- Particle formation -

Transcription

1 - Particle formation - after ION Water Treatment

2 Introduction The ION water conditioning system of the Düsseldorf-based company ION Deutschland GmbH has been used for industrial and private water treatment for around 3 decade. According to the company, the mode of operation of the device is based essentially on the electro-galvanic principle. The centre piece of ION water treatment is an ultrapure zinc sacrificial anode, around which water is turbulently circulated by two stainless steel turbulence chambers. The conductive connection of the brass jacket with the zinc sacrificial anode produces a conductive cell when filled with water. The associated release of zinc ions promotes the agglomeration of dissolved water constituents. This agglomeration of dissolved water constituents is regarded by the ION Deutschland GmbH as a competitive reaction to the scaling of the pipe walls. Ions that have been precipitated out of the water can no longer be deposited on the pipe walls and are removed from the piping system with the flowing water. The object of the research project of ION Deutschland GmbH was the analysis of mineral precipitations by the use of a commercially available ION water treatment system in pipe systems carrying flowing water. The focus of the investigations was the quantitative analysis of the particle size range and to provide evidence of the postulated changes in particle quantities and sizes. The investigations were supported by various chemical analyses of drinking water by ION Deutschland GmbH. Materials and methods All the particle investigations were performed on a test rig provided by ION. The test rig included a commercially available ION water treatment unit through which water flowed in a circulatory system made up of commercially available drinking water installation components driven by an electric pump. For the performance of control tests, the ION water treatment unit was replaced by a copper tube. The investigations involved combined experiments with two different water types (drinking water and deionised water) which were carried out with or without an ION water conditioning unit (Table 1). Each experiment was repeated in parallel to demonstrate the reproducibility of any effects. 1

3 Table 1: Test batches Blank sample for sedimentation chamber 2x deionised water Batch 1 (Background particle concentration in drinking water) 2x drinking water Batch 2 (Test-related particle release) 2x deionised water with 15 minute ION water conditioning Batch 3 (control test with drinking water) 2x drinking water with 15 minute treatment in test rig, ION water treatment unit replaced by copper pipe Batch 4 (ION water treatment) 2x drinking water with 15 minute ION water treatment To increase the accuracy of measurement, 3 parallel sedimentation chambers were examined under inverted microscopy and the particles were digitally documented in randomly selected image sections. The number of particles was counted and particle sizes measured digitally with the image processing software analysis of Soft Imaging System GmbH. For microscopic analysis, an inverted Olympus microscope (IX 70) was used. A total of 10 digital photos were taken and analysed from each sedimentation chamber. Depending on the particle density, up to 50 particles per photo were counted and measured. Furthermore, various chemical water parameters (ph, CH d, GH d, K a1,4, Cl -, SO4 2-, NO3 -, Cu 2+, Zn 2+ ) were analysed before and after the experimental runs by the laboratory of ION Deutschland GmbH. The total parameters ph value and conductivity were determined with a combined instrument from Hanna Instruments (glass electrode and conductivity probe). The remaining water parameters were measured photometrically (LASA 100) using the appropriate test cuvettes from Dr. Lange. 2

4 Results and discussion After installation of the test rig and various cleaning and test runs, 8 experiments (batches 1-4 x 2 parallels) were conducted. Since small irregularities in the chamber bottom (glass defects, microscopic scratches) can affect the accurate counting of particles by automatic image analysis, additional image analysis of the bottom of the sedimentation chambers was carried out in order to exclude any falsification of the results due to unavoidable optical material defects (blank sample). Due to the heterogeneous contrast structure of the sedimented particles, it was not possible to automatically detect and measure these. The use of different computer processes (contrast enhancement / reduction, information complexity reduction by 8-bit reduction and subsequent pixel analysis, morphological filters) did not lead to the identification of any particle-specific properties that could be used to perform automatic particle recognition. Another confounding factor was small amounts of bacteria, which could not be automatically subtracted from the particle images. Therefore, a manual, computer-aided approach to measurement of the particles was adopted. The manual approach was more time-consuming but at the same time much more selective in the separation of biological structures and chemical agglomerates. Even on initial analysis, clear differences were apparent between the batches. Thus, Fig. 1 a-d clearly show that after the experimental run, the numbers of particles in the treated water increased significantly compared to the untreated water. This visual impression was confirmed after the measurement of the particle concentrations for the two test runs. After deduction of the specific zero value for the respective chamber, particle concentrations of approx. 47, ,000 ml -1 were calculated for the untreated water sample (drinking water). After treating the water in the test rig with the ION water treatment unit, the number of particles increased on average by factors of 15 to 68 to values of 1,308,085 1,717,540 ml -1 in the first of the two test runs. Any release of particles from the installed technical components (e.g. due to pump wear) could be ruled out in the first test run due to the low number of particles in the Deionised water with ION water treatment batch (Fig. 2 a). In addition to the observed increase in particle concentrations in the ION treated water batch, an increase in the number of particles in the control batch (ION water treatment unit substituted by a copper tube), which was, however, significantly lower than in the batch on which ION water treatment was carried out. This particle formation in the control batch is possibly attributable to temperature-dependent recrystallisation processes in the test batch (BIRKEN personal communication). During 3

5 the test run due to the high pumping capacity the temperatures increased by about 4-5 C, whereby subsequent cooling could have led to an increased precipitation rate in the batches. Furthermore, even under the most rigorous laboratory conditions, it cannot be ruled out that crystallisation nuclei (dusts, bacteria) could have entered the system during the treatment and transfer of the drinking water sample into the circulatory system. In assessing the results, however, it should be noted that these effects had an equal impact on the control batch and the test batch that received ION water treatment. In spite of the relatively high particle background concentration in the control, the effect of ION water treatment in causing a mean increase in particle concentrations by a factor of 2.2 in test run 1 was clear. The effect of ION water treatment on the particle concentration was reproduced in the second test run. In this case, too, clear particle formation after the introduction of the drinking water sample into the test system occurred. In the second run, the particle count (particle concentration) in the ION water treatment batch increased by a factor of 1.6. However, in terms of the absolute values of the total particle numbers, the latter were significantly lower compared to the first test run. Possibly, the lower particle concentration is related to lower overall ion concentrations in the drinking water used. Due to the source of the drinking water, a certain natural variability in the natural ion concentrations is not unlikely, and accordingly a lower ion concentration would also be reflected in a lower particle formation rate. As there is no data available so far on the chemistry composition on the water in the second test run, it will only be possible to answer this question at a later date. 4

6 b) Batch 4 (drinking water with ION water treatment) a) Batch 1 (drinking water without ION water treatment) d) c) Blank sample for sedimentation chamber (deionised water without ION water treatment) Fig. 1 a-d): Microscopic images from the indicated test batches. 5 Batch 2 (deionised water with ION water treatment)

7 2e+6 Particle count [ml-1] 2e+6 1e+6 8e+5 4e+5 0 4e+5 Particle count [ml-1] 3e+5 2e+5 1e+5 0 Deionised water with ION water treatment Drinking water without ION water treatment Drinking water with ION water treatment Fig. 2: Number [ml -1 ] of particles from test runs 1 and 2 and standard deviation from three sedimentation chambers counted in parallel. 6

8 The postulated effect of the particle size shift to higher size classes as a result of ION water treatment was evident when the size spectra of the control batch particles was compared with those of batches receiving ION water treatment: Fig. 3 shows the plot of all counted and measured particles in different size classes in the range of μm 2 adjusted to a volume of 10 ml. In both batches, an exponential decrease in the particle area from the smaller to the larger size classes was evident. The highest fraction of particles of the total particle count in both batches was therefore found in size classes below 50 µm 2. However, it was also found that the relative increase in particle counts in the ION water-treated samples was more pronounced in the higher size classes. Thus, in the strongly represented classes up to 50 μm 2 average particle concentrations increased by a factor of 1.5. On the other hand, in the higher classes up to 250 μm 2, there was a significantly more pronounced increase by a factor of 3.9. This was also evident in the percentage distribution of particle abundance. Fig. 4 plots the percentage fractions of particle size classes for the ranges 10 50, , , and μm 2. As it was not possible to further differentiate smaller particles in biological or mineral terms in the image analysis without the use of additional staining techniques, a threshold value of 10 μm 2 was set for the evaluation of the particle size spectrum; smaller particles were not included in the evaluation. A comparison of the size class spectra showed that the use of ION water treatment led to a shift in the relative frequency of individual size classes. While in batches without ION water treatment 62% of the particles were assigned to the smallest size class μm 2, the fraction of small particles in the batch with ION water treatment dropped to 44%. In contrast, the proportion of particles in the next higher size class ( μm 2 ) in the treated batch increased from 21 to 30%. Even in the higher size classes up to 250 μm 2, a clear increase in the percentage proportions could be detected, which can be interpreted as a growth of the crystalline particles up to 250 μm 2. 7

9 Particle count [10 ml -1 ] with ION treatment with ION water treatment unit replaced by cooper pipe ION water treatment unit replaced by copper pipe Size classes [µm 2 ] Fig. 3: Total number of all counted and measured particles from both test runs for size classes from 10 µm 2 to 250 µm 2 for the test batches with ION water treatment or without ION water treatment. 8

10 µm 2 8% µm µm 2 3% 6% µm 2 21% µm 2 62% Batch without ION water treatment µm 2 8% µm 2 4% µm 2 14% µm 2 44% µm 2 30% Batch with ION water treatment Fig. 4: Percentage distribution of the counted and measured particles [counts 10 ml -1 ] from both test runs for size classes up to 250 µm for the test batch with ION water treatment or without ION water treatment. 9

11 Water analysis For the assay of the drinking water used in the test batches, the parameters summarized in Table 2 were determined. Table 2: Chemical water parameters before and after ION water treatment and chemical water parameters before and after the control ION water treatment substituted by copper pipe. Drinking water Drinking water Drinking water Parameter Deion. H 2O with before after before Drinking water after ION water ION water ION water treatment treatment treatment Copper pipe Copper pipe ph Conductivity [µs cm -1 ] CH [ d] GH [ d] K a1.4 [mmol l -1 ] Cl - [mg l -1 ] n/a SO4 [mg l -1 ] n/a NO3 - [mg l -1 ] n/a Cu 2+ [mg l -1 ] n/a Zn 2+ [mg l -1 ] As expected, there were no differences in ph values between the samples before and after drinking water treatment. However, the comparison of the conductivity as an aggregate parameter for dissolved salts showed a decrease in conductivity of about 70 μs cm -1 after ION treatment with water, possibly due to a reduction in the concentrations of dissolved ions. This tendency continued in the sum parameters of carbonate and total hardness and could also be seen in the comparison of the chloride sulphate and nitrate concentrations. The particle formation induced by the test treatment and the use of ION water treatment, as also demonstrated by COETZEE et al. 1996, after the introduction of zinc ions into drinking water, resulted accordingly in a reduction in the concentration of measured free ions. Noticeable in this context is the decrease in copper ion concentration in the batch with ION water treatment, which was reduced by 90% of the original concentration. This is due to the electrogalvanic mode of action of the zinc sacrificial anode, since zinc is oxidized in the course of ION water treatment and copper ions are reduced to metallic copper, which is no longer photometrically detectable. In with the reduced copper ion concentration, 10

12 higher zinc concentrations should be detectable after treatment. In fact, however, the increase in zinc concentration was not significant. It should be noted, however, that only the dissolved zinc ions are detected with the photometric analysis used to date with commercial tests (BIRKEN personal communication). The crystal-bound zinc is not accessible to the available analytical techniques. The result therefore lends support to the claim that zinc ions play a significant role in particle formation and particle growth. In particular, the identified reduction in copper concentrations on integration of ION water treatment is an interesting aspect for further investigations. Copper is one of the biologically essential metals in human nutrition. For example, the WHO (World Health Organisation) recommends a daily intake of 1-2 mg d -1 for infants and children and 2-4 mg d -1 for adults (WHO 1996, However, elevated copper concentrations in drinking water can have biologically toxic effects. In particular, diseases related to chronic high copper concentrations can be problematic in early child development. The guideline set by the Drinking Water Ordinance (TrinkwV 1991) is therefore 3 mg l -1. Copper pipes in household domestic installations, as present in 60% to 70% of all households in West German federal states can, however, lead to copper levels of up to several mg/l in drinking water due to corrosion processes (WAGNER et al. 1996). This is possibly a further possible application of ION water treatment for the purpose of improving the quality of domestic drinking water. A more detailed analysis of this effect would therefore be desirable. The analysis of the chemical parameters of the control batch showed that the copper pipe also affected the water chemistry after the test run. This affected in particular the parameter conductivity as well as the concentrations of the anions. While the conductivity decreased by 76 μs cm -1, sulphate concentration increased by about 10 mg l -1. By contrast, the concentrations of chloride and nitrate decreased by 15.8 mg l -1 and 1.8 mg l -1 respectively. These divergent trends in the reduction and increase in the concentration of different ions show that complex chemical conversions also occur in the control system, which cannot be fully elucidated with the analyses used so far. However, the principal mode of action of ION water treatment became evident when comparing the degrees of hardness. While treatment with ION water treatment resulted in a significant reduction in dissolved alkaline earth metals, their concentration in the control batch with copper tubing remained essentially the same. In this context, too, more detailed analyses are required, whereby the focus should be on the specific analysis of particulate or bound hardening agents. 11

13 Summary The subject of the investigations was the review of the claims by ION Deutschland GmbH regarding the effect of ION water treatment on particle formation. For this purpose, drinking water and deionised water underwent treatment in a model cycle by a commercially available ION water treatment unit. In the control tests, the ION water treatment unit was replaced by a simple copper tube. Particle samples were precipitated from the obtained water samples and measured by image analysis. It was demonstrated that ION water treatment in the model cycle induces an increase in particle concentrations by a factor of 1.6 to 2.2. At the same time, an increase in the frequency of particle sizes over 10 μm 2 to 250 μm 2 was detected. The photometric analysis of the chemical water parameters showed a general decrease in the salts dissolved in the water, probably due to the increase in the number of particles formed. In particular, there was a significant reduction in copper concentrations. Literature WHO (1996): Trace elements in human nutrition and health. Geneva, World Health Organization. MORTIMER, CHARLES E. (1987) : Chemistry: a conceptual approach 5th edition, Georg Thieme Verlag Stuttgart New York, p.608 Annex. D. WAGNER, W.R. FISCHER, H.H. PARIS, O. VON FRANQUÉ (1996): Microbiological Influenced Corrosion, in Copper Potable Water Installations. In Microbially Influenced Corrosion of Metals, EDS. E. Heitz, H.-C. Flemming, W. Sand, Springer-Verlag, Berlin 1996, p Coetzee, P.P., Yacoby, M., Howell, S. (1996): The role of zinc in magnetic and other physical water treatment methods for the prevention of scale. WATER SA 22 (4):