Membrane capacitive deionization (MCDI) is a water desalination technique based on applying a cell voltage between two oppositely placed porous electrodes sandwiching a spacer channel that transports ...the water to be desalinated. In MCDI, ion-exchange membranes are positioned in front of each porous electrode to prevent co-ions from leaving the electrode region during ion adsorption, thereby enhancing the salt adsorption capacity. MCDI can be operated at constant cell voltage (CV), or at a constant electrical current (CC).
In this paper, we present both experimental and theoretical results for desalination capacity and rate in MCDI (both in the CV- and the CC-mode) as function of adsorption/desorption time, salt feed concentration, electrical current, and cell voltage. We demonstrate how by varying each parameter individually, it is possible to systematically optimize the parameter settings of a given system to achieve the highest average salt adsorption rate and water recovery.
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► Data for salt adsorption in membrane capacitive deionization are presented. ► Both constant-voltage and constant-current operation are considered. ► Varying all possible process parameters individually allows for systematic optimization. ► Average salt adsorption rate and water recovery defined as key performance indicators. ► We present a two-porosity modified Donnan model which well describes our data.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK, ZRSKP
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► Charged porous electrodes may first adsorb one ion and then exchange for another. ► Time-dependent ion selectivity can be used to selectively desalinate water. ► Combined EDL and ...electrode transport theory describes time-dependent ion selectivity. ► Expressions given for ion adsorption in salt mixtures for EDL Gouy-Chapman theory.
In a combined experimental and theoretical study, we show that capacitive charging of porous electrodes in multicomponent electrolytes may lead to the phenomenon of time-dependent ion selectivity of the electrical double layers (EDLs) in the electrodes. This effect is found in experiments on capacitive deionization of water containing NaCl/CaCl2 mixtures, when the concentration of Na+ ions in the water is five times the Ca2+-ion concentration. In this experiment, after applying a voltage difference between two porous carbon electrodes, first the majority monovalent Na+ cations are preferentially adsorbed in the EDLs, and later, they are gradually replaced by the minority, divalent Ca2+ cations. In a process where this ion adsorption step is followed by washing the electrode with freshwater under open-circuit conditions, and subsequent release of the ions while the cell is short-circuited, a product stream is obtained which is significantly enriched in divalent ions. Repeating this process three times by taking the product concentrations of one run as the feed concentrations for the next, a final increase in the Ca2+/Na+-ratio of a factor of 300 is achieved. The phenomenon of time-dependent ion selectivity of EDLs cannot be explained by linear response theory. Therefore, a nonlinear time-dependent analysis of capacitive charging is performed for both porous and flat electrodes. Both models attribute time-dependent ion selectivity to the interplay between the transport resistance for the ions in the aqueous solution outside the EDL, and the voltage-dependent ion adsorption capacity of the EDLs. Exact analytical expressions are presented for the excess ion adsorption in planar EDLs (Gouy-Chapman theory) for mixtures containing both monovalent and divalent cations.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK
Information on the removal of antibiotics and ARGs in full-scale WWTPs (with or without additional treatment technology) is limited. However, it is important to understand the efficiency of ...full-scale treatment technologies in removing antibiotics and ARGs under a variety of conditions relevant for practice to reduce their environmental spreading. Therefore, this study was performed to evaluate the removal of antibiotics and ARGs in a conventional wastewater treatment plant (WWTP A) and two full-scale combined with additional treatment technologies. WWTP B, a conventional activated sludge treatment followed by an activated carbon filtration step (1-STEP® filter) as a final treatment step. WWTP C, a treatment plant using aerobic granular sludge (NEREDA®) as an alternative to activated sludge treatment. Water and sludge were collected and analysed for 52 antibiotics from four target antibiotic groups (macrolides, sulfonamides, quinolones, tetracyclines) and four target ARGs (ermB, sul 1, sul 2 and tetW) and integrase gene class 1 (intI1). Despite the high removal percentages (79–88%) of the total load of antibiotics in all WWTPs, some antibiotics were detected in the various effluents. Additional treatment technology (WWTP C) showed antibiotics removal up to 99% (tetracyclines). For ARGs, WWTP C reduced 2.3 log followed by WWTP A with 2.0 log, and WWTP B with 1.3 log. This shows that full-scale WWTP with an additional treatment technology are promising solutions for reducing emissions of antibiotics and ARGs from wastewater treatment plants. However, total removal of the antibiotics and ARGS cannot be achieved for all types of antibiotics and ARGs. In addition, the ARGs were more abundant in the sludge compared to the wastewater effluent suggesting that sludge is an important reservoir representing a source for later ARG emissions upon reuse, i.e. as fertilizer in agriculture or as resource for bioplastics or bioflocculants. These aspects require further research.
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•Good removal (79-88%) of total antibiotics was observed at all WWTPs.•NEREDA® (2.3 log) and conventional WWTP (2.0 log) are more effective for log reduction of ARG than 1-STEP® filter (1.3 log).•The tested additional treatment technologies did not fully remove antibiotics and ARGs from the waterphase.•ARGs were detected in sludge, and the sludge is an important reservoir for ARGs.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
•PVA/CS and PVA/CS/Fe assists in anammox biomass immobilization and improves NRR.•EPS entangles anammox cells within the gel beads, resulting in compact aggregates.•The interaction between Fe and EPS ...strongly promotes the granule compactness.
Granule-based immobilization of anammox biomass assisted by polyvinyl alcohol/chitosan (PVA/CS) and PVA/CS/Fe gel beads was studied, via the operation of three identical up-flow reactors (R1 without gel beads, R2 with PVA/CS, R3 with PVA/CS/Fe) for 203 days. In the end, the nitrogen removal rates (NRR) were 5.3 ± 0.4, 10.0 ± 0.3 and 13.9 ± 0.5 kg-N m−3 d−1 for R1, R2 and R3, respectively. The porous PVA/CS and PVA/CS/Fe created a suitable eco-niche for anammox bacteria to grow and attach, thus being retained in the reactor. The EPS entangles newly grown cells within the gel beads, resulting in compact aggregation. The interaction between Fe ions added to PVA/CS/Fe gel beads and negatively charged EPS groups strongly promoted granule strength and compactness. The immobilization method proposed by this study was found to effectively improve biomass retention in the reactors, which is promising for advanced anammox process applications.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPUK, ZAGLJ, ZRSKP
Ion exchange membranes (IEMs) are used for selective transport of ions between two solutions. These solutions are often different in concentration or composition. The membrane resistance (RM) is an ...important parameter affecting power consumption or power production in electrodialytic processes. In contrast to real applications, often RM is determined while using a standard 0.5M NaCl external solution. It is known that RM increases with decreasing concentration. However, the detailed effect of a salinity gradient present over an IEM on RM was not known, and is studied here using alternating and direct current. NaCl solution concentrations varied from 0.01 to 1.1M. The results show that RM is mainly determined by the lowest external concentration. RM can be considered as two resistors in series i.e. a gel phase (concentration independent) and an ionic solution phase (concentration dependent). The membrane conductivity is limited by the conductivity of the ionic solution when the external concentration, cext<0.3M. The membrane conductivity is limited by the conductivity of the gel phase when cext≥0.3M, then differences of RM are small. A good approximation of experimentally determined RM can be obtained. The internal ion concentration profile is a key factor in modeling RM.
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•IEM resistance largely depends on the lowest external solution ion concentration.•An IEM can be regarded as existing from two conductive phases placed in series.•These two phases stem from structural inhomogeneity of the membrane pore.•The ion concentration profile in the membrane defines largely the IEM conductance.•The profile is influenced by the size of the (electro-) osmotic water flux.
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•UV-LED/TNAs could be efficient for photocatalytic degradation of metoprolol (MTP).•Morphology and crystalline composition of TNAs have impact on MTP degradation.•Operational ...parameters affecting UV-LED/TNAs MTP degradation were studied.•Bicarbonate ions were found to be able to quench conduction band electrons.•MTP degradation mechanisms in UV-LED/TNAs treatment was elucidated.
The aim of this study was to evaluate the use of self-organized TiO2 nanotube arrays (TNAs) as immobilized catalyst and UV-LED as light source (UV-LED/TNAs) for photocatalytic degradation of the β-blocker metoprolol (MTP) from aqueous solution. Firstly we employed electrochemical anodization to synthesize self-organized TNAs, and the effect of anodization potential and annealing temperature was examined. Characterization by SEM demonstrated a linear relation between the diameter of TiO2 nanotubes produced and the anodization potential, while Raman measurement revealed the vital role of annealing on crystallographic composition of the anodic produced TiO2 nanotubes. Regarding their performance in photocatalytic MTP degradation, surface morphology and crystallographic composition of the TNAs were found to impose crucial influence: only TNAs with diameter not smaller than 53nm enabled rapid MTP degradation, and highest MTP degradation was obtained when a mixture of anatase and rutile were present in the TNAs. Secondly, the effect of operational parameters, i.e initial MTP concentration, pH, was investigated. Initial MTP concentration at low level had no detrimental effect on the process performance. Rapid MTP degradation and high total removal were achieved in a wide pH range (3–11). To evaluate the applicability of TNAs for water treatment, experiments were first carried out in the presence of three different commonly present water constituents, i.e bicarbonate ions, phosphate ions, and natural organic matters (NOMs). The results show that bicarbonate and phosphate ions have no inhibitory effect at concentration levels up to 200mg/L, and NOMs exhibit detrimental effect when their concentration exceeds 5mg/L. The total removal MTP degradation reduced from 87.09±0.09% to 62.05±0.08% when tap water samples were applied, demonstrating reasonable efficacy for practical applications. Regarding the degradation mechanism, formic acid and tert-butanol were added as scavenger for photo-generated holes (h+) and hydroxyl radicals (·OH), respectively. The obtained results demonstrate that primary degradation process occurred in liquid phase with participation of hydroxyl radicals in the liquid phase (·OH liquid), while smaller portion of MTP were degraded on the catalysis surface via reaction with h+ and hydroxyl radicals adsorbed on the catalyst surface (·OH surface). Other reactive species, e.g photo generated electrons and superoxide radical anions, did also play a minor role in MTP degradation. The mechanistic aspect was further confirmed by identification of degradation products by LC–MS/MS. The TNAs exhibited good stability after repeated use under varied operation conditions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
In this work desalination of a ternary salt mixture and artificial North Sea water is studied with a lab scale electrodialysis stack, which was used in a recycling batch mode. During desalination ...samples were taken and the ionic composition of the dilute stream was determined. The effect of applied current density (10–300A/m2) on this composition was investigated.
A clear effect of applied current density was observed. A lower applied current density leads to a more complete reduction in concentration of divalent ions, in an earlier extent of desalination. This influence of the applied current density could be related to the concentration polarization effects that occur in the diffusional boundary layer and are explained with a model based on the Nernst–Planck flux equation. It was found that the lower initial ion concentration of Ca2+, Mg2+, but also of K+, and SO42− compared to respectively Na+ and Cl−, leads to stronger depletion of these ions in the transport layer adjacent the membrane. These boundary layer effects are more pronounced at higher applied current densities, resulting in reduced transport of ions with a low initial concentration. High monovalent over divalent ion ratios can be found at low applied current.
•A theory of the permselectivity of ion exchange membrane system was developed.•Membrane selectivity is mainly governed by concentration polarization.•Lower applied current densities lead to higher divalent ion removal.•The monovalent over divalent ion ratio can be increased by a factor 20–60.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK
High-loaded membrane bioreactors (HL-MBRs), i.e. MBRs which are operated at extremely short sludge and hydraulic retention times, can be applied to flocculate and concentrate sewage organic matter. ...The concentrated organics can be used for energy recovery, or for the production of more valuable organic chemicals. Little is known about the effect of the dissolved oxygen concentration (DO) on this bioflocculation process. To examine this effect, two HL-MBRs were operated, respectively at a low (1 mg L−1) and a higher (4 mg L−1) DO. The higher DO resulted in a better flocculation efficiency, i.e. 92% of the colloidal COD in the sewage flocculated compared to 69% at the lower DO. The difference was attributed to a higher microbial production of extracellular polymeric substances at a DO of 4 mg L−1 and to more multivalent cations (calcium, iron and aluminium) being distributed to the floc matrix. In addition, the HL-MBR that was operated at a DO of 4 mg L−1 gave a bigger mean floc size, a lower supernatant turbidity, better settleability and better membrane filterability than the HL-MBR that was operated at a DO of 1 mg L−1.
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•HL-MBR operation at high DO (4 mgO2 L−1) resulted in improved bioflocculation.•Improved bioflocculation was positively correlated to higher concentrations of EPS.•More multivalent cations were distributed to the floc matrix in the high DO reactor.•Sludge flocs in the high DO reactor were bigger than in low DO reactor.•Improved bioflocculation was accompanied by a lower membrane fouling potential.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK
High loaded MBRs (HL-MBR) can concentrate sewage organic matter by aerobic bioflocculation for subsequent anaerobic conversion to methane or volatile fatty acids. In the range of very short solid ...retention times (SRT), the effect of SRT on bioflocculation and EPS production in HL-MBR was investigated. This short SRT range was selected to find an optimum SRT maximising recovery of organics by aerobic bioflocculation and minimizing losses of organics by aerobic mineralization. Bioflocculation was studied in five HL-MBRs operated at SRTs of 0.125, 0.25, 0.5, 1 and 5 d. The extent of flocculation, defined as the fraction of suspended COD in the concentrate, increased from 59% at an SRT of 0.125 d to 98% at an SRT of 5 d. The loss of sewage organic matter by biological oxidation was 1, 2, 4, 11 and 32% at SRT of 0.125–5 d. An SRT of 0.5–1 d gave best combination of bioflocculation and organic matter recovery. Bound extracellular polymeric substances (EPS) concentrations, in particular EPS-protein concentrations, increased when the SRT was prolonged from 0.125 to 1 d. This suggests that these EPS-proteins govern the bioflocculation process. A redistribution took place from free (supernatant) EPS to bound (floc associated) EPS when the SRT was prolonged from 0.125 to 1 d, further supporting the fact that the EPS play a dominant role in the flocculation process. Membrane fouling was most severe at the shortest SRTs of 0.125 d. No positive correlation was detected between the concentration of free EPS and membrane fouling, but the concentration of submicron (45–450 nm) particles proved to be a good indicator for this fouling.
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•We examined bioflocculation of wastewater in HL-MBRs at very short SRTs and HRTs.•We studied EPS concentration at various short SRTs in relation to bioflocculation.•Bioflocculation and EPS concentration increased when SRT was prolonged to 1 d.•Amount of COD mineralized increased from 1 to 32% when SRT was prolonged (0.125–5 d).•Fouling was reduced as bioflocculation was improved.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK
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