Metal-laden Wastewater Research Articles

COMPETITIVE ADSORPTION OF Fe2+, Pb2+, AND Zn2+ IONS FROM MULTI-METAL ION SOLUTION ON AMMONIUM OXALATE MODIFIED KAOLINITE CLAY

The competitive adsorption of Fe2+, Pb2+, and Zn2+ ions from mixed multi-metal aqueous solution on ammonium oxalate-modified kaolinite clay (AOK) was studied to determine the competitive influence of the metal ions on the adsorption of other metal ions. The kaolinite clay was modified by treating it with 0.2 M of ammonium oxalate solution at 50 oC. The adsorption of the metal ions was carried out using initial concentrations of 20, 35, and 50 mg L-1 in both the single and multi-metal ion solutions. The results revealed that at a low concentration of 20 mg L-1, the adsorption capacity for the uptake of the metal ions on AOK is non-competitive. At higher adsorbate concentrations of 35 and 50 mg L-1, the single to multi-metal ions equilibrium adsorption capacity ratio value obtained was less than 1. This indicated an antagonistic effect on competing for the adsorption site in the following order: Pb2+ (9.9 mg g-1) > Fe2+ (3.85 mg g-1) > Zn2+ (2.85 mg g-1). The outcome revealed that ammonium oxalate-modified kaolinite is a potential adsorbent for remediation of multi-heavy metal-laden wastewater with preferentially higher affinity for Pb2+ ions than other metal ions.

Optimization of trypan blue and brilliant green dyes photocatalytic degradation and adsorption of lead(II) and chromium (VI) heavy metal ions by copper sulfide nanoparticles

The use of nanoparticles for to remove organic pollutants and heavy metals is a rapidly expanding field in environmental sciences. However, process optimization for practical, real-world applications is still underexplored. In this work, copper sulfide nanoparticles prepared from a single-source precursor were characterized using SEM, TEM, EDX, FTIR, and UV-visible spectroscopy. The copper sulfide nanoparticles demonstrated high photocatalytic degradation efficiency of trypan blue (TB) and brilliant green (BG) dyes. The as-prepared nanoparticles efficiently removed lead(II) (Pb2+) and chromium(VI) (Cr6+) ions. Response surface methodology (RSM) with a Box-Behnken design (BBD) was employed to optimize reaction time, pH, and nanoparticle dosage. The optimal conditions for TB degradation were pH 10.91, 77.46 minutes, and 4.999 g/L, while for BG, they were pH 3, 70 minutes, and 5 g/L. For Pb2+ removal, optimal conditions were pH 7.06, 100.38 minutes, and 0.94 g/L, and for Cr6+ removal, pH 3.03, 168.20 minutes, and 0.98 g/L. Under these optimal conditions, CuS nanoparticles achieved up to 99.35% degradation for TB, 100% for BG, 100% removal for Pb2+, and 98.54% for Cr6+. ANOVA confirmed the models' significance, with high regression coefficients (R²: 0.9852 for BG, 0.9846 for TB, 0.9980 for Pb2+, and 0.9901 for Cr6+). The CuS photocatalyst remained stable over three reuse cycles, with minimal efficiency reduction (8.88% for TB and 19.01% for BG). This study demonstrates the effectiveness of copper sulfide nanoparticles in environmental remediation and highlights the practicality of using RSM to optimize nanoparticles as efficient materials to remove organic dyes and heavy metal-laden wastewater.

Screening and performance optimization of fungi for heavy metal adsorption in electrolytes.

The resource recovery and reuse of precious metal-laden wastewater is widely recognized as crucial for sustainable development. Superalloy electrolytes, produced through the electrolysis of superalloy scrap, contain significant quantities of precious metal ions, thereby possessing substantial potential for recovery value. This study first explores the feasibility of utilizing fungi to treat Superalloy electrolytes. Five fungi resistant to high concentrations of heavy metals in electrolytes (mainly containing Co, Cr, Mo, Re, and Ni) were screened from the soil of a mining area to evaluate their adsorption characteristics. All five fungi were identified by ITS sequencing, and among them, Paecilomyces lilacinus showed the best adsorption performance for the five heavy metals; therefore, we conducted further research on its adsorption characteristics. The best adsorption effect of Co, Cr, Mo, Re, and Ni was 37.09, 64.41, 47.87, 41.59, and 25.38%, respectively, under the conditions of pH 5, time 1 h, dosage 26.67 g/L, temperature 25-30°C, and an initial metal concentration that was diluted fivefold in the electrolyte. The biosorption of Co, Mo, Re, and Ni was better matched by the Langmuir model than by the Freundlich model, while Cr displayed the opposite pattern, showing that the adsorption process of P. lilacinus for the five heavy metals is not a single adsorption mechanism, but may involve a multi-step adsorption process. The kinetics study showed that the quasi-second-order model fitted better than the quasi-first-order model, indicating that chemical adsorption was the main adsorption process of the five heavy metals in P. lilacinus. Fourier transform infrared spectroscopy revealed that the relevant active groups, i.e., hydroxyl (-OH), amino (-NH2), amide (- CONH2), carbonyl (-C = O), carboxyl (-COOH), and phosphate (PO43-), participated in the adsorption process. This study emphasized the potential application of P. lilacinus in the treatment of industrial wastewater with extremely complex background values.

Biodegradation of sulfate and elimination of heavy metals by immobilized-microbial bioaugmentation coupled with anaerobic membrane bioreactor

Sulfate-rich metal-laden wastewater (SRMLW) shows a significant threat on the ecological environment and human health. Sulfate-reducing bacteria (SRB) can remove sulfate from wastewater in anaerobic membrane bioreactor (AnMBR). This study constructed recombinant genetic engineered SRB (rSRB) and investigated the sulfate and heavy metals removal efficiency for treating SRMLW by immobilized-microbial bioaugmentation using rSRB (IMrSRB) coupled with AnMBR (Bio-AnMBR). The results show that Bio-AnMBR removed sulfate (99.4%) from SRMLW by upregulating key genes (Sat, DsrAB, AprAB, QmoABC, DsrC and DsrMKJOP) and enzymes (APS reductase, Dissimilatory sulfite reductase, Trithionate reductase and Thiosulfate reductase) in dissimilatory sulfite and sulfate respiration processes. Bio-AnMBR achieved synergistic biodegradation of sulfate and nitrogen by stimulating the activity of these bacteria related to the conversion of nitrogen and sulfate. Microbial analysis indicated that the relatively high abundance of rSRB (79.2%) and functional genes (70.1%) upregulated the activities of key enzymes associated with sulfate metabolism system, thus increasing the production of S (66.4 mg/L) and H2S (23.8 mg/L). Bio-AnMBR significantly improved the tolerance to heavy metals by increasing concentrations of CO32–, S2-, and HS-, which was configured to reduce heavy metals (95.6%) via precipitation of metal sulfide (81.3 mg/L), metal carbonates (30.7 mg/L) and metal hydroxides (18.7 mg/L). Bio-AnMBR increased system stability, shorted hydraulic retention time (HRT), decreased the production of soluble microbial products (SMP), extracellular polymeric substances (EPS) and waste-sludge production (WSP), as well as improved effluent quality. In conclusion, data in this study indicate that application of Bio-AnMBR is a feasible strategy for the treatment of SRMLW.

Investigation of rhamnolipid addition on the microbial fuel cell performance and heavy metal capture in metal laden wastewater

Wastewater loaded with metals was investigated in this study for their remediation, it was used a dual chamber microbial fuel cell aided with rhamnolipid biosurfactant at 100 mg/L and 500 mg/L in the anode and inoculated with Shewanella oneidensis MR-1, and K3Fe(CN)6 50 mM in 100 mM of phosphate buffer solution was used in the cathode chamber. The bacteria demonstrated a higher specific growth rate of 0.11 h−1 and better biofilm formation analyzed by the SEM. The highest power density was 13.9 mW/m2 determined at 100 mg/L of rhamnolipid. Furthermore, the internal resistance for the same concentration was 2.8 Ω, which indicates the low resistance of electrons through the external circuit. Metal removal had the highest removal of 60.2 %, 89.5 %, 83.9 %, 90.6 %, and 47.9 % for Cu, Mg, Mn, Zn, and Na, respectively, corresponding to the wastewater coupled with rhamnolipid at concentration of 500 mg/L. Furthermore, COD removal was 28.7 % and 17.0 % for biosurfactant concentrations of 100 mg/L and 500 mg/L, respectively. These results demonstrated the high efficiency of microbial fuel cells with wastewater loaded with rhamnolipid.

Integrating Ultrafiltration Membranes with Flocculation and Activated Carbon Pretreatment Processes for Membrane Fouling Mitigation and Metal Ion Removal from Wastewater.

The presence of metal ions in an aqueous medium is an ongoing challenge throughout the world. Processes employed for metal ion removal are developed continuously with the integration of these processes taking center stage. Herein, an integrated system consisting of flocculation, activated carbon (AC), and an ultrafiltration (UF) membrane was assessed for the removal of multiple metal ions contained in wastewater generated from a university chemistry research laboratory. The quality of the wastewater was established before and further determined after treatment with inductively coupled plasma optical emission spectrometry (ICP-OES) for metal content, total dissolved solids (TDS), turbidity, electrical conductivity (EC), and pH. Assessing the spent AC indicated minimal structural changes, indicating a potential for further reuse; for instance, the BET for both the pristine and spent AC exhibited type I isotherms with a mesoporous structure, indicating no major structural changes due to metal complexation. The relative performance of the integrated system indicated that the use of flocculation improved the water quality of metal-laden wastewater for safe disposal. The integrated treatment systems exhibited high removal efficiencies between 80 and 99.99% for all the metal ions except for Mn (<0.008 mg L-1) and Cr (<0.016 mg L-1) both at ca. 70%, indicative of the positive influence of the polyelectrolyte in the treatment process. The fabricated UiO-66-NH2@GO membranes (Z4 and Z5) exhibited high fouling resistance and reusability potential as well as relatively high pure water flux. Consequently, the integrated process employed for the treatment of laboratory metal-containing wastewater is promising as a generic approach to improving the quality of metal-containing wastewater to meet the standards of discharging limits in South Africa.

Heavy Metal Removal from Aqueous Solutions Using Biomaterials and/or Functional Composites: Recent Advances and the Way Forward in Wastewater Treatment Using Digitalization

Due to its low cost, over the past decades, biosorption technology has been extensively carried out to treat heavy metal-laden wastewater using biosorbents. Recent studies on heavy metal biosorption mechanisms and the simulation of mathematical modeling on the biosorption process have enhanced scientific understanding about the binding between target metal cations and the functional group on different surfaces of biomasses as a biosorbent. However, so far, none have provided an overview of mechanistic studies on heavy metal removal from aqueous solutions using inexpensive biosorbents. To close this knowledge gap, this article discusses the applicability of the surface complexation (SC) model for biosorption of a target pollutant. Insightful ideas and directions of future research in wastewater treatment using digital technologies are also presented. It was conclusive from a literature survey of 115 articles (1987–2023) that Aspergillus niger, Penicillium chrysogenum, and Rhizopus nigricans represent biomaterials that have substantial adsorption capacities, up to 200 mg of Au(I)/g, 142 mg of Th/g, and 166 mg of Pb(II)/g, respectively. The metal-binding mechanisms involved include ion exchange, surface complexation, and micro-precipitation. Ion exchange is the only mechanisms that play key roles in sequestering heavy metal using fungal cells with chitin and chitosan. X-ray energy dispersion (XED) and scanning electron microscopy (SEM) analysis were used to evaluate biosorption mechanisms of the inorganic pollutants using physico-chemical characterization on the cell surfaces of the biomass. As metal removal by the biosorbent is affected by its surface properties, surface complexation also occurs. The affinity of the surface complexation depends on the type of functional groups such as phosphate, carboxyl, and amine.

Sulfur disproportionation realizes an organic-free sulfidogenic process for sustainable treatment of acid mine drainage

Biological sulfidogenic processes (BSPs) have been considered effective biotechnologies for the treatment of organic-deficit acid mine drainage (AMD) and heavy metal recovery. However, high-rate sulfide production relies on the continuous addition of exogenous organic substrates as electron donors to facilitate dissimilatory sulfate reduction, which substantially increases the operational cost and CO2 emission and also limits the wide application of BSPs in AMD treatment. In this study, we proposed a novel chemoautotrophic elemental sulfur disproportionation (SD) process as an alternative to conventional BSPs for treating AMD, in which sulfur-disproportionating bacteria (SDB) disproportionates sulfur to sulfide and sulfate without organic substrate supplementation. During the 393-day lab-scale test, we observed that the sulfur-disproportionating reactor (SDR) achieved a stable high-rate sulfide production, with a maximal rate of 21.10 mg S/L-h at an organic-substrate-free condition. This high rate of sulfide production suggested that the SD process could provide sufficient sulfide to precipitate metal ions from AMD. Thermodynamics analysis and batch tests further revealed that alkalinity rather than sulfate was the critical factor influencing the SD process, suggesting that the abundant sulfate present in AMD would not inhibit the SD process. The critical condition of SD in the SDR was therefore determined. Microbial community analysis showed that Dissulfurimicrobium sp. was the dominant SDB during the long-term operation regardless of dynamic sulfate and/or alkalinity concentrations, which provides evidence that SDB can be employed for sustainable and high-rate sulfide production for engineering purposes. A multi-stage AMD treatment system equipped with a SDR removed over 99% of the influent metals (i.e., Fe, Al, Zn, Cu, Pb) from AMD except for Mn. This study demonstrated that the novel SD process is a green and promising biotechnology for the sustainable treatment of organic-deficient metal-laden wastewater, such as AMD.

Reusable self-floating carriers recover heavy metals from industrial wastewater through heterogeneous nucleation for resource reuse

Coagulation-flocculation in industrial wastewater treatment drives environmental pollution from landfilling heavy metal-laden sludge. Efficient separation of the sludge is crucial for cost-effective metal recovery. This study explored a new separation method of Cu2+, Ni2+, Zn2+ and Cr3+ via self-floating metal hydroxides assisted by hollow glass microsphere (HGM) carriers. The amount of OH− was stoichiometric to the positive charges of metal ions, mixed with 1 mg mL−1 HGM, causing metal hydroxides to attach to HGM surface via heterogeneous nucleation. The self-floating system removed 37.5% and 14.0% more metals than sedimentation at 50 and 200 mg L−1 metal concentrations. HGM additions increased the particle size of metal hydroxides by up to 12.5 times to that of HGM at 18.8 ± 1.1 µm, benefiting their solid-liquid separation. By pumping the wastewater downward in column reactor at velocities equal to or less than the self-floating sludge, 96.4% metals were removed in continuous flow. The recovery rates of HGM and metals reached 92.0 ± 2.2% and 92.7 ± 3.2%, and the concentration of the recovered metal reached 19,339 ± 394 mg L−1 for potential reutilization in industrial electroplating. This research investigated a new separation strategy based on solid self-flotation for sustainable treatment of metal-laden wastewater.

Adaptive response mechanisms of granular and flocculent sulfate-reducing sludge toward acidic multi–metal–laden wastewater

Dissimilatory sulfate reduction–based processes have long been a viable option for treating acidic metal-laden wastewater (AMW). Such processes can be optimized through enhancing sulfidogenic activity and the microbial consortia's resilience against a harsh environment. This study investigated how granular and flocculent sulfate-reducing bacteria (SRB) sludge respond to AMW as well as the mechanisms through which they adapt to the wastewater, with particular focuses on the stability of the sulfidogenic activities, metal removal, and the bacteria's resistance over the long-term: the flocculent SRB lost more than 50% of their treatment capacity after 35 days of treating AMW with the presence of Cd2+, Cu2+, Zn2+, and Ni2+ at 30 mg/L each, under pH = 4.5. In contrast, the granular SRB maintained its metal removal rate at 91% throughout the 161-day trial. Despite the SRB abundance remaining at approximate 40%, organics-partial oxidizing genera (Desulfobulbus and Desulfobacter) began to dominate due to their kinetic advantage. The extracellular glycosyl compositions were revealed to be critical for the stability of the granular structure and microbial activity as the extracellular proteins disintegrated irreversible. Usage the molecular dynamic simulation, the mobility of the metal ions in the SRB granular system was suppressed by the presence of a more diverse glycosyl composition compared with the flocculent system (10–50% diffusion coefficients differences). All of the identified glycosyls (especially xylose and rhamnose) exhibited strong interactions with Cu2+ (-470 kJ mol−1), while the maximum binding strength of Cd2+ to glycosyls was greater than -40 kJ mol−1, suggesting a low Cd2+complexation efficiency. The findings of this study shed light on the defensive mechanisms of SRB granules against multi-metal stress, and provide clues for efficient AMW treatment.

Efficient removal of EDTA-chelated Cu(II) by zero-valent iron and peroxydisulfate: Mutual activation process

• Enhanced Cu(II)-EDTA separation by ZVI due to addition of peroxydisulfate. • Removal of 77.2% of Cu and 55.2% of TOC in Cu-EDTA solution by ZVI/PDS system. • Elucidating Cu-EDTA removal mechanism by ZVI/PDS system. • ZVI not only activates PDS to destroy organic ligands but also generate Fe(III) to displace Cu(II) from Cu(II)-EDTA. Metal complexes pose a significant challenge to remediate heavy metal-laden wastewater by classical techniques due to their stable chelating structure. The application of zero-valent iron (ZVI) to activate peroxidized sulphate (PDS) has been synergistically (ZVI/PDS) proposed for effective removal of EDTA-chelated Cu from aqueous media. In contrast to ZVI alone, ZVI/PDS process improved the EDTA-chelated Cu or total organic carbon (TOC) removal rate by 6.2 or 7.8 fold, respectively. Factors including Cu/EDTA molar ratio, initial pH, ZVI dosage, and PDS dosage affect the removal efficiency of complexed copper. The formation of Fe ions and sulfate radicals in the solution strengthens the removal effect of zero-valent iron on EDTA complexed Cu. After the reaction, ZVI EDS, XRD, and XPS analyses revealed that Cu was eventually reduced to Cu 0 and immobilized on the ZVI surface. A possible decomposition mechanism followed by a Cu reduction was also proposed. In conclusion, this study presents new perspectives for the removal of complex heavy metals from contaminated water.

Target-directed design of dual-functional Z-scheme AgIn5S8/SnS2 heterojunction for Pb(II) capture and photocatalytic reduction of Cr(VI): Performance and mechanism insight

• Dual-functional Z-scheme AgIn 5 S 8 /SnS 2 heterojunction was target-directed designed. • AgIn 5 S 8 /SnS 2 has high adsorption capacity for Pb(II) capture. • AgIn 5 S 8 /SnS 2 shows superior photocatalytic activity for Cr(VI) reduction. • Pb(II) adsorption was attributed to S-Pb coordination and electrostatic attraction. • Z-scheme photocatalytic mechanism was based on internal electric field. Target-directed design and synthesis of dual-functional materials with superior adsorption for Pb(II) and photocatalytic activity for Cr(VI) reduction are challenging but of vital importance for heavy metal-laden wastewater remediation. In this work, dual-functional Z-scheme AgIn 5 S 8 /SnS 2 heterojunctions were designed according to hard-soft acid-base theory and band structure matching, and were synthesized by simple hydrothermal reaction. The AgIn 5 S 8 /SnS 2 has high adsorptive capacity for Pb(II) with almost 100% Pb(II) removal, and the adsorptive capacity of AgIn 5 S 8 /SnS 2 for Pb(II) is about 5 and 3.3 times that of AgIn 5 S 8 and SnS 2 , respectively. Moreover, AgIn 5 S 8 /SnS 2 shows outstanding visible-light photocatalytic performance for Cr(VI) reduction with 96% reduction efficiency. The XPS analysis, Zeta potential, DFT calculation reveal that S atoms are dominant adsorption sites, and the adsorption of Pb(II) is more favorable on AgIn 5 S 8 (3 1 1)/SnS 2 (1 0 1) than SnS 2 (1 0 1) or AgIn 5 S 8 (3 1 1) due to the remarkable coordination of S atoms with Pb(II) and strong electrostatic attraction. Furthermore, the photocatalytic mechanism of Z-scheme AgIn 5 S 8 /SnS 2 heterojunction for Cr(VI) reduction was identified and uncovered by experimental studies.

Adsorption of metal on pineapple leaf biochar: Key affecting factors, mechanism identification, and regeneration evaluation

Although tremendous works have been done on metal adsorption via biochar, mechanisms responsible for metal adsorption remain uncertain. This is the first work that provides direct evidence on the identification of Ni(II), Zn(II), and Cu(II) adsorption mechanisms on pineapple leaf biochar (PLB) using surface characteristics analyses, including X-ray photoelectron spectroscope (XPS), Fourier transform infrared spectroscope (FTIR), and scanning electron microscope with energy-dispersive X-ray spectroscope (SEM-EDS). From Langmuir isotherm fitting, the maximum adsorption capacity of PLB for Ni(II), Zn(II), and Cu(II) are 44.88, 46.00, and 53.14 mg g−1, respectively, surpassing all biochars reported in the literature. Findings of surface characterization techniques coupled with cation released during adsorption, cation exchange, and surface complexation mechanisms were proposed. PLB is reusable and remains sufficient adsorption capacity even six consecutive cycles via pressure cooker regeneration. With high regenerability and ultrahigh adsorption capacity, PLB defines itself as a promising adsorbent for future applications in metal-laden wastewater.

PH-dependent biological sulfidogenic processes for metal-laden wastewater treatment: Sulfate reduction or sulfur reduction?

Both biological sulfate reduction process and sulfur reduction process are attractive technologies for metal-laden wastewater treatment. However, the acidity stress of metal-laden wastewater could affect the sulfidogenic performance and the microbial community, weaken the stability, efficiency and cost-effectiveness of the biological sulfidogenic processes (BSP). In this study, long-term lab-scale trials were conducted with a sulfate-reducing bioreactor and a sulfur-reducing bioreactor to evaluate the effects of acidity on sulfidogenic activities and the microbial community of the BSP. In the 300-day trial, the sulfate-reducing bacteria (SRB)-driven BSP was stable in terms of sulfidogenic performance and microbial community with the decline of pH, while the sulfur-reducing bacteria (S0RB)-driven BSP achieved high-rate and low-cost sulfide production under neutral conditions but unstable under acidic conditions. With the decline of pH, the sulfide production rate (SPR) of the SRB-driven BSP stably increased from 30 to 83 mg S/L-h; while it decreased from 56 to 37 mg S/L-h in the S0RB-driven BSP with high fluctuation. The results of estimation were consistent with the thermodynamical calculations, in which the sulfur reduction process showed a better performance at pH 5–7, while the sulfate reduction process might gain more energy when pH<5. The stable sulfidogenic performance and microbial community diversity of the SRB-driven BSP could be attributed to the alkalinity produced in sulfate reduction to buffer the acidic stress. In comparison, the microbial community in the S0RB-driven BSP was significantly re-shaped by acidity stress, and the predominant sulfidogenic bacterium changed from Desulfovibrio at neutral condition, to Desulfurella at pH≤5.4. The stability of the microbial community significantly affected the SPR and the operational cost. Nevertheless, the organic consumption for sulfide production of the S0RB-driven BSP was still less than the SRB-driven BSP even in acidic conditions. Collectively, the S0RB-driven BSP was recommended under neutral or mild acid conditions, while the SRB-driven BSP was more suitable under fluctuating pH conditions, especially at low pH. Overall, this study presented the long-term performance of SRB- and S0RB-driven BSP under varying pH conditions, and provided guidance to determine the suitable BSP and operational cost for different metal-laden wastewater.

A pilot-scale sulfur-based sulfidogenic system for the treatment of Cu-laden electroplating wastewater using real domestic sewage as electron donor

Elemental sulfur (S0) reduction process has been demonstrated as an attractive and cost-efficient approach for metal-laden wastewater treatment in lab-scale studies. However, the system performance and stability have not been evaluated in pilot- or large-scale wastewater treatment. Especially, the sulfide production rate and microbial community structure may significantly vary from lab-scale system to pilot- or large-scale systems using real domestic sewage as carbon source, which brings questions to this novel technology. In this study, therefore, a pilot-scale sulfur-based sulfidogenic treatment system was newly developed and applied for the treatment of Cu-laden electroplating wastewaters using domestic sewage as carbon source. During the 175-d operation, >99.9% of Cu2+ (i.e., 5580 and 1187 mg Cu/L for two types of electroplating wastewaters) was efficiently removed by the biogenic hydrogen sulfide that produced through S0 reduction. Relatively high level of sulfide production (200 mg S/L) can be achieved by utilizing organics in raw domestic sewage, which was easily affected by the organic content and pH value of the domestic sewage. The long-term feeding of domestic sewage significantly re-shaped the microbial community in sulfur-reducing bioreactors. Compared to the reported lab-scale bioreactors, higher microbial community diversity was found in our pilot-scale bioreactors. The presence of hydrolytic, fermentative and sulfur-reducing bacteria was the critical factor for system stability. Accordingly, a two-step ecological interaction among fermentative and sulfur-reducing bacteria was newly proposed for sulfide production: biodegradable particulate organic carbon (BPOC) was firstly degraded to dissolved organic carbon (DOC) by the hydrolytic and fermentative bacteria. Then, sulfur-reducing bacteria utilized the total DOC (both DOC degraded from BPOC and the original DOC present in domestic sewage) as electron donor and reduced the S0 to sulfide. Afterwards, the sulfide precipitated Cu2+ in the post sedimentation tank. Compared with other reported technologies, the sulfur-based treatment system remarkable reduced the total chemical cost by 87.5‒99.6% for the same level of Cu2+ removal. Therefore, this pilot-scale study demonstrated that S0 reduction process can be a sustainable technology to generate sulfide for the co-treatment of Cu-laden electroplating wastewater and domestic sewage, achieving higher Cu2+removal and higher cost-effectiveness than the conventional technologies.

Adsorption of Fe , Pb , Zn and Cr ions from aqueous solutions using natural, ammonium oxalate and sodium hydroxide modified Kaolinite clay

In this paper, Fe2+ , Pb2+ , Zn2+ and Cr6+ ions removal from contaminated water with natural Nigerian kaolinite clay (AK-clay), and that removed with kaolinite clay modified with either ammonium oxalate (AK-AO) or sodium hydroxide (AK-S) were presented. The clay was characterized using X-Ray Diffractometry (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Brunanuer-EmmettTeller (BET) method. The parameters investigated include pH, adsorbent particle size, shaking speed, metal ion concentration and temperature. The optimum conditions were applied to the modified samples. Design-expert software was used to design the experimental conditions using Response Surface Methodology (RSM). The mineralogical characterization showed the purified 63 µm fraction of the clay as kaolin. Analysis of Variance shows the adsorption of the metal ions was statistically significant with p-valves &gt; 0.0001 at 95 % confidence limit. Pseudo second-order kinetic model was found to fit the adsorption data for all the metal ions. The adsorption of Fe2+ , Pb2+ and Cr6+ ions was best described by the Langmuir isotherm model, while Freundlich isotherm model best fitted the adsorption data for Zn2+ ion. Thermodynamic analysis of adsorption data shows the metal ions adsorption was spontaneous, endothermic and accompanied by positive entropy change. Compared to unmodified natural clay, AK-S clay increased adsorption capacity for Fe2+ , Pb2+ , Zn 2+ and Cr 6+ ions from 14.1 to 18.425 mg/g, 18.4 to 19.8 mg/g, 16.875 to 19.9 mg/g and 7.65 to 8.15 mg/g respectively. The AK2+ AO2+ clay increased the uptake of Fe ion from 14.1 to 17.35 mg/g with a slight increase for Zn ion (16.875 to 16.95 mg/g). The adsorption capacity of AK-clay for all the metal ions was enhanced by NaOH modification 2+ while the ammonium oxalate modification significantly enhanced the adsorption capacity only for Fe ion. The results show that NaOH and ammonium oxalate modified kaolinite clay are effective for remediation of heavy metal-laden wastewater.&#x0D; Keywords: Kaolinite, metal ions, adsorption, kinetics, adsorption isotherm

Photo-electrochemical Osmotic System Enables Simultaneous Metal Recovery and Electricity Generation from Wastewater.

Global depletion of natural resources provides an impetus for developing low-cost, environmentally benign technologies for the recovery of valuable resources from wastewater. In this study, we present an autonomous photo-electrochemical osmotic system (PECOS) that can recover a wide range of metals from simulated metal-laden wastewater with sunlight illumination while generating electricity. The PECOS comprises a draw solution chamber with a nickel nanoparticle-functionalized titanium nanowire (Ni-TiNA) photoanode, a feed solution chamber containing synthetic wastewater with an immersed carbon fiber cathode, and a forward osmosis (FO) membrane mounted between the chambers as a separator. Using a Na2-EDTA anolyte as a draw solution at neutral pH, we demonstrate that a sunlit PECOS achieves copper recovery at a rate of 51 g h-1 per m-2 of membrane area from simulated copper-laden wastewater while simultaneously producing a maximum power density of 228 mW m-2. Moreover, because of the osmotic pressure difference generated by the photo-electrochemical reactions, the PECOS reduces the wastewater volume by extracting fresh water through the FO membrane at a water flux of 0.84 L m-2 h-1. We further demonstrate the feasibility of the PECOS in recovering diverse metals from a simulated metal-laden industrial wastewater under sunlight irradiation. Our proof-of-concept PECOS prototype provides a sustainable technological solution that leverages sunlight in an electrochemical osmotic system to recover multiple resources from wastewater.

Elemental sulfur-driven sulfidogenic process under highly acidic conditions for sulfate-rich acid mine drainage treatment: Performance and microbial community analysis

Elemental sulfur-driven sulfidogenic process has been demonstrated to be more economical and energy-efficient than sulfate-driven sulfidogenic process when treating metal-laden wastewater. In previous studies, we observed that the polysulfide-involved indirect sulfur reduction ensured the superiority of sulfur over sulfate as the electron acceptor in the sulfidogenic process under neutral or weak-alkaline conditions. However, realizing high-rate sulfur reduction process for acid mine drainage (AMD) treatment without pH amelioration is still a great challenge because polysulfide cannot exist under acidic conditions. In this study, a laboratory-scale sulfur-packed bed reactor was therefore continuously operated with a constant sulfate concentration (~1300 mg S/L) and decreasing pH from 7.3 to 2.1. After 400 days of operation, a stable sulfide production rate (38.2 ± 7.6 mg S/L) was achieved under highly acidic conditions (pH 2.6–3.5), which is significantly higher than those reported in sulfate reduction under similar conditions. In the presence of high sulfate content, elemental sulfur reduction could dominate over sulfate reduction under neutral and acidic conditions, especially when the pH ≥ 6.5 or ≤ 3.5. The decreasing pH significantly reduced the diversity of microbial community, but did not substantially influence the abundance of functional genes associated with organic and sulfur metabolisms. The predominant sulfur-reducing genera shifted from Desulfomicrobium under neutral conditions to Desulfurella under highly acidic conditions. The high-rate sulfur reduction under acidic conditions could be attributed to the combined results of high abundance of Desulfurella and low abundance of sulfate-reducing bacteria (SRB). Accordingly, sulfur reduction process can be developed to achieve efficient and economical treatment of AMD under highly acidic conditions (pH ≤ 3.5).

An assessment of sulfate reducing bacteria on treating sulfate-rich metal-laden wastewater from electroplating plant

Electroplating effluent contaminated with heavy metals posed a major threat on the aquatic ecosystems. The effect of the sulfate-reducing bacteria (SRB) enriched sludge on simultaneous removals of sulfate and nickel was identified. Batch tests showed that SRB biogenic precipitation could completely eliminate the nickel (100 %) with sodium lactate as carbon source at pH 7 within 3 d, and enhanced in the presence of Fe2+ and Fe3+, while inhibited at high concentrations. The formation of NiS2 (confirmed by XRD, EDS and FTIR) indicated that the nickel was removed mainly through chemical bond. RDA analysis showed that COD/S ratios and the iron had the greatest influence on the performance. High-throughput sequencing indicated that the SRB enriched sludge was dominant with Desulfovibiro (43.3 %) at genus level. Finally, a pilot-scale experiment with SRB biological precipitation demonstrated that it could partially replace chemical precipitation for removing sulfate and nickel, and greatly improved the removals of ammonia-N, total nitrogen and total phosphorus in the sequential Anaerobic-Anoxic-Oxic process. This approach could greatly minimize the secondary contamination and chemicals dosing for pH adjusting and chemical coagulation. Therefore, SRB-based metal removal performance is a promising technology to realize a high-rate and low-cost process for treating practical sulfate rich metal-laden wastewater. This study is the first report about the comprehensive effect of SRB reactor with practical electroplating wastewater treatment system, which provides a new application template for electroplating wastewater treatment.

Treatment of small scale gold mining wastewater using pilot-scale sedimentation and Cocopeat filter bed system

The use of amalgamation process to recover gold from mined ores by the small-scale gold miners in the Philippines and other developing countries produces and dispose of untreated wastewater to the receiving water bodies. In this study, a field-scale filter bed system was constructed to treat heavy metal metal-laden wastewater collected from small-scale gold mining site in Paracale, Camarines Norte, Philippines. The filter bed system was consists of sedimentation tank and filter bed with Cocopeat, a by-product of coconut husk, as adsorbent. Physico-chemical parameters (temperature, pH, oxidation-reduction potential, electrical conductivity, turbidity, dissolved oxygen, total dissolved solids, salinity, total suspended solids, color) and heavy metal (As, Ba, Cd, Hg, Pb) concentrations were monitored during the 50 days experiment at a flow rate of 40 Liter per hour for 3 hours daily wastewater application. Significant reduction was achieved on heavy metals; As (97.11%), Ba (39.75%), Cd (74.24%), Hg (97.02%), Pb (98.82%) from small-scale gold mining (SSGM)wastewater in sedimentation phase and further reductions on As (1.39%), Ba (28.00%), Cd (4.95%), Hg (2.91%), Pb (0.97%) were achieved by adsorption in the Cocopeat filter bed. Measured effluent physico-chemical parameters and heavy metal concentrations were within the respective regulatory limits. Other effluent parameters with strong correlation with total suspended solids such as turbidity and color, though not regulated, were reduced significantly. All adsorbed heavy metals accumulated in the upper 25 cm of the Cocopeat column in the filter bed. Measured heavy metal concentrations in Cocopeat suggest that the adsorbent was not saturated and further application of small-scale gold mining wastewater is recommended to determine its useful life.