rejection

Rejection: A Crucial Concept in Water Treatment

In the realm of environmental and water treatment, rejection plays a crucial role, representing the efficiency of purification processes in removing undesirable contaminants from water. Specifically in the context of reverse osmosis (RO), rejection signifies the percentage of dissolved solids that are successfully blocked by the semipermeable membrane during the purification process. This is often referred to as "salt rejection" due to the primary focus on removing dissolved salts.

Understanding Rejection:

Imagine a sieve, separating large particles from smaller ones. In RO, the membrane acts as a highly selective sieve, allowing water molecules to pass through while blocking larger dissolved solids, such as salts, minerals, and organic compounds. The percentage of these contaminants that are rejected, or not allowed to pass through, is the rejection rate.

Measuring Rejection:

Rejection is typically expressed as a percentage, calculated as:

Rejection (%) = [(Concentration of contaminants in feedwater - Concentration of contaminants in permeate water) / Concentration of contaminants in feedwater] x 100

For instance, if the feedwater contains 1000 ppm of dissolved solids and the permeate water contains 100 ppm of dissolved solids, the rejection rate would be 90%.

Importance of Rejection:

A high rejection rate is critical for effective water purification. It indicates the system's ability to produce high-quality, clean water, meeting specific standards for different applications.

Factors Affecting Rejection:

Several factors influence the rejection rate of an RO system, including:

• Membrane type and characteristics: Different membranes possess varying pore sizes and selectivity, affecting their ability to reject specific contaminants.
• Feedwater quality: The concentration and nature of dissolved solids in the feedwater can impact the rejection rate.
• Operating pressure: Higher pressure forces water through the membrane, increasing the rejection rate.
• Temperature: Higher temperatures can decrease rejection due to increased permeability of the membrane.
• Flow rate: Higher flow rates can reduce the residence time of water in the membrane, impacting rejection.

Relative Accuracy Test Audit (RATA):

A Relative Accuracy Test Audit (RATA) is a crucial quality control measure for ensuring the accurate measurement of rejection in an RO system. It involves comparing the measured rejection against a reference standard or a previously calibrated system. RATA helps to identify potential issues with the measurement instrumentation or the system itself, ensuring consistent and reliable data.

Conclusion:

Rejection is a fundamental concept in environmental and water treatment, quantifying the effectiveness of purification processes, particularly in reverse osmosis. Understanding rejection rates and the factors affecting them is vital for optimizing system performance and producing high-quality water for various applications. Regular RATA assessments ensure the accuracy of rejection measurements, safeguarding the reliability of water treatment systems and the quality of the treated water.