Removal of chromium and lead by a sulfate-reducing consortium using peat moss as carbon source

Reductive Cr(VI) Removal under Different Reducing and Electron Donor Conditions—A Soil Microcosm Study

Increased groundwater and soil contamination by hexavalent chromium have led to the employment of a variety of detoxification methods. Biological remediation of Cr(VI) polluted aquifers is an eco-friendly method that can be performed in situ by stimulating the indigenous microbial population with organic and inorganic electron donors. In order to study the effect of different redox conditions on microbial remediated Cr(VI) reduction to Cr(III), microcosm experiments were conducted under anaerobic, anoxic, and sulfate-reducing conditions and at hexavalent chromium groundwater concentrations in the 0–3000 μg/L range, with groundwater and soil collected from an industrial area (Inofyta region). As electron donors, molasses, emulsified vegetable oil (EVO), and FeSO4 were employed. To quantitatively describe the degradation kinetics of Cr(VI), pseudo-first-order kinetics were adopted. The results indicate that an anaerobic system dosed with simple or complex external organic carbon sources can lead to practically complete Cr(VI) reduction to Cr(III), while the addition of Fe2+ can further increase Cr(VI) removal rate significantly. Furthermore, Cr(VI) microbial reduction is possible in the presence of NO3− at rates comparable to anaerobic Cr(VI) microbial reduction, while high sulfate concentrations have a negative effect on Cr(VI) bioreduction rates in comparison to lower sulfate concentrations.

Enriched Co-Treatment of Pharmaceutical and Acidic Metal-Containing Wastewater with Nano Zero-Valent Iron

Among traditional hazardous waste sources, pharmaceutical-containing wastewater and acidic mine drainage need treatment to preserve the expected water supply quality. A nano zero-valent iron (nZVI)-enriched treatment of these two streams is evaluated for simultaneous removal of various heavy metal ions, organic pollutants, sulfates, the efficiency of the treatment system, and separation of reaction products in the fluidized-bed reactor. The reactor packed with silica sand was inoculated with sludge from an anaerobic digester, then 1–3 g/L of nZVI slurry added to cotreat a hospital feed and acid mine wastewater at 5:2 v/v. The biotreatment process is monitored through an oxidation–reduction potential (Eh) for 90 days. The removal pathway for the nZVI used co-precipitation, sorption, and reduction. The removal load for Zn and Mn was approximately 198 mg Zn/g Fe and 207 mg Mn/g Fe, correspondingly; achieving sulfate (removal efficiency of 94% and organic matter i.e., chemical oxygen demand (COD), biological oxygen demand (BOD), dissolved organic carbon (DOC), total dissolved nitrogen (TDN) reduced significantly, but ibuprofen and naproxen achieved 31% and 27% removal, respectively. This enriched cotreatment system exhibited a high reducing condition in the reactor, as confirmed by Eh; hence, the nZVI was dosed only a few times in biotreatment duration, demonstrating a cost-effective system.

Removal of Hexavalent Chromium from Aqueous Solutions Using Sulfonated Peat

Peat, a loose and porous material, contains rich organic matter and can be used as an adsorbent. In this study, it is chemically modified by adding sulfuric acid under different conditions, with the aim of producing a modified peat with optimized Cr(VI) adsorption capability. The modified peat exhibited a higher adsorption efficiency than the natural peat throughout the adsorption experiments. The adsorption of Cr(VI) from aqueous solutions correlates with the pseudo-second order kinetic model. In addition, the Langmuir model indicated a maximum loading capacity approximately of 105.4 mg/g, which is a markedly high value compared to some other reported adsorbents. The present study performed single factor experiments and the results indicated that higher temperature conditions result in better adsorption capability, whilst an increase in the pH played a contrary role. According to the orthogonal tests, the pH had the greatest impact on adsorption. The obtained results indicated that sulfonated peat can be effectively applied in removing Cr (VI).

Simultaneous mitigation of tissue cadmium and lead accumulation in rice via sulfate-reducing bacterium

The objectives of this study were to investigate the mechanism responsible for Cd and Pb immobilization by sulfate reduction to sulfide and effectiveness of decreasing Cd²⁺ and Pb²⁺ bioavailability in culture solution and paddy soils via sulfate-reducing bacterium (SRB1-1). The SRB1-1 strain, exhibiting high resistances to Cd²⁺ and Pb²⁺, was isolated from bulk soils in the metal(loid)-contaminated paddy field. During the culture of the SRB1-1 strain, the removal percentages of Cd²⁺ and Pb²⁺ from culture solution reached 99.5% and 76.0% in 72 h, respectively. The surface morphology and composition of metal precipitates formed by SRB1-1 strain were analyzed by transmission electron microscopy (TEM) and further confirmed to be CdS and PbS by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). When living SRB1-1 strain was applied in Cd and Pb-contaminated soils, the SRB1-1 strain could stably colonize using its resistance to rifampicin, and showed significantly impact on the bacterial community composition. Cd and Pb contents in rice grains were decreased by 29.5% and 26.2%, respectively, while Cd and Pb contents in the roots, culms, leaves, and husk were also decreased ranging from 19.1% to 43%, respectively. Due to growth in highly Cd and Pb contaminated soils, Cd content of the rice grains did not meet the standard for limit of Cd and Pb, but safe production of rice plants may be obtained in slightly or moderately metal(loid)-contaminated soils in the presence of the living SRB1-1 strain. These results indicated that the SRB1-1 strain could effectively reduce the Cd and Pb bioavailability in soils and uptake in rice plants. Our results highlighted the possibility to develop a new bacterial-assisted technique for reduced metal accumulation in rice grains, and also showed potential for effective synergistic bioremediation of SRB1-1 strain and rice plants in metal(loid)-contaminated soils.

Immobilization of cadmium by immobilized Alishewanella sp. WH16-1 with alginate-lotus seed pods in pot experiments of Cd-contaminated paddy soil

This study prepared immobilized Alishewanella sp. WH16-1 using alginate and lotus seed pods as a matrix and investigated the effects of its immobilization on Cd²⁺ in a culture solution and in soil. Compared with the free WH16-1 strain, the immobilized WH16-1 strain possessed greater stability for long-term use and storage and higher removal ability for Cd²⁺ in the culture solution. A model of Cd²⁺ removal by the immobilized WH16-1 strain was proposed. The immobilized WH16-1 strain was incubated in the pot experiments of Cd-contaminated paddy soil for 120 days, and the pot experiments of Cd-contaminated paddy soil without the immobilized WH16-1 strain were used as a control. Compared with the control, the exchangeable and carbonate-bound Cd in the paddy soil incubated with the immobilized WH16-1 strain significantly decreased by 33.6% (P < 0.05) and 17.36%, respectively, and the Cd concentrations in the rice significantly decreased by 78.31% (P < 0.05). The results indicate that alginate-lotus seed pods can be used as excellent cost-effective cell carriers for the immobilization of Alishewanella sp. WH16-1 and that the immobilized WH16-1 strain may be applicable for the biological stabilization of Cd in Cd-contaminated paddy soil.

Enhanced biological stabilization of heavy metals in sediment using immobilized sulfate reducing bacteria beads with inner cohesive nutrient

A series of experiments were conducted for treating heavy metals contaminated sediments sampled from Xiangjiang River, which combined polyvinyl alcohol (PVA) and immobilized sulfate reducing bacteria (SRB) into beads. The sodium lactate was served as the inner cohesive nutrient. Coupling the activity of the SRB with PVA, along with the porous structure and huge specific surface area, provided a convenient channel for the transmission of matter and protected the cells against the toxicity of metals. This paper systematically investigated the stability of Cu, Zn, Pb and Cd and its mechanisms. The results revealed the performance of leaching toxicity was lower and the removal efficiencies of Cu, Zn, Pb and Cd were 76.3%, 95.6%, 100% and 91.2%, respectively. Recycling experiments showed the beads could be reused 5 times with superbly efficiency. These results were also confirmed by continuous extraction at the optimal conditions. Furthermore, X-ray diffraction (XRD) and energy-dispersive spectra (EDS) analysis indicated the heavy metals could be transformed into stable crystal texture. The stabilization of heavy metals was attributed to the carbonyl and acyl amino groups. Results presented that immobilized bacteria with inner nutrient were potentially and practically applied to multi-heavy-metal-contamination sediment.

Preparation of metal-resistant immobilized sulfate reducing bacteria beads for acid mine drainage treatment

Novel immobilized sulfate-reducing bacteria (SRB) beads were prepared for the treatment of synthetic acid mine drainage (AMD) containing high concentrations of Fe, Cu, Cd and Zn using up-flow anaerobic packed-bed bioreactor. The tolerance of immobilized SRB beads to heavy metals was significantly enhanced compared with that of suspended SRB. High removal efficiencies of sulfate (61-88%) and heavy metals (>99.9%) as well as slightly alkaline effluent pH (7.3-7.8) were achieved when the bioreactor was fed with acidic influent (pH 2.7) containing high concentrations of multiple metals (Fe 469 mg/L, Cu 88 mg/L, Cd 92 mg/L and Zn 128 mg/L), which showed that the bioreactor filled with immobilized SRB beads had tolerance to AMD containing high concentrations of heavy metals. Partially decomposed maize straw was a carbon source and stabilizing agent in the initial phase of bioreactor operation but later had to be supplemented by a soluble carbon source such as sodium lactate. The microbial community in the bioreactor was characterized by denaturing gradient gel electrophoresis (DGGE) and sequencing of partial 16S rDNA genes. Synergistic interaction between SRB (Desulfovibrio desulfuricans) and co-existing fermentative bacteria could be the key factor for the utilization of complex organic substrate (maize straw) as carbon and nutrients source for sulfate reduction.

Biological treatment of acidic coal refuse using sulphate-reducing bacteria with chicken manure as carbon source

The performance of using chicken manure as carbon source to promote sulphate-reducing bacteria (SRB) activity within acidic coal refuse to prevent the generation of acidic leachate was investigated in batch and column bioreactors. The bioreactors showed satisfactory performance in biological sulphate reduction, evidenced by the increase in effluent pH, high removal efficiencies of sulphate and metals, and the presence of large numbers of SRB. Scanning electron microscope-energy dispersive spectrometry (EDS) analysis of the formed precipitate indicated the formation of metal sulphides. Chicken manure was observed to play an important role in this treatment, which could not only provide carbon source but also reduce the adverse effect of strong acidity and metal toxicity on SRB activity. Metal removal could be mainly attributed to sulphides precipitation and sorption to chicken manure. This study indicated that SRB with chicken manure could be a novel alternative used for the prevention of acidic leachate from coal refuse.