IMPROVING EFFICIENCY OF PROTOTYPE RO PLANT USING PRE-TREATMENT TECHNIQUES

Abstract

Realising the problem of saline ground water (GW) in Pakistan especially in Sindh and Punjab, it is imperative to develop a desalination technique to make the ground water suitable for drinking purposes. It has been observed that the problem of saline ground water is most severe in Cholistan district of Bahawalpur. A project has also been initiated by Pakistan Council of Research in Water Resources to solve the problem of saline GW in Cholistan District, to install a Reverse Osmosis plant in the area. A prototype RO has been fabricated and installed at PCRWR labs at Islamabad. The aim of this study is to carry out extensive study on this Prototype RO plant considering various parameters like TDS removal efficiency, pH variations before and after passing through the system, and finally percentage rejection of salts. Highpressure polyamide membrane is used in Prototype RO plant. Percent Rejection Efficiency of prototype RO plant extending upto 98%. Reduction of TDS ranges from 30 to 100 mg/L provided feed water TDS of 1050 to 2160 mg/L respectively. Electrical Conductivity from prototype RO plant reduced upto 90 to 300 PS/cm for feed water Electrical conductivity ranges from 2000 to 4500 PS/cm respectively. Percent Recovery of Prototype RO plant extended upto 50%. Another important aspect for long term reliability of any RO plant is designing a proper pre- treatment system for it . Thus second part of this study aims at designing of Rapid Sand Filtration and Activated Carbon Filter as a pre-treatment for the Prototype RO plant. For Filtration Silver Coated Sand is used as filter media to serve dual purpose i.e. filtration and disinfection. For Adsorption Granular Activated Carbon is used as filter media. Both these filters are helpful to prevent the RO membrane from various kinds of fouling. Silver Coated Sand Filter was tested for Turbidity, Suspended Solids and Bacterial removal. Turbidity Removal from Silver Coated Sand Filter ranges from 15 to 3 NTU approximately, Suspended Solids reduction ranges from 64 to 1 NTU. To serve this purpose an economical setup of filters has been designed and fabricated. Both the filters show excellent results and are suited for domestic purposes on small scale basis. However, it can be extended to large scale if length of column has been increased and will be economical compared to branded and sophisticated systems. Disposal of Brine stream from Prototype RO plant is found to be one of the major concern. Also it is required to develop post-treatment system for this Prototype RO plant as filtrate water from RO membrane becomes de-ionized and needs ionic blending for making it fit for potable use. Further research on these aspects is recommended in this thesis document.