications in many fields,but also poses serious potential risks to human health and the environment.In this study,the adsorptive properties of GO toward Ca~(2+) and Na+were investigated using batch adsorption experiments,zeta potential measurements,and spectroscopic analysis.When pH increased from 4 to 9,Ca~(2+)adsorption by GO and the zeta potential of GO increased significantly.Raman spectra suggest that Ca~(2+)was strongly adsorbed on the GO via –COO Ca~+ formation.On the other hand,Na+was adsorbed into the electrical diffuse layer as an inert counterion to increase the diffuse layer zeta potential.While the GO suspension became unstable with increasing pH from 4 to 10 in the presence of Ca~(2+),it was more stable at higher pH in the NaC l solution.The findings of this research provide insights in the adsorption of Ca~(2+)on GO and fundamental basis for prediction of its effect on the colloidal stability of GO in the environment.     

The effect of low-molecular-weight organic-acids (LMWOAs) on treatment of chromium-contaminated soils by compost-phytoremediation: Kinetics of the chromium release and fractionation

A soil–plant biological system was developed from chromium(Cr) polluted soil treated by the compost-phytoremediation method. The transformation and migration of the Cr in this system is comprehensively studied in this research. The results illustrated that the co-composting treatment can reduce the Cr availability from 39%(F1 was about 31% of total, F2 was about 8% of total) to less than 2% by stabilizing the Cr. However, herbaceous plants can accumulate the concentrations of Cr from 113.8 to 265.2 mg/kg in the two crops,even though the concentration of soluble Cr in the substrate soil was below 0.1 mg/L.Cr can be assimilated and easily transferred in the tissues of plants because the lowmolecular-weight organic-acids(LMWOAs) derived from the plant root increase the bioavailability of Cr. The amount of extracted Cr dramatically increased when the organic acids were substituted in this order: citric acid malic acid tartaric acid oxalic acid acetic acid. On average the maximum(147.4 mg/kg) and the minimum(78.75 mg/kg) Cr were extracted by 20 mmol/L citric acid and acetic acid, respectively. The desorption of Cr in different acid solutions can be predicted by the pseudo second-order kinetics. The exchangeable Cr, carbonate-bound Cr, and residual Cr decreased, while Fe–Mn oxide bound Cr and organic bound Cr increased in the soil solid phase. According to the experimental results, the organic acids will promote the desorption and chelation processes of Cr, leading to the remobilization of Cr in the soil.     

Phosphate recovery from anaerobic digester effluents using CaMg(OH)4

Dolomite lime(DL)(CaMg(OH)_4) was used as an economical source of Mg~(2+)for the removal and recovery of phosphate from an anaerobic digester effluent of a municipal wastewater treatment plant(MWWTP) wastewater. Batch precipitation results determined that phosphate was effectively reduced from 87 to less than 4 mg-P/L when the effluent water was mixed with 0.3 g/L of DL. The competitive precipitation mechanisms of different solids in the treatment system consisting of Ca~(2+)–Mg~(2+)–NH_4~+–PO_4~(3-)CO_3~(2-)were determined by comparing model predictions with experimental results. Thermodynamic model calculations indicated that hydroxyapatite(Ca_(10)(PO_4)_6(OH)_2), Ca_4H(PO_4)_3?3H_2O, Ca_3(PO_4)_2(beta), and Ca_3(PO_4)_2(am2)were more stable than struvite(MgNH_4PO_3?6H_2O) and calcite(CaCO_3). However, X-ray diffraction(XRD) analysis determined the formation of struvite and calcite minerals in the treated effluent. Kinetic experimental results showed that most of the phosphate was removed from synthetic effluent containing NH_4~+within 2 hr, while only 20% of the PO_4~(3-)was removed in the absence of NH_4~+after 24 hr of treatment. The formation of struvite in the DL-treated effluent was due to the rapid precipitation rate of the mineral. The final pH of the DL-treated effluent significantly influenced the mass ratio of struvite to calcite in the precipitates. Because more calcite was formed when the p H increased from 8.4 to 9.6, a p H range of 8.0–8.5 should be used to produce solid with high PO_4~(3-)content. This study demonstrated that DL could be used for effective removal of phosphate from the effluent and that resultant precipitates contained high content of phosphate and ammonium.     

CO2 sequestration utilizing basic-oxygen furnace slag: Controlling factors, reaction mechanisms and V–Cr concerns

Basic-oxygen furnace slag(BOF-slag) contains 35%CaO,a potential component for CO_2sequestration.In this study,slag-water-CO_2 reaction experiments were conducted with the longest reaction duration extending to 96 hr under high CO_2 pressures of 100-300 kg/cm2 to optimize BOF-slag carbonation conditions,to address carbonation mechanisms,and to evaluate the extents of V and Cr release from slag carbonation.The slag carbonation degree generally reached the maximum values after 24 hr slag-water-CO_2 reaction and was controlled by slag particle size and reaction temperature.The maximum carbonation degree of 71%was produced from the experiment using fine slag of0.5 mm under 100℃and a CO_2 pressure of 250 kg/cm~2 with a water/slag ratio of 5.Vanadium release from the slag to water was significantly enhanced(generally 2 orders) by slag carbonation.In contrast,slag carbonation did not promote chromium release until the reaction duration exceeded 24 hr.However,the water chromium content was generally at least an order lower than the vanadium concentration,which decreased when the reaction duration exceeded 24 hr.Therefore,long reaction durations of 48-96 hr are proposed to reduce environmental impacts while keeping high carbonation degrees.Mineral textures and water compositions indicated that Mg-wustite,in addition to CaO-containing minerals,can also be carbonated.Consequently,the conventional expression that only considered carbonation of the CaO-containing minerals undervalued the CO_2 sequestration capability of the BOF-slag by~20%.Therefore,the BOF-slag is a better CO_2 storage medium than that previously recognized.     

Effects of surfactants on the combined toxicity of TiO2 nanoparticles and cadmium to Escherichia coli

The combined ecological toxicity of TiO₂ nanoparticles (nano-TiO₂) and heavy metals has been paid more attention. As the common pollutants in water environment, surfactants could affect the properties of nanoparticles and heavy metals, and thus further influence the combined toxicity of nano-TiO₂ and heavy metals. In this study, the effects of sodium dodecyl benzene sulfonate (SDBS) and Tween 80 on the single and combined toxicities of Cd^2 + and nano-TiO₂ to Escherichia coli (E. coli) were examined, and the underlying influence mechanism was further discussed. The results showed both SDBS and Tween 80 enhanced the toxicity of Cd^2 + to E. coli in varying degrees. The reaction of SDBS and Cd^2 + could increase the outer membrane permeability and the bioavailability of Cd, while Tween 80 itself could enhance the outer membrane permeability. The combined toxicity of nano-TiO₂ and Cd^2 + to E. coli in absence of surfactant was antagonistic because of the adsorption of Cd^2 + to nano-TiO₂ particles. However, in the presence of SDBS, both SDBS and nano-TiO₂ influenced the toxicity of Cd^2 +, and also SDBS could adsorb to nano-TiO₂ by binding to Cd^2 +. The combined toxicity was reduced at Cd^2 + lower than 4 mg/L and enhanced at Cd^2 + higher than 4 mg/L under multiple interactions. Tween 80 enhanced the combined toxicity of nano-TiO₂ and Cd^2 + by increasing the outer membrane permeability. Our study firstly elucidated the effects of surfactants on the combined toxicity of nano-TiO₂ and Cd^2 + to bacteria, and the underlying influencing mechanism was proposed.     

Simultaneous removal of arsenic and antimony from mining wastewater using granular TiO2: Batch and field column studies

Coexisting arsenic (As) and antimony (Sb) in mining wastewater is a common and great concern. On-site simultaneous removal of As and Sb from mining wastewater was achieved by using a reusable granular TiO₂ column in this study. To evaluate the accuracy of the scale-up procedure, As and Sb adsorption from wastewater was studied in both large (600 g TiO₂) and small columns (12 g TiO₂) based on the proportional diffusivity rapid small-scale column tests (PD-RSSCTs) design. The comparable As and Sb breakthrough curves obtained from small and large columns confirmed the accuracy of the PD-RSSCT theory in the design of large-scale columns. Meanwhile, the consistent As and Sb adsorption results from batch and column experiments suggested that TiO₂ adsorption for As and Sb can be predicted from bench-scale tests. Charge distribution multi-site complexation (CD-MUSIC) and one-dimensional transport modeling integrated in the PHREEQC program were performed to study the adsorption behaviors of As and Sb on the TiO₂ surface. Coexisting ions, such as Ca^2 +, Mg^2 +, and Si^4 +, play an important role in As and Sb adsorption, and the breakthrough curves were well simulated after considering the compound ion effects. The results from this study highlight the surface reactions of As and Sb on TiO₂ and provide a practical way for on-site remediation of industrial wastewater.     

Attenuation of arsenic in a karst subterranean stream and correlation with geochemical factors: A case study at Lihu, South China

Arsenic （As） pollutants generated by human activities in karst areas flow into subterranean streams and contaminate groundwater easily because of the unique hydrogeological characteristics of karst areas. To elucidate the reaction mechanisms of arsenic in karst subterranean streams, physical-chemical analysis was conducted by an inductively coupled plasma mass spectrometer and an X-ray fluorescence spectrometer. The results show that inorganic species account for most of the total arsenic, whereas organic arsenic is not detected or occurs in infinitesimal amounts. As（III） accounts for 51.0% ± 9.9% of the total inorganic arsenic. Arsenic attenuation occurs and the attenuation rates of total As, As（III） and As（V） in the Lihu subterranean stream are 51%, 36% and 59%, respectively. To fully explain the main geochemical factors influencing arsenic attenuation, SPSS 13.0 and CANOCO 4.5 bundled with CanoDraw for Windows were used for simple statistical analysis and redundancy analysis （RDA）. Eight main factors, i.e., sediment iron （SFe）, sediment aluminum （SAI）, sediment calcium （SCa）, sediment organic matter （SOM）, sediment manganese （SMn）, water calcium （WCa^2＋）, water magnesium （WMg^2＋）, and water bicarbonate ion （WILCOX） were extracted from thirteen indicators. Their impacts on arsenic content rank as： SFe〉SCa〉WCa^2＋〉SAl〉wHCO3^-〉SMn〉SOM〉WMg^2＋. Of these factors, SFe, SAl, SCa, SOM, SMn, WMg^2＋ and WCa＆2＋ promote arsenic attenuation, whereas WHCO3^- inhibits it. Further investigation revealed that the redox potential （Eh） and pH are adverse to arsenic removal. The dramatic distinction between karst and non-karst terrain is that calcium and bicarbonate are the primary factors influencing arsenic migration in karst areas due to the high calcium concentration and alkalinity of karst water.     

Investigation on mechanism of phosphate removal on carbonized sludge adsorbent

For the removal of phosphate (PO₄^3 -) from water, an adsorbent was prepared via carbonization of sewage sludge from a wastewater treatment plant: carbonized sludge adsorbent (CSA). The mechanism of phosphate removal was determined after studying the structure and chemical properties of the CSA and its influence on phosphate removal. The results demonstrate that phosphate adsorption by the CSA can be fitted with the pseudo second-order kinetics and Langmuir isotherm models, indicating that the adsorption is single molecular layer adsorption dominated by chemical reaction. The active sites binding phosphate on the surface are composed of mineral particles containing Si/Ca/Al/Fe. The mineral containing Ca, calcite, is the main factor responsible for phosphate removal. The phosphate removal mechanism is a complex process including crystallization via the interaction between Ca^2 + and PO₄^3 -; formation of precipitates of Ca^2 +, Al^3 +, and PO₄^3 -; and adsorption of PO₄^3 - on some recalcitrant oxides composed of Si/Al/Fe.     

Effect of air-exposed biocathode on the performance of a Thauera-dominated membraneless single-chamber microbial fuel cell (SCMFC)

To investigate the effect of air-exposed biocathode(AEB) on the performance of singlechamber microbial fuel cell(SCMFC), wastewater quality, bioelectrochemical characteristics and the electrode biofilms were researched. It was demonstrated that exposing the biocathode to air was beneficial to nitrogen removal and current generation. In Test 1 of 95%AEB, removal rates of ammonia, total nitrogen(TN) and chemical oxygen demand(COD)reached 99.34% ± 0.11%, 99.34% ± 0.10% and 90.79% ± 0.12%, respectively. The nitrogen removal loading rates were 36.38 g N/m~3/day. Meanwhile, current density and power density obtained at 0.7 A/m3 and 104 m W/m~3 respectively. Further experiments on opencircuit(Test 2) and carbon source(Test 3) indicated that this high performance could be attributed to simultaneous biological nitrification/denitrification and aerobic denitrification, as well as bioelectrochemical denitrification. Results of community analysis demonstrated that both microbial community structures on the surface of the cathode and in the liquid of the chamber were different. The percentage of Thauera, identified as denitrifying bacteria, maintained at a high level of over 50% in water, but decreased gradually in the AEB. Moreover, the genus Nitrosomonas, Alishewanella, Arcobacter and Rheinheimera were significantly enriched in the AEB, which might contribute to both enhancement of nitrogen removal and electricity generation.     

An innovative approach to minimize excess sludge production in sewage treatment using integrated bioreactors

The present investigation deals with an application of integrated sequential oxic and anoxic bioreactor(SOABR) and fluidized immobilized cell carbon oxidation(FICCO) reactor for the treatment of domestic wastewater with minimum sludge generation. The performance of integrated SOABR-FICCO system was evaluated on treating the domestic wastewater at hydraulic retention time(HRT) of 3 hr and 6 hr for 120 days at organic loading rate(OLR)of 191 ± 31 mg/(L·hr). The influent wastewater was characterized by chemical oxygen demand(COD) 573 ± 93 mg/L; biochemical oxygen demand(BOD5) 197 ± 35 mg/L and total suspended solids(TSS) 450 ± 136 mg/L. The integrated SOABR-FICCO reactors have established a significant removal of COD by 94% ± 1%, BOD5 by 95% ± 0.6% and TSS by 95% ± 4% with treated domestic wastewater characteristics COD 33 ± 5 mg/L; BOD59 ± 0.8 mg/L and TSS 17 ± 9 mg/L under continuous mode of operation for 120 days. The mass of dry sludge generated from SOABR-FICCO system was 22.9 g/m~3. The sludge volume index of sludge formed in the SOABR reactor was 32 mL/g and in FICCO reactor it was 46 mL/g. The sludge formed in SOABR and FICCO reactor was characterized by TGA, DSC and SEM analysis. Overall, the results demonstrated that the integrated SOABR-FICCO reactors substantially removed the pollution parameters from domestic wastewater with minimum sludge production.     

Hollow TiO2 spheres with improved visible light photocatalytic activity synergistically enhanced by multi-stimulative: Morphology advantage, carbonate-doping and the induced Ti3 +

Great efforts have been devoted to improve the photocatalytic activity of TiO_2 in the visible light region. Rational design of the external structure and adjustment of intrinsic electronic status by impurity doping are two main effective ways to achieve this purpose. A facile onepot synthetic approach was developed to prepare C-doped hollow TiO_2 spheres, which simultaneously realized these advantages. The synthesized TiO_2 exhibits a mesoporous hollow spherical structure composed of fine nanocrystals, leading to high specific surface area(~180 m~2/g) and versatile porous texture. Carbonate-doping was achieved by a postthermal treatment at a relatively low temperature(200°C), which makes the absorption edge red-shifted to the visible region of the solar spectrum. Concomitantly, Ti~(3+) induced by C-doping also functions in improving the visible-light photocatalytic activity by reducing the band gap. There exists a synergistic effect from multiple stimulatives to enhance the photocatalytic effect of the prepared TiO_2 catalyst. It is not out of expectation that the asprepared C-doped hollow TiO_2 spheres exhibits an improved photocatalytic activity under visible light irradiation in organic pollutant degradation.     

Inhibitive effects of chlortetracycline on performance of the nitritation-anaerobic ammonium oxidation (anammox) process and strategies for recovery

The short-and long-term effects of chlortetracycline(CTC) on the nitritation-anaerobic ammonium oxidation(anammox) process were evaluated. The half maximal inhibitory concentration of CTC in the batch tests of the nitritation-anammox process was 278.91 mg/L at an exposure time of 12 hr. The long-term effects of CTC on the process were examined in a continuous-flow nitritation-anammox reactor. Within 14 days, the nitrogen removal rate significantly decreased from 0.61 to 0.25 kg N/m~3/day with 60 mg/L CTC in the influent.The performance suppressed by CTC barely recovered, even after CTC was removed from the influent. Furthermore, the inhibition of CTC also reduced the relative abundance of ammonium oxidizing bacteria(AOB) and anaerobic ammonium oxidizing bacteria(An AOB)in the reactor, resulting in both a decreased amount of and an imbalance between AOB and An AOB. When fresh anammox sludge was reseeded into the nitritation-anammox reactor,the nitrogen removal rate recovered to 0.09 ± 0.03 kg N/m~3/day.     

Characterizing the antibiotic resistance genes in a river catchment: Influence of anthropogenic activities

Previous studies on environmental antibiotics resistance genes(ARGs) have focused on the pollution sources such as wastewater treatment plants, aquaculture and livestock farms,etc. Few of them had addressed this issue in a regional scale such as river catchment. Hence,the occurrence and abundances of 23 ARGs were investigated in surface water samples collected from 38 sites which located from the river source to estuary of the Beijiang River.Among them, 11 ARGs were frequently detected in this region and 5 ARGs(sul I, sul II, tet B,tet C, and tet W) were selected for their distribution pattern analysis. The abundances of the selected ARGs were higher in the upstream(8.70 × 10~6 copies/ng DNA) and downstream areas(3.17 × 10~6 copies/ng DNA) than those in the midstream areas(1.23 × 10~6 copies/ng DNA), which was positively correlated to the population density and number of pollution sources. Pollution sources of ARGs along the Beijiang River not only had a great impact on the abundances and diversity, but also on the distribution of specific ARGs in the water samples. Both sul I and sul II were likely originated from aquaculture farms and animal farms,tet W gene was possibly associated with the mining/metal melting industry and the electric waste disposal and tet C gene was commonly found in the area with multiple pollution sources.However, the abundance of tet B was not particularly related to anthropogenic impacts. These findings highlight the influence of pollution sources and density of population on the distribution and dissemination of ARGs at a regional scale.