Selenium Removal Research Articles

Erratum: Selenium removal from petroleum refinery wastewater using an electrocoagulation technique

Erratum: Selenium removal from petroleum refinery wastewater using an electrocoagulation technique

Se(VI) reduction by continuous-flow reactors packed with Shigella fergusonii strain TB42616 immobilized by Ca2+-alginate gel beads

Selenium at high levels may cause adverse health effects on human beings and endanger aquatic lives due to its toxicity. Se(VI) reduction in continuous-flow reactors packed with Shigella fergusonii strain TB42616 immobilized by Ca2+-alginate gel beads was investigated under various hydraulic retention times (HRT) and influent Se(VI) concentrations. Removal efficiency up to 98.8 % was achieved after 96 days operation under an HRT of 5 days and an influent Se(VI) concentration of 400 mg/L. The results showed that the overall selenium removal efficiency was affected by the HRT and the bed height of the reactor but not the influent Se(VI) concentration. The steady-state data were analyzed using a mathematical model and Monod-type kinetics. Biokinetic parameters of half-velocity constants and maximum specific reduction rates were optimized using steady-state data obtained under a range of HRTs (0.73–5.0 days) at a constant influent Se(VI) concentration of 50 mg/L. The model was validated using steady-state data obtained under influent Se(VI) concentrations ranging from 10 to 400 mg/L while maintaining the HRT at 5.0 days. The high correlation coefficients between model calculated Se(VI) and Se(IV) concentrations and the experimental data indicate that the model is robust to predict the performance of the continuous-flow bioreactor.

Development of a sulfidogenic bioreactor system for removal of co-existent selenium, iron and nitrate from drinking water sources

The present study showed for the first time that selenium, iron, and nitrate could be simultaneously removed in a sulfidogenic bioreactor to meet drinking water standards. A bioreactor inoculated with mixed bacterial consortium was operated for around 330 days in anoxic environment at 30 °C under varying combination of influent selenate (200–1000 μg/L as selenium), and iron (3–10 mg/L) in presence of 50 mg/L of nitrate. Required amount of acetic acid (as carbon source) and sulfate were supplied and the reactor was operated at different empty bed contact time (EBCT) of 45–120 min. Along with complete removal of nitrate, the reactor removed both selenium and iron to meet the drinking water standards. Field emission transmission electron microscopy (FETEM) and X-ray diffraction (XRD) analyses confirmed the formation of selenium sulfide (SeS), achavalite (FeSe) and pyrite (FeS2), which were the possible removal mechanisms of selenium and iron. Thus, this study exhibited that selenium, iron, and nitrate can be simultaneously removed to meet the drinking water standards in a sulfidogenic bioreactor.

Biological removal of selenite from wastewater and recovery as selenium nanoparticles using inverse fluidized bed bioreactor

This study evaluated the performance of an inverse fluidized bed (IFB) bioreactor with anerobic biomass immobilized onto Kaldness-K1 media as the biosupport material for selenite removal and recovery as selenium nanoparticle from waste stream. The effect of different process parameter and nutrient supplement on selenium removal was first studied in a batch system using serum bottles. The results revealed that among the different nitrogen substrates, ammonium bicarbonate was most suitable, whereas, lactate was found to be the preferred carbon substrate with 98% selenite removal efficiency and 90% COD removal. Later studies with the continuously operated IFB bioreactor operated at different hydraulic retention time (HRT) and different influent selenite concentrations revealed an efficient removal of selenite at 24 h HRT and 1.0 mM of influent Se (IV). Furthermore, selenium nanoparticles formed at the bottom of the bioreactor were successfully recovered with a recovery efficiency in the range 35–58% with a maximum recovery obtained at 1.0 mM selenite concentration and 24 h HRT. The extracellular produced selenium nanoparticles were found to be spherical in shape with 90–150 nm in size. Fourier transform infrared (FTIR) spectroscopy confirmed the presence of extracellular polymeric substances (EPS) as capping agent on the outer surface of Se nanoparticles.

Graphene Oxide Nanocomposite Hydrogel Beads for Removal of Selenium in Contaminated Water

Selenium in water is becoming of increasing risk to human exposure because only recently serious health effects have been associated with their presence in water resources. The present study invest...

Selenium removal by activated alumina in batch and continuous-flow reactors.

Selenium removal by activated alumina (AA) in batch and continuous-flow reactors was investigated in this study. The adsorption kinetics fitted pseudo-first as well as pseudo-second order models with equilibrium time for Se(VI) and Se(IV) adsorption of 8 and 12hr, respectively. A significant higher adsorption capacity for Se(IV) than Se(VI) was observed in isothermal adsorption experiments. The adsorption isotherms of Se(VI) and Se(IV) agreed well with both Langmuir and Freundlich adsorption models. The results also showed that Se(VI) adsorption was adversely affected by NaHCO3 concentrations, while Se(IV) adsorption was not due to the selectivity of activated alumina for anions. In the continuous-flow reactor packed with AA and inoculated with Shigella fergusonii strain TB42616 under a hydraulic detention time of 3days, approximately 74% and 70% Se(VI) were removed after 40days at influent concentrations of 10 and 50mg/L, respectively. Effluent concentrations of Se(IV) from the bioreactor were insignificant due to the combination of bioactivities and adsorption. The AA-packed bioreactor is promising in both Se(VI) and Se(IV) removal as better removal efficiency may be accomplished by increasing the liquid retention time. PRACTITIONER POINTS: The adsorption capacity for Se(IV) of activated alumina was significantly higher than that for Se(VI). Se(VI) adsorption was inhibited by NaHCO3 , while Se(IV) adsorption was not. Se(IV) formed by biological Se(VI) reduction was adsorbed by activated alumina in continuous-flow reactors. Both Se(VI) and Se(IV) were significantly removed by activated alumina-packed continuous-flow reactors.

Selenium(VI) removal from caustic solution by synthetic Ca–Al–Cl layered double hydroxides

Abstract To extract selenium(VI) from the highly caustic leachate of copper anode slime, the Ca–Al–Cl layered double hydroxides (Ca–Al–Cl–LDHs) with a formula of Ca2Al(OH)6Cl·2H2O by three co-precipitation methods were synthesized. A plate-like morphology and hexagonal crystal structure with typical mineral phases and functional groups were identified by the FESEM, XRD, FTIR, BET and XPS analysis. The forward feeding sample exhibits the best adsorption capacity of Se(VI). The factor experiments then reveal a favorable adsorption process with low temperature, low NaOH concentration and high adsorbent dosage. Furthermore, the adsorption kinetics and isotherm parameters can be well described by the Langmuir isotherm and the pseudo-second-order models, respectively. Accordingly, the maximum adsorption amount of Se(VI) onto Ca–Al–Cl–LDHs reaches 188.6 mg/g at 50 °C.

Genome-resolved metagenomics links microbial dynamics to failure and recovery of a bioreactor removing nitrate and selenate from mine-influenced water

A packed-bed bioreactor designed for selenium removal from coal waste leachate experienced reduced hydraulic conductivity and loss of performance soon after forward flow of mine-influenced water containing nitrate and selenate as the main contaminants. A metagenomic study was initiated to help diagnose the causes for the bioreactor’s poor operation. Despite being inoculated with a custom consortium of Pseudomonas strains capable of nitrate and selenate reduction, the microbial community shifted towards dominance by Trichococcus- and Candidatus Saccharibacteria- related species. Metagenomic assembled genomes for these revealed that they did not have the metabolic potential for denitrification or selenate reduction, and displayed an affinity for carbohydrate carbon sources through the PTS pathway. We speculate that the sugar-based carbon sources fed to the bioreactor lead to favourable growth of the filamentous forms of these species under the conditions of the bioreactor, which may have allowed for infiltration of oxygen. Decreasing ORP coincided with decrease in relative abundance of the filamentous species and increase in relative abundance of uncharacterized species in the Burkholderiales and Rhodocyclales orders with the metabolic potential for all steps of the denitrification pathway including nitrate reductases closely related to those with an affinity for selenate as well as nitrate.

Ion flotation removal of a range of contaminant ions from drinking water

The effect of a natural, biodegradable surfactant obtained using a novel and efficient chemical reaction between cysteine (a thiol-based amino acid) and an octanoyl (C8) compound, was investigated for its application to the ion flotation removal of low levels of different contaminant ions from aqueous solution. The synthesised amino acid-based single-chain surfactant shows a high water solubility and exhibits extensive foaming in a typical flotation chamber over a wide pH range. In a batch ion flotation process, this surfactant was able to remove 97–99% of the 5ppm of strontium, lanthanum, arsenic and different heavy metal ion levels present in contaminated water, in a simple, single-stage physiochemical process; while this surfactant showed significantly lower efficiency for the removal of iron, selenium and gold ions. In a solution mixed with heavy-metal ions, including arsenic, copper, cadmium, magnesium, lanthanum, chromium, lead and iron, the surfactant shows high affinity to bind with arsenic, copper and chromium compared with the others. Moreover, the effectiveness of this surfactant for removal of gold ions from aqueous binary mixtures in the presence of iron and mercury ions has been explored. This new surfactant is highly efficient compared with commercial surfactants (e.g., SDS and CTAB) for ion flotation. Importantly it is an environmentally acceptable compound. It can be decomposed into cysteine (amino acid) and octanoic acid (caprylic acid, which is taken as a dietary supplement). The surfactant has the potential for wide usage in ion flotation and in froth flotation.

Eco-materials for Arsenium and Selenium Removal from Aqueous Solutions

Environmental engineering have a great importance because is dealing with different fields, most important of them being water resource protection. It is well known that natural waters and especially groundwater contain dissolved substances, most of them unharmful for human and animal life, but some of them still potentially harmful. Ground waters containing dissolved arsenic and / or selenium are harmful and not suitable for human an animal life. Selenium represents a human life prerequisite microelement which can become toxic when higher quantities are ingested or accumulated. In comparison arsenic has an acute toxic effect over the human body even when very low quantities are ingested. In both cases the maximum amount were limited by OMS at 10 mg L-1. A new technique was used to produce an ecofriendly composite material by doping graphite with iron oxide, which was used for retention of arsenic and selenium from aqueous solutions. Synthesized material was characterized using SEM, EDX, XRD and DTA. Adsorption capacity and adsorption mechanism were established through equilibrium studies. Maximum adsorption capacity was 400 �g As(V) and 625 �g Se(VI) per gram of adsorbent.

Electrochemical Evaluation of Selenium (IV) Removal from Its Aqueous Solutions by Unmodified and Modified Graphene Oxide.

The removal of selenium from superficial and waste water is a worldwide problem. The maximum limit according to the World Health Organization (WHO) for the selenium in the water is set at a concentration of 10 μg/L. Carbon based adsorbents have attracted much attention and recently demonstrated promising performance in removal of selenium. In this work, several materials (iron oxide based microparticles and graphene oxides materials) and their composites were prepared to remove Se(IV) from water. The graphene oxides were prepared according to the simplified Hummer’s method. In addition, the effect of pH, contact time and initial Se(IV) concentration was tested. An electrochemical method such as the differential pulse cathodic stripping voltammetry was used to determine the residual selenium concentration. From the experimental data, Langmuir adsorption model was used to calculate the maximum adsorption capacity. Graphene oxide particles modified by iron oxide based microparticles was the most promising material for the removal of Se(IV) from its aqueous solution at pH 2.0. Its adsorption efficiency reached more than 90% for a solution with given Se(IV) concentration, meanwhile its maximal recorded adsorption capacity was 18.69 mg/g.

Layered Double Hydroxide Sorbents for Removal of Selenium from Power Plant Wastewaters

Selenium is an essential trace element but is increasingly becoming a contaminant of concern in the electric power industry due to the challenges of removing solubilized selenate anions, particularly in the presence of sulfate. In this work, we evaluate granulated layered double hydroxide (LDH) materials as sorbents for selenium removal from wastewaters obtained from a natural gas power plant with the aim to elucidate the effect of competing ions on the sorption capacities for selenium removal. We first present jar test data, followed by small-scale column testing in 0.43 inch (1.1 cm) and 2 inch (5.08 cm) diameter testbed columns for the treatment of as-obtained cooling tower blowdown waters and plant wastewaters. Finally, we present field results from a pilot-scale study evaluating the LDH media for treatment of cooling tower blowdown water. We find that despite the high levels of total dissolved solids and competing sulfate ions, the selenium oxoanions and other regulated metals such as chromium and arsenic are successfully removed using LDH media without needing any pre-treatment or pH adjustment of the wastewater.

Biological treatment of selenate-containing saline wastewater by activated sludge under oxygen-limiting conditions

Selenium often coincides with high salinity in certain industrial wastewaters, which can be a limitation in the practical application of biological treatment. However, there are no studies on the biological treatment of selenate-containing saline wastewater. A sequencing batch reactor inoculated with activated sludge was applied to treat selenate in the presence of 3% (w/v) NaCl. Start-up of the sequencing batch reactor with a 7-day cycle duration and excessive acetate as the sole carbon source succeeded in removing above 98% and 72% soluble and solid selenium, respectively, under oxygen-limiting conditions. Further selenium removal experiments with a shorter cycle duration of 3 days and a stepwise decrease of acetate addition achieved soluble and total selenium removal efficiencies in most batches above 96% and 80%, respectively. Mass balance analysis revealed that selenate was converted into elemental selenium, most of which was accumulated in the sludge. Microscopic analyses also found that elemental selenium particles were primarily present as approximately 2 μm large rods, with some extremely large particles above 10 μm. Although the bacterial populations responsible for selenium removal, especially selenate reduction, could not be identified by microbial community analysis, this study reported for the first time that selenate could be biologically treated in the presence of considerable salinity, offering implications for the practical treatment of selenium in certain industrial wastewaters.

Selenium in wastewater: fast analysis method development and advanced oxidation treatment applications.

Selenium, a ubiquitous non-metal in nature, is potentially toxic to natural ecosystems due to its bioaccumulation potential. Due to increased monitoring and enforcement of selenium regulations, the need to be able to measure and treat selenium efficiently has taken on an increased importance. The principal aqueous forms of inorganic selenium are selenite (Se(IV)) and selenate (Se(VI)). Selenate, due to its high mobility and lack of affinity to conventional adsorbents, is typically much more difficult to treat and remove. To address both measurement and removal, an analytical method is reported for quantification of selenium in wastewater (WW) using UV-Vis spectrophotometer followed by removal studies using advanced oxidation processes (AOPs). Malachite green and azure blue were selected for colorimetric analysis using UV-Vis. Malachite green indicator showed the best results for analysis. The reported UV-Vis method was applied to establish the effect of AOPs on selenium removal. It was noted that all of the AOP treated samples showed removal of selenium and it was established that the UV-Vis method has a lower limit of detection at 2 mg/L. Further, through this study, it was found that the chemical cavitation yield and selenium removal efficiency peaked at low frequency ultrasound of 40 kHz.

Electrochemical peroxidation using iron nanoparticles and anodic iron dissolution to remove selenium from oil refinery wastewater

AbstractExperimental results for selenium removal from oil refinery wastewater applying the electrochemical peroxidation process (ECP) using either graphite electrodes with iron nanoparticles (nZVI) or carbon steel electrodes with anodic iron dissolution (AD) on laboratory scale are presented. Operating parameters were: current density, iron‐selenium molar ratio and treatment time. It was found that when applying ECP and nZVI, selenium removal reached 93%. On the contrary, when the ECP and AD process was applied, selenium removal only reached 64%. Therefore, the ECP process and use of iron nanoparticles could be a feasible technology to remove selenium from oil refinery wastewater.

Selenium removal from mining and process wastewater: a systematic review of available technologies

Selenium removal from mining and process wastewater: a systematic review of available technologies

Selenium removal and biotransformation in a floating-leaved macrophyte system

Selenium (Se) is an essential micronutrient for animals with a relatively narrow margin between essentiality and toxicity. To evaluate Se removal efficiency by a constructed wetland treatment system and its potential eco-risk, a floating-leaved macrophyte system was constructed, consisting of three main trophic levels. Over 21-d treatment, water Se concentration was gradually reduced by 40.40%, while 24.03% and 74.41% of the removed Se were found in the plant Nymphoides sp. and sediment, respectively. Among plant tissues, roots accumulated the highest Se level, although the greatest total Se was found in stems, followed by leaves, roots and rhizomes. X-ray absorption spectroscopy revealed that 82.65% of the absorbed selenite by the plants was biotransformed to other forms, as organo-Se species accounted for 45.38% of the Se retained in the sediment, which was primarily responsible for the entry of Se into the detritus food chain. The proportion of organo-Se compounds increased with trophic levels from sediments to fish, indicating, instead of direct uptake of selenite, the food chain transfer and biotransformation of Se may serve as a key exposure route for Se in aquatic organisms. When exposed to organo-Se compounds, i.e., SeCys and SeMet, the plants, shrimp and fish tended to accumulate more Se. However, the greater trophic transfer factor was obtained for selenate, leading to higher Se levels accumulated in fish. Overall, in addition to key mechanisms involved in Se removal, our research also provides a much better understanding of the potential eco-risk that may be posed by the floating-leaved plant system for bioremediation of Se via food chain transfer and biotransformation, paving the way for a low eco-toxic treatment system for Se remediation.

A review on environmental selenium issues

Selenium is an essential element since it is necessary for metabolism and is also toxic to the living things if it is consumed above the desirable limit. For instance, up to 40 µg per d of dietary selenium is essential for human health; however, consumption of a little over 400 µg per d could result in adverse physiological problems. In the environment, selenium occurs in different species; of which selenate and selenite are its most toxic forms accounting for 95% of selenium toxicity. Though, selenium fortification is important for normal human physiology in selenium deficient environments, it needs to be minimized or removed from selenium rich environmental media. Thus, its quantification is significantly important to control per limit. Currently there is advancement in the detection and quantification of selenium in environmental including the use of a Hydride Generating Atomic Absorption Spectroscopy. Due to the excess occurrences of selenium in different locations the removal techniques from geogenic or anthropogenic sources include microbial metabolism, phytoremediation, sorption, membrane separation, coagulation, ion exchange and catalytic reduction. Most of all, the microbial removal is applied in drinking water supply and in selenium recovery from wastewater sludge. Though current selenium removal from sorption studies reported better efficiency, phytoremediation appears attractive due to its field scale application advantage. However, the fate of selenium following phytoremediation remains unaddressed.

Relationship between selenium removal efficiency and production of lipid and hydrogen by Chlorella vulgaris

In our previous studies, Chlorella vulgaris had proven highly efficient in removing selenium (Se) from water, while the disposal of Se containing in algal biomass was still an issue of concern. Firstly, this research suggests algal Se could be released back to water, posing risks to aquatic wildlife. Thus, we further explored the possibility of using C. vulgaris to remove Se and produce lipid and hydrogen simultaneously. Our results show the higher percentage of saturated fatty acids, especially palmitic acid, was found in the sulfur (S) deprived algae exposed to either selenate or selenite, although the highest lipid content (21.9%) was found in the selenite treated algae in full BG11 medium. In addition, compared with the Se free algae, hydrogen production rate was 2.1- and 4.3-fold higher for the selenate and selenite treated algae, respectively. Se removal efficiency achieved by the selenite treated algae through accumulation and volatilization was 2.3-fold higher than the selenate treatment under hypoxic condition with S deprived, which is in contrast to the results obtained under aerobic conditions.

Development of an algal treatment system for selenium removal: Effects of environmental factors and post-treatment processing of Se-laden algae.

In developing an algal treatment system, selenium (Se) removal efficiency by Chlorella vulgaris was evaluated under various conditions such as Se concentration, algal density, temperature and pH. A maximum removal efficiency plateau of ∼90% was observed between 1000-3000 μg Se/L while the tolerance of Se toxicity was found at 6000 μg Se/L. C. vulgaris of 0.75 g DW/L showed the highest removal efficiency (84%), and volatilization was dominant below 1.37 g DW/L. Se volatilization was two times higher at 25 °C than at 20 °C in the first 24 h. Moreover, the highest removal efficiency (77%) was obtained at pH 8.0, compared to 66.5% at pH 6.5 and 40% at pH 10.0. To prevent ecotoxicity, Se laden algae were further burned to ashes or filtered out by Anodonta woodiana. After burning, biomass Se was reduced by 99%, with organo-Se entirely converted into inorganic Se, lowering Se bioavailability. A. woodiana removed 54% of Se in 24 h, leading to Se bioaccumulation in soft tissues, which may serve as dietary Se supplements for human health. Our results suggest the cleanup of Se-contaminated water from either agricultural runoff or industrial discharge could be achieved using an algal treatment system with minimum potential ecotoxicity.