INVESTIGATIONS INTO THE MEMBRANE PERFORMANCE AND BUILD-UP OF SOLUTE IN A SMALL-SCALE OF REVERSE OSMOSIS SYSTEM

Nasir, Subriyer (2006) INVESTIGATIONS INTO THE MEMBRANE PERFORMANCE AND BUILD-UP OF SOLUTE IN A SMALL-SCALE OF REVERSE OSMOSIS SYSTEM. In: Curtin Engineering Faculty Research Qolloquium, 14 November 2006, Curtin University of Technology, Perth Australia.

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    Abstract

    This investigation discusses the effects of sodium chloride and calcium carbonate on spiralwound membrane performance during reverses osmosis (RO) operation. Experiments were carried out in a small scale of RO (2 m3/d of capacity). The parameters chosen for this study include operating pressure and concentrations of sodium chloride and calcium carbonate. Several feed water samples used for the experiments including, sodium chloride, calcium carbonate and combined between sodium chloride and calcium carbonate solutions at different concentration in raw water; groundwater and secondary effluent. For convenience, the solutions containing salts are hereafter referred to as simulated feed water samples. The variables considered for the tests are operating pressure (1,250 to 4,750 kPa), sodium chloride concentration (from 100 to 5,000 mg/L), the mixtures of sodium hydrogen carbonate (from 0.0005 to 0.002 M) and calcium chloride concentration (between 0.00025 M and 0.001 M). The simulated feed water samples were prepared by diluting sodium chloride, sodium hydrogen carbonate and calcium chloride mixtures, and sodium chloride and calcium carbonate mixtures into demineralized water in a polyethylene tank with a capacity of 1 m3. All experiments are performed at ambient conditions (typically 20 ± 0.5 oC). At the end of specified time (typically every 15 minutes), both permeate and reject samples are collected. All the samples are subjected to various analytical techniques. Atomic Absorption Spectroscopy (Varian AAS type 110) technique is used to determine the sodium and calcium concentrations of both permeate and rejection streams. Samples are taken periodically 15 minutes and analysed by AAS using Natrium and Calcium lamp at wavelength of 489 and 422.7 nm respectively with the standard method (APHA-AWWA-WEF 1992). Total dissolved solids (TDS) and pH were determined by a Hanna pH-EC-TDS meter. The electrical conductivity is measured using a Yokogawa SC 82 conductivity meter. Results indicated that there is no significant effect on membrane performance for sodium chloride with concentration below 1,200 mg/L and applied pressure lower than 2,250 kPa. However, experimental runs at high operating pressures appears to affect both build up of sodium and calcium on the membrane surface and the overall membrane performance. For typical small scale of RO used in this experiment, build up of solute significantly decreased with applied pressure due to turbulence in bulk solution. The osmotic pressure of solution also strongly affected the permeate flow rate in particular for relatively higher sodium concentration. Hence, due to higher osmotic pressure there is no permeate flux when sodium chloride concentration greater than 5,000 mg/L and applied pressure lower than 1750 kPa. An attempt has been to made to perform an economic assessment for the desalination of tested samples. Estimates of energy consumption for desalting of sodium chloride, combined sodium and calcium carbonate solutions were found to be in the range of 1.11-3.42 and 1.5 –6.3 kwh/m3 respectively. For groundwater and secondary effluent, they are estimated to 1.2 - 3.0 and 1.29 - 3.54 kWh/m3 respectively. Unit cost for desalting of sodium chloride solution, sodium chloride and calcium carbonate, ground water and secondary effluent are $ 1.95-2.38, 2.96-3.57, 1.89-2.81 and 1.99 –3.03 respectively. In RO plants, unit cost of water production from feed water is primarily governed by the energy required for pumping raw water. Energy cost for RO plants can also be reduced by increasing the total capacity. Normally, a typical small scale RO unit (as the current one used for experimental investigations) has at least two pumps namely feed transfer pump and high pressure pump. Based on the experimental results, it appears that the characteristics of feed water samples affect the membrane performance and it should also be considered in an attempt to reduce the unit cost.

    Item Type: Conference or Workshop Item (Paper)
    Subjects: T Technology > TP Chemical technology
    Divisions: Faculty of Engineering > Department of Chemical Engineering
    Depositing User: Dr. Subriyer Nasir
    Date Deposited: 22 Jun 2012 02:19
    Last Modified: 22 Jun 2012 02:19
    URI: http://eprints.unsri.ac.id/id/eprint/1005

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