Potential use of magnetic fields — a perspective

The critical area of concern at the start of the millenium continues to be the biofouling of seawater/brackish water and the pre-treatment methods practiced. Practical studies indicate that with widely fluctuating raw water chemistry, the Gulf seawater which predominantly operates on open intake is more susceptible to biological fouling and algae growth thereby forcing plant downtime. In such a scenario, one often encounters with prohibitive water cost and probable mechanical damage to the equipment. The grave area of concern in the beginning of the millenium continues to be the sharp increase in the build-up of biofilm. The No.1 killers of RO plant are the colloidal solids and biological contaminants. This has motivated the author to moot the introduction of energy efficient systems incorporating defouling device. By such a device almost all the suspended particles and colloids is reduced which is primarily achieved by incorporation of turbulence generating flow distributors and EMF device. In the overall analysis, such a modification in the membrane module should be a forerunner in the efficient operation and maintenance of membrane based units. Apart from energy saving by as much as 18%, one of the basic benefits is significant reduction in downtime.

5. Cost benefit analysis As shown in Table 3, the capital cost of such plants with EMF is higher by 13% as compared to conventional ones. The downtime is marginally The fouling rate of the membranes is considerably reduced by the introduction of new generation of membranes when induced with magnetic field. Considerable cost saving is obtained in the operation and maintenance. One Table 3 Design and estimated cost data Design data Operating time, h/d Capacity, m³/h Backwashing duration, freq./pressure, min/bar Chemical cleaning frequency, weeks Expected membrane life time, years Operating cost, $/m³ Energy consumption, kWh/m³ Coagulant Chemical cleaning Recovery, % Cost data Investment cost, US$ Interest rate, % Capacity, m³/y Electricity cost Specific cost, $/m³ Depreciation Energy, Chemicals Maintenance and staff Membrane replacement 0.45 20/1.5 1/3 0.55 0.4 0.078 0.17 35,000 0.25 0.37 0.16 0.028 0.015 0.032 perceptible observation is the 20% reduction in the transmembrane pressure drop, not observed in conventional operation. In effect this improves the overall performance of the plant. What is noteworthy, is the cleaning-in-place (CIP) intervals are extended by three-fold. Scale-up and commercialization of the described set-up will follow optimization of process variables. Undoubtedly, the cost is competitive with conventional processes and is designed to result in higher reliability along with improved economics of desalting technology. The combined savings due to lower investment and operating cost, besides the ability to optimize system operating conditions on account of better feed water quality result in 8% reduction in total water cost.