Heavy Metals In Wastewater Research Articles

Changes in Desulfovibrio desulfuricans sub sp EPS components and adsorption performance under exogenous sulfur induction and its mediation role in the biosynthesis of ZnS QDs

Sulfate Reducing Bacteria(SRB) can remove heavy metal ions by producing metal sulfide precipitation, which has aroused the research interest of scholars recently. For SRB, exogenous sulfur is one of the most important nutrients, however, there are few reports about the impact of exogenous sulfur on SRB, especially its EPS. Here, we investigated the inducible effect of sulfur sources (Na2SO4, Na2SO3, and Na2S2O3·H2O) on EPS production from SRB for the first time. The results found that exogenous sulfur can significantly increase the production of EPS, especially protein. The increased functional groups(C–O/C–N, CN) in the protein are favorable to adsorption of more heavy metals. Moreover, S2– was added to the system after adsorption of Zn(II) for the biosynthesis of ZnS QDs from the resource recovery point. The experiments and tests showed the yield of cubic β-ZnS QDs correlated with the amount and adsorption performance of EPS. The PL spectrum of EPS present red-shifted and enhanced antibacterial properties due to the adhesion of EPS to ZnS QDs, the basic amino acid His in EPS played an important role in the adsorption of Zn(Ⅱ) and the nucleation of ZnS QDs. This research brings new horizons for using EPS to treatment heavy metal wastewater and resource recycling.

High-efficiency adsorption removal for Cu(II) and Ni(II) using a novel acylamino dihydroxamic acid chelating resin

Cu/Ni-bearing wastewater contamination has recently been a challenge for the environmental protection worldwide. Herein, a novel poly(2-acrylamide-pentanedihydroxamic acid) (PAPDA) resin containing –CONHOH and –COOH groups was prepared and applied to effectively remove Cu2+ and Ni2+ from heavy metal wastewater. The batch adsorption experiments revealed that the maximum adsorption capacities of PAPDA resin for Cu2+ and Ni2+ were 436.08 and 195.05 mg·g−1, respectively, which were 10.20 and 9.45 times higher than that of polyacrylic resin. Specifically, the adsorption kinetics and thermodynamics of PAPDA were respectively consistent with the pseudo-second-order kinetic model and the Langmuir isotherm model, indicating that the adsorption is a single-layer chemisorption process. Besides, the adsorption mechanism was investigated by SEM, XRD, FT-IR, XPS, DFT calculations, suggesting that the PAPDA resin possessing abundant active sites could effectively adsorb the heavy metal ions. Noticeably, the –CONHOH groups represented the strong affinity towards Cu2+ and Ni2+ by forming stable five-membered rings. In addition, column experiments were conducted to study the practical adsorption process of PAPDA resin to heavy metal ions. Overall, the results proved that the novel PAPDA resin as a green and highly efficient adsorbent has a promising potential for the treatment of heavy metals-containing wastewater.

Estimation of Subsurface Pollutant Load and Its Seasonal Variation in an Irrigation Channel

Concentrations of heavy metals in irrigation water and soil were examined to determine the level of contamination in a particular irrigation channel in Gazipur, Bangladesh. In this conduit, effluent from households, industries, and municipalities was combined with irrigation water. The study was carried out in order to estimate pollutant loads along a wastewater irrigation channel and to conceptualize seasonal changes in composite wastewaters. A total of six wastewater and nine contaminated soil samples were collected directly from the study area and analyzed for this project. From February to March, before the monsoon, the pH of the water is too low for this channel to be used for irrigation. At the end of the monsoon season, from April through May, all wastewater tests were within these parameters, making them suitable for irrigation. Considering the standard limits, Pb, Cr, and Cu concentrations in all wastewater samples were found unsuitable for irrigation and thus problematic for soils and crops. The concentration of Cd in the wastewater samples ranged from 27.82 to 88.36 mg/L, whereas the tolerance limit for Cd in irrigation water is 0.01 mg/L. In soil samples from the three places chosen, the levels of Pb were below the safe limit and the levels of Cr were above the safe limit. The heavy metal pollution index of all the sites crossed the safe limit. On the basis of the geo-accumulation index and the pollution index, Pb indicates no pollution and Cd indicates very high levels of pollution in all locations. The maximum enrichment factor was found for Cd, Pb, and Cu, which have minor enrichment, Ni, which has no enrichment, and Cr, which has moderate enrichment. The study also tried to link heavy metals in wastewater to their deposition in soil and seasonal and temporal variations. The study revealed that industrial effluent utilized for irrigation was closely related to the accumulation of heavy metals in soils. Since irrigated agricultural soils are likely to be exposed to harmful wastes, it is crucial that the effluents from the industrial region of Gazipur are appropriately controlled.

Efficient removal of heavy metals by endophytic bacteria Staphylococcus succinus H3.

Heavy metal pollution is a serious and difficult environmental problem. With increasing heavy metal content in industrial wastewater, an environmentally friendly and efficient treatment method must be identified. Considering the ability of endophytic bacteria to adsorb metal ions, this paper explored the heavy metal resistance, adsorption, and adsorption mechanisms and performance of S. succinus H3, an endophytic bacterium. S. succinus H3 exhibited metal resistance at 4 mM Cu2+ and 5 mM Mg2+. The adsorption rate of Cu2+ and Mg2+ ions by the live/dead strain was approximately 70%, and the adsorption capacity was positively correlated with the metal ion concentration. The kinetics and isothermal models were used to study the process of S. succinus H3 adsorption on Cu2+. It exhibits a good correlation with the Freundlich isothermal model. The N-H group, protein C=O group, polysaccharide C-O group, O-H group and some lipids are the main functional groups in the cell wall. S. succinus H3 may bond with the amine group to adsorb Mg2+ through complexation/coordination and may form a copper complex after adsorbing Cu2+. S. succinus H3 has a live adsorption rate of 15% in eight mixed metal ion systems at a 50 mg/L concentration. The study results can lay a foundation for expanding the bacterial resource pool of pollutant treatment and improving the efficiency for sewage treatment. The high heavy metal adsorption capacity of microorganisms has a decisive role in industrial wastewater treatment by microorganisms. Such microorganisms with high metal resistance and adsorption capacity to heavy metals can thrive in industrial wastewater, remove heavy metals efficiently, and greatly improve the efficiency of wastewater treatment. The study results can lay a theoretical foundation for the use of S. succinus H3 to biologically treat heavy metal wastewater in the future.

S-scheme tubular g-C3N4/BiOI heterojunctions for boosting photodegradation of tetracycline and Cr(VI): Mechanism insight, degradation pathway and DFT calculation

A unique tubular g-C3N4 (TCN)/BiOI S-scheme heterojunction with BiOI microspheres grown on the surface of 1D TCN was successfully prepared by hydrothermal treatment and calcination. Herein, adjusting BiOI additive amount can effectively tune electronic band structures and photocatalytic properties of TCN/BiOI heterojunctions. Impressively, the TCN/BiOI composite (CB-2) with a TCN: Bi3+ molar ratio of 1:2 shows the best photocatalytic performance, where the photodegradation efficiencies for tetracycline (TC) and Cr(VI) ions can both achieve more than 77 % and 90 % within 10 and 30 min, respectively. Particularly, the photodegradation efficiencies for TC and Cr(VI) reach up to 90.1 % and 96.8 % at 30 and 40 min, respectively. Notably, the rate constants for photodegradation of TC and Cr(VI) reach 0.1687 and 0.0718 min−1, which are 27.2 and 8.5 times higher than those of bulk g-C3N4, respectively. The distinguished photocatalytic performance of CB-2 is attributed to the high-quality electron transport channels provided by its tubular structure and the effective separation of photogenerated carriers based on the S-scheme heterojunction. Further, O2−, 1O2 and h+ are manifested to be the main active species for the photodegradation of TC. DFT calculations and radical-related experiments fully confirm the formation of S-scheme heterojunctions. Several crucial factors (such as pH, inorganic salts) for wastewater purification are verified to be little effect on the photocatalytic performance. The degradation pathways of TC are proposed. This work establishes a new route to design and prepare high-efficiency S-scheme photocatalysts for the photodegradation of antibiotics and the photoreduction of heavy metal ions in wastewater.

A composite hydrogel beads bio-sorbent for removal of copper: Effect of pH of copper solution

Heavy metals, being the main contaminant in the wastewater and water streams were previously proven to be hazardous for both human and environmental health. Current heavy metal wastewater treatment technology that possibly leads to secondary pollution is concerning due to the disposal of the synthetic materials that’s being implemented. Therefore, an environmentally friendly composite hydrogel beads bio-sorbent is introduced in this study by cross-linking and encapsulation of cellulose-chitosan-magnetite-alginate (abbreviated as CCMA) as an initiative towards a greener environmental remediation technology for the removal of common heavy metal copper. The effect of pH of copper (Cu) solution was investigated through this study in a pH variation of 3–6. In which pH 5 of Cu solution was proven to be the best for the removal of Cu with the percentage removal of 62.25 %. Other than that, the net surface charge of CCMA hydrogel beads was characterized by zeta potential measurement. In which, a negatively charged CCMA was proven at −16.30 mV, which indicates that there is a possibility of electrostatic interaction as the adsorption mechanism between CCMA and Cu cations. Thus, this shows that the environmentally friendly CCMA is potentially beneficial as a bio-sorbent for the removal of heavy metals.

Association of Plant and Microorganisms on Textile Wastewater Remediation

Phytoremediation of heavy metals containing textile wastewater using vetiver grass (Chrysopogone zizanioides) associated with Bacillus sp. and Pseudomonas aeruginosa has been performed. Two levels of heavy metal in wastewater (<1 and 100 ppm) in two replication were treated using C. Zizanioides associated with Bacillus sp. and C. Zizanioides associated with Pseudomonas aeruginosa. Assessment of C. zizanioides capability was determined by the efficiency of heavy metals (Cu and Cr) removal and its accumulation in both of leaves and roots of the plants. It was obtained that the experiment of low concentration of Cr was totally eliminated from 0.06 to 0.00 ppm and on the other hand, about 42.6 percent (of 118.65 to 66.06 ppm) for high concentration decreased using C. zizanioides with Bacillus sp. The use of C zizanioides associated with P. aeruginosa was also able to eliminate totally low concentration Cr in textile wastewater (0.08 to 0.00 ppm) and about 69.2 percent (158.76 to 48.9 ppm) of the high Cr concentration. Elimination of Cu from wastewater was 74.4% (0.48 to 0.12) and 55.7% (61.34 to 27.16 ppm) for the treatment using C. zizanioides with Bacillus sp. at a low and high level of concentrations respectively. Meanwhile, combined C. zizanioides with Pseudomonas aeruginosa absorb the Cu 100% (0.36 to 0.00 ppm) and 65% (64.93 to 22.77 ppm) for wastewater with low and high concentrations of Cu respectively. Combination of C. zizanioides, Bacillus sp., and Pseudomonas aeruginosa are fruitful in heavy metals containing wastewater remediation.

Bioimmobilization and transformation of chromium and cadmium in the fungi-microalgae symbiotic system

Microalgae and fungi in the fungi-microalgae symbiotic system(FMSS) can solve the problems of deep purification of heavy metals in wastewater and harvesting of microalgae cell by synergistic interaction. Therefore, it is of great significance to use the FMSS for remediation of heavy metal pollution. However, at present, the immobilization and transformation mechanism of heavy metals in the FMSS is not clear, which limits the development and industrial application of the FMSS with high adsorption performance, high selectivity, and high tolerance. In this study, the FMSS constructed using Aspergillus funigatus and Synechocystis sp. PCC6803, was used as the research object to explore heavy metal adsorption performance. Under optimal conditions, the adsorption efficiencies of Cd(II) and Cr(VI) were as high as 90.02% and 80.03%, respectively. The adsorption process was controlled by both internal and external diffusion. Extracellular absorption was dominant, and intracellular absorption was secondary. XRD, XPS, SEM-EDX and TEM-EDX results revealed that ionic crystals and precipitates (Cd(OH)2, CdCO3, calcium oxalate crystals, Cr(OH)3, Cr2O3, and CrCl3) were formed after adsorption. The adsorption of Cr(VI) involved the reduction of Cr(VI). Functional groups, such as amino, carboxyl, aldehyde, and ether groups, on the cell surface also interact with heavy metal ions. To summarize, by constructing the FMSS, optimizing the symbiosis conditions, exploring the adsorption and accumulation rules of Cd(II) and Cr(VI) inside and outside the cells in the system, and revealing the molecular response mechanism, we were able to establish a theoretical basis for further understanding the interaction between the FMSS and heavy metals.

Preparation and Application of Graphene–Based Materials for Heavy Metal Removal in Tobacco Industry: A Review

Heavy metals are nondegradable in the natural environment and harmful to the ecological system and human beings, causing an increased environmental pollution problem. It is required to remove heavy metals from wastewater urgently. Up until now, various methods have been involved in the heavy metal removals, such as chemical precipitation, chemical reduction, electrochemical, membrane separation, ion exchange, biological, and adsorption methods. Among them, adsorption by graphene–based materials has attracted much more attentions for the removal of heavy metals from wastewater systems in recent years, arising due to their large specific surface area, high adsorption capacity, high removal efficiency, and good recyclability. Therefore, it is quite important to review the heavy metal removal with the graphene–based material. In this review, we have summarized the physicochemical property and preparation methods of graphene and their adsorption property to heavy metals. The influencing parameters for the removal of heavy metals by graphene–based materials have been discussed. In addition, the modification of graphene–based materials to enhance their adsorption capability for heavy metal removal is also reviewed. The heavy metal removal by modified graphene–based materials in the tobacco industry has been especially described in detail. Finally, the future trend for graphene–based materials in the field of heavy metal wastewater treatment is proposed. This knowledge will have great impacts on the field and facilitate the researchers to seek the new functionalization method for graphene–based materials with high adsorption capacity to heavy metals in the tobacco industry in the future.

Programmable and low-cost biohybrid membrane for efficient heavy metal removal from water

Heavy metal pollution in rivers and lakes from industrial development poses great challenges to environmental remediation, especially of low-concentration metal ions. Current technologies for removing low-concentration heavy metal ions are typically expensive, and there is therefore an urgent need to develop new strategies. Low-cost microbial amyloid nanofibers (MAN) have demonstrated excellent abilities in removing heavy metal ions. In this study, we used synthetic biology strategies to design programmable MAN in silico and create artificial MAN for biohybrid membrane preparation. It was found that MAN could be largely produced and self-assembled, and it exhibited a removal rate of more than 98 % for 50 mg/L lead ions. Furthermore, genetic edits of MAN with functional peptides endowed the specific binding ability to heavy metals even at 1 mg/L. Impressively, biohybrid membranes using activated carbon as the supporting material based on programmable MAN showed long lifecycles and low costs in scale-up water purification systems. This study provides a programmable and low-cost strategy for the efficient treatment of heavy metal wastewater.

Adsorption of Heavy Metal Ions Copper, Cadmium and Nickel by Microcystis aeruginosa.

To investigate the treatment effect of algae biosorbent on heavy metal wastewater, in this paper, the adsorption effect of M. aeruginosa powder on heavy metal ions copper, cadmium and nickel was investigated using the uniform experimental method, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and TG-DSC comprehensive thermal analysis. The experimental results showed that the initial concentration of copper ion solution was 25 mg/L, the temperature was 30 °C, the pH value was 8 and the adsorption time was 5 h, which was the best condition for the removal of copper ions by algae powder adsorption, and the removal rate was 83.24%. The initial concentration of cadmium ion solution was 5 mg/L, the temperature was 35 °C, the pH value was 8 and the adsorption time was 4 h, which was the best condition for the adsorption of cadmium ion by algae powder, and the removal rate was 92.00%. The initial nickel ion solution concentration of 15 mg/L, temperature of 35 °C, pH value of 7 and adsorption time of 1 h were the best conditions for the adsorption of nickel ions by algae powder, and the removal rate was 88.67%. The spatial structure of algae powder changed obviously before and after adsorbing heavy metals. The functional groups such as amino and phosphate groups on the cell wall of M. aeruginosa enhanced the adsorption effect of heavy metal ions copper, cadmium and nickel. Additionally, M. aeruginosa adsorption of heavy metal ions copper, cadmium, nickel is an exothermic process. The above experiments show that M. aeruginosa can be used as a biological adsorbent to remove heavy metals, which lays a theoretical foundation for the subsequent treatment of heavy metal pollution by algae.

Activated sludge process enabling highly efficient removal of heavy metal in wastewater.

Activated sludge process was a low-cost alternative method compared to the conventional physicochemical process for the treatment of heavy metal-containing wastewater. In the present study, the removal efficiency of Pb2+, Cu2+, and Ni2+ from wastewater by a sequencing batch reactor (SBR) activated sludge system was investigated, and the mechanism was revealed by static adsorption experiment of activated sludge. The results showed that the activated sludge in the SBR system was effective in removing Pb2+ and Cu2+ from wastewater at 10mg·L-1 initial concentration, with a removal efficiency of 83.1 ~ 90.0% for Pb2+ and 74.3 ~ 80.6% for Cu2+, respectively. However, the removal efficiency for Ni2+ was only 0 ~ 6.2%. Static adsorption experiments showed that the adsorption capacity of activated sludge for three heavy metals was shown as Pb2+ > Cu2+ > Ni2+. When the initial concentration was 20mg·L-1, the equilibrium adsorption capacity of activated sludge for Pb2+, Cu2+, and Ni2+ was 18.35mg·g-1, 17.06mg·g-1, and 8.37mg·g-1, respectively. The main adsorption mechanisms for Pb2+ and Cu2+ were ligand exchange, electrostatic adsorption, and surface organic complexation processes, but Ni2+ removal mechanism mainly included electrostatic adsorption and surface organic complexation processes, showing that Ni2+ removal was inhibited in the presence of Pb2+ and Cu2+. The physicochemical properties and microbial diversity of activated sludge were greatly affected by the heavy metals in the SBR system, and genus Rhodobacter was found to be dominant bacteria enabling resistance to heavy metal ions.

Removal of Cr(VI) from aqueous solutions by nZVI-loaded sludge-derived biochar: performance and mechanism.

With the rapid development of highland railways in China, a large amount of heavy metal wastewater was inevitably generated during the manufacturing process of alloy materials required for railway construction. In this paper, pyrolysis of municipal sludge was followed by ball milling to obtain ball milling sludge-derived biochar(SDBC), and then nZVI-loaded SDBC materials (nZVI@SDBC) were prepared by liquid-phase reduction. The effects of different factors on the Cr(VI) removal were investigated. The maximum Cr(VI) adsorption capacity of nZVI@SDBC(2:1) was 178.05 mg/g. The Cr(VI) removal process could be fitted by the Langmuir isotherm and pseudo-second-order kinetic model. The Cr(VI) removal mechanism mainly included complexation, reduction, electrostatic interaction, and coprecipitation. The Cr(VI) removal by nZVI@SDBC(2:1) was maintained at over 90% after five replicate experiments. nZVI@SDBC(2:1) was capable of removing most of the Cr(VI) from real electroplating wastewater. The cost of using nZVI@SDBC(2:1) to remove 1 m3of actual wastewater is approximately325.7162 USD/m3.This workprovided a new ideafor thesolutionof Cr(VI)-containingwastewater from the production of railway materials.

The Capacity of Heavy Metal Remediation by Cyperus alternifolius, Chrysopogon zizanioides (L.) Roberty, and Aloe vera (L.) Burm.f. under Industrial and Urban Wastewater Treatment

Abstract Urban wastewater (UWW) and industrial wastewater (IWW) release lots of heavy metals into the environment, leading to various risks regarding agricultural production, food quality, human and animal health, and environmental safety. Phytoremediation is known as one of the best and most affordable strategies to eliminate or reduce heavy metals in different environments. This study examined the phytoremediation ability of three plant species (Cyperus alternifolius, Chrysopogon zizanioides (L.) Roberty, and Aloe vera (L.) Burm.f) to absorb heavy metals of Zn, Cr, Pb, Cu, Mn, Ni, and Mg from the contaminated soil with UWW and IWW for 14 months. The result showed that all three examined plants reduced heavy metal pollution of the soil using the phytostabilization method. The metal accumulation index (MAI) of the root in V. zizanioides was higher than C. alternifolius and A. vera. While MAI of the shoot in A. vera was higher than C. zizanioides and C. alternifolius. Based on the results, it is suggested to cultivate C. zizanioides and A. vera in the polluted areas to decrease the amount of soil contaminants and create a green belt. Keywords: Heavy metal, Industrial and urban wastewater, Metal accumulation index, Phytoremediation, Phytostabilization

Performance assessment of constructed wetland-microbial fuel cell for treatment of mariculture wastewater containing heavy metals

Mariculture wastewater poses potential risks to the sustainability of the coastal environment. In this study, different types of constructed wetland-microbial fuel cells (CW-MFC), including up-flow CW-MFC (UCW-MFC), down-flow CW-MFC (DCW-MFC), and hybrid up-flow/down-flow CW-MFCs (HCW-MFC) were constructed to evaluate their efficiency to treat mariculture wastewater containing heavy metals (Cu and Zn). The results showed that both the UCW-MFC and DCW-MFC operated with aeration demonstrated better removal performance for conventional pollutants. The presence of heavy metals in wastewater reduced the removal of NH4+-N and total inorganic nitrogen, but had no significant effect on the removal of chemical oxygen demand (COD) and total phosphorus (TP). The HCW-MFC had better removal performance than the UCW-MFC and DCW-MFC, especially when treating heavy metal containing wastewater. All systems had excellent removal performance for (Cu2+ and Zn2+), resulting in concentrations below the first discharge standard. All the systems produced S2-, which could react with Cu2+/Zn2+ to form CuS/ZnS, leading to the removal of heavy metals from the systems. The average output voltage of the three systems was 561.64 ± 16.64 mV for UCW-MFC, 634.73 ± 9.33 mV for DCW-MFC, and 1074.88 ± 49.90 mV for HCW-MFC, respectively. In addition, the maximum power density (PAmax) increased by 160.81 % and 44.16 % in HCW-MFC compared to those of UCW-MFC and DCW-MFC systems, respectively. Further, connecting the three systems successfully derived a light-emitting diode to emit light, which indicated that CW-MFC systems have promising application prospects for both pollutant removal as well as energy recycling.

Synthesis and study of adsorption for ion Cu(II) from aqueous solution by chitosan beads

Chitosan beads were synthesized by sodium lauryl ether sulfate (SLES) gelation process and alkaline treatment. The characterization and morphology of chitosan beads were investigated by Fourier-transform infrared spectroscopy technique (FT-IR), optical microscope and scanning electron microscope technique (SEM). The influence of NaOH concentration, pH, reaction time and adsorption isotherm was studied. Langmuir and Freundlich adsorption models were applied to describe isothermal lines. The alkalization process enhanced significantly Cu(II) adsorption capacity of CS/SLES/NaOH to 4489,6 mg/g. The results showed that chitosan beads would be a promising material to remove heavy metals in wastewater.

A novel electrocoagulation process with centrifugal electrodes for wastewater treatment: Electrochemical behavior of anode and kinetics of heavy metal removal

Anodic passivation is a key problem to impair the efficiency of in the electrocoagulation (EC) process. Process intensification of EC has attracted increasingly greater attention. In this work, a novel centrifugal electrode reactor was designed and applied in EC process to enhance the treatment of simulated heavy metal wastewater using aluminum anode. Results showed that the removal efficiency of heavy metals was significantly improved by the centrifugal electrodes, compared with the stationary electrodes. Electrochemical behavior of centrifugal electrodes was analyzed by an improved rotating disk electrode system. Anodic polarization behavior of aluminium showed a typical characteristic of dissolution in centrifugal electrodes, rather than passivation in static condition. Anode dissolution was controlled by the diffusion of Cl− ion that was enhanced by centrifugal electrodes. Thus, anode passivation was reduced. In addition, the kinetics analysis indicated that the removal of heavy metals in EC by centrifugal electrodes conformed to Variable-Order-Kinetic (VOK) model based on the Langmuir adsorption.

Denitrification-induced carbonate precipitation by bio-composite material with Pseudomonas aeruginosa for simultaneous nitrate and cadmium remediation

The presence of nitrate and heavy metals in wastewater are common but serious problem throughout the world. Thus, considering their toxicity, in the present study, denitrification-induced carbonate precipitation by Pseudomonas aeruginosa was researched in the simultaneous removal of nitrate and cadmium. Prior to the experimentation, P. aeruginosa was immobilized in bio-composite material (BCM) comprised of varying concentration of bentonite and alginate. The BCM with formulation 3% (m/v) bentonite and 1% (m/v) alginate (BA3) was found to more sustained and controlled release of bacterial cells in the solution, thus was utilized for bioremediation studies. The BCM with formulation BA3 effectively removed nitrate and Cd2+ by 93 and 74% (m/m), when their initial concentrations were 100 and 5 mg/L, respectively, in 24 h. Further, the P. aeruginosa cells inside the BCM were able to produce nitrite reductase and nitrate reductase in the spiked solution. Based on experimental results, denitrification by BCM reduced nitrate, generated alkalinity, and formed bicarbonate ions that, when reacting with Cd2+ ions, formed cadmium carbonate. The research presented in this study is important to know the significance of bio-composite material with denitrifiers in actively producing key enzymes of denitrification leading to simultaneous removal of nitrate and heavy metal from water.

Electrochemical Responses and Microbial Community Shift of Electroactive Biofilm to Acidity Stress in Microbial Fuel Cells

Microbial community changes in response to acid stress in microbial fuel cells (MFCs) were studied. Acid mine drainage (AMD) wastewater is usually difficult to treat because of the high concentration of sulfate and heavy metals. MFCs, which have multiple functions based on the principle of synergistically treating organic and heavy metal wastewater while generating electrical energy, represent a promising direction for the development of new heavy metal wastewater treatment technologies. Maintaining a neutral or slightly alkaline wastewater pH in MFCs facilitates the growth of electricity-producing microorganisms in the anode chamber. Studies on the response of anode electroactive biofilms to acidic pH stress and its correlation with changes in AMD treatment capacity have not been reported. Results showed that the anolyte pH of 4.0 and 5.0 affected the electron output capacity of the electrogenic microbial community in the MFCs. In contrast, MFCs working at an anolyte pH of 6.0 exhibited a high efficiency of chemical energy conversion to electrical energy. The microbial abundance and microbial diversity of the electroactive biofilm were significantly affected by the H+ concentration in the medium when the ambient acidity was continuously reduced. The classic exoelectrogen Geobacter decreased gradually with the increase of H+ concentration in the medium. In addition, Cu2+ was recovered from the simulated AMD in the MFCs cathodic chambers at low anode pH, but the removal rate of Cu2+ decreased as the pH of the anode environment decreased. At 48 h, 86.2% of Cu2+ was removed from the MFCs cathode solution at pH 5.0, while the removal rate of Cu2+ from the MFCs cathode solution at pH 4.0 was 84.2%. Trace amounts of Cu2O and Cu3(OH)2[CO3]2 were present on the cathode, which reduced the amount of Cu2+ that precipitated on the cathode carbon cloth. Conversely, the concentration of Cu2+ in the catholyte of MFCs with electroactive biofilm at pH 6.0 decreased rapidly, and by 36 h, no detectable Cu2+ was present in the cathodic solution. This study will provide researchers with valuable information regarding the optimal pH for resource recovery with MFCs.

Health risks of industrial wastewater heavy metals based on improved grey water footprint model

The Belt and Road Initiative (B&RI) promotes cooperation among participating countries from multiple perspectives, especially infrastructure construction and investment, which is a critical driving force for industrial activities. The accelerated industrial development would inevitably cause environmental consequences in participants, in which pollution and related health risks caused by industrial heavy metal emissions were among the most concerned. In this study, an improved grey water footprint of industrial heavy metal emissions (GWFHMs) was proposed from the perspective of health risks to address the limitation of conventional GWF in reflecting their properties and impacts of pollutants, such as the health toxicity of heavy metals. Meanwhile, the water pollution level of GWFHMs (WPLHMs) was estimated to reveal the degree of aquatic industrial heavy metal pollution concerning health risks. We use China, the B&RI member with severe heavy metal pollution, as a case. The spatial distribution of GWFHMs (at the resolution of 1 km × 1 km) and WPLHMs (at the watershed level) monthly during 1998–2015 were uncovered. Results show that the GWFHMs of China have significantly decreased in this period, but WPLHMs in some regions are still high due to cyclical fluctuations in heavy metal emissions and water runoffs. The middle reaches of the Yangtze River had the highest GWFHMs but relatively low WPLHMs due to abundant water runoffs. In contrast, the Liaohe watersheds in north China had the highest WPLHMs due to water shortage, especially in dry seasons (from December to February). This study reveals critical periods and hotspot regions for heavy metal pollution, which would support decision-making for delicacy industrial heavy metal control measures concerning human health in B&RI countries. In addition to direct emission control, production activities and the following industrial wastewater emissions should also consider the time variation of water runoffs in each region, which would contribute to keeping the health risks of industrial heavy metal emissions within acceptable limits.