Membranlı Su Yumuşatma Sistemleri Ve Çamaşır Makinesine Entegrasyonu

Abstract

Son yıllarda endüstrileşmenin ve nüfus artışının hız kazanmasıyla birlikte su kaynakları giderek azalmakta ve su ihtiyacı her geçen gün artmaktadır. Azalan su kaynaklarına karşın hızla artan su gereksinimlerini karşılayabilmek için; su tasarrufu modellerinin geliştirilmesi, yaygınlaştırılması ve sudan geri dönüşümle yararlanılması konusundaki çalışmalar hız kazanmaktadır. Membran proseslerin içme ve kullanma suyu üretimi amaçlı kullanımı dünyada ve ülkemizde hızla yaygınlaşmaktadır. Bugün dünyada, membran prosesler ile yapılmış çok büyük ölçekli içme ve kullanma suyu arıtma sistemleri mevcuttur. Bu örnekler, gelecekte yeterli düzeyde kaliteli içme ve kullanma suyu sıkıntısı gündeme geldiğinde hızla artacaktır. Yıkama teknolojinde sürdürülen en temel araştırma konularından biri enerji tüketiminin azaltılmasıdır. Yapılan çalışmalarda su yumuşatma ile daha yüksek yıkama etkinliği değerlerine ulaşılması amaçlanmış, sıcaklık ve yıkama optimizasyonu ile enerji tüketiminin düşürülmesi hedeflenmiştir. Bu çalışmada, çamaşır makinelerine su yumuşatma amaçlı membran proseslerinin entegrasyonu incelenmiştir. Bu amaçla önce nanofiltrasyon ve ters ozmos membranlarının su yumuşatma performansları incelenmiştir. Test edilen NF ve RO membran modülleri ticari olarak temin edilmiş ve bu membranlar için kapasitelerine uygun olan 3 adet pompa seçilmiştir. Her iki membran sistemi için su yumuşatma deneyleri gerçekleştirilmiş ve membranların performansları karşılaştırılmıştır. Yapılan deneyler sonucunda, ters ozmos membranların iyon giderme performanslarının NF membranlara göre daha yüksek olduğu ancak NF membranların işletim sürelerinin daha kısa olduğu görülmüştür. Bu membranlar ile gerçekleştirilen deneyler sonucunda membranların su yumuşatma performansı ve süreleri ile harcanan pompa gücüne göre sistem optimizasyonu gerçekleştirilmiştir. Su yumuşatma deneylerinden elde edilen sonuçlarla uygun olduğuna karar verilen NF ve RO membranlar ile istenilen güç ve debiyi sağlayan pompa sırasıyla bir çamaşır makinesine adapte edilmiştir. EN 60456:2005 çamaşır makinesi standardına uygun olarak enerji performans deneyleri gerçekleştirilmiş ve membranlı su yumuşatma sisteminin çamaşır makinesinin yıkama etkinliği ve enerji tüketimi üzerindeki etkileri incelenmiştir. Yumuşatılmış su ile gerçekleştirilen yıkama işlemlerinde beklendiği gibi yıkama etkinliğinin arttığı görülmüştür. Artan yıkama etkinliği ilk referans değerine inene kadar ana yıkama suyu sıcaklığı düşürülerek enerjide iyileşme elde edilmiştir. İlk referans değeri çamaşır makinesinin su yumuşatma yapılmadan gerçekleştirilen deneylerde verdiği yıkama etkinliği değeridir. Son olarak sıcaklık ve besleme suyu sertliği parametrelerinin membranların su yumuşatma performansı ve süreleri üzerindeki etkisi incelenmiştir. Deneysel çalışmalarda, sisteme beslenen Ca+2, Mg+2, Na+, Cl-, (SO4)-2 ve (HCO3)- iyonlarını içeren 15, 25 ve 35 dH’deki besleme sularının her biri 5, 15 ve 25°C sıcaklıklarda ayrı ayrı test edilmiştir. NF membran 4 bar transmembran basıncında, RO membranlar ise 5 bar transmembran basıncında çalıştırılmıştır. Yapılan deneyler sonucunda, her iki membran için de giriş suyunun sıcaklığı arttıkça sistemin çalışma süresinin azaldığı ancak su sertliği arttıkça bu sürenin arttığı görülmüştür.

In recent years, with increasing rate of industrialization and population growth, water resources have depleted and become polluted. Despite diminishing water resources, studies on development and generalization of water-saving models and use of recycled water are gaining speed to meet the rapidly growing water demand. Water treatment industry is expected to become a very important sector all over the world in the 21st century. Water purification has become a necessity due to the increasing demand for high-quality water larger amounts of waste water containing different types of pollutants, and depleting clean water resources. With the increasing importance of water treatment and recycling of waste water, membrane technology has taken its place among the advanced treatment technologies. The use of membrane processes for the production of drinking water is becoming increasingly common in Turkey and in the world. U.S. Environmental Protection Agency (EPA) defines membrane technology as one of the best water treatment technologies. Large-scale drinking and potable water treatment systems using membrane processes are being used all over the world. The use of membrane processes are expected to increase with increasing shortage of sufficient high-quality drinking and potable water. Membrane processes are used for the purposes of filtration, concentration and purification. With the development of membrane technology, modular separation systems have been developed and become more attractive for large-scale applications. Membrane operations such as reverse osmosis (RO) and nanofiltration (NF) are now the dominant technologies to treat surface, well, brackish, and sea water in order to produce drinking or potable water of several characteristics. Over the past few decades, the advancements in membrane technology have improved the economics of water purification and recovery significantly. One of the main research topics in washing technology is reducing energy consumption. Studies aim to reach higher cleaning efficiency while reducing the energy consumed. For this purpose, softened water may be used to increase cleaning efficiency during the wash cycle. A well known problem with water-soluble substances is hardness. Dissolved calcium (Ca+2) and magnesium (Mg+2) in water cause hardness. The hardness ions in water affect the washing media negatively by binding surface active agents which are required for washing and cleaning. Thus, the amount of detergent to be used for cleaning increases. In addition, Ca+2 and Mg+2 ions, which cause water hardness, lead to the formation of lime scale in the washing machine and lime accumulated over time affects the performance and energy consumption of the washing machine negatively. One of the methods for improving the energy performance of the washing machines is the use of softened water during main wash step. Softened water improves the cleaning efficiency of the washing machine and gives the opportunity to reduce the temperature of the main wash step. This study aims to investigate the integration of membrane separation into washing machines for water softening. For this purpose, in the first part of this study, the removal of hardness ions from water by using nanofiltration (NF) and reverse osmosis (RO) membranes is studied. Four different membrane modules are obtained commercially: (1) Dow Filmtec NF270 polyamide thin film composite membrane, (2) GE - Osmonics CK series cellulose triacetate/diacetate NF membrane, (3) Oltemare Extra Low RO polyamide thin film composite membrane, and (4) Koch Low RO polyamide thin film composite membrane. The Dow Filmtec NF270 model thin film composite polyamide NF membrane module has 102 cm length and 6.1 cm diameter. The manufacturer‘s specifications include a MgSO4 rejection of > 97%, a chlorine tolerance of < 0.1 ppm, an operating pressure of about 4.8 bar, and a filtrate flux of about 2.23 l/min. The GE-Osmonics CK Series 2.5x40 model cellulose triacetate/diacetate blend module also has 102 cm length and 6.1 cm diameter. The manufacturer’s specifications include a MgSO4 rejection of 94-97%, a chlorine tolerance of 1 ppm (continuous), an operating pressure of about 15.3 bar, and a filtrate flux of about 1.58 l/min. The Oltemare Extra Low RO Membrane 4.0x21 model polyamide thin film composite module has 53.3 cm length and 10 cm diameter. The manufacturer‘s specifications include a MgSO4 rejection of >99%, a chlorine tolerance of < 0.1 ppm, and an operating pressure of about 6.9 bar, filtrate flux of about 2.69 l/min. The RO membrane obtained from Koch Company is a composite polyamide low RO membrane module with 30 cm length and 6 cm diameter. The specifications of the RO membranes include a MgSO4 rejection of 90%, a chlorine tolerance of 1 ppm, a continuous operating pressure of 3.4 bar, and a filtrate flux of 0.8 L/min. The experiments are carried out in an experimental set-up which involves circulation and reuse of the concentrate stream from the membrane unit. For experiments tap water samples are collected from the local water supply system and conditioned to get feed hardness values of 15, 25 and 35 German Hardness (GH) by adding Ca2+, Mg2+, Na+, Cl, (SO4)2 and (HCO3) ions in appropriate quantities. Before entering the membrane unit, feed water is passed through an active carbon filter (ACF) to remove free chlorine which may be harmful for the membrane and to reduce membrane fouling. Water exiting the ACF is stored in a tank and then sent to the membrane by means of a pump. The membrane modules are tested using three different pumps suitable to membrane capacities. Water at 15C temperature and 15 dH hardness value is fed to the water softening system. Each membrane-pump pair is operated at the appropriate transmembrane pressures. Experiments are repeated three times for each pressure value, and the system has been operated until 15 liters of softened water is obtained. Water softening performance of membranes are compared. During experiments, feed water, softened water (permeate), and hard water (concantrate) temperatures are measured with a thermocouple. The electrical conductivity and pH of feed, permeate, and retentate samples are determined by using a 720 ORION 150 model portable conductivity meter and a inoLab portable pH measuring device, respectively. Calcium and magnesium hardness values are measured by using the EDTA-titrimetric method. Analysis are performed with commercially available kits (ammonium chloride, ethylene diamine tetra acetic acid, magnesium disodium salt, sodium carbonate and sodium sulfide) developed by HACH Company and 0.015 M EDTA titrant solution. Free active chlorine measurements for feed water and water passing through the ACF are obtained by using o-tolidine kit. Because of the low amount of chlorine ions in feed water a significant measurement could not be obtained. Between the NF membranes tested, Dow Filmtec NF270 is found to show the best performance at 4 bar transmembrane pressure by softening water to 5 dH hardness in 12 minutes. Between the RO membranes tested, Koch Low RO Membrane modules are found to show the best performace at 5 bar transmembrane pressure by softening water to 1dH hardness in 15 minutes. It can be concluded that ion removal performance of the RO membranes are higher than that of NF membranes, however NF membranes have exhibited less operating time. Consequently, system optimization is carried out based on the pumping power, water softening performance and operation time of the membranes. In the second stage of this work, the NF and RO membranes which exhibited the best performance and the pump that provides the required power and flow rate are adapted to a washing machine. Energy performance experiments are carried out in accordance with the EN 60456:2005 washing mahine standard and effects of membrane water softening system on washing efficiency and energy consumption of the washing machine are studied. As expected, it was observed that the washing efficiency increases when softened water is used for the washing process. Energy recovery is obtained by reducing the main wash water temperature until increased washing efficiency is reduced to its first reference value. Reference value for washing efficiency is determined by testing the washing machine without a softening system and it is found as 1,060. It has been determined that, for the Dow Filmtec NF270 membrane, lowering the main wash temperature results in an approximately 5% improvement in the energy consumption. The washing efficiency is found to be 1.061. On the other hand, for the Low RO membrane, approximately 13,7% improvement in energy consumption is obtained by lowering the main wash temperature and washing efficiency is obtained to be 1.059 which is very close to the reference value. Finally, the effect of temperature and hardness parameters on water softening performance and operating time of the membranes are investigated. Inlet water samples including Ca2+, Mg2+, Na+, Cl, (SO4)2 and (HCO3) ions with 15, 25, and 35 German Hardness (GH) values are fed to the system and tested for feed temperatures of 8, 15 and 24C. The transmembrane pressure for the NF and RO membranes is 4 bar and 5 bar, respectively. The filtered water is taken out of the system while concentrated water is sent back to the water tank by means of a return line. In both membrane processes the system is operated until approximately 13 liters of filtrate is obtained. The results have shown that the NF membrane can reduce the feed water at 15, 25, and 35 GH to 7, 15, and 21 GH, respectively. Reverse osmosis membranes can reduce the same feed water hardnesses values to approximately 1 GH. For both membrane processes, operating time reduces with increasing inlet water temperature but increases with increasing water hardness.