Research

2262 KiB

Open AccessFeature PaperArticle

Impact of Powdered Activated Carbon Structural Properties on Removal of Organic Foulants in Combined Adsorption-Ultrafiltration

by Martin Schulz, Sönke Bünting and Mathias Ernst

Water 2017, 9(8), 580; https://doi.org/10.3390/w9080580 - 03 Aug 2017

Cited by 12 | Viewed by 5335

Abstract

The impact of structural properties of three commercial PACs as well as two mechanically ground PACs on their efficiency in NOM removal and fouling reduction in combined adsorption-ultrafiltration (PAC-UF) of northern German groundwater was investigated. All PACs showed highest adsorption affinity for medium [...] Read more.

The impact of structural properties of three commercial PACs as well as two mechanically ground PACs on their efficiency in NOM removal and fouling reduction in combined adsorption-ultrafiltration (PAC-UF) of northern German groundwater was investigated. All PACs showed highest adsorption affinity for medium molecular weight NOM fractions. The meso-pore surface area rather than the total surface area (B.E.T.) mainly governed the extent of NOM removal. However, adsorption of macromolecular NOM fractions, which were found to be the main contributor to total and irreversible fouling, was limited by tested commercial carbons, and no significant mitigation of fouling was achieved by any tested PAC concentration. Lowering the particle size by grinding of the PAC, however, enhanced removal of macromolecular NOM fractions considerably, and fouling mitigation occurred at substantially lower PAC concentrations compared to raw carbons. A larger external surface area probably let to more shell adsorption, a more homogeneous particle distribution on the membrane surface and a better mass transport. In addition, comparison of the adsorption isotherms of raw and milled PACs showed that, due to the grinding of PAC particles, additional inner pores structures became available for NOM adsorption. Results of this study point out that structural properties of PAC dramatically influence the efficiency of combined PAC-UF, which needs to be considered during PAC selection and process design. Full article

(This article belongs to the Special Issue Assessment of Water Quality and Treatment Technologies in Potable Water Use)

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1464 KiB

Open AccessArticle

Efficiency of Mn Removal of Different Filtration Materials for Groundwater Treatment Linking Chemical and Physical Properties

by Joanna Jeż-Walkowiak, Zbysław Dymaczewski, Agnieszka Szuster-Janiaczyk, Ariadna B. Nowicka and Mirosław Szybowicz

Water 2017, 9(7), 498; https://doi.org/10.3390/w9070498 - 08 Jul 2017

Cited by 17 | Viewed by 6040

Abstract

This paper presents research on Fe and Mn removal from groundwater. In treatment systems of aeration followed by rapid filtration (no chemical dosage), manganese removal is possible due to the manganese dioxide catalyst present on the grains of filtration material. The goal of [...] Read more.

This paper presents research on Fe and Mn removal from groundwater. In treatment systems of aeration followed by rapid filtration (no chemical dosage), manganese removal is possible due to the manganese dioxide catalyst present on the grains of filtration material. The goal of the presented research was to find a correlation between the catalyst layer’s composition as well as its internal porosity and the effectiveness and stability of manganese removal in the filtration process. In order to establish the influence of catalyst characteristics on manganese removal effectiveness, the filtration experiment was conducted using filtration materials with catalytic contact layers of different origin. Oxide coated auto-activated silica sand and Gabon manganese ore were tested. Inactive silica sand was used as reference. The results of filtration experiments were combined with analyses of chemical composition, internal porosity, and crystalline parameters of catalyst contact layers of grains. For the determination catalyst contact layer parameters, the following methods were used: Raman spectroscopy, X-ray powder diffractometry (XRD), Scanning Electron Microscope – Energy dispersive spectroscopy (SEM-EDAX), nitrogen adsorption. Pilot scale research on the filtration process demonstrated that auto-activated filtration material was characterized by the highest efficiency of manganese removal and stability of effects during the whole research. The effectiveness of Gabon manganese ore dropped from 90% and stabilized on the level of ca. 60% within 15 days of the experiment. Full article

(This article belongs to the Special Issue Assessment of Water Quality and Treatment Technologies in Potable Water Use)

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1656 KiB

Open AccessArticle

Fate of Trace Organic Compounds in Granular Activated Carbon (GAC) Adsorbers for Drinking Water Treatment

by Alexander Sperlich, Mareike Harder, Frederik Zietzschmann and Regina Gnirss

Water 2017, 9(7), 479; https://doi.org/10.3390/w9070479 - 30 Jun 2017

Cited by 26 | Viewed by 7478

Abstract

Granular activated carbon (GAC) adsorbers for drinking water treatment were operated for approx. 14 months and the breakthrough of dissolved organic carbon (DOC) and trace organic chemicals (TOrCs) was monitored. Effluent concentration profiles of gabapentin and valsartan acid increase already at throughputs of [...] Read more.

Granular activated carbon (GAC) adsorbers for drinking water treatment were operated for approx. 14 months and the breakthrough of dissolved organic carbon (DOC) and trace organic chemicals (TOrCs) was monitored. Effluent concentration profiles of gabapentin and valsartan acid increase already at throughputs of <10,000 BV. The corresponding breakthrough curves flatten out without reaching the influent concentration level. This strongly indicates biological degradation of these substances in the GAC adsorbers under aerobic conditions, contributing to a more efficient use of GAC. The observed biodegradation in pilot GAC adsorbers also confirms recent reports of biodegradation of gabapentin and valsartan acid during managed aquifer recharge. Oxypurinol is comparatively well adsorbed and no breakthrough was observed during the experimental period. Adsorption capacity and breakthrough characteristics of oxypurinol appear very similar to carbamazepine. Breakthrough of GAC adsorbers operated with drinking water was compared to those of groundwater-fed adsorbers. The results show, that it is generally advisable to use previously aerated influents for GAC fixed-bed adsorbers because this can substantially improve biological removal of otherwise poorly adsorbable compounds and ensure full GAC accessibility for adsorbates by avoiding the undesirable formation of inorganic precipitates on adsorption sites. Full article

(This article belongs to the Special Issue Assessment of Water Quality and Treatment Technologies in Potable Water Use)

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2365 KiB

Open AccessArticle

Modelling of Ozone Mass-Transfer through Non-Porous Membranes for Water Treatment

by Matthew J. Berry, Caitlin M. Taylor, William King, Y. M. John Chew and Jannis Wenk

Water 2017, 9(7), 452; https://doi.org/10.3390/w9070452 - 23 Jun 2017

Cited by 25 | Viewed by 8634

Abstract

The mass transfer of ozone and oxygen into water through non-porous membranes was studied using computational fluid dynamics (CFD) modelling and fundamental convection-diffusion theory. Ozone is a gaseous oxidant that is widely applied in drinking water treatment. Membrane contactors are an alternative to [...] Read more.

The mass transfer of ozone and oxygen into water through non-porous membranes was studied using computational fluid dynamics (CFD) modelling and fundamental convection-diffusion theory. Ozone is a gaseous oxidant that is widely applied in drinking water treatment. Membrane contactors are an alternative to conventional gas dispersion methods for injection of ozone gas mixtures into water. Few studies have explored computational approaches for membrane based ozone transport. In this investigation, quantitative concentration profiles across a single polydimethylsiloxane (PDMS) capillary membrane tube with internal gas flow and external liquid flow were obtained, including single mass transfer resistances and overall mass transfer coefficients for ozone and oxygen for varying membrane lengths, thicknesses, and laminar flow liquid side velocities. Both the influence of diffusivity and solubility of gases in the membrane were considered with the applied model. Previous studies have neglected the solubility of gases in the membranes in their analysis of ozone and oxygen gas fluxes. This work shows that the solubility has a significant impact of the overall mass transfer coefficients, in particular for oxygen. The main resistance for ozone was found in the liquid side, while for oxygen it was in the membrane. Mass transfer correlations based on heat transfer analogies revealed Sherwood (Sh) correlations for ozone and oxygen with good agreement to literature data, indicating that the applied computational model returns sensible results. The outcome of this study provides an initial basis for computational predictions of ozone and oxygen mass transfer for different membrane materials, flow conditions and reactor designs. Full article

(This article belongs to the Special Issue Assessment of Water Quality and Treatment Technologies in Potable Water Use)

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1902 KiB

Open AccessFeature PaperArticle

Effect of Organic Matter on Cr(VI) Removal from Groundwaters by Fe(II) Reductive Precipitation for Groundwater Treatment

by Anna Gröhlich, Margarethe Langer, Manassis Mitrakas, Anastasios Zouboulis, Ioannis Katsoyiannis and Mathias Ernst

Water 2017, 9(6), 389; https://doi.org/10.3390/w9060389 - 01 Jun 2017

Cited by 21 | Viewed by 5579

Abstract

Due to its toxicity, Cr(VI) is undesirable in groundwater. Its chemical reduction to Cr(III) species, followed by precipitation is the most widely practiced treatment technique for the removal of Cr(VI) from polluted waters. The resulting Cr(III) species present low solubility, is much less [...] Read more.

Due to its toxicity, Cr(VI) is undesirable in groundwater. Its chemical reduction to Cr(III) species, followed by precipitation is the most widely practiced treatment technique for the removal of Cr(VI) from polluted waters. The resulting Cr(III) species present low solubility, is much less toxic, and can be subsequently removed either by precipitation, or by adsorption onto iron oxy-hydroxides and co-precipitation. The effects of several parameters, such as the pH value of water to be treated, the applied Fe(II) dose, and the presence of appropriate mineral surfaces, are well investigated and understood. However, the impact of the presence of humic acids (HAs) in this process has only been considered by rather few studies. The main aim of this study was to determine the effect of humic substances on Fe(II) reductive precipitation of Cr(VI) within a pH range relevant for drinking water treatment. Jar test experiments were performed, using artificial groundwater of defined composition and initial Cr(VI) concentration 100 μg/L, ferrous sulphate dosages 0.25–2 mg Fe(II)/L, and pH values 6.5–8. It was found that Cr(VI) and total chromium (Cr(total)) can be reliably removed in the absence of HAs in the tested pH range with the addition of Fe(II) dosage of 1 mg Fe(II)/L. Further on, the results indicated that the reduction of Cr(VI) is only slightly affected by the presence of HAs. However, increased residual total Cr concentrations were found at lower Fe(II) dosages and/or higher pH values. Additionally, the removal of the Cr(III) species formed during Cr(VI) reduction was strongly inhibited by the presence of HAs under the examined experimental conditions, since residual concentrations higher than 60 μg/L were determined. The results of this study will have implications to the ongoing discussion of a new, stricter, European Union regulation limit, regarding the presence of total chromium in drinking water. Full article

(This article belongs to the Special Issue Assessment of Water Quality and Treatment Technologies in Potable Water Use)

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1280 KiB

Open AccessFeature PaperArticle

Impacts of Accumulated Particulate Organic Matter on Oxygen Consumption and Organic Micro-Pollutant Elimination in Bank Filtration and Soil Aquifer Treatment

by Josefine Filter, Martin Jekel and Aki Sebastian Ruhl

Water 2017, 9(5), 349; https://doi.org/10.3390/w9050349 - 16 May 2017

Cited by 24 | Viewed by 5755

Abstract

Bank filtration (BF) and soil aquifer treatment (SAT) are efficient natural technologies in potable water reuse systems. The removal of many organic micro-pollutants (OMPs) depends on redox-conditions in the subsoil, especially on the availability of molecular oxygen. Due to microbial transformation of particulate [...] Read more.

Bank filtration (BF) and soil aquifer treatment (SAT) are efficient natural technologies in potable water reuse systems. The removal of many organic micro-pollutants (OMPs) depends on redox-conditions in the subsoil, especially on the availability of molecular oxygen. Due to microbial transformation of particulate and dissolved organic constituents, oxygen can be consumed within short flow distances and induce anoxic and anaerobic conditions. The effect of accumulated particulate organic carbon (POC) on the fate of OMPs in BF and SAT systems is not fully understood. Long-term column experiments with natural sediment cores from the bank of Lake Tegel and from a SAT basin were conducted to investigate the impact of accumulated POC on dissolved organic carbon (DOC) release, on oxygen consumption, on mobilization of iron and manganese, and on the elimination of the organic indicator OMPs. The cores were fed with aerated tap water spiked with OMPs to exclude external POC inputs. Complete oxygen consumption within the first infiltration decimeter in lake sediments caused mobilization of iron, manganese, and DOC. Redox-sensitive OMPs like diclofenac, sulfamethoxazole, formylaminoantipyrine, and gabapentin were eliminated by more than 50% in all sediment cores, but slightly higher residual concentrations were measured in effluents from lake sediments, indicating a negative impact of a high oxygen consumption on OMP removal. Full article

(This article belongs to the Special Issue Assessment of Water Quality and Treatment Technologies in Potable Water Use)

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2450 KiB

Open AccessArticle

Understanding and Control of Biopolymer Fouling in Ultrafiltration of Different Water Types

by Xing Zheng, Frederik Zietzschmann, Stephan Plume, Hendrik Paar, Mathias Ernst, Zi Wang and Martin Jekel

Water 2017, 9(4), 298; https://doi.org/10.3390/w9040298 - 23 Apr 2017

Cited by 17 | Viewed by 5638

Abstract

The present work focuses on understanding and control of biopolymer fouling in ultrafiltration of a typical surface water and nearby secondary effluent for direct and indirect portable use. Characterization results show that both kinds of biopolymers are of similar molecular weight. Longer than [...] Read more.

The present work focuses on understanding and control of biopolymer fouling in ultrafiltration of a typical surface water and nearby secondary effluent for direct and indirect portable use. Characterization results show that both kinds of biopolymers are of similar molecular weight. Longer than one year water quality monitoring results show that the C/N ratio in the secondary effluent biopolymers was relatively constant at around 4.8, while that in the surface water macromolecules fluctuated at around 6.9. Under a similar mass load, the investigated secondary effluent biopolymers lead to hydraulic resistance slightly higher than that caused by filtering surface water macromolecules; however, the correspondingly formed fouling is significantly less reversible by hydraulic backwashing. The quantity of the nitrogenous biopolymers in the secondary effluent demonstrated a strong correlation with the extent of the irreversible fouling in ultrafiltration (UF), while that from the surface water did not. In membrane fouling cleaning tests, certain detergent demonstrated high efficiency in removing the irreversible fouling after UF of the secondary effluent, but presented no effect in eliminating fouling caused by the surface water foulants. In-line coagulation using FeCl₃ prior to UF was shown as an effective fouling control method, but the effect depends heavily on the type of feed water. Full article

(This article belongs to the Special Issue Assessment of Water Quality and Treatment Technologies in Potable Water Use)

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2225 KiB

Open AccessFeature PaperArticle

Sorption Dynamics of Uranium onto Anion Exchangers

by Marcel Riegel and Volker Schlitt

Water 2017, 9(4), 268; https://doi.org/10.3390/w9040268 - 10 Apr 2017

Cited by 22 | Viewed by 6164

Abstract

Uranium can occur naturally in groundwater which is used for drinking water production. Depending on its concentration levels, uranium elimination might become necessary. In German waterworks, anion exchange technology represents the state of the art for selective uranium removal. Operation times usually vary [...] Read more.

Uranium can occur naturally in groundwater which is used for drinking water production. Depending on its concentration levels, uranium elimination might become necessary. In German waterworks, anion exchange technology represents the state of the art for selective uranium removal. Operation times usually vary between one and two years until the exchanger is exhausted. In order to study uranium removal by anion exchange on a scientific base, column experiments at the pilot scale were performed in several waterworks. The resin with the highest capacity for uranium showed operation times between 120,000 and >300,000 bed volumes until breakthrough occurred, strongly depending on the water composition. To forecast uranium breakthrough on a theoretical base, a computer program was established using the model of combined film and surface diffusion. Both equilibrium data and kinetic parameters necessary for applying the model had been determined in previous research work. Modelled breakthrough curves were compared to experimental data from lab scale column experiments. As a rule, the time-dependency of the column effluent concentration can be well predicted by the theoretical model. By modelling the sorption dynamics, diffusion through the liquid film was identified as the rate controlling transport step. By increasing the filter velocity, the thickness of the liquid film decreases and the diffusion in the liquid accelerates. As a consequence for treatment plants in waterworks, the filter velocity can be increased by optimising the filter geometry. A smaller filter diameter is more appropriate for efficient uranium adsorption and longer times of operation might be achieved. Full article

(This article belongs to the Special Issue Assessment of Water Quality and Treatment Technologies in Potable Water Use)

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