Strong Gradients in Weak Magnetic Fields Induce DOLLOP Formation in Tap Water

Article Strong Gradients in Weak Magnetic Fields Induce DOLLOP Formation in Tap Water

Martina Sammer 1, Cees Kamp 2, Astrid H. Paulitsch-Fuchs 1, Adam D. Wexler 1, Cees J. N. Buisman 1 and Elmar C. Fuchs 1,* 1 Wetsus, European Centre of Excellence for Sustainable Water Technology, Oostergoweg 9, 8911 MA Leeuwarden, The Netherlands; [email protected] (M.S.); [email protected] (A.H.P.-F.); [email protected] (A.D.W.); [email protected] (C.J.N.B.) 2 Kamp Consult, Deventerweg 81, 7203 AD Zutphen, The Netherlands; [email protected] * Correspondence: [email protected]; Tel.: +31-58-284-3162 Academic Editor: Wilhelm Püttmann Received: 21 January 2016; Accepted: 23 February 2016; Published: 3 March 2016

Abstract: In 2012 Coey proposed a theory on the mechanism of magnetic water treatment based on the gradient of the applied field rather than its absolute strength. We tested this theory by measuring the effect of very weak field magnets (ď 10 G) containing strong magnetic inhomogeneities (∆B = 770 G¨m´1 (WCM 62081992) and 740 G¨m´1 (WCM 62083545)) on tap water samples by the use of electric impedance spectroscopy (EIS) and laser scattering. Our results show an increased formation of nm-sized prenucleation clusters (dynamically ordered liquid like oxyanion polymers or “DOLLOPs”) due to the exposure to the magnetic field and thus are consistent with Coey’s theory which is therefore also applicable to very weak magnetic fields as long as they contain strong gradients.

Keywords: magnetic water treatment; EIS; DOLLOPs

1. Introduction

1.1. Magnetic Water Treatment For a long time claims that the influence of a magnetic field on hard water influences the structure and morphology of the calcium carbonate crystallisation have been met with scepticism by the scientific community. This was mostly due to the absence of any plausible mechanism that could explain the lasting effect of magnetic fields even after the exposure itself had ceased. Over the past 40 years a lot of research has been done on the effects of magnetic or electromagnetic treatment on water, and over a hundred articles and reports are available in the literature [1–20]. Most of these papers deal with calcium carbonate precipitation, a few report on biological effects. Researches have convincingly shown [4,13,15,16] that magnetic treatment can influence the size and morphology of calcium carbonate crystals, shifting the preferred habitus from calcite to aragonite. A probable explanation was offered by Coey [21] based upon the works of Gebauer et al. [22] and Pouget et al. [23]. They describe a non-classical nucleation mechanism through the existence of stable prenucleation clusters in subsaturated calcium carbonate solutions. Such clusters are discussed by Raiteri and Gale [24], Gebauer and Cölfen [25], and were experimentally verified by ultracentrifuge experiments, cryo-TEM and mass spectrometry [23–26]. It has been found that they remain hydrated [24]. They can account for up to 50% of the calcium present in solution [23]. Whereas their structure has not been determined yet, molecular dynamics simulations [27] describe them as disordered, hydrated flexible ionic polymers or DOLLOPs (dynamically ordered liquid like oxyanion polymers). They

Water 2016, 8, 79; doi:10.3390/w8030079 www.mdpi.com/journal/water Water 2016, 8, 79 2 of 19 can aggregate into larger particles (up to about 100 nm) and form a liquid emulsion [26]. Coey [21] describes how a magnetic field gradient can act on the DOLLOPs, which could account for the so-called “magnetic memory” of water. He shows that contrary to pure mechanical stress, which is unable to induce changes to the structure of DOLLOPs directly, a magnetic field gradient can act on the DOLLOP surface and affect its growth dynamics. Bicarbonate ions, the predominant carbonate species in solution at neutral pH, are considered to sit next to each other on one side of a polar nucleation cluster and form the negatively charged surface. The other, positive, side is occupied by Ca2+ ions. ´ For the cluster to grow on the negatively charged side, protons in the HCO3 ions must be replaced by Ca2+ ions. It is upon these protons that the magnetic field acts: An inhomogeneous magnetic field, i.e., gradients in the magnetic field, can force the exchange of singlet and triplet states of the proton spin ´ 2+ dimers present in the HCO3 layer, thereby facilitating their replacement by Ca ions. This facilitation is achieved by spin-dephasing of a proton dimer induced by the magnetic field gradient, because proton spins precess at different rates at different field strengths. More exactly, the proton spins precess ´1 in a given field B at the Larmor frequency fpB (fp = 42.6 MHzT ). In order to dephase the spins in a proton dimer; they must precess at different frequencies so that the accumulated phase difference ∆φ fulfils the condition ∆φ ě π (1)

Based on this inequality Coey [21] derived a condition for an appreciable magnetic ﬁeld effect, by the use of which the effectiveness of the magnetic ﬁelds in this work will be analysed,

L C “ 2 f a∇B ě 1 (2) v p where C is the Coey criterion, L the length of the magnetic device, v the velocity of the DOLLOPs, fP the Larmor frequency of a proton, a the spin separation (0.25 nm) and ∇B the magnetic ﬁeld gradient. If C ě 1, then the magnetic device can effectively inﬂuence the crystallisation of calcium carbonate.

1.2. Water Core Magnets (WCMs) Even before a reasonable theory on their mechanism was derived many companies had commercialized various types of magnetic water treatment devices [28,29]. WCMs, a type of commercially available devices, are employed to treat different kinds of water, like, e.g., potable tap water or water in cooling loops [30]. A WCM consists of two parallel stainless steel cylinders, welded together. Each cylinder is weakly magnetized and filled with water. The WCM is placed into the water to be treated. There is experimental evidence [2] that treatment devices can leak small amounts of iron from their casing changing the chemical and physical properties of the fluid to be treated and can thus influence scaling in a merely chemical way [31]. In order to avoid such leakage, we chose to expose our water samples to the WCM without contact to the device itself. Thus any effects measured would stem only from exposure to the magnetic field. The average absolute field strength of the WCMs used in this study is very weak, < 10 G at a distance of 5 mm from the surface, only one order of magnitude above the earth’s field and 2–3 orders of magnitude lower than that of a hard ferrite magnet [32]. However, its field contains a remarkable fine structure of strong gradients (~770 G¨m´1 (WCM 62081992) and 740 G¨m´1 (WCM 62083545), see results section). Such strong gradients are, as described above, a prerequisite for Coey’s theory. Therefore, WCMs provide an excellent basis for testing this theory.

1.3. Electrical Impedance Spectroscopy (EIS) EIS allows the depiction and simulation of a liquid as simple electric circuit. An aqueous solution behaves like a resistor and a capacitor in parallel: At frequencies below 105–106 Hz ions can move along with the field (resistive behaviour), and at frequencies above that, the dielectric properties of the solution begin to show (capacitive behaviour). At low frequencies (<104 Hz), ions are fast Water 2016, 8, 79 3 of 19 enough to form layers at the electrodes, causing the so-called electrode polarisation (also referred to as Maxwell-Wagner polarisation). Mesoscale objects like DOLLOPs are much heavier than ions. They cannot follow the field as quickly and do not show the same polarisation behaviour. Electrode polarisation has no direct electric circuit equivalent, but can be simulated as a combination of certain elementsWater 2016 [33, ]:8, 79 A constant phase element (CPE)[34] with a Warburg impedance (W) in parallel3 of 19 to account for ion migration; R and W impedance represent bulk properties of the electrolyte solution andaccount diffusion for features ion migration; of the R probe and W in impedance the solution represent [35]. The bulk formation properties of of DOLLOPs the electrolyte should solution thus be detectableand diffusion by EIS features in a threefold of the manner:probe in the the solution increase [35]. of R Theaq due formation to the lowerof DOLLOPs number should of ions thus available, be the decreasedetectable of by the EIS electrode in a threefold polarisation manner: the for increase the same of reason,Raq due to and the the lower inability number of of the ions (much available, heavier) DOLLOPsthe decrease to follow of the the electrode electric polarisation field and buildfor thelayers, same reason, which and should the inability appear of as the a change(much heavier) of the CPE and DOLLOPsW parameters, to follow respectively. the electric Figure field and1 depicts build thelayers, measured which should spectrum appear of aas tap a change water sampleof the CPE (dots) and W parameters, respectively. Figure 1 depicts the measured spectrum of a tap water sample (dots) and the calculated spectrum (line). The contribution of electrode polarisation is shown by simulating and the calculated spectrum (line). The contribution of electrode polarisation is shown by simulating curves using the equivalent circuit (Figure1a) without both Warburg impedance and CPE. These curves using the equivalent circuit (Figure 1a) without both Warburg impedance and CPE. These simulationssimulations are are shown shown as as dotted dotted curves curves in in Figure Figure1 1aa,b.,b. The contributions of of the the electrode electrode polarisation polarisation are highlightedare highlighted as blueas blue areas. areas.

Figure 1. (a) Equivalent circuit; (b) exemplary impedance Z; (c) phase spectra (φ, subfigure c) of tap Figure 1. (a) Equivalent circuit; (b) exemplary impedance Z;(c) phase spectra (ϕ, subfigure c) of water incl. fitting results. R, W and CPE are resistance, Warburg impedance and constant phase tap water incl. fitting results. R, W and CPE are resistance, Warburg impedance and constant phase element simulating electrode polarization and ion migration; C and Raq the capacitance and resistance element simulating electrode polarization and ion migration; C and R the capacitance and resistance of tap water. aq of tap water. 1.4. Motivation for the Research Presented 1.4. Motivation for the Research Presented 1.4.1. WCM as Treatment Device 1.4.1. WCM as Treatment Device Until recently the use of magnetic devices for water treatment or scale prevention was mostly consideredUntil recently charlatanry the use by of a magnetic majority devicesof the scientific for water community. treatment The or scale main prevention argument was was that mostly consideredexplanatory charlatanry models, which by a majoritywere based of on the the scientific absolute community. field strength The of the main devices argument through was the that explanatoryLorentz force, models, failed which to explain were the based observed on theeffects absolute fully or field at least strength in part of the devices through the Lorentz force, failed to explain the observed effects fully or at least in part =(+×) (3) The model of Coey [21], however, whichF “ isqp basedE ` v uponˆ Bq the existence of the DOLLOPs and their (3) agglomerations [27], entails that not absolute field strength but magnetic field gradients impact crystal growth dynamics. According to that theory very weak magnets can influence crystallisation as long as strong gradients are present. The WCMs investigated in this research fulfil this criterion:

Water 2016, 8, 79 4 of 19

The model of Coey [21], however, which is based upon the existence of the DOLLOPs and their agglomerations [27], entails that not absolute field strength but magnetic field gradients impact crystal growth dynamics. According to that theory very weak magnets can influence crystallisation as long as strong gradients are present. The WCMs investigated in this research fulfil this criterion: Their field is so weak (<10 G) that any appreciable Lorentz force action can be excluded, but it contains a fine structure of multiple strong local gradients as preamble for Coey’s theory. Water 2016, 8, 79 4 of 19 1.4.2. Tap Water as Sample Their field is so weak (<10 G) that any appreciable Lorentz force action can be excluded, but it contains Thea fine effectiveness structure of multiple of magnetic strong local treatment gradients devices as preamble on for artificially Coey’s theory. prepared water solutions (defined calcium carbonate solutions) has been shown and discussed several times; the most 1.4.2. Tap Water as Sample recent investigations include (but are not limited to) the works of Higashintani, Coey, Kobe and Knez [4,13,15The,16 effectiveness]. Their research of magnetic provides treatment the devices ground on artificially for this prepared practically water oriented solutions work: (defined Since in calcium carbonate solutions) has been shown and discussed several times; the most recent most industrialinvestigations applications include (but the are water not limited treated to) is the tap works water, of [ 28Higashintani,–30] we deliberately Coey, Kobe choseand Knez tap water as sample.[4,13,15,16]. The ion Their content research of our provides samples the was ground analysed for this in practically five random oriented samples work: takenSince in over most the time period ofindustrial this investigation. applications the The water results treated of is this tapstudy water, show[28–30] that we deliberately the ion content chose tap varied. water However,as even withsample. this variability,The ion content general of our conclusions samples was aboutanalysed the in effectiveness five random samples of the treatmenttaken over the can time be drawn, and crystallisationperiod of this behaviour investigation. appears The results to be of this influenced study show according that the ion to content Coey’s varied. model. However, even with this variability, general conclusions about the effectiveness of the treatment can be drawn, and 2. Materialscrystallisation and Methods behaviour appears to be influenced according to Coey’s model. 2. Materials and Methods 2.1. Treatment Procedure 2002.1. mL Treatment of tap water Procedure were filled into 250 mL beakers. To ensure proper sampling, beakers were filled after the200 tap mL waterof tap water ran for were 1 min.filled Twointo 250 beakers mL beakers. were To put ensure next proper to the sampling, treatment beakers devices were (WCMs, type DZKL,filled after IPF GmbH,the tap water Austria; ran for see 1 min. Figure Two2 beakera,b, twos were were put next placed to the in treatment the same devices room (WCMs, at the same ambienttype conditions DZKL, IPF for GmbH, at least Austria; 24 h and see atFigure most 2a,b, 7 days two atwere two placed positions in the several same room meters at the apart same in order ambient conditions for at least 24 h and at most 7 days at two positions several meters apart in order to avoid inadvertent treatment of the reference sample. to avoid inadvertent treatment of the reference sample.

(a)

(b)

Figure 2. (a) Sketch showing the set-up for the treatment and the reference; S: plastic base (table), Figure 2. (a) Sketch showing the set-up for the treatment and the reference; S: plastic base (table), WCM: water core magnet, W: watch glass covering the beakers, T: treated beakers, R: reference WCM: waterbeakers. core (b) magnet, Water core W: magnet watch treatment glass covering device type the beakers,DZKL (cylinder T: treated radius beakers, 2.25 cm, R: height reference 15 cm, beakers. (b) Waterdistance core magnet between treatmentcylinders 1 cm) device type DZKL (cylinder radius 2.25 cm, height 15 cm, distance between cylinders 1 cm). At both locations the local magnetic field (without the presence of the treatment device) was lower than 0.5 G. Beakers and the water core magnets were put on plastic-covered, wooden (non-

Water 2016, 8, 79 5 of 19

At both locations the local magnetic field (without the presence of the treatment device) was lower than 0.5 G. Beakers and the water core magnets were put on plastic-covered, wooden (non-conducting and non-magnetic) surfaces. Treatment and reference position were randomly interchanged. Humidity and temperature were the same for both reference and treatment position (ambient conditions), since they were in the same laboratory at the same elevation. Two different treatment devices of the same type (water core magnet double cylinder) were used and exchanged randomly for different experiments. The beakers were covered with a watch glass to prevent dust and particulate contamination and to allow for continuous equilibration between the sample and atmosphere. After the treatment, at least three samples were taken from each beaker (two treated and two untreated beakers at least) resulting in a total of at least 12 individual measurements per experiment. All measurements were performed at room temperature. In order to check for the possibility of instrument drift of the impedance analyser, the sequential arrangement of measurements (treated and untreated) was changed in some experiments. The sequence of measurement had no influence on the results. As additional test for measurement reproducibility and sample location influence, several times test water samples were measured over days. These samples were placed at the same respective locations in the lab where the treatment and the reference samples were placed, but without the WCM near the treated sample. In these cases no significant differences between the samples of the two locations were found.

2.2. Tap Water Analysis For the tap water analysis the following analytical instruments were used: A Perkin Elmer ICP type Optima 5300 DV with an ESI autosampler type SCA DX and a Polyscience water cooler type 6106P (PolyScience 6600 W. Touhy Avenue, Niles, Illinois 60714-4516 USA ). The software was Perkin Elmer WinLab32 version 4.0.2.0380; the internal standard solution was of 100 mg/L Y+3 and 2% nitric acid as rinse solution. The detection limit was 25–750 µg¨L´1 with an upper limit of 10,000 µg¨L´1. The total organic carbon (TOC) was measured with a Shimadzu TOC-L using a Shimadzu ASI-L autosampler and the standard software of that equipment. As reagents 2 M Hydrochloric acid and 25% Phosphoric acid were used. The detection limit was 1.00 mg¨L´1. For the IC anion analysis a Metrohm Compact IC Flex 930 ion chromatograph with a Metrohm Metrosep A Supp 5150/4.0 mm column was used. The pre-column was a Metrohm Metrosep A Supp 4/5 Guard. The conductivity detector, the CO2 and the chemical suppressor are built into the ion chromatograph. A Spark Optimas auto sampler was used; the processing unit was a Metrohm, type MagIC Net. As reagents a mobile phase of 3.2 mM sodium carbonate and 1 mM sodium bicarbonate solution + 1% acetone was applied; the suppressor liquid was diluted phosphoric acid; the settings applied were a mobile phase ﬂow of 0.7 mL¨min´1; Flow suppressor solutions 0.4 mL¨min´1; and runtime 20 min; the injection volume was 20 µL. The detection limit was 0.05–0.10 mg¨L´1 with an upper limit of 80 mg¨L´1 for Cl´ and 20 mg¨L´1 otherwise.

2.3. Impedance Analysis All measurements were performed using an Impedance/Gain Phase Analyzer HP 4194A (Hewlett-Packard, CA, USA) which was connected via four BNC cables to a BDS 1200 connection head containing a BDS 1309 measurement cell (NOVOCONTROL Technologies, Montabaur, Germany). The BDS 1309 consists of two gold plated electrodes with a Teflon isolation ring in between, the diameter of the electrodes was 11 mm and the distance between the electrodes was 6.1 mm. This sample cell is especially designed for high permittivity liquids. A bipolar electrode configuration allowed measuring current separately while voltage was applied. The software WinDETA (NOVOCONTROL Technologies, Montabaur, Germany) was used to calibrate the system using the stray capacity of the cell (1.2 pF) and to perform the measurements. The complex impedance of the water samples were measured in a frequency range from 100 Hz to 10 MHz. In each spectrum 65 data points on a logarithmic scale from 100 Hz to 10 MHz were recorded with threefold internal averaging per point. Obtained impedance and Water 2016, 8, 79 6 of 19 phase spectra were fitted with “EIS Spectrum Analyser” software [36] using the Powell algorithm [37]. When treated and untreated water were compared, the electrode resistance (R) was determined in one Waterfit and 2016 kept, 8, 79 constant during the other. 6 of 19

2.4.2.4. SEM/EDX SEM/EDX SEM/EDXSEM/EDX was was performed performed with with a aJEOL JEOL JSM JSM 6480 6480 LV LV microscope microscope (JEOL (JEOL Technics Technics Ltd., Ltd., Tokyo, Tokyo, Japan)Japan) in in high high vacuum vacuum mode mode (emission (emission electrons electrons detection, detection, acceleration acceleration voltage voltage 10 10 kV, kV, operating operating distancedistance 10 10 mm). mm).

2.5.2.5. Magnetic Magnetic Field Field Measurements Measurements and and Visualisations Visualisations MagneticMagnetic fields fields of of the the WCMs WCMs were were measured measured with with a magnetometer a magnetometer (VGM, (VGM, AlphaLab, AlphaLab, Inc., Salt Inc., LakeSalt LakeCity, City, UT, UT,USA) USA) mounted mounted via viaa 30 a cm 30 cm long long Plex Plexiglasiglas rod rod on on a aXYZ XYZ stage. stage. This This stage stage consisted consisted of of twotwo Thorlabs LTSLTS 300/M 300/M translation translation units units for for X and X and Y, and Y, oneand LTS one 150/M LTS for150/M the Zfor direction the Z direction (Thorlabs (ThorlabsGmbH, Dachau/Munich, GmbH, Dachau/Munich, Germany). Germany). The whole The set-up whole was mountedset-up was on mounted a TMC anti-vibration on a TMC anti- plate vibration(75SSC-103-12 plate TMC (75SSC-103-12 Vibration control,TMC Vibration TMC, 15 Centennialcontrol, TMC, Drive, 15 Peabody, Centennial MA, Drive, USA). ThePeabody, WCM MA, to be 2 USA).scanned The was WCM put to on be a Plexiglasscanned was plate put atop on a a wooden Plexiglas table. plate An atop area a wooden of 20 ˆ 20 table. cm Anwas area sampled of 20 with× 20 cmsteps2 was of 1sampled mm, 5 mm with above steps the of 1 double mm, 5 cylinders mm above (see the Figure double3). Beforecylinders each (see measurement, Figure 3). Before the sensor each measurement,was zeroed inside the sensor a zero was Gauss zeroed chamber inside a (ZGC, zero Gauss AlphaLab chamber Inc.) (ZGC, that AlphaLab reduces the Inc.) environmental that reduces themagnetic environmental field (Earth magnetic field) tofield near (Earth zero field) (<0.002 to G).near Each zero point (<0.002 was G). repeatedly Each point measured was repeatedly until all measuredvalues (x, yuntiland allz direction values (x of, y the and magnetic z direction field) of would the magnetic not differ field) more would than 5% not from differ each more other than in two5% fromsubsequent each other measurements. in two subsequent The magnetic measurements. fields were thenThe visualizedmagnetic fields by mapping were then the absolutevisualized values by mappingof the X, Ytheand absoluteZ components values of onto the theX, Y RGB and colorZ components space in each onto point. the RGB This color procedure space isin describedeach point. in Thisdetail procedure with the exampleis described of a in bar detail magnet with in the the ex resultsample section.of a bar magnet in the results section.

Figure 3. Sketch showing the area (20 ˆ 20 cm2) scanned for the magnetic ﬁeld measurements with the Figurewater core3. Sketch magnet showing underneath the area (two (20 cylinders,× 20 cm2) scanned 18 cm length, for the 5 magnetic cm diameter, field 1 measurements cm apart). with the water core magnet underneath (two cylinders, 18 cm length, 5 cm diameter, 1 cm apart). 2.6. Laser Scattering Measurements 2.6. Laser Scattering Measurements For the laser scattering 22 samples of each analyte were measured using laser scattering in a microcapillaryFor the laser system scattering (Guava 22 samples easycyte of 8HT, each Merck analyte Millipore, were measured Merck KGaA, using Darmstadt, laser scattering Germany). in a microcapillaryForward and sideward system (Guava scatter easycyte of nm sized 8HT, particles Merck Millipore, were detected Merck in twoKGaA, dedicated Darmstadt, photomultiplier Germany). Forwardtubes. Milli-Q and sideward water (deionized scatter of water, nm sized Millipore particle Corporation,s were detected resistivity in two 18 dedicated MΩ¨cm) wasphotomultiplier run as blank. tubes.Data analysesMilli-Q water was done(deionized using water, the InCyte Millipore software Corporation, package resistivity of the system. 18 MΩ Particle·cm) was count run as data blank. was Data analyses was done using the InCyte software package of the system. Particle count data was retrieved plotting the forward scatter (logscale) and side scatter (logscale) data. Background noise was defined with the help of scattering data from Milli-Q water (blank value). The region was drawn into the plot leaving as little background data as possible in the actual counted area which was then used to retrieve the counts/sample.

Water 2016, 8, 79 7 of 19 retrieved plotting the forward scatter (logscale) and side scatter (logscale) data. Background noise was deﬁned with the help of scattering data from Milli-Q water (blank value). The region was drawn into the plot leaving as little background data as possible in the actual counted area which was then used Waterto retrieve 2016, 8, the79 counts/sample. 7 of 19

2.7. Statistical Statistical Analysis Analysis Statistical analyses have have been performed using using GenStat GenStat 17th 17th Edition Edition (VSN (VSN international international Ltd., Ltd., Hemel Hempstead, UK). UK). For each experiment every frequency ( (nn > 5) 5) has has been compared to blank values ( (nn >> 5) 5) using using a atwo two sample sample two-sided two-sided t-testt-test with with a 95% a 95% confidence conﬁdence interval. interval. The Thebinominal binominal test hastest hasbeen been performed performed as a as two-sided a two-sided two two sample sample test test with with a a95% 95% confidence conﬁdence interval interval using using normal approximation. Analyses of the data obtained have been performed using t-test. φϕ and Z of 65 single frequencies per experiment have been compared to blankblank values.values.

3. Results Results

3.1. Tap Tap Water Analysis During the time period of the experiments fi ﬁveve random tap water samples were taken and analysed. The The concentration concentration of of their their constituents constituents is is given given in in Figures Figures 44–6.–6. TheThe datadata waswas splitsplit inin threethree graphs to increase their readability. In In all all graphs graphs the the same same scale scale on on the the ordinate was chosen for reasons of comparison. Next to the ions shown, NO ´, PO 3´, Fe2+, Fe3+ were also investigated; reasons of comparison. Next to the ions shown, NO2-,2 PO43−, 4Fe2+, Fe3+ were also investigated; their concentrationstheir concentrations were were below below the theLOQ LOQ (<0.05 (<0.05 mg/L). mg/L). The The analysis analysis sh showsows that that the the ion ion concentrations concentrations were fairly constant throughout the whole period (2.5 years).years).

Figure 4. Cation concentration of 5 random tap water samples during the investigation period. The Figure 4. Cation concentration of 5 random tap water samples during the investigation period. error bars show the precision of the measurement (5%), the lines are the averages and the shaded The error bars show the precision of the measurement (5%), the lines are the averages and the shaded regions depict the standard deviations over the 5 samples. regions depict the standard deviations over the 5 samples.

Water 2016, 8, 79 8 of 19 Water 2016, 8, 79 8 of 19 Water 2016, 8, 79 8 of 19

Figure 5. Anion concentration of 5 random tap water samples during the investigation period. The Figure 5.5. AnionAnion concentrationconcentration of of 5 random5 random tap tap water water samples samples during during the investigationthe investigation period. period. The error The error bars show the precision of the measurement (3%), the lines are the averages and the shaded barserror showbars show the precision the precision of the measurementof the measurement (3%), the (3%), lines the are lines the are averages the averages and the and shaded the regionsshaded regions depict the standard deviations over the 5 samples. depictregions the depict standard the standard deviations deviations over the over 5 samples. the 5 samples.

Figure 6. Total carbon (TC), inorganic carbon (IC) and non-purgable organic carbon (NPOC) Figure 6. Total carbon (TC), inorganic carbon (IC) and non-purgable organic carbon (NPOC) concentrationsFigure 6. Total of 5 carbon random (TC), tap water inorganic samples carbon during (IC) the and investigation non-purgable period. organic IC was carboncalculated (NPOC) from concentrations of 5 random tap water samples during the investigation period. IC was calculated from asconcentrations difference of of TC 5 randomand NPOC. tap waterThe error samples bars duringshow the the precision investigation of the period. measurement IC was calculated (5%), the lines from as difference of TC and NPOC. The error bars show the precision of the measurement (5%), the lines areas difference the averages of TC and and the NPOC. shaded The regions error depict bars show the standard the precision deviations of the over measurement the 5 samples. (5%), the lines are the averages and the shaded regionsregions depictdepict thethe standardstandard deviationsdeviations overover thethe 55 samples.samples. Independent from this analysis, the tap water did sometimes contain minute amounts of visible Independent from this analysis, the tap water did sometimes contain minute amounts of visible precipitate which was probably from scaling in the pipes that broke free. Experiments both with and precipitate which was probably from scaling in the pipes that broke free. Experiments both with and without such precipitates were carried out, the results are discussed in Section 3.4. without such precipitates were carried out, the results are discussed in Section 3.4.

Water 2016, 8, 79 9 of 19

Independent from this analysis, the tap water did sometimes contain minute amounts of visible precipitate which was probably from scaling in the pipes that broke free. Experiments both with and without such precipitates were carried out, the results are discussed in Section 3.4. Water 2016, 8, 79 9 of 19 3.2. Magnetic Fields 3.2.Water Magnetic 2016, 8, 79 Fields 9 of 19 In order to be able to read the magnetic field scan images properly, the analysis of a cylindrical bar In order to be able to read the magnetic field scan images properly, the analysis of a cylindrical magnet3.2. isMagnetic presented Fields first. Figure7 shows the field of such a magnet scanned with the device described bar magnet is presented first. Figure 7 shows the field of such a magnet scanned with the device 2 in thedescribed methodIn order in section the to bemethod inable an to section area read of the in 14 anmagneticˆ area14 cmof field14, 3× cm14sc ancm above images2, 3 cm the aboveproperly, magnet. the themagnet. analysis of a cylindrical bar magnet is presented first. Figure 7 shows the field of such a magnet scanned with the device described in the method section in an area of 14 × 14 cm2, 3 cm above the magnet.

Figure 7. Magnetic field of a bar magnet (image on the right shown to scale) in x, y and z direction. Figure 7. Magnetic ﬁeld of a bar magnet (image on the right shown to scale) in x, y and z direction. The scale goes from −28 to 28 G for x, −53 to +53 for y and −71 to +71G for z, respectively. The scale goes from ´28 to 28 G for x, ´53 to +53 for y and ´71 to +71G for z, respectively. Figure 7. Magnetic field of a bar magnet (image on the right shown to scale) in x, y and z direction. BecauseThe scale forgoes the from present −28 to analysis 28 G for xthe, −53 sign to +53 (N foror S)y andis not −71 important, to +71G for the z, respectively. field can also be displayed Becausein terms of for absolute the present intensity, analysis and the the three sign compon (N or S)ents is not can important,then be translated the ﬁeld to canthe three also beprimary displayed in termscolours, ofBecause absolute red ( xfor), greenthe intensity, present (y) and andanalysis blue the (z the). three These sign components (Nimages or S) areis not then can important, combined then be the translated to field a composite can also to the be RGB threedisplayed image. primary colours,Thisin terms redprocedure (ofx), absolute green is shown ( yintensity,) and in Figure blue and ( z8.the). Thesethree compon imagesents are can then then combined be translated to a to composite the three primary RGB image. colours, red (x), green (y) and blue (z). These images are then combined to a composite RGB image. This procedure is shown in Figure8. This procedure is shown in Figure 8.

Figure 8. Magnetic field of a bar magnet in x, y and z direction in absolute values. The x, y and z images are added to form the final composite RGB representation of the magnetic field. Figure 8. Magnetic field of a bar magnet in x, y and z direction in absolute values. The x, y and z FigureWithimages 8. Magnetic the are method added field to describe form of a barthe magnetabove,final composite composite in x, y andRGB imagz representatidirectiones of magnetic inon absolute of the magneticfields values. of field.two The differentx, y and z WCMsimages are(serial added numbers to form 62083545 the final and composite 62081992) RGB are representation shown in Figure of the9. The magnetic dark lines field. are sudden changes in magneticWith field the methodstrengths describe resembling above, strong composite gradients. imag Gradientses of magnetic in x direction fields of havetwo different been calculated WCMs (serial numbers 62083545 and 62081992) are shown in Figure 9. The dark lines are sudden changes in

magnetic field strengths resembling strong gradients. Gradients in x direction have been calculated

Water 2016, 8, 79 10 of 19

With the method describe above, composite images of magnetic ﬁelds of two different WCMs

Water(serial2020, numbers12, 0 62083545 and 62081992) are shown in Figure9. The dark lines are sudden changes2 of 3 in Watermagnetic2020, 12, 0 field strengths resembling strong gradients. Gradients in x direction have been calculated2 of 3 and are shown in Figure 10. Here a scale from white to the primary colours is used in order to make 5. a clearFigure distinction 9 should from be replaced the composite by the following images in figure: Figure9. 5. FigureWater 2020 9 should, 12, x FOR be PEER replaced REVIEW by the following figure: 2 of 3 Water 2020, 12, x FOR PEER REVIEW 2 of 3 Water 2020, 12, x FOR PEER REVIEW 2 of 3 Water 2020, 12, x FOR PEER REVIEW 2 of 3

6.Figure Figure 9. 10RGB should composite be replaced magnetic by the field following visualisations figure: of WCMs 62083545 (a, left) and 62081992 6. Figure6. Figure 10 should 10 should be replacedbe replaced by by the the following following figure:figure: 6. Figure6.( b, right).Figure 10 should The10 should image be replaced be is 20replacedˆ 20 by cm by the2, the every following following pixel is figure:figure: 1 mm. 6. Figure 10 should be replaced by the following figure:

Reasons: Reasons: Reasons: Reasons: All changes: in the publication [1], this correction refers to the magnetic fields of the water core Reasons:FigureAll changes: 10. Magnetic in the field publication gradients (d[1],/d xthis) of correction WCM 2. WCMs refers 62083545 to the magnetic (a) and 62081992 fields of (bthe). Thewater image core Reasons:magnetsAll changes:(WCMs). in In the order publication to read out [1], the this data correction from the refers magnetometer, to the magnetic a program fields written of the waterand tested core magnetsis 20 ˆ 20(WCMs). cm2, every In order pixel to is read 1 mm. out the data from the magnetometer, a program written and tested Allinmagnets changes:Delphi2005All changes: (WCMs). in was the in In publicationused.the order publication The to read program [1 out], [1], this the thiswas correction data correction then from migrated the refers refers magnetometer, to toto the Delphithe magnetic magnetic XE6,a program which fieldsfields written ofis, the in contrastwater waterand tested core core to Allin changes:Delphi2005 in was the publicationused. The program [1], this was correction then migrated refers to to the Delphi magnetic XE6, which fields ofis, thein contrast water core to magnetsmagnetsDelph2005,in Delphi2005 (WCMs). (WCMs). based Inwas orderInon used. order 16 to bitThe to read readUnicode, program outout the not was data data on then fr8 fromom bit migrated the ASCII. the magnetometer, magnetometer, toWhereas Delphi all XE6,a program data awhich program types written is, were in written contrastand changed tested and to magnetsDelph2005, (WCMs). based In orderon 16 tobit read Unicode, out the not data on 8 from bit ASCII. the magnetometer, Whereas all data a program types were written changed and testedinaccordingly,Delph2005, inAs Delphi2005 Delphi2005 can be based seenthe was wasfact from onused. used.that 16 Figure bitThethe The Unicode, outpprogram program10ut, the of notcertainwas magnetic was on then then8functions bitmigrated field migratedASCII. gradientsalso toWhereas changedDelphi to Delphi of allXE6, thefrom XE6,data WCMs which 8 typesbit which tois, are 16werein is, in bitcontrast in the changedwas contrast order not to of testedaccordingly, in Delphi2005´1 the wasfact used.that the The outp programut of certain´ was1 thenfunctions migrated also changed to Delphi from XE6, ´8 1bit which to 16 is, bit in was contrast not to770 Delph2005,Delph2005,takenaccordingly, G¨m into(WCM based account based the 62081992) onfact onproperly. 16 that 16 bit bitthe Unicode, and This Unicode,outp 740 mistakeut Gof not ¨mnot certain onresulted on(WCM 8 8 bitfunctions bit in ASCII. 62083545)ASCII. some also WhereasbytesWhereas changed or to 0.077 be allall translated from T datadata¨m 8 typesbit(WCM incorrectly, to were 16 62081992)bit changed changedwas which not and taken into account properly. This mistake resulted in some bytes to be translated incorrectly, which toaccordingly,0.074 Delph2005,accordingly,intaken Tturn¨m into´ the 1resulted based(WCM factaccount the that on fact 62083545).in properly. the 16 artefactsthat bit output the Unicode, This Moreover,outpvisible of certainmistakeut of notas certain allfine functions onresulted gradients 8line bitfunctionss ASCII.inin also some alsothe changedalso Whereasfields seembytes changed to toof from be havethe all translatedfrom 8 datawater bit a finer to8 typesbit 16core structureincorrectly,to bit were16magnets, was bit not changedwas embedded. which taken but,not intaken turn into resulted account in properly. artefacts This visible mistake as fine resulted lines inin some the fieldsbytes toof bethe translated water core incorrectly, magnets, which but, accordingly,intoBecause accountcoincidentally,in turn the the properly. resulted 3-axis fact thatnot probe Thisin thein artefacts the mistake output of fields the visible ofVGM resultedof certain the magnetometeras bar infinefunctions somemagn lineet.s bytes alsoin These hasthe tochanged itsbefieldsartefacts translatedthree fromof sensorsthewere 8 waterbit incorrectly, interpreted to placed 16core bit magnets, withinwas which as magnetic not in less takenbut, turn than coincidentally,in turn resulted not in in −artefacts1 the fields visible of the as bar fine magn lineet.s in These the fieldsartefacts of thewere water interpreted core magnets, as magnetic but, intoresulted1.5 accountgradients mmcoincidentally, in (accordingartefacts properly. of 2 kG·m visiblenot toThis in the. astheThe mistake manual) fine fieldserror lines resulted andof of inthe all the barsubsequent in fieldsprobe’s somemagn of byteset. end,the errorsThese water toaspatial be (martefacts coreagnetic translated magnets,resolution weregradients, incorrectly, interpreted but, beyond Coey coincidentally, whichcriterion thatas magnetic cannot in and turn not be gradients of 2 kG·m−1. The error and all subsequent errors (magnetic gradients, Coey criterion and resultedcoincidentally,minimumgradients in artefacts ofL value)2 visiblekG·mnot havein−1 . astheThe now fine fields error been lines ofand corrected. inthe all the bar subsequent fields magn The of correctet. the errorsThese water maximum (martefacts coreagnetic magnets, gradients were gradients, interpreted but, are Coey coincidentally,740, 210 criterionas andmagnetic 620 and not G1 inrecorded. the fields of The the presented bar magnet. gradients These artefactswith a step were size interpreted of 1 mm are as magneticprobably gradientsalready spatial of 2 kG averages,m− . minimumgradients−1 ofL value)2 kG·m have−1. The now error been and corrected. all subsequent The−1 correct errors maximum (magnetic gradients gradients, are Coey740, 210 criterion and 620 and G1 in themminimum fields (WCM of the L62083545) value) bar magnet. have and now 770, These been 170 and artefactscorrected. 560 G were mThe (WCM correct interpreted 62081992) maximum as magneticfor gradients x, y and´ gradients are1z, respectively, 740, 210 of and 2 kG which 620·m −G . Theand error the−1 and actual all subsequent gradients present errors (magnetic are probably gradients,− even1 higher Coey thancriterion 0.077 and T¨m minimum(WCML 62081992)value) have and mminimum (WCM L62083545) value) have and now 770, been 170 and corrected. 560 G mThe (WCM correct 62081992)− maximum1 for gradients x, y and arez, respectively, 740,−1 210 and which 620· G The errorcorrespondm−1 and(WCM all 62083545) subsequentto Coey criteria and errors 770, between 170 (magnetic and C 560= 1.8 G gradients, (for m− 1170 (WCM G·m Coey 62081992)) and criterion C = for 8.1 x and(for, y and 770 minimum1 zG·m, respectively,), Lwhichvalue) in which haveturn now been−1 corrected. The correct maximum gradients−1 are 740,−1 210 and 620 G m− (WCM−1 62083545) and correspondmmeans (WCM that 62083545) inequalityto Coey criteria and(1) is 770, fulfilled between 170 and for C 560=both 1.8 G WCMs(for m 170 (WCM in G·m all 62081992)directions,−1) and C = for 8.1and x (for, ally and conclusions7701 zG·m, respectively,−1), which remain in which valid. turn now beencorrespond corrected. to Coey The1 correctcriteria maximumbetween C gradients= 1.8 (for 170 are G·m 740,) 210 and and C =620 8.1 (for G m 770− (WCM G·m ), 62083545)which in turn and 770, 170 and 560 G m (WCM 62081992) for x, y and z, respectively,−1 which correspond−1 to Coey criteria meanscorrespondThe that change inequality to Coey− 1of the criteria (1) symbol is fulfilled between “≥” tofor C “ ≤both=” 1.8 in WCMsthe(for conclusions 170 in G·m all directions,) and (correction C = and8.1 (for 1eall) conclusionsis770 the G·m correction), whichremain of in avalid. typoturn 770, 170means and 560that Ginequality m− (WCM (1) is1 62081992) fulfilled for for bothx, y WCMsand z, in respectively, all1 directions, which and all correspond conclusions to remain Coey criteria valid. betweenmeansCThe= that1.8 change (forinequality 170 of the G (1)m symbol− is) fulfilled and “≥C” =to for 8.1“ ≤both” (for in theWCMs 770 conclusions G inm −all), directions, which (correction in and turn 1e all means) isconclusions the thatcorrection inequality remain of a valid. typo (1) is and unrelatedThe change to ofthe the above· symbol1 mentioned “≥” to “ ≤issue.” in the conclusions· 1 (correction 1e) is the correction of a typo betweenandC unrelated= 1.8 (for to 170 the G abovem− ) mentioned and C = 8.1 issue. (for 770 G m− ), which in turn means that inequality (1) is fulfilledand for unrelatedThe both change WCMs to ofthe the in above· allsymbol directions, mentioned “≥” to “ and ≤issue.” in all the conclusions conclusions· remain (correction valid. 1e) is the correction of a typo fulfilledand for unrelated both WCMs to the in above all directions, mentioned and issue. all conclusions remain valid.

Water 2016, 8, 79 11 of 19

0.074 T¨m´1 (WCM 62083545). A higher gradient would not change the results of this investigation, nevertheless the authors plan to measure the field with a different system providing a higher resolution in the future. As mentioned in the introduction, Coey [21] derived an inequality based on which the effectiveness of a magnetic device can be evaluated. For the sake of clarity and because of its importance, this inequality (2) is repeated here, L C “ 2 f a∇B ě 1, (4) v p where C is the criterion, L the length of the magnetic device, v the velocity of the DOLLOPs, fP the Larmor frequency of a proton, a the spin separation (0.25 nm) and ∇B the magnetic field gradient. If C ě 1, then the magnetic device can effectively influence the crystallisation of calcium carbonate. For the experiments presented, the magnetic device is larger than the volume of water treated, so the beaker diameter, 6 cm is used instead. One might argue at this point that for WCMs the actual width of the inhomogeneities, which is sometimes only a few mm, should be used, and not the measures of the device. Doing that does reduce C, but does not change the result (C ě 1, see end of this chapter) down to L values of 8 mm. The velocity of the DOLLOPs can be calculated from the Brownian motion in a liquid using Fick’s Dmg law, v “ . In a dynamic equilibrium velocity is equal to the settling speed according to the kBT Stokes-Einstein equation,

Dmg 1 1 v “ “ µmg “ mg “ mg (5) kBT ζ 6πηr where D is the diffusion coefficient, kB the Boltzmann constant, T the absolute temperature, µ and m are the mass and mobility of the DOLLOP, g is the acceleration due to gravity, ξ the drag coefficient, η the viscosity of the medium, and r the radius of a (assumingly) spherical DOLLOP. To know the mass of a 100 nm DOLLOP sphere, first its density must be calculated. Since a DOLLOP consists of ´3 ´3 both water (ρ25˝C = 1.00 g¨cm ) and aragonite (ρ = 2.93 g¨cm ), we assess its density as an equal ´3 ´15 mixture of both, so ρDOLLOP,25˝C = 1.97 g¨cm , resulting in a DOLLOP mass of 1.03 ˆ 10 g. Taking ´4 water’s dynamic viscosity η25˝C = 0.89 ˆ 10 Pa s, the resultant DOLLOP velocity due to Brownian motion is 0.012 mm¨s´1. The magnetic field gradients of the WCMs are in the order of 770 G¨m´1 (WCM 62081992) and 740 G¨m´1 (WCM 62083545) or 0.077 T¨m´1 (WCM 62081992) and 0.074 T¨m´1 (WCM 62083545) (see Figure8), resulting in a Coey criterion of C = 8.1 (WCM 62081992) and C = 7.8 (WCM 62083545), thus clearly ě 1. The real gradients are probably higher as mentioned above, which would further increase the value of C and allow for higher fluid velocities. Smaller DOLLOPs than 100 nm are slower (the decrease of their mass in equal. 5 outweighs the increase of their mobility) and will therefore also further increase the value of C (velocity in Equation (4) is in the denominator). The velocity of a DOLLOP also allows an estimation of the time required for the treatment to be effective. A straight travel from one side of the beaker to the other (6 cm) would take a 100 nm DOLLOP 1.4 h. During such a journey, a DOLLOP would encounter a number of magnetic field gradients. One should, however, also consider that Brownian motion is not unidirectional, the DOLLOP might be smaller and thus slower, and so the time should be multiplied by a factor of 10 or more in order to guarantee a successful treatment. This estimation matches with the observed time frames for a measureable treatment effect of about 24–48 h.

3.3. Evaporation It has been shown [20] that magnetic fields can change the evaporation rate of electrolytic solutions. Within the measurement precision of our balances (1 mg) we did not see such an effect. It should be noted that a difference in evaporation was reported for field strengths much higher (~150 G) than Water 2016, 8, 79 12 of 19 applied in the present case (<10 G), which is why this observation is consistent with the proposed model and an additional confirmation of the stability of the atmospheric parameters.

3.4. Complex Impedance The proposed DOLLOP formation was tested in 16 independent experiments with at least 12 measurements per experiment, one measurement comprising the complex impedance at 65 frequencies, measuring two parameters (phase and impedance) per frequency. In each experiment at least two treated and two untreated samples were compared, and every sample was measured at least three times. t-test results for the treated samples compared to blank values showed statistically highly significant differences in 15 of 16 experiments (binominal exact probability < 0.001) either for phase (ϕ), for impedance (Z) or for both parameters. One experiment with 48 h treatment time did not show significant differences. In 9 of 16 experiments, Z showed frequency dependent variations which were highly different from the blank. In the case of differences a minimum of 4 and a maximum of 65 frequencies showed a significant difference, highly different results were obtained for 4 to 65 frequencies. In 15 of 16 experiments, ϕ showed frequency dependent variations which were highly different from the blank. Statistically significant differences in frequencies for a given ϕ occurred in a minimum of 2 and a maximum of 59 cases, highly significant results were calculated for 1 to 56 frequencies. In sum Z and ϕ showed statistically significant differences in a minimum of 3 and a maximum of 110 cases, highly different results in 2 to 106 frequencies. The exact binominal probability for an experiment to show a statistically highly different behaviour of treated water compared to untreated water is p < 0.001 (with 15 out of 16 cases positive for significant statistical values). These results are summarized in Table1.

Table 1. Statistics of the results of the WCM tapwater treatment. In each experiment, 65 frequencies between 100 Hz and 10 Mhz were scanned.

Parameter Number Number of experiments 16 Measurements per sample ě3 Frequencies per measurement 65 Parameters per frequency 2 Signiﬁcant difference (95% conﬁdence interval) 15

Figure 11 shows exemplary impedance and phase changes of treated compared to untreated tap water. In addition to impedance (a,d) and phase (b,e), a Nyquist-plot of the data is shown (c,f). In this plot both the real and imaginary part of the impedance, |Z|¨cos(ϕ) and -|Z|¨sin(ϕ), are plotted against each other. On a Nyquist plot the impedance is a vector with characteristic length and angle, therefore a mandatory precondition is equal scales of the ordinate and abscissa axes. Such a scaling would, however, be unfavorable for the details of the spectra presented in this work, thus, we chose to omit this precondition in favor of a better representation of spectral details knowing well that the from such depictions the impedance can no longer be read out directly.Whereas a Nyquist plot does not give frequency information it is better in showing differences between spectra over the same frequency range since it combines both impedance and phase in one curve. The curves depicted in Figure 11 were ﬁtted using the model shown in Figure1. The parameters of the circuit elements are given in Table2 (case a) and Table3 (case b), respectively. Next to that, average curves of all 16 measurements were ﬁtted with this model. Although sample composition and treatment time were not identical for all experiments as described in the experimental section, the most important model parameter, the conductivity of the water (Raq), shifted consistently depending on the case (a or b). This result is shown in Table4. Water 2016, 8, 79 13 of 19 Water 2016, 8, 79 13 of 19

Figure 11. Examples of the two effects accompanying the DOLLOP formation. Depending on the Figure 11. Examples of the two effects accompanying the DOLLOP formation. Depending on the presencepresence ofof precipitate,precipitate, thethe impedanceimpedance eithereither increasesincreases oror decreases. decreases. TheseThese effectseffects areare shownshown asas impedanceimpedance ( a,(da,),d phase), phase (b, e()b and,e) Nyquistand Nyquist plots (cplots,f): Case (c,f): a (aCase,b,c) wasa (a encountered,b,c) was encountered without precipitate; without caseprecipitate; b (d,e,f) wascase foundb (d,e, whenf) was a found small amountwhen a ofsmall precipitate amount was of foundprecipitate in the was reference found beaker, in the butreference none inbeaker, the treated but none beaker in the after treated treatment. beaker The after error treatmen bars representt. The error the bars measurement represent the error. measurement error.

Table 3. Parameter fit for Figure 11, case a. The errors represent the quality of the fit for each element. Blue and red font colours are used to highlight an increasing or decreasing trend, respectively.

Absolute Relative Parameter Untreated Treated Difference Difference R/Ω 238 ±9 238 ±6 0 0% Aw/Ω·s−0.5 22,593 ±11 21,202 ±511 −1391 −6% CPE P × 107 2.01 ±0.32 4.37 ±0.37 2.36 +118% CPE n 1.00 ±0.02 0.97 ±0.01 −0.031 −3% C/pF 17.7 ±0.98 16.8 ±1.4 −0.989 −6% Raq/Ω 870 ±9 951 ±8 81 +9%

Water 2016, 8, 79 14 of 19

Table 2. Parameter ﬁt for Figure 11, case a. The errors represent the quality of the ﬁt for each element. Blue and red font colours are used to highlight an increasing or decreasing trend, respectively.

Parameter Untreated Treated Absolute Difference Relative Difference R/Ω 238 ˘9 238 ˘6 0 0% ´0.5 Aw/Ω¨s 22,593 ˘11 21,202 ˘511 ´1391 ´6% CPE P ˆ 107 2.01 ˘0.32 4.37 ˘0.37 2.36 +118% CPE n 1.00 ˘0.02 0.97 ˘0.01 ´0.031 ´3% C/pF 17.7 ˘0.98 16.8 ˘1.4 ´0.989 ´6% Raq/Ω 870 ˘9 951 ˘8 81 +9%

Table 3. Parameter ﬁt for Figure 11, case b. The errors represent the quality of the ﬁt for each element. Blue and red font colours are used to highlight an increasing or decreasing trend, respectively.

Parameter Untreated Treated Absolute Difference Relative Difference R/Ω 232 ˘7 232 ˘10 0 0% ´0.5 Aw/Ω¨s 21,721 ˘10 24,967 ˘1064 3246 +15% CPE P ¨ 107 3.63 ˘0.34 1.10 ˘0.25 ´2.53 ´70% CPE n 0.98 ˘0.01 1.00 ˘0.03 0.019 +2% C/pF 16.9 ˘0.65 17.3 ˘1.1 0.342 +2% Raq/Ω 917 ˘7 877 ˘11 ´40 ´4%

Table 4. Case dependent average of tap water resistance parameter Raq ﬁtted according to the model presented in Figure1, including standard error. The quality of the ﬁts can be appreciated from the

average ﬁtting error of this parameter, ERaq,av and its associated standard error.

Case ∆ Raq,av /Ω ERaq,av /Ω a (8 experiments) 31 ˘ 9 14 ˘ 3 b (8 experiments) ´39 ˘ 9 13 ˘ 2

The direction in which this change was observed depended on the constituents of the original tap water:

‚ Case a: No precipitation

When no micro precipitation was present in the beakers before and after the treatment, the impedance of the treated sample increased at high frequencies (case a, see Figure 11a–c, increase of Raq in Table2). Because fewer ions are available in the solution due to DOLLOP formation, there is less electrode polarisation at low frequencies (smaller phase shift in Figure7b at low frequencies and decrease of Aw (ion diffusion constant) and C in Table2). As mentioned in Section 3.1 sometimes the initial tap water contained tiny crystals. In some cases, precipitation would form during the treatment time in the reference beaker. Both of these cases are summarized in this work as case b:

‚ Case b: precipitation

If there was visible micro precipitate in the reference beakers after the treatment or both beakers before treatment, the impedance of the treated sample was lower at high frequencies than the reference meaning that there were more ions in solution (case b, see Figure 11d–f, decrease of Raq in Table3), and higher at low frequencies due to increased electrode polarisation caused by these ions (larger phase shift in Figure 11e at low frequencies and increase of Aw and C in Table2). Also here DOLLOPs are formed as described in case a, but the solubility product allows additional ions to dissolve from the precipitate. The solution is thus in a dynamic equilibrium between the formation of DOLLOPs and the solvation of the µm sized particles (see Figure 12). The impedance increase observed suggests that Water 2016, 8, 79 15 of 19

Water 2016, 8, 79 15 of 19 the magneticand ﬁeldion migration. gradient Differences does not in only the mobility facilitate of the the ionic formation content of ofthe DOLLOPs solution due but to the also DOLLOP the dissolution of micro crystals.formation The are also authors reflected plan in different to investigate parameters this of hypothesisthe CPE. in subsequent work. A simplified sketch of this mechanism is given in Figure 12.

Figure 12. Simplified sketch of the two cases of a WCM acting on tap water. Case a: no precipitate is Figure 12.present,Simplified and the sketch field ofinduces the twoDOLLOP cases formation of a WCM (small acting grey circles). on tap Case water. b: If Case a precipitate a: no precipitate is is present, andpresent, the field DOLLOPs induces are formed DOLLOP as well formation, and the precipitate (small grey is dissolved. circles). Case b: If a precipitate is present, DOLLOPs are formed as well, and the precipitate is dissolved. These findings are in line with the many observations reported in theliterature [4,6,13,15,16,38– 40] and most importantly, they agree with the model of Coey [21]: the strong local gradients act on In nothe case mechanism was precipitation of precipitation foundand induce in DOLLOP the treated formation. beaker In case after a, the treatment, ions form many corroborating small the DOLLOP formationnuclei, DOLLOPs, hypothesis. which form In general,a colloid and the are shift thus in no case longerb was able smallerto follow thanthe alternating in case aelectric; and in the one case wherefield we during did not the seeimpedance a significant measurement. effect of the treatment, a trend towards case b was observable. Next3.5. to ionLaser diffusion Scattering constant, capacity and resistivity; parameters of the constant phase element (CPE) show largeSince differences these DOLLOPs between are much the smaller fits of than the 1 spectraµm, theirfrom colloid treated is invisible and to untreatedthe naked eye samples, due again in oppositeto directionthe small cross-sections for cases a forand Rayleighb like scattering the other. Next parameters. to the EIS measurement, The physical we meaningwere able to of a CPE is an ongoingconfirm discussion their presence in general; by investigating however, samples for the from purpose two experiments of this work with laser it is scattering. sufficient We to say that, accordingcompared to the model, 22 treated together to 22 untreated with the samples Warburg in each impedance experiment itand represents found a significant electrode increase polarisation up and to 25% of nm sized objects in the treated sample (p < 0.001) compared to the reference. Figure 13 ion migration.shows Differencesexemplary scattering in the plots mobility for deionized of the ionicwater content(milli-Q water, of the background), solution due treated to theand DOLLOP formationuntreated are also sample; reflected Table in 6 different summarizes parameters the results of of these the experiments.CPE. A simplified sketch of this mechanism is given in Figure 12. These findings are in line with the many observations reported in theliterature [4,6,13,15,16,38–40] and most importantly, they agree with the model of Coey [21]: the strong local gradients act on the mechanism of precipitation and induce DOLLOP formation. In case a, the ions form many small nuclei, DOLLOPs, which form a colloid and are thus no longer able to follow the alternating electric field during the impedance measurement.

3.5. Laser Scattering Since these DOLLOPs are much smaller than 1 µm, their colloid is invisible to the naked eye due to the small cross-sections for Rayleigh scattering. Next to the EIS measurement, we were able to conﬁrm their presence by investigating samples from two experiments with laser scattering. We compared 22 treated to 22 untreated samples in each experiment and found a signiﬁcant increase up to 25% of nm sized objects in the treated sample (p < 0.001) compared to the reference. Figure 13 shows exemplary scattering plots for deionized water (milli-Q water, background), treated and untreated sample; Table5 summarizes the results of these experiments. Water 2016, 8, 79 16 of 19 Water 2016, 8, 79 16 of 19

Water 2016, 8, 79 16 of 19

Figure 13. (a) Exemplary laser scattering data from deionized water; (b) an untreated sample; (c) a Figure 13. (a) Exemplary laser scattering data from deionized water; (b) an untreated sample; (treatedc) a treated sample sample showing showing forward forward against against side side scatte scatterr intensity. intensity. Each Each dot dot represents represents one one scattering particle.Figure 13. Only (a) the Exemplary red area laser(R2) is scattering evaluated; data very from weak deionized scatterers water; between (b) anthe untreated red area and sample; the green (c) a linetreated (detection sample limit) showing are consideredcons forwardidered against backgroundbackground side scatte noise.noise.r intensity. Each dot represents one scattering particle. Only the red area (R2) is evaluated; very weak scatterers between the red area and the green Tableline (detection 5.6. NumberNumber limit) of of objects areobjects cons determined determinedidered background by by laser laser scattering noise. scattering in twoin two treated treated and and untreated untreated solutions solutions from from22 samples 22 samples each. each. Table 6. Number of objects determined by laser scattering in two treated and untreated solutions Experiment Untreated/104 counts mL−1 Treated/104 counts mL−1 Difference Treated vs. Untreated from 22 samples each. 4 ´1 4 ´1 Experiment 1 Untreated/10 2.72 ± Counts0.02 mL Treated/10 3.01 ± Counts0.04 mL DifferencePTreated < 0.001 vs. Untreated ExperimentExperimentExperiment 1 2 Untreated 5.172.72/10 ˘±4 0.02counts0.02 mL−1 Treated 7.00/10 3.01 4±counts ˘0.100.04 mL−1 Difference TreatedP P< 0.001< 0.001 vs. Untreated ExperimentExperiment 2 1 5.172.72 ˘± 0.02 3.01 7.00 ± ˘0.040.10 P P< <0.001 0.001 3.6.Experiment SEM/EDX 2 5.17 ± 0.02 7.00 ± 0.10 P < 0.001 3.6. SEM/EDX Precipitate was collected from the reference beaker with a spatula and investigated using 3.6. SEM/EDX SEM/EDX.Precipitate The analysis was collected revealed from it to the be referencemainly oxygen, beaker calcium with a and spatula carbon. and Their investigated ratios suggest using hydrogenSEM/EDX.Precipitate carbonate The analysiswas andcollected revealedpossibly from itthe tothe presence be reference mainly of oxygen, organicbeaker calcium material.with a andspatula A carbon.representative and Their investigated ratios image suggest ofusing the precipitatehydrogenSEM/EDX. carbonate fromThe analysis the untreated and revealed possibly sample it the to is presencebe shown mainly in of oxygen, Figure organic 14;calcium material. a representative and A carbon. representative EDX Their analysis ratios image issuggest ofgiven the precipitateinhydrogen Table 7. carbonate from the untreated and possibly sample the is presence shown in of Figure organic 14; material. a representative A representative EDX analysis image is given of the in Tableprecipitate6. from the untreated sample is shown in Figure 14; a representative EDX analysis is given in Table 7.

Figure 14. SEM image of precipitate found in the reference beakers. The length of the white bar is 500 µm. Figure 14. SEM image of precipitate found in the reference beakers. The length of the white bar is Figure 14. SEM image of precipitate found in the reference beakers. The length of the white bar is 500 µm. 500 µm.

Water 2016, 8, 79 17 of 19

Table 6. EDX analysis of the precipitate shown in Figure 10.

Element, Line Weight % Atom % Carbon, K 13.23 18.87 Oxygen, K 68.28 73.11 Magnesium, K 0.40 0.28 Phosphorus, K 0.00 0.00 Sulfur, K 0.01 0.01 Potassium, K 0.06 0.02 Calcium, K 18.03 7.71 Iron, L 0.00 0.00 Total 100.00 100.00

4. Conclusions According to a theory derived by Coey [21], crystallisation of calcium carbonate can be influenced by strong magnetic field gradients independent of the absolute field strength of the magnet. We tested this theory by exposing tap water samples to so-called water core magnets (WCMs). The absolute fields of WCMs are weak (<10 G). However, these fields display a fine pattern of strong field gradients (ď770 G¨m´1 (WCM 62081992) and 740 G¨m´1 (WCM 62083545)). By electrical impedance spectroscopy (EIS) and laser scattering we measured significant differences in crystallisation behaviour of exposed tap water samples. The results can be interpreted as an enhanced formation of DOLLOPs, mesoscale prenucleation clusters, due to exposure to a WCM field. We have thus shown that, as Coey’s inequality predicts, magnetic treatment with very weak fields can be effective as long as strong gradients are present in the field.

Acknowledgments: This work was performed in the cooperation framework of Wetsus, European Centre of Excellence for Sustainable Water Technology (www.wetsus.nl). Wetsus is co-funded by the Dutch Ministry of Economic Affairs and Ministry of Infrastructure and Environment, the European Union Regional Development Fund, the Province of Fryslân, and the Northern Netherlands Provinces. The authors like to thank the participants of the research theme “Applied Water Physics” for the fruitful discussions and their financial support, Marianne Heegstra and the Wetsus lab team for the chemical analyses, Philipp Kuntke, Bert Hamelers and Jakob Woisetschläger for long and helpful discussions. Author Contributions: Cees J.N. Buisman, Cees Kamp and Elmar C. Fuchs conceived and designed the experiments. Martina Sammer, Cees Kamp, Astrid H. Paulitsch-Fuchs and Elmar C. Fuchs performed the experiments. Astrid H. Paulitsch-Fuchs and Adam D. Wexler analyzed the data. Elmar C. Fuchs wrote the paper. Conflicts of Interest: The authors declare no conflict of interest. The funding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.

Abbreviations BNC Bayonet Neill–Concelman connector C Capacitance C Coey criterion CPE Constant phase element cryo-TEM Cryo transmission electron microscopy DOLLOP liquid-like oxyanion polymer EDX Energy-dispersive X-ray spectroscopy EIS Electrical impedance spectroscopy IC Ion chromatography IC Inorganic carbon ICP Inductively coupled plasma spectroscopy K X-ray electron shell notation L X-ray electron shell notation Water 2016, 8, 79 18 of 19

LOQ Limit of quantiﬁcation Milli-Q trademark created by Millipore Corporation to describe 'ultrapure' water of "Type 1", as deﬁned by ISO 3696 MDPI Multidisciplinary Digital Publishing Institute NPOC Non-purgable organic carbon R Resistance

Raq Resistance of water RGB Red,green, blue (additive colour model) SEM Scanning electron microscopy TC Total carbon TOC Total organic carbon W Warburg impedance WCM Water core magnet Z complex impedance ϕ phase

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