EXPERIMENTAL INVESTIGATION OF HYDRAULIC RESISTANCE IN PIPE AERATORS

Marek Kalenik, Dariusz Morawski, Grzegorz Stańko
Division of Water Supply and Sewage Systems, Department of Civil Engineering and Geodesy, Warsaw Agricultural University, Poland

ABSTRACT

The paper presents and analyses the results of the research on hydraulic resistance in pipe aerators for waters from Tertiary and Quaternary periods, under conditions of technical exploitation of water treatment plant. Hydraulic resistance investigation was conducted in concurrent pipe aerators filled with the Białecki rings of 12 and 25 mm diameters. The research methodology comprised of measuring hydraulic resistance in the case of clean rings (after the start of water treatment plant operation) and in the case of silted ones (after some two years of water treatment plant operation). On the basis of that researches, some hydraulic phenomena occurring in pipe aerators filled with the Białecki rings were recognized and exploitation rules for this kind of aerators were established.

Key words: water, pipe aerator, water treatment plant, hydraulic resistance, Bialecki rings.

INTRODUCTION

Building new water treatment plants and modernising the old ones are indispensable to provide people with water of adequate quality and sufficient quantity. Nowadays, various modern building materials may be used for construction of water treatment plants. Such materials are cheaper than the traditional ones and may be exploited for longer. The materials of that type are plastics used for manufacturing windows, pipes, and tanks of potable water.

Fresh water is scarce in many regions of the world. In 1995 – for example – about 1.76 billion people on the Earth suffered from the lack of fresh water [7]. In some 20 years’ time this deficit will intensify due to quick growth of population. It is estimated that in 2025 about 2.8 billion people in the world will be troubled with the lack of fresh water. In consequence it is absolutely necessary to conduct scientific research, constantly improve the methods of water treatment for drinking and domestic purposes, as well as improve the rules of hydraulic calculations for optimal design of water treatment plants in terms of energy minimisation and high efficiency. The skills of hydraulic resistance calculating in particular water installations enable a selection of proper water intake pumps and pressure booster units. Well-chosen pumps work with high efficiency and performance. They are energy-saving and rarely break down. The devices that work properly from the view of hydraulic resistance during the exploitation of water plant do not generate additional costs of repairs that influence the final water price.

There is no information about hydraulic phenomena occurring during the real work of pipe aerators filled with the Białecki rings in available professional literature [1, 3, 6, 8, 12]. It lacks design instructions, either. Recent research conducted for clean rings [4] shows that an enlargement of pipe aerator diameter has stronger impact on the reduction of hydraulic resistance at concurrent pipe aerators filled with the Białecki rings than an enlargement of rings diameter.

The presentation and results analysis of the research on hydraulic resistance in pipe aerators for water from Tertiary and Quaternary periods, under conditions of technical exploitation of water treatment plant, are the aims of the paper. The scope of this article contains the research in concurrent pipe aerators filled with the Białecki rings of 12 and 25 mm diameters.

STRUCTURE AND OPERATING PRINCIPLES OF WATER TREATMENT PLANT

The Scientific-Research Water Plant at Warsaw Agricultural University (NBSW SGGW) was modernized in 2004. Full level of automation has been applied and it has been equipped with the Endress+Hauser monitoring and measuring devices. The water plant produces water mainly for a campus at Warsaw-Ursynów. There are two water treatment production systems. The first is dedicated to treat water from Quaternary periods while the second one treats water taken from Tertiary periods. Quaternary water is drawn from three drilled wells (figure 1), whereas Tertiary water from one drilled well (figure 2). Quaternary water characterises of exceeded iron and manganese concentrations, whereas the concentration of iron in the Tertiary water is too high [5]. Therefore, parameters of water must be adjusted to current requirements set up in the Ordinance of the Ministry of Health [9]. The treatment technology of Quaternary water is based on the processes of water aeration in the pipe aerators, water filtration in the quartz sand bed in the iron remover and then – in water filtration through the activated quartz sand bed in the manganese remover. The treatment technology of Tertiary water is based on the processes of water aeration in the pipe aerator and water filtration in the quartz sand bed in the iron remover. Water treatment of Quaternary periods is conducted on two technological paths (section No. 1 and 2, figure 1), which are made up of a pipe aerator (A), iron remover (Fe), manganese remover (Mn) and potable water reserve and compensating tank (ZZ-W). Water treatment of Tertiary periods is conducted on one technological path (figure 2), which consists of an aerator (A), two iron removers (Fe) and hydrophore (H). The concurrent pipe aerators are filled with the Białecki rings.

At the Quaternary water treatment production system, the diameter of aerators is 0.2 m, their length is 1.5 m, the diameter of rings is 12 mm and the depth of charge is 0.75 m (figure 3). The construction of iron and manganese removers is identical. Their diameter is 2.4 m. The quartz sand depth of charge is 1.0 m and diameters of grains are from 0.8 mm to 1.2 mm. The support depth of charge is 0.3 m and diameters of grains are from 5 to 15 mm.

At the Tertiary water treatment production system, the diameter of aerator is 0.1 m, its length is 1.5 m, the diameter of rings is 25 mm and the depth of charge is 0.75 m (figure 3). The construction of iron beds of section 3 (figure 2) is the same as of those in sections 1 and 2 (figure 1).

The aerator of Quaternary water treatment production system is filled with rings in 94 %; whereas Tertiary water treatment production system is filled in 56 % (figure 3). The support rings grid has a size of 8 mm × 8 mm. The grid occupies 40 % of aerator’s cross-section surface.

Figure 1. Scheme of water treatment plant [4]: 1 – deep-well pump, 2 – bored well, 3 – automatic cut-off valve, 4 – aerator, 5 – iron remover, 6 – ball vent, 7 – electronic differential pressure meter, 8 – cut-off valve with pulse connector, 9 – manometer, 10 – cutt-off valve, 11 – jet pump for water aeration, 12 – manual cut-off valve, 13 – pulse cable, 14 – drain discharger, 15 – manganese remover, 16 – electronic flowmeter, 17 – manual valve for flow control, 18 – compressor, 19 – air blower, 20 – washing pumps, 21-reserve and compensating tank, 22 – suction rose, 23 – pressure booster unit, 24 – water-pipe network, 25-washings settling tank, 26-sewerage system

Figure 2. Scheme of section No. 3 of water treatment plant, for Oligocene water: 1 – deep-well pump, 2 – bored well, 3 – automatic cut-off valve, 4 – aerator, 5 – iron remover, 6 – ball vent, 7 – electronic differential pressure meter, 8 – cut-off valve with pulse connector, 9 – manometer, 10 – cut-off valve, 11 – manual cut-off valve, 12 – pulse cables, 13 – drain discharger, 14 – electronic flowmeter, 15 – manual valve for flow control, 16 – hydrophore, 17 – compressor, 18 – air blower, 19 – washing pumps, 20 – reserve and compensating tank, 21 – suction rose, 22 – water-pipe network, 23 – washings settling tank, 24 – sewerage system

Figure 3. Scheme of pipe aerator : a) aerator of section No. 3 according to fig. 2, b) aerator of section 1 and 2 according to fig. 1 1 – air supply conduit, 2 – water supply conduit, 3 – support rings grid, 4 – lock plate, 5-Białecki rings filler, 6 – pulse cable, 7 – stop valves, 10 – electronic differential pressure meter, 11 – vent

RESEARCH METHODOLOGY

The investigation of hydraulic resistance at water treatment facilities of Warsaw Agricultural University’s Scientific-Research Water Plant was conducted without air, so that air bubbles could not cause false measurement results [2]. A measurement of hydraulic resistance in flow of water-air mixture is impossible because during the measurement process air bubbles get into pulse connectors which results in false readings from the electronic differential pressure meter. Pipe aerators filled with the Białecki rings are characterized by a high concentration of air in water. It causes that effluent water from the aerator contains large amount of dissolved oxygen [10, 11] indispensable for correct processes of water iron and manganese removal.

The investigation of hydraulic resistance was led at concurrent pipe aerators, during ordinary technological exploitation of Scientific-Research Water Plant. Measurement of hydraulic resistance was carried out in the aerator of section No. 3 (figure 2; diameter of 0.1 m) filled with the Białecki rings (figure 3a; diameter of 25 mm) and in the aerator of section No. 1 (figure 1; diameter of 0.2 m) filled with the Białecki rings (figure 3b; diameter is 12 mm). Measurement was conducted after switching the Water Plant control system from automatic into manual control and after switching deep-well pumps on.

Section No. 2 was working during hydraulic resistance measurement in the aerator of section No. 1 (figure 1). The measurement was conducted after switching the Water Plant control system into manual mode, followed by starting deep-well pumps and degassing filter beds. Hydraulic resistance measurements in the pipe aerator consisted in establishing proper intensity of water flow with the help of electronic flowmeter – 16. Water flow was adjusted with a precise water flow valve – 17. Next, when proper intensity of water flow in the aerator was set up, the reading of electronic differential pressure meter – 7 was made by switching appropriate cut-off valves – 8. Electronic differential pressure meter was connected at the inflow and outflow of the pipe aerator by means of pulse cables – 13 and cut-off valves. Measurement range of intensity water flow varied from 5 m³/h to 40 m³/h, at intervals of 5 m³/h. Hydraulic resistance measurement in the aerator of section No. 3 (figure 2) consisted in establishing proper intensity of water flow with the help of electronic flowmeter – 25. Adjustment of intensity of water flow was made with use of throttling valve – 26. Consequently, when proper intensity of water flow in the aerator was set up, the reading of electronic differential pressure meter – 7 was done by switching appropriate cut-off valves – 8. Electronic differential pressure meter was connected at the inflow and outflow of the pipe aerator by means of pulse cables -12 and cut-off valves. Measurement range of intensity water flow varied between 5 m³/h and 40 m³/h at intervals of 5 m³/h. When appropriate intensity water flow has been stabilized, two digital readings were taken every second minute by means of electronic differential pressure meter. Such measurements were carried out once a month. For every hydraulic resistance measurement, three measurement series were conducted.

Every time after the hydraulic resistance measurement was carried out in the aerator of section no. 3 (figure 2), water was tapped and after that, fifty rings were taken out randomly and weighed in groups of ten on laboratory scales. Having been weighted the rings were put back to the aerator. For water intensity flow equal to 15 m³/h and intensity air flow equal to 0.4 Nm³/h, 0.6 Nm³/h, 0.8 Nm³/h, 1.0 Nm³/h, respectively, samples of water from behind the aerator were taken, after which contents of dissolved oxygen was determined at laboratory.

DISCUSSION OF THE RESULTS

Water from Tertiary periods treated at Scientific-Research Water Plant at Warsaw Agricultural University (NBSW SGGW) contains about 2.7 mg Fe/dm³ and about 0.5 mg Mn/dm³. Water from Quaternary periods contains about 3.2 mg Fe/dm³ and about 0.1 mg Mn/dm³ [5]. Therefore, it means that contents of iron and manganese at water form Quaternary and Tertiary periods are comparable. When analysing results of hydraulic resistance measurement as a function of water flow presented in figures 4 and 5, one can notice that hydraulic resistance increases with intensity of water flow. This finding is in line with expectations. Local hydraulic resistance coefficients, expressed as a function of the Reynolds number, calculated on the basis of conducted measurements are shown in figures 6 and 7. Conducted studies have shown (figure 4 and 5) that during the work of concurrent pipe aerators (i.e. during the water aeration) filled with the Białecki rings, the accumulation of iron compounds on the surface of rings occurs and hydraulic resistance increases. These compounds precipitate during water aeration. After longer time of operation, the aerators become completely silted. The silting develops from the top to the bottom, opposite to the direction of water flow. Compounds of iron are not rinsed from the aerator entirely due to the fact that water and air, while flowing through rings, decrease their flow speed which results in longer contact time between air and water and – consequently – the precipitation of iron compounds which accumulate on the latter part of the aerator.

Figure 4. Hydraulic resistance of aerator section No. 1, filled with 12 mm diameter rings

Figure 5. Hydraulic resistance of aerator section No. 3, filled with 25 mm diameter rings

Figure 6. Dependences of local resistance coefficients ζ on the Reynolds number Re in the aerator of section No. 1, filled with 12 mm diameter rings

Figure 7. Dependences of local resistance coefficients ζ on the Reynolds number Re in the aerator of section No. 3, filled with 25 mm diameter rings

The rings’ diameter in the section No. 1 was 12 mm and the aerator’s diameter was 0.2 m (figure 4) while the ring’s diameter in the section No. 3 was 25 mm and the aerators’ diameter was 0.1 m (figure 5). When analysing the influence of the Białecki rings and the aerator’s diameter, one can say that the diameter of aerator has stronger impact on the increase of hydraulic resistance in the concurrent pipe aerators than the diameter of rings. Simultaneously, the conducted research implies that the increase in hydraulic resistance, caused by colmatation of the aerator, is directly proportional to the volume of water, which flows through the aerator.

When the aerator is rinsed by raw water, mechanical cleaning is ineffective. Visible result of mechanical cleaning was achieved (figure 4) when the aerator was rinsed by compressed air of flow higher than 4.5 Nm³/h and by raw water of flow 5 m³/h, where every 30 seconds compressed air was switched off for 30 seconds at permanent water flow. The rinsing was carried on for about 30 minutes until straw-coloured outflow from aerator has been observed. The best result was obtained when applying chemical cleaning (figure 4), extracting the rings from the aerator and washing them in a diluted oxalic acid.

Figure 8 shows iron growth in singular ring of 25 mm’s diameter in the working aerator of the section No. 3. Analysis of results shown in figure 8 supports the view that trend for iron increase in the singular ring is linear. This trend depends on volume of water that flows through the aerator; in that case the growth was about 0.2 g per month.

Figure 8. Weights fo a singular 25 mm diameter ring, from the aerator of section No. 3

Figure 9 shows the contents of dissolved oxygen in water after aeration in the section No. 3 during particular months of aerator’s work in relation to the flow of air delivered to the aerator. The research shows that dissolved oxygen contents after aerator amounted on average to 7.4 mg O₂/dm³ after one month of work, 7.8 mg O₂/dm³ after second month of work, 7.0 mg O₂/dm³ after third month of work and to small extent depended on the air flow delivered to the aerator. The period of three months of aerator’s work is too short to conclude unanimously that colmatation of the aerator by precipitated iron compounds reduces the efficiency of water aeration.

Figure 9. Concentration of dissolved oxygen in water after aeration in section No. 3, filled with 25 mm diameter rings

Figure 10a shows the Białecki rings of diameter 12 mm after chemical cleaning and before inserting them back to the concurrent pipe aerator (clean rings). Figure 10b shows the same rings removed from the silted aerator after 22 months of its operation but before their chemical cleaning (silted rings). From the figure 10b one can find out that the inner parts of the rings are completely silted by iron compounds. As a consequence, the silted rings have completely lost their ability to mix water and air during their flow through the aerator. Figure 11 shows the Białecki rings of diameter 25 mm after three months of operation the section No. 3. One can clearly see iron compounds accumulated on the surface of them, in the shape of small clots. An accumulation of the iron compounds begins also inside rings, where in the upper part of the aerator a jamming of the rings during flow of water has occurred.

Figure 10. Views of the Białecki 12 mm diameter rings: a) clean, b) silted

Figure 11. Top views of the Białecki 25 mm diameter rings in the aerator of the section No. 3 after three month of work: a) top layer, b) bottom layer

CONCLUSIONS

1. In the course of water aeration conducted at concurrent pipe aerator filled with the Białecki rings, precipitated iron compounds accumulate in the rings, which causes their clogging and an increase in hydraulic resistance. As result in a long run, i.e. after approximately two years of the aerator’s operation its complete clogging has occured.

2. Mechanical cleaning with raw water of the concurrent pipe aerator filled with the Białecki rings is hardly effective. A better result can be achieved when the aerator is rinsed with raw water with intensive pulsatory stream of air flow. Only chemical cleaning ensures complete removal of iron compounds from rings’ surface. Thus, for concurrent pipe aerators exploitation it is recommended to perform mechanical cleaning with raw water with pulsatory air stream flow every month and chemical cleaning (i.e. extraction of rings from the aerator and washing them in the diluted oxalic acid) every year.

3. Further investigation of concurrent pipe aerators filled with the Białecki rings are needed to answer the question whether clogging of aerators with precipitated iron compounds reduces the efficiency of water aeration.

REFERENCES

1. Bagieński J., 1996: Compressed air system in water treatment plants. Gas, Water and Sanitary Technique. No 12: 448-453 [in Polish].

2. Grabarczyk Cz., 1997: Flows of liquids in pipes. Calculation methods. Envirotech. Poznan.

3. Heidrich Z., Roman M., Tabernacki J., Zakrzewski J., 1980: Water treatment facilities. Rules of design and calculation examples. Arkady. Warsaw.

4. Kalenik M., Morawski D., 2004: Investigation of hydraulic resistance of selected water treatment facilities. Melioration and Meadows News. Problems of Rural Environment Engineering. No 4: 199-202 [in Polish].

5. Kossakowska D., 2004: Water-Law Statement concerning underground water consumption from Quaternary and Tertiary periods for area of Scientific-Research Water Plant at Warsaw Agricultural University in Warsaw, Nowoursynowska Street 166. GEO-COM.

6. Kowal A.L., Maćkiewicz J., Swiderka-Bróż M., 1998: The basis of treatment water systems design. Printing house of Wroclaw Technical University, Wroclaw.

7. Montaigne F., 2002: Fresh water. National Geographic No 9(36): 42-70.

8. Nawrocki J., Biłozor S., 2000: Water treatment. Chemical and biological processes. PWN (Polish Scientific Publishers).

9. Ordinance of Minister of Health of 19 November 2002 on requirements concerning water quality for a purpose of public consumption. Government Regulations and Laws Gazette No 168, Head 1763.

10. Siwiec T., Morawski D., 1999: Investigation of water aeration efficiency on the example of Scientific-Research Water Plant at Warsaw Agricultural University. III Scientific-technical conference. Underground water treatment – investigation, designing and exploitation. Printing house of Warsaw Technical University.: 113-122.

11. Siwiec T., Morawski D., Zaleski K., 2003: Investigation of water aeration efficiency for pipe aerators with the Białecki rings. Instal No 2: 44-49.

12. Szpindor A., 2003: Country water supply and canalization. Arkady. Warsaw.

 

Accepted for print: 19.12.2006

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Marek Kalenik
Division of Water Supply and Sewage Systems,
Department of Civil Engineering and Geodesy,
Warsaw Agricultural University, Poland
Nowoursynowska St. 159, 02-776 Warsaw, Poland
email: marek_kalenik@sggw.pl

Dariusz Morawski
Division of Water Supply and Sewage Systems,
Department of Civil Engineering and Geodesy,
Warsaw Agricultural University, Poland
Nowoursynowska St. 159, 02-776 Warsaw, Poland

Grzegorz Stańko
Division of Water Supply and Sewage Systems,
Department of Civil Engineering and Geodesy,
Warsaw Agricultural University, Poland
Nowoursynowska St. 159, 02-776 Warsaw, Poland
email: grzegorz_stanko@o2.pl

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Responses to this article, comments are invited and should be submitted within three months of the publication of the article. If accepted for publication, they will be published in the chapter headed 'Discussions' and hyperlinked to the article.

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