REVERSE OSMOSIS WATER SYSTEM FOR INDUSTRIAL USE

Transcription

1 JOURNAL OF APPLIED ENGINEERING SCIENCES VOL. 2(15), issue 2_2012 ISSN ISSN-L (Print) / e-issn: REVERSE OSMOSIS WATER SYSTEM FOR INDUSTRIAL USE FRCA Anagabriela, Technical University of Cluj-Napoca, anagabriela.farcas@insta.utcluj.ro A B S T R A C T This paper presents the use of reverse osmosis in water treatment. Reverse osmosis is a baromembrane process that separates water from a solution as a result of pressure. The water and the water solution are separated by a membrane that allows only the water molecules to pass through. The case study represents a reverse osmosis equipment that purifies water for a technological process. In order to observe and test the efficiency of this system it was taken water samples in different phases of the process. In analyzing the water samples it was taken into account the following parameters: manganese, iron, ammonium, turbidity, ph levels, conductivity, permanganate index, water hardness and chlorides. The values of these parameters were compared to the limiting values stipulated by the law. Using the two-stage reverse osmosis process a high efficiency will be achieved. Received: July 31, 2012 Accepted: July 31, 2012 Revised: August 10, 2012 Available online: October 31, 2012 Keywords: membrane, baromembrane processes, water conductivity, water treatment INTRODUCTION Osmosis is a natural phenomenon which occurs when two water solutions with different ion concentration are separated by a semi-permeable membrane [1]. The semi-permeable membranes only allow the water molecules to pass through, therefore the water would flow towards the highly concentrated solution until the two solutions are equally concentrated. For the water to flow towards the less concentrated solution, a force should be applied on the highly concentrated solution. This is the reverse osmosis process, which provides water separation from different water sources. The membrane is an interposed structure between two phases or compartments which can prevent or aggravate substance transport or which can allow only certain particles to pass through. The separation will take place on the membrane surface or inside the membrane, where the molecular interactions take place. The permeability trough membrane implies both the occurrence of diffusion and the solubility of the diffusing species, but in order for the components to be transferred through the membrane, a driving force is necessary [1]. In the reverse osmosis process the driving force is pressure. On an economic level, the membrane is supposed to block some substances and to allow the water molecules to pass through. Fig.1. Membran schematic diagram [1]

2 MATERIALS AND METHODS 1. The Experimental Equipment / System The paper presents a reverse osmosis equipment that purifies water pulled from a 35 meter deep well. The resulting water is used for a tehnological process. The process optimum functioning parameters are equal to the drinking water quality parameters, as regulated by the 458/2002 and 311/2004 laws. Fig.2. Two-stage reverse osmosis equipment The reverse osmosis equipment is supplied with water from a well, using a 32 mm wide pipe, with a 5.7 m 3 /h flow. A 5 µm filter stops any contingent impurities and manometers measure the filter clogging degree both upstream and downstream. The water hardness is measured by a device located before the manometer which is placed in front of the filter. The samples to be analyzed are collected from the tap, located after the filter. The pressure needed for the reverse osmosis process is produced by a vertical multistage centrifugal pump. Downstream from it two manometers are installed, the first belongs to the pump, and the second is meant for observing the pressure of water entering the first stage of reverse osmosis. At this stage a polyamide and polysulphones spiralmembrane module is provided. The first stage permeate quantity is measured by a flow gauge set on the permeate pipe. The first stage reject is redirected towards the second stage of the reverse osmosis process, where there is another polyamide and polysulphones spiral-membrane module. The second stage permeate is collected together with the first stage permeate. Some of the concentrate resulted from the second stage of the reverse osmosis process is recycled - it re-enters the process right before the reverse osmosis pump, and the rest of it, is evacuated in the sewer system. The samples for the two reverse osmosis stages are provided by the two faucets installed after each membrane module. The resulting permeate and concentrate quantities are determined by flow gauges found downstream from the membrane modules. A pipe that would allow a certain amount of permeate re-enter back in the reverse osmosis system is optional.

3 JOURNAL OF APPLIED ENGINEERING SCIENCES VOL. 2(15), issue 2_2012 ISSN ISSN-L (Print) / e-issn: Fig.3. Functional diagram of two stage reverse osmosis equipment (1 Manometer before the filter; 2 Filter cartridge 5 µm; 3 Manometer before the filter; 4' Sampling valve; 4 electro-valve; 5 Pressure switch; 6 CR Pump; 7 Pump manometer; 8 Ball valve; 9 Entering pressure manometer; 10 Permeate entering ball valve; 11 Stage I module membrane; 12 Stage II module membrane; 13 Stage I sampling valve; 14 Stage II sampling valve; 15 Stage II concentrate manometer; 16 electro-valve; 17 Concentrate control needle valve; 18 Control ball valve for recycled concentrate from stage I; 19 Stage I concentrate flow gauge; 20 Stage I concentrate one-way valve; 21 Permeate one-way valve; 22 Permeate flow gauge; 23 Permeate 3-way valve; 24 Concentrate 3-way valve; 25 Concentrate flow gauge; 26 Permeate measuring element; 27 One-way valve; 28 electro-valve; 29 electro-valve; 30 Water hardness monitoring unit) In order to analyze the efficiency of the reverse osmosis system, samples are collected as water enters the system, after the first stage and after the second stage. As shown above, special valves are placed for analytical sampling. 2. Methods of Water Analysis The water samples have been collected on a weekly basis and have been tested for the following indicators: turbidity, ph, conductivity, permanganate index, hardness, chlorides and iron. The samples were analyzed by an accredited laboratory; therefore the methods of analysis stipulated by the laws and standards in force were respected. The procedures took place at a 20 o C, ± 2 o C room temperature, as stipulated by STAS 6300/1998 and a humidity ratio of less than 65%. In order to determine the turbidity levels, the samples were analyzed congruent to SR EN ISO 7027/2001, using a stationary LP 2000 turbidimeter with a microprocessor provided with a tank and a tank cover. The turbidimeter s precision is ±0.5 FTU at a 20 o C temperature. The ph level was determined by the analysis method stipulated by SR ISO 10523/2009, using a laboratory ph meter ThermoFisher Scientific Orion 3-Star, made in USA. The ph meter is provided with a temperature adjustment device and with a thermometer readable to 0.5 o C. The ph measurement accuracy is 0.01 units. The electronic conductivity was determined using the analysis method stipulated by SR EN 27888/97, using a laboratory conductivity meter - ThermoFisher Scientific Orion 3-Star, made in USA. The device has a relative accuracy of 3.5% of the average readings and is provided with a ±0.1 o C relative accuracy thermometer. The permanganate index is determined by using the analysis method congruent to SR EN ISO 8467/2001. The following devices were used: Radvag AS 220/C/2 analytical balance (Poland); WSC/4D Hamilton-Glass double distillation cabinet still, made in UK and a TW 20 Julabo water bath, made in Germany. The water bath is provided with a rack that holds the 100 mm test tubes; it

4 ensures a quick temperature rise to o C for all the test tubes simultaneously as well as temperature stability afterwards. The ammonium levels are measured by the SR EN ISO /2001 analysis methods, using the following equipment: Radvag WPS 2100/C/2 precision balance (Poland) with a load capacity of g and second class precision; Radvag AS 220C/2 analytical balance (Poland), with a load capacity of g and first class precision; HCH 1500 chemical hood, ElectronicApril SRL Cluj Napoca; Julabo TW 20 water bath (Germany); WSC/4D Hamilton-Glass double distillation cabinet still, made in UK; Orion 2 Star ph meter with digital display and ph triode Orion 9157 BNMD, series LQ 16371; UV-VIS Specord 50 Analitik Zena spectophotometer (Germany) with a measuring range between nm. The water hardness is determined by using the EDTA titrimetric method as required by the SR ISO 6059/2008. The following devices were used: Radvag AS 220C/2 analytical balance (Poland), with a load capacity of g and first class precision; WSC/4D Hamilton-Glass double distillation cabinet still, made in UK; Orion 2 Star laboratory ph meter with a temperature adjustment device that has a 0.01 units accuracy and a ph triode, produced by ThermoFisher Scientific, USA. The levels of chlorides in the water are measured by the Mohr method, as stipulated by SR ISO 9297/2001. The equipment used: Radwag AS 220/C/2 analytical balance (Poland) with a load capacity of g and first class precision; HCH 1500 chemical hood, ElectronicApril SRL, Cluj Napoca. The iron levels in the water are measured according to SR ISO 6332/1996. The following devices were used: Radvag WPS 2100/C/2 precision balance (Poland) with a load capacity of g and second class precision; Radwag AS 220/C/2 analytical balance (Poland) with a load capacity of g and first class precision; HCH 1500 chemical hood, ElectronicApril SRL, Cluj Napoca; Julabo TW 20 water bath (Germany); WSC/4D Hamilton-Glass double distillation cabinet still, made in UK; Orion 2 Star ph meter with digital display and Orion 9157 BNMD ph triode, series LQ 16371; UV-VIS Specord 50 Analitik Zena spectophotometer (Germany) with a measuring range between nm; filter funnels provided with low porosity membranes below 0.45 µm. For the manganese levels in the water samples an atomic absorption spectophotometer analysis method was used, as stipulated by SR /1997. The laboratory equipment included: Radwag AS 220/C/2 analytical balance (Poland), with a load capacity of g and first class precision; HCH 1500 chemical hood, ElectronicApril SRL, Cluj Napoca; Julabo TW 20 water bath (Germany); WSC/4D Hamilton-Glass double distillation cabinet still, made in UK; Orion 2 Star ph meter with digital display and Orion 9157 BNMD ph triode, series LQ 16371; UV-VIS Specord 50 Analitik Zena spectophotometer (Germany) with a measuring range between nm; Analitik Yena atomic absorption spectophotometer with a measuring range between nm. RESULTS AND DISCUSSION For the reverse osmosis system presented in this paper, the above mentioned indicators were measured on a regular basis. The results are presented in tables 1, 2, 3 and 4. Table 1. Week 1 Parameter Source MAC values*[2,3] Manganese 53(µg/l) 50 (µg/l) BDL (µg/l) BDL (µg/l) Iron 0.001(mg/l) 200 (µg/l) BDL (mg/l) BDL (mg/l)

5 JOURNAL OF APPLIED ENGINEERING SCIENCES VOL. 2(15), issue 2_2012 ISSN ISSN-L (Print) / e-issn: Ammonium 0.02(mg/l) 0,50 (mg/l) BDL (mg/l) BDL (mg/l) Turbidity 0.65(NTU) 1,00 (NTU) 0.45 (NTU) 0.28 (NTU) ph Conductivity 1944(µS/cm) <2500 (µs/cm) (ms/cm) (ms/cm) Permanganate index 1.34(mgO 2 /l) 5.00 (mgo 2 /l) 0.51 (mgo 2 /l) 2.94 (mgo 2 /l) Hardness 32.9( o G) 5,00 ( o G) 6.84 ( o G) 4.48 ( o G) Chlorides 257(mg/l) 250 (mg/l) (mg/l) 8.79 (mg/l) * MAC maximum accepted concentration NTU nephelometric turbidity units BDL below detection limit Table 2. Week 2 Manganese 41.1 (µg/l) 50 (µg/l) BDL (µg/l) BDL (µg/l) Iron (mg/l) 200 (µg/l) BDL (mg/l) BDL (mg/l) Ammonium 0.02 (mg/l) 0,50 (mg/l) BDL (mg/l) BDL (mg/l) Turbidity 0.57 (NTU) 1,00 (NTU*) 0.26 (NTU) 0.27 (NTU) ph Conductivity 1961 (µs/cm) <2500 (µs/cm) 60.6 (ms/cm) 44.9 (ms/cm) Permanganate index 0.19 (mgo 2 /l) 5.00 (mgo 2 /l) 0.12 (mgo 2 /l) 0.96 (mgo 2 /l) Hardness 32.7 ( o G) 5,00 ( o G) 9.64 ( o G) 4.71 ( o G) Chlorides 282 (mg/l) 250 (mg/l) 13.7 (mg/l) 10.7 (mg/l) Table 3. Week 3 Manganese 42 (µg/l) 50 (µg/l) BDL (µg/l) BDL (µg/l) Iron (mg/l) 200 (µg/l) BDL (mg/l) BDL (mg/l) Ammonium (mg/l) 0,50 (mg/l) BDL (mg/l) BDL (mg/l) Turbidity (NTU) 1,00 (NTU*) 0.06 (NTU) 0.1 (NTU) ph Conductivity 1938 (µs/cm) <2500 (µs/cm) 47.3 (ms/cm) 32.5 (ms/cm) Permanganate index 0.32 (mgo 2 /l) 5.00 (mgo 2 /l) 0.25 (mgo 2 /l) 0.8 (mgo 2 /l) Hardness 36.8 ( o G) 5,00 ( o G) 8.86 ( o G) 2.24 ( o G) Chlorides 244 (mg/l) 250 (mg/l) 9.4 (mg/l) 8.5 (mg/l) Table 4. Week 4 Manganese 39 (µg/l) 50 (µg/l) BDL (µg/l) BDL (µg/l) Iron 0.09 (mg/l) 200 (µg/l) BDL (mg/l) BDL (mg/l) Ammonium (mg/l) 0,50 (mg/l) BDL (mg/l) BDL (mg/l) Turbidity 0.74 (NTU) 1,00 (NTU*) 0.14 (NTU) 0.03 (NTU) ph Conductivity 2050 (µs/cm) <2500 (µs/cm) 66.8 (ms/cm) 32.8 (ms/cm) Permanganate index 0.64 (mgo 2 /l) 5.00 (mgo 2 /l) 0.34 (mgo 2 /l) 0.64 (mgo 2 /l)

6 Hardness 28.6 ( o G) 5,00 ( o G) 9.4 ( o G) 3.2 ( o G) Chlorides 286 (mg/l) 250 (mg/l) 10.4 (mg/l) 7.4 (mg/l) By analysing the date given in the above tables it results that a number of the measured parameters have values below the limits given by the norms. It should be emphasized that the value of a certain parameter - conductivity, which indicates the chemical quality of water, i.e. the quantity of substances dissolved in water, is drastically reduced after passing through membranes (e.g. from 1938 µs/cm to 47.3 ms/cm at stage I, respectively 32 ms/cm at stage II). Chlorides, i.e. the chlorine combined with other chemical elements, also indicate the chemical quality of water. In the source water they almost reach the maximum accepted concentration, or sometimes even exceed it, but after stage I the values drop to 9.4 mg/l, respectively 8.5 mg/l. The source water is clean, organic substances are found in small quantities. This is reflected by the permanganate index or by the oxidizability of water that also indicates the chemical quality of water, the source water having values between 1.34 mgo 2 /l and 0.19 mgo 2 /l, which are below the maximum accepted limits. Nevertheless, by using the reverse osmosis process, the values dropped from 0.19 to CONCLUSIONS In the end we can appreciate that using the reverse osmosis in different technological processes allows for the values of different physico-chemical parameters to be adjusted in a way that can be difficult to obtain by using other methods. Using the two-stage reverse osmosis provides an increased efficiency. REFERENCES 1. BADEA, Gheorghe (2010), Alimentri cu ap (Water supply), Editura Risoprint, Cluj Napoca, Romania. 2. *** Legea 458 din 8 iulie 2002 privind calitatea apei potabile (Law 458/July 8th 2002 on the quality of drinking water). *** Legea 311 pentru modificarea i completarea Legii nr. 458/2002 privind calitatea apei potabile (Law 311 for modifying and completing Law 458/2002 on the quality of drinking water). 3. BADEA, Gheorghe (2008), Instalaii Sanitare (Sanitary Installations), Editura Risoprint, Cluj Napoca, Romania.