The MBR membrane, also known as a membrane bioreactor, is a cutting-edge water treatment technology that combines the activated sludge process with membrane separation techniques. Currently, there are four main types of MBR membranes: hollow fiber membranes, flat membranes, ceramic membranes, and tubular membranes.

Hollow fiber membranes and flat membranes are collectively referred to as "organic membranes," with PVDF (polyvinylidene fluoride) being the primary material—currently the most widely used membrane material on the market. However, a new PTFE (polytetrafluoroethylene) material has emerged, reportedly offering superior performance compared to PVDF, as it produces a more uniform pore size distribution when the membrane is stretched. PTFE is even hailed as the "king of plastics."

Ceramic membranes are also a recent innovation. Together with organic flat membranes, they are collectively referred to as "flat membranes." Ceramic membranes boast excellent chemical stability, resisting acids, alkalis, organic solvents, and high temperatures; they also offer the advantages of a narrow pore size distribution and exceptionally high separation efficiency.

As a type of membrane element, organic tubular membranes are suitable for membrane separation technologies such as ultrafiltration, microfiltration, and even nanofiltration. They require relatively low pre-treatment precision. Additionally, tubular membranes are easy to clean—beyond chemical cleaning agents, mechanical and physical scrubbing methods can also be employed.

A flat membrane is a sheet—typically made of ABS—featuring flow channels on both sides, backed by lining fabric and PVDF material, and seamlessly welded together.

How to clean an MBR membrane module?

The flat membrane operates at a working pressure of 0–35 kPa. Under the action of a self-priming pump, the mixed liquid in the membrane tank is filtered through a microporous filter made from polymer material (with each cycle lasting 10 minutes—8 minutes of pumping followed by a 2-minute pause). The membrane’s uniform pore size effectively traps particles, bacteria, and other contaminants in the water, preventing them from passing through and ensuring thorough removal of solids and impurities from the biochemical wastewater. Meanwhile, the reaction tank facilitates efficient sludge-water separation. Thus, the MBR flat membrane plays a critical role in the filtration process.

1. The membrane captures microorganisms within the reactor, significantly increasing the concentration of activated sludge in the tank (typically ranging from 6,000 to 12,000 mg/L), which enhances wastewater degradation. As a result, the biochemical reactions proceed more rapidly and thoroughly.

2. Due to the membrane's high filtration precision, it ensures clear and transparent effluent, resulting in high-quality product water. However, this highlights that membranes are not a universal solution—they have tiny pores, and anything small enough to pass through these pores cannot be filtered out. Don’t place all your hopes for improving standards solely on this technology. If contaminants aren’t effectively removed, they’ll accumulate near the membrane’s pores, leading to fouling—essentially clogging the membrane—and ultimately reducing water production to an insufficient level, failing to meet the desired flow rate.

When it comes to membrane fouling, we must talk about cleaning membrane elements. Cleaning is primarily divided into two types: online cleaning and offline cleaning.

The cleaning cycle depends on the degree of membrane fouling. If the water quality is good—such as with domestic wastewater—you can clean the membrane every 3 to 4 months, typically by monitoring water consumption and negative pressure. When preparing the cleaning solution, a common approach is to first perform an alkaline wash followed by an acid wash, depending on the specific situation. Alternatively, some cases may call for an acid wash before an alkaline one.

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