Perchlorate Removal Research Articles

(Invited) Separation and Hydrogenation of Ions By Micro-Scale Capacitive-Faradaic Adsorbing Fuel Cells

Capacitive deionization processes are aimed at separation of ions from water and wastewater. Since late 1960-s, when the CDI concept was proposed, the technique was improved via incorporation of ion exchange membranes (MCDI), utilization of slurry electrodes (FCDI) and introduction of one or two battery electrode(s) into the process to enhance the salt adsorption capacity of the cell and to reduce the energy demand of the process. In all these processes the monopolar electrodes must be physically connected to the DC power supply via wires, and cathodes and anodes should be separated to prevent short-circuiting. These and other requirements of CDI processes result in serious drawbacks, limitations and sophisticated design of water treatment reactors.A novel CDI-based method for separation of ions from water and wastewater using micro-scale (10µm – 5 mm) fuel cells is proposed1. The fuel cells comprise activated carbon particles loaded with bi-functional catalyst for hydrogen oxidation and oxygen reduction reactions. Within the proposed process of ions removal, the particles act as the micro-scale capacitive-faradaic adsorbing fuel cells (MS-CF-AFC) which require oxygen and hydrogen gases for adsorption of ions during the water treatment step and desorption of ions in brine production.Within the O2-induced adsorption of anions, thereduction of oxygen on Pt (faradaic electrode of the MS-CF-AFC) results in depletion of electrons from the carbonaceous part (i.e. the capacitive electrode) of the micro-scale fuel cell, which leads to adsorption of anions in the electrical double layer of carbon. The hydrogen oxidation that occurs during the regeneration of the anions-loaded MS-CF-AFCs results in accumulation of electrons in the capacitive electrode and in repulsion of perchlorate ions into the regenerant solution. This way the chemical energy of H2 and O2 is converted by the MS-CF-AFCs into the electrical energy which is utilized for separation of ions. For the separation of cations, the MS-CF-AFCs are powered by the H2 gas during the cationsadsorption step and by the O2 gas in brine production.The O2-induced adsorption of anions (and desorption of cations) results in pH increase in the treated water. Consequently, within the MS-CF-AFC treatment the separated anions are “exchanges” with OH- ions. The rate of the process is faster at lower pH values in the treated water. Higher anions adsorption capacity is achieved at higher O2 pressure. The H2-induced desorption of anions (and adsorption of cations) is accompanied by decrease in the pH. Thus, the cations removal process can be regarded as an exchange of separated cations with the H+ ions. The H2-induced step of the MS-CF-AFC processes is faster at higher pHs, and higher cations removal capacity is obtained at higher H2 pressure. To enhance the salt adsorption capacity of MS-CF-AFCs for anions and cations the activated carbon in the cells can be decorated with appropriate surface groups, e.g., carboxylic and amine groups (respectively).The process was proved for the removal of perchlorate, copper and nitrate ions using pure solutions of NaClO4, KNO3 and CuCl2 salts in deionized water and in groundwater, using batch and packed-bed reactors for two types of platinum loaded (5wt%) MS-CF-AFCs prepared from Lewatit AF5 microporous carbon and a powdered activated charcoal.The main disadvantage of the process described above is its inability to “deactivate” toxic NO3 - and ClO4 - ions as the process only concentrates the pollutant (similarly to the well-known ion-exchange). It was shown that Pt-Cu MS-CF-AFCs are capable to adsorb nitrate ions from water and to reduce them into the N2 gas during the H2-induced step of anions desorption from the MS-CF-AFCs.The proposed MS-CF-AFCs can be performed in batch, continuous stirred (CSTR), fixed-bed and other types of reactors normally applied in adsorptive water treatment processes.Potential advantages of the MS-CF-AFCs process are: (1) the process can be utilized for separation of all types of anions and cations (appropriate carbon modification might be required); (2) the process can be performed in any type of adsorption reactors; (3) desalinating hybrid capacitive-faradaic micro-scale fuel cells do not require any wiring as opposite to CDI, previously proposed desalinating fuel cells and battery electrode desalination processes; (4) the regeneration of the MS-CF-AFCs does not require any concentrated solutions of acids, bases or salts; and (5) the hydrogen required for the process can be produced on-site using hydrogen generators and air can be utilized as the oxygen source.[1] Gendel, Y., Amikam, G., Nativ, P., 2020. Separation of Anions and Cations from Water and Wastewater Using Micro-Scale Capacitive-Faradaic or Pseudocapacitive-Faradaic Adsorbing Fuel Cells. US Provisional Patent Application 62/983,689. Figure 1

Electro-assisted autohydrogenotrophic reduction of perchlorate and microbial community in a dual-chamber biofilm-electrode reactor

The electro-assisted autohydrogenotrophic reduction of perchlorate (ClO4−) was investigated in a dual-chamber biofilm-electrode reactor (BER), in which the microbial community was inoculated from natural sediments. To avoid the effect of extreme pH and direct electron transfer on perchlorate reduction, a novel cathode configuration was designed. The pH of the cathode compartment was successfully controlled in the range of 7.2–8.4 during whole experiment. The effective biological autohydrogenotrophic reduction of perchlorate was achieved using hydrogen generated in-situ on the electrode surface, and the removal rate of 10 mg L−1 perchlorate reached 98.16% at HRT of 48 h. The highest perchlorate removal flux reached to 1498.420 mg m−2·d−1 with a 0.410 kW·h g-perchlorate−1 energy consumption. The microbial community evolution in the BER was determined by high-throughput sequencing and the results indicated that the Firmicutes and Bacteroidetes were dominant at phylum level when perchlorate concentration was 10 mg L−1 or lower. And the Proteobacteria became ascendant at the perchlorate concentration of 20 mg L−1. The functional populations for perchlorate reduction were successfully enriched including Nitrosomonas (30%), Thermomonas (9%), Comamonas (8%) and Hydrogenophaga (3%). Meanwhile, the proportion of functional population in biofilm linked to perchlorate concentration. With the increase of influent perchlorate concentration, the perchlorate-reducing bacteria (PRB) were enriched successfully and became ascendant.

Perchlorate contamination of drinking water sources in Kerala, South India, and its degradation using advanced chemical treatment

Perchlorate is an inorganic chemical reported to be resulting in widespread contamination of water bodies and even drinking water systems. The presence of perchlorate was identified in various drinking water sources (well, tap, borewell and bottled water) using liquid chromatography–mass spectrometry technique. The concentration of perchlorate in these samples is found in the order of bottled water ≫ well water > tap water > bore well water. Since most of the people in the study area depend upon this contaminated water for drinking purpose without any treatment, another important goal of this study was to propose suitable methods to remove or minimize the perchlorate concentration. This has been accomplished by advanced reduction processes (ARPs). Screening experiments including advanced oxidation processes such as UV photolysis, sonolysis, Fenton’s reaction in combination with reducing agents like sulfite, persulfate, ferrous iron at different pH and various concentrations were done. The experiments with ARPs are found to be degrading the perchlorate up to 32% in 5 h in Fenton-type reaction, and further experiments with modifications in the activation methods and reducing agents may give promising results for perchlorate degradation. Therefore, ARP technique offered more prominent results in terms of perchlorate removal, which can be easily extended in large-scale applications.

Emerging investigator series: capacitive deionization for selective removal of nitrate and perchlorate: impacts of ion selectivity and operating constraints on treatment costs

A parameterized costing model was used to investigate the impacts of ion selectivity on water treatment price for selective ion removal with capacitive deionization (CDI) systems.

Removal of perchlorate from wastewater through adsorption and reductive degradation using Ni-Fe bimetallic nanoparticles supported on modified activated carbon: A simple strategy to degrade persistent pollutants

In the present study, nickel and iron (Ni/Fe) bimetallic nanoparticles (Ni-Fe NPs) were produced in the presence of activated carbon (AC) to prepare supported Ni/Fe bimetallic nanoparticles (Ni-Fe NPs/AC). The NPs were modified using cetylpyridinium chloride and used for the simultaneous adsorption and degradation of perchlorate. Synthesized Ni-Fe NPs/AC was characterized using FE-SEM, EDS, and XRD. The influential factors in the removal of perchlorate by Ni-Fe NPs/AC were optimized based on experimental design. According to the results, adsorption and degradation efficiencies were 96.98% and 78.81%, respectively, which could be achieved to the efficiency of nearly 100% by increasing the process time to 110 minutes. Reaction kinetics complied with the pseudo-first-order characteristics. Moreover, the rate constant of adsorption and degradation were estimated at 0.0848 and 0.0199 min-1 at 303 K, and the activation energy for adsorption and degradation was 42.39 and 12.47 kJ/mol, respectively. The proposed method could effectively remove perchlorate from well water and industrial wastewater. Therefore, Ni-Fe NPs/AC could be an effective nanomaterial for the complete degradation of perchlorate. This novel method could also remove persistent organic and inorganic pollutants and promote the industrial application of bimetallic NPs in environmental remediation.

Efficiency of magnetic chitosan supported on graphene for removal of perchlorate ions from wastewater

ABSTRACT In this study, we used a synthesized cross-linked magnetic chitosan with graphene oxide beads to study the removal of perchlorate from wastewater. The prepared complex was characterized using transmission electron microscopy (TEM), Fourier Transformation Infrared spectroscopy (FT-IR), vibrating sample magnetometry (VSM) and Thermal gravimetric analysis (TGA). Several parameters were studied including the effect of pH, contact time and the co-existing anions. The study showed that the adsorption could be studied in a wide range of pH. The study showed that the adsorption follows a pseudo-second-order model and Langmuir adsorption isotherm. The enthalpy and negative Gibbs standard free energy showed that the adsorption process was exothermic and spontaneous. The perchlorate adsorbent can be regenerated well by 0.1% NaCl solution.

Smart cationic coordination polymer: A single-crystal-to-single-crystal approach for simultaneous detection and removal of perchlorate in aqueous media

As a kind of novel persistent pollutant, perchlorate has been received a great deal of attention on toxicology transfer, degradation mode and remediation, making it an urgent task to exploit smart multifunctional material for simultaneous adsorption and detection of ClO4− in aqueous media. Here, a water-stable cationic porous coordination polymer (named as 1 ∩ NO3) has been rationally designed and constructed to achieve this goal. The resultant 1 ∩ NO3 exhibits fast sorption kinetics (30 min) and excellent capacity (108.70 mg/g) toward ClO4− anion with good repeatability and high selectivity. Luckily, the structure of ClO4−-loaded framework can be obtained directly via SC-SC approach, which proves the obvious spatial confinement of 1 ∩ NO3 towards ClO4− anion. Moreover, the fluorescence of 1 ∩ NO3 has dependent change with the concentration of ClO4−, making it as an excellent sensor with superior selective and sensitive (17.4 μg/L). It is much lower than the acceptable limit (24.5 μg/L) in drinking water standard of the US Environmental Protection Agency (EPA). These indicate that the smart adsorbent 1 ∩ NO3 is expected to be used in the synchronous detection and adsorption of ClO4− in aqueous solutions, providing a viable option in water quality monitoring and wastewater treatment.

Adsorption of perchlorate from water using quaternary ammonium‐functionalized chitosan beads

AbstractPerchlorate, one of the persistent inorganic pollutants, was efficiently removed from water using quaternary ammonium‐functionalized cross‐linked chitosan beads (QACB). This synthesized bead was found to be efficient in terms of perchlorate removal capacity, 100% regeneration of used beads (using HCl or NaCl) and selectivity in the presence of coanions, namely, chloride, sulfate, carbonate, and nitrate. QACB removes perchlorate by exchange of chloride ions. QACB was able to remove >95% perchlorate from brackish water. Batch studies were carried out in order to optimize the condition for maximum perchlorate removal. The perchlorate removal capacity of QACB from 1,000 mg/L of aqueous solutions was 153.0 mg/g. The outcome of pH variation studies indicated that QACB is able to remove perchlorate in the pH ranges of 2–11. Equilibrium isotherm data of adsorption of perchlorate at temperature 303, 313, and 323 K were well fitted to the linear Freundlich, Langmuir, and Dubinin–Radushkevich isotherm models. The adsorption kinetics data were best described by the pseudo‐second‐order kinetic model. FTIR was used to confirm the interaction of perchlorate with QACB. A small‐scale column test was carried out to evaluate the capacity of QACB for removing perchlorate from brackish water.

Integrating cationic metal-organic frameworks with ultrafiltration membrane for selective removal of perchlorate from Water

We design a novel cationic metal-organic framework hybrid ultrafiltration polyvinylidene fluoride membrane (PVA/Cu-iMOFs/PVDF-0.05) and report its unique capture of aqueous perchlorate (ClO4−) at ppm-level. This membrane outperformed traditional adsorption materials and exhibited a specific affinity toward ClO4− in the presence of various competing anions at greater levels (up to a concentration ratio of 20). In the batch experiment, the ClO4− removal ratio reached 99.6% over a wide pH range (3˜10). Membrane filtration by using a 12.56 cm2 PVA/Cu-iMOFs/PVDF-0.05 membrane could effectively treat 4.71 L of ClO4−-contaminated water before breakthrough occurred, while maintaining a satisfactory permeability (˜627.32 L/(m2 h bar)) and antifouling property. The exhausted membrane could easily be regenerated in aminoethanesulfonic acid solution for repeated use with a negligible decrease in capacity. Moreover, the membrane showed excellent long-term stability in a cross-flow filtration process due to the amido bond between the Cu-iMOFs and membrane surface as well as the "protection" of polyvinyl alcohol. Selective and reversible ion-exchange between the sulfonic acid (R-SO3) ligands of Cu-iMOFs and tetrahedral oxo-anionic species was verified to be the pathway for ClO4− trapping. Thus, other problematic elements that also occur in tetrahedral form in water can be removed by this method.

Biological perchlorate reduction: which electron donor we can choose?

Biological reduction is an effective method for removal of perchlorate (ClO4-), where perchlorate is transformed into chloride by perchlorate-reducing bacteria (PRB). An external electron donor is required for autotrophic and heterotrophic reduction of perchlorate. Therefore, plenty of suitable electron donors including organic (e.g., acetate, ethanol, carbohydrate, glycerol, methane) and inorganic (e.g., hydrogen, zero-valent iron, element sulfur, anthrahydroquinone) as well as the cathode have been used in biological reduction of perchlorate. This paper reviews the application of various electron donors in biological perchlorate reduction and their influences on treatment efficiency of perchlorate and biological activity of PRB. We discussed the criteria for selection of appropriate electron donor to provide a flexible strategy of electron donor choice for the bioremediation of perchlorate-contaminated water.

Perchlorate bio-reduction in a methane-based membrane biofilm reactor in the presence and absence of oxygen

Perchlorate has been widely detected in various water environments and could cause serious health problems. Methane has been proposed as a promising electron donor to remove perchlorate from contaminated water, yet it is unclear whether and how microbial methane oxidation couples with perchlorate reduction, in particular under anoxic conditions. Here, the feasibility and performance of perchlorate reduction driven by methane in the presence and absence of oxygen were investigated and compared in a lab-scale methane-based membrane biofilm reactor. Long-term operational performance suggested that perchlorate was reduced to chloride, with 4 mg Cl/L/d of perchlorate removal rate under anoxic conditions. Differently, perchlorate removal rate increased to 16 mg Cl/L/d, and volatile fatty acids (VFAs) were produced from methane partial oxidation when a limited oxygen (10 mg/L/d) was externally supplied. Regardless of oxygen conditions, microbial perchlorate reduction driven by methane might be mediated through synergistic interactions by a microbial consortium, but with different key microbial members under both oxygen regimes. Under anoxic conditions, aerobic methanotrophs (likely Methylocystaceae and Methylococcaceae) might micro-aerobically oxidize methane by utilizing internal oxygen from microbial perchlorate reduction, which might be mediated by Rhodocyclaceae. In contrast, under oxygen-limiting conditions, methanogens (e.g., Methanosarcina) and fermenters (e.g., Veillonellaceae) likely jointly converted methane into VFAs, then dissimilatory perchlorate-reducing bacteria (e.g., Rhodocyclaceae) utilized the produced VFAs to reduce perchlorate to chloride. Our findings provide evidence to link methane oxidation with perchlorate reduction under both oxygen regimes, which could be facilitated to design a process to remove perchlorate from groundwater.

Perchlorate Removal in Microbial Electrochemical Systems With Iron/Carbon Electrodes.

Perchlorate removal was tested in the cathode chamber of microbial electrochemical systems (MESs). Dual-chambers MESs were constructed and operated in batch mode with four kinds of cathode materials including Fe/C particles (Fe/C), zero valent iron particles (ZVI), blank carbon felt (CF), and active carbon (AC). Without external energy supply or perchlorate-reducing microbial pre-enrichment, perchlorate () removal could be achieved in the cathode chambers of MESs at different efficiencies. The highest removal rates in these reactors were 18.96 (Fe/C, 100 Ω, 2 days), 15.84 (ZVI, 100 Ω, 2 days), 14.37 (CF, 100 Ω, 3 days), and 19.78 mg/L/day (AC, 100 Ω, 2 days). degradation products were mainly Cl− and , and the total chlorine in the products was lower than the theoretical input. The non-conservation of the total chlorine may be caused by the adsorption and co-precipitation related to the electrode materials. Coulombs and coulombic efficiency calculation showed that electron provided by MESs was partially responsible for reduction, for the Fe/C cathode reactors, about a quarter of electron was provided by MESs.

A combined heterotrophic and sulfur-based autotrophic process to reduce high concentration perchlorate via anaerobic baffled reactors: Performance advantages of a step-feeding strategy

The combined anaerobic baffled reactors (ABRs) of heterotrophic and sulfur-based autotrophic processes were first investigated for the removal of high perchlorate concentration under different feeding strategies. The removal efficiency of the step-feeding ABR (SF-ABR) reached 97.56% at 800 mg/L perchlorate, which was significantly superior to the normal-feeding ABR (NF-ABR). In three components of the extracellular polymeric substances (EPS), the fluorescence intensity of the tryptophan-like component were identified by fluorescence excitation–emission matrix (EEM) spectra with parallel factor (PARAFAC) analysis, and exhibited a positive relationship with the perchlorate removal rate in the heterotrophic perchlorate reduction unit (HPR unit) of the SF-ABR (R2 = 0.9791) and NF-ABR (R2 = 0.9860). Bacterial community analysis suggested the dominating perchlorate reducing bacteria and the diversity in two ABRs. Principal component analysis indicated that the electron donor affected the microbial community structures. The study confirms that the SF-ABR is a powerful bioreactor for the combined heterotrophic and sulfur-based autotrophic process.

Removal of Perchlorate from Salt Water Using Microorganisms

Removal of Perchlorate from Salt Water Using Microorganisms

Multilayered surface for the interactive separation of perchlorate from aqueous medium

Environmental contextPerchlorate from rocket fuel plants or firework manufacturing units can seriously contaminate drinking water. We developed a separation skin on a microfiltration membrane and on sand that can remove perchlorate from water in the presence of competing ions. This method is suitable for a domestic water purification unit selective for perchlorate removal. AbstractThis study reports an interactive separation of perchlorate (ClO4−) by polyethyleneimine (PEI) and poly (styrene sulfonate) (PSS) deposited on a microfiltration membrane and on sand surfaces. The variation of the interaction with respect to deposition and feed variables was assessed. The 9 bilayered ((PEI/PSS) 0.15M NaCl, pH 6)) membranes showed a ClO4− rejection of ~80%. An increase in the feed concentration to 25mgL−1 reduced the rejection to 58%. With a feed pH from 4 to 10, the rejection varied between almost 100% and 16%. The presence of ions reduced the rejection percentage of ClO4− with the interference by the ions in the order of SO42−>HCO3−>NO3−>Cl−. The interference is attributed to the characteristics of the competing ions and the nature of the multilayers. A positive impact of post-treatment (98%) and capping layers on rejection percentage (80% to nearly complete) for synthetic and ClO4− contaminated field water samples is clearly established. The presence of competing ions is also accounted for by a capped membrane system. The selectivity of the competing ions increases with capping layers of 1M NaCl in the order of HCO3−>NO3−>SO42−. In the field water samples up to a SO42− concentration of 3.0mgL−1, the capping layers with 0.4M NaCl result in a near complete rejection of ClO4−, whereas further enhancement requires a capping layer of 1M NaCl. A sand filtration system was developed by incorporating the pre-optimised polyelectrolyte multilayer on sand. Deposition of a single bilayered PEI/PSS multilayer on sand effectively (nearly completely) removes ClO4−.

Development of ion exchangers for the removal of health-hazardous perchlorate ions from aqueous systems

In order to investigate diffusion models and adsorption mechanism of polymeric ligand exchangers (PLE) for the removal of perchlorate from tap water Lewatit MonoPlus TP 220-Cu, Lewatit MonoPlus TP 220-CuEDDS, Dowex 4195-Cu and M 4195-CuEDDS were prepared and compared with commercial Lewatit TP 220 and Dowex M 4195. Based on the adsorption experiments, diffusion mechanisms were studied using the intraparticle diffusion, film diffusion, Boyd, Dumwald-Wagner models. The pore diffusion coefficient (Dp), film diffusion coefficient (Df) as well as well-known kinetic models like the pseudo first and the pseudo second order were also applied to fit the experimental data. The adsorption study was carried out at pH equal 7.0 and different contact time. The kinetics of adsorption was based on the pseudo second order model. The adsorption studies show that the adsorption rate controlling step is realized mainly by intraparticle diffusion. The basic surface structural changes before and after the perchlorate sorption on each sorbent were investigated using ATR-FTIR. After sorption the band at 1085 cm−1 appeared which showed efficiency of the sorption process. The adsorbents were also characterized by the nitrogen adsorption/desorption isotherms, thermogravimetry (TG) and derivative thermogravimetry (DTG) analysis. The study proved efficiency of Lewatit MonoPlus TP 220-Cu and Lewatit MonoPlus TP 220-CuEDDS, Dowex 4195-Cu and M 4195-CuEDDS for perchlorate removal from water.

Perchlorate removal from brackish water by capacitive deionization: Experimental and theoretical investigations

Capacitive deionization (CDI) has attracted increasing attention over the past decade for the facile removal of ions from aqueous solutions. Nowadays, CDI is rapidly growing and evolving, and has been applied in many aspects. One important application field is water remediation, i.e., removing ionic contaminants of concern from water. Herein, we investigated the feasibility of perchlorate removal from brackish waters by batch-mode CDI technology. Effects of various operating parameters on dynamic electrosorption processes of both perchlorate and chloride were examined. Meanwhile, a one-dimensional CDI process model for dual-anions was developed to quantitatively describe the electrosorption kinetics of perchlorate and chloride, and an excellent agreement between the modeling results and the experimental data was observed. Experimental results revealed a favorably strong preferential adsorption of ClO4− over Cl− in the studied CDI system under various conditions. Moreover, only slight discrepancy between adsorption-desorption cycles was found, demonstrating the good regeneration of electrodes and operational stability of the CDI cell. Finally, the scale-up studies indicated that the CDI stack with multiple pairs of electrodes could achieve a much more superior ion removal performance than the CDI cell with only one pair of electrodes. To conclude, these results showed that the CDI system was effective for perchlorate selective removal in the presence of other major ions and had potential in treatment of perchlorate-contaminated brackish water.

Column adsorption and regeneration study of magnetic biopolymer resin for perchlorate removal in presence of nitrate and phosphate

A magnetized and quaternary amine-functionalized bio-resin derived from corn stalk (CS-MNB) was successfully synthesized and applied for perchlorate removal by combining of column adsorption and biological/chemical regeneration in presence of nitrate and phosphate. Characterization by SEM, TEM, XRD, Zeta potential, BET and XPS revealed that CS-MNB had well-developed pore structure, large surface area and lots of quaternary-amine groups, enhancing the diffusion and removal of anion. Column adsorption of co-anions was investigated considering the bed depths, flow rates, influent pHs and anion concentrations using CS-MNB. The performance of fixed-bed column was optimal at the condition of bed depth of 2.15 cm, flow rate of 5 mL/min, and pH 4. The maximum adsorption capacities of CS-MNB were calculated to be 23.16, 6.48 and 48.73 mg/g for perchlorate, nitrate and phosphate, respectively. These three anions could be efficiently removed by the magnetic bio-resin, through an ion-exchange reaction between Cl− in quaternary amine groups and the dissolved anions. After being adsorbed by the bio-resin, the concentrated anions could be efficiently bio-reduced by the acclimated sludge predominated by Proteobacteria species. The simultaneous perchlorate and nitrate reductions were achieved by biological regeneration, although a lower bio-regeneration efficiency (26–89%) was observed as compared with that of chemical regeneration (90–93%).

Sulfur disproportionation tendencies in a sulfur packed bed reactor for perchlorate bio-autotrophic reduction at different temperatures and spatial distribution of microbial communities

This study investigates the sulfur (S) disproportionation tendencies in a sulfur packed bed reactor for perchlorate bio-autotrophic reduction at different temperatures. The reactor was operated with over 99% efficiency for 21.00 ± 1.40 mg L−1 perchlorate removal when the hydraulic retention time (HRT) ranged from 12.00 h to 0.75 h at 27 ± 2 °C. When HRT was controlled at 1.00 h, the perchlorate removal efficiency was only 8 ± 1% as the temperature dropped to 6 ± 1 °C. The half-order model fit both perchlorate removal and S disproportionation reaction well. Compared with S disproportionation, the decrease of temperature had a greater influence on perchlorate reduction. As the temperature dropped from 27 ± 2 °C to 6 ± 1 °C, the 1/2K1/2v,R for perchlorate reduction decreased from 7.37 mg1/2 L−1/2 h−1 to 0.19 mg1/2 L−1/2 h−1. Meanwhile, the 1/2K1/2v,S for S disproportionation decreased from 3.04 mg1/2 L−1/2 h−1 to 1.96 mg1/2 L−1/2 h−1. The reaction activation energy of perchlorate reduction and S disproportionation was 120.28 kJ mol−1 and 13.44 kJ mol−1, respectively. The S disproportionation reaction proceeded remarkably at the beginning of the reduction, a longer HRT and higher temperature promoted S disproportionation, resulting in excessive sulfate generation and alkalinity consumption. Besides, the spatial distribution of the microbial communities and the dominant bacteria function under different HRTs was analyzed using high-throughput sequencing.

Bio-mixotrophic perchlorate reduction to control sulfate production in a step-feed sulfur-based reactor: A study of kinetics, ORP and bacterial community structure

Excess sulfate production and low concentration of perchlorate removal are the main problems for sulfur-based perchlorate reduction reactor. In this study, the problems were firstly solved by step-feeding under mixotrophic conditions. The performances of step-feed sulfur-based reactor (SFSBR) and up-flow sulfur-based reactor (UFSBR) are compared. At perchlorate of 194 mg/L, acetate of 28.8 mg/L and hydraulic retention time of 0.9 h, the Half-order reaction rate constant and the sulfate production of SFSBR were 29.7 mg1/2/L1/2·h and 171 mg/L, respectively, which were superior to those of UFSBR. The oxidation-reduction potential values of SFSBR were lower than that of UFSBR. Meanwhile, the biodiversity along the height of the reactor was decreased by step-feeding. Principal component analysis showed significant interrelations existed among the bacterial community composition and the operational/environmental conditions in each treatment zone. Consequently, the SFSBR provides an effectively alteration for the removal of high perchlorate concentration and control sulfate.