How Does Membrane Separation Work? Here's The Process

Membrane separation is a critical part of wastewater treatment in many industrial settings.

Membrane separation is the selective permeation of molecules through a membrane barrier that separates molecules based on their size, charge, and other characteristics. 

Today, we’re looking at how membrane separation works, so you can decide if it’s right for your wastewater treatment needs.

What Is a Membrane?

A membrane is a thin, semi-permeable layer that acts as a barrier for separating substances. Membranes are made of varying substances like polymers, ceramics, and metals. A membrane’s structure allows specific molecules to pass through while blocking others. 

The pore size of a membrane and the chemical composition of a substance affect its ability to pass through the membrane, which purifies and separates substances based on their size and charge. 

How Are Membranes Separated?

Membranes are separated using pressure difference across the membrane. High pressure is applied on one side of the membrane, forcing the smaller molecules through the pores and blocking larger molecules. 

The specific type of membrane separation process depends on the size of the separated molecules, the desired separation efficiency, and other factors such as temperature, pH levels, and concentration. 

Types of Membrane Separation

Membrane separation types include microfiltration, ultrafiltration, nanofiltration, and reverse osmosis. Let’s take a closer look at each kind.

1. Microfiltration. Microfiltration uses a membrane with small pores to filter out particles and microorganisms from a liquid or gas.
   Pressure is applied to force the liquid or gas through the membrane, where particles that are too large to pass through the pores are trapped on the surface of the membrane. This allows for the separation of larger particles, such as bacteria, algae, and suspended solids.

2. Ultrafiltration. Ultrafiltration uses a membrane with smaller pore sizes than microfiltration. Applied pressure to the liquid or gas forces it through the membrane and separates larger molecules like proteins.
   Ultrafiltration can be used to concentrate or purify substances, depending on the specific application.

3. Nanofiltration. Nanofiltration uses a membrane with even smaller pore sizes than ultrafiltration. Pressure is applied to the liquid or gas being filtered, pushing it through the membrane and separating smaller molecules like salts. 

   Nanofiltration is used for industrial water, removing dissolved salts and minerals that can affect the water’s taste or quality. 

   It can be used in the food and beverage industry to remove impurities from liquids and produce certain chemicals and pharmaceuticals, where it is necessary to separate specific ions and other small molecules.
   Nanofiltration is known for its high selectivity, making it an effective tool for purifying liquids with a high degree of precision.

4. Reverse osmosis. Reverse osmosis uses a semi-permeable membrane with very small pores to separate dissolved substances from water. The process works by applying high pressure to the water, causing it to flow in the reverse direction of the normal flow, a process known as osmosis.
   The pressure forces the water to pass through the membrane, leaving dissolved substances like salts and minerals behind. Reverse osmosis is ideal for treating industrial water, as it can remove dissolved impurities and contaminants, purifying it for its subsequent use. 

   Reverse osmosis is also used in the food, beverage, and pharmaceutical industries to remove specific ions and small molecules from the water. Reverse osmosis is known for its high efficiency and ability to produce high-purity water.

Factors Affecting Membrane Separation

1. Pressure. Without pressure, membrane separation wouldn’t work. The pressure difference across the membrane determines which substances can get through versus which are blocked. 

   Generally speaking, the higher the pressure, the more efficient the membrane separation process will be. But that pressure is limited by the membrane material’s strength and durability and the size and characteristics of the substances that are being separated. 

   A pump can help maintain the right amount of pressure difference across the membrane, ensuring that the separation process is efficient and consistent.

2. Concentration. Concentration impacts how effective separation is, making it crucial to the membrane separation process. The concentration of the substances being separated can influence the size of the pores in the membrane and the pressure required to drive the separation.

   When the substance concentration is too high, it increases the pressure required to force it through the pores. This can clog the membrane and decrease the efficiency of the process.

   In some cases, a concentration gradient can be established, where the substance’s concentration is higher on one side of the membrane than the other. This helps drive the separation.
   The substance’s concentration can also affect the diffusion rate through the pores, which can impact the overall efficiency of the separation.

3. Temperature. The temperature can affect the physical properties of the substances being separated, including viscosity and solubility, which can, in turn, affect the diffusion rate through the membrane pores.
   In some cases, a temperature increase causes the substances to lose some of their viscosity, making it easier for them to pass through the pores. In other cases, a decrease in temperature can have the same effect. The temperature can also impact how stable the membrane material is, which affects its ability to maintain its structure and function over time.
   Additionally, the temperature can impact the efficiency of the pumping and filtration systems used in membrane separation processes.

4. pH levels. The pH level of the substances being separated can affect the solubility, charge, and stability of the substances, which can, in turn, impact the rate of diffusion through the membrane pores.
   In some cases, a change in pH level can cause a substance to become more or less soluble, affecting its ability to pass through the pores. Additionally, the pH level can affect the membrane material’s stability and structure, impacting its ability to function effectively over time. 

   Controlling the membrane separation system’s pressure, concentration, temperature, and pH levels will provide high-quality water. 

Get Your Mobile Membrane Separation System from J.Mark Systems

Are you looking at membrane separation as your wastewater treatment solution? Look no further. J.Mark Systems offers mobile membrane separation systems that will work well in any industrial setting, from food and beverage to pharmaceutical to metal finishing. 

Our mobile WTRBOX systems make wastewater treatment affordable and accessible. Get started today with a free water optimization audit, and let J.Mark Systems provide you with the wastewater treatment system you need for your company.