RO technology has long played an important role in the field of water treatment. Many technological improvement efforts have been made over the past decades to improve the treatment efficiency of RO membranes. In particular, the improvement of the feed-spacer plays a very important role affecting the performance of the RO membrane. In this article, we will learn about membranes and new innovations in conductive buffer technology of RO NanoH2O membranes.
What is Feed Spacer ?
In a reverse osmosis (RO) process, pressure is applied to the saline side of a semi-permeable membrane to produce low salinity water. Upon application of the feed pressure, water molecules pass through the membrane while most of the dissolved solids remain on the saline side. The saline water then travels through a channel created by a feed spacer sandwiched between two flat sheet membranes (“membrane leaves”). The primary function of the feed spacer is to separate the two leaves so the feed can freely flow between the membrane leaves while creating turbulence flow to minimize concentration polarization on the membrane surface. The low salinity water produced is called “permeate” and travels through the permeate channels filled with permeate carrier toward the central product water tube.
Effect of Feed Spacer Thickness on Reverse Osmosis (RO) Membrane Performance
Membrane elements are available with feed spacers in different thickness. 26- or 28-mil were standard spacer thickness adopted by many manufacturers in the earlier generation of membrane elements. With advancements in RO membrane manufacturing technology, it is now possible to accommodate thicker 34-mil RO feed spacer while still maintaining standard 400 square feet of active membrane area in an 8-inch diameter and 40-foot length membrane configuration.
Thickness of the feed spacer has several impacts on RO membrane performance. It has been found that when the feed flow rate is kept constant, linear liquid velocity becomes a function of the spacer thickness and a higher fluid velocity is achieved for thinner (e.g., 26- or 28-mil) spacer geometry. This thinner spacer geometry produces a higher initial pressure drop while the thicker feed spacer (e.g., 34-mil) has a lower initial feed pressure drop. More importantly, the pressure drop increase due to biofilm forma- tion was found less in the thicker spacer compared to the thinner spacer. As a result, energy can be saved by using the 34-mil feed spacer. For poor water quality with higher biofouling potential, the membrane element with the 34-mil feed spacer will not experience biofouling channel plugging as rapidly, and therefore can be more easily cleaned.
Advanced Feed Spacer technology of NanoH2O RO membranes
The primary function of a feed spacer is to separate two membrane leaves allowing the feed stream to freely flow between membrane leaves while creating turbulence to minimize concentration polarization. Broadly described, the latter phenomenon is the accumulation of solutes near the membrane surface, leading to membrane performance degradation.
As the feedwater passes through the RO element, it loses pressure due to overcoming feed spacer resistance, which is how differential pressure forms. At constant operating conditions, the differential pressure depends on the geometry of the membrane feed spacer that includes mesh size, strand diameter and its shape, and the angle between the adjacent strands.
To improve the spacer design, LG Chem researchers experimented with spacer configurations to achieve optimal flow and low resistance while maintaining a sufficient level of turbulence and mechanical integrity of the mesh spacer. The result is the new L spacer, a 34-mil thickness mesh with improved strand arrangement and geometry that minimizes flow disturbance and pressure losses without increasing concentration polarization.
The new L spacer lowers dP at the same high process efficiency and:
- Delays the onset of fouling during system operation;
- Reduces fouling rate;
- Improves chemical cleaning efficiency.
The following LG NanoH₂O™ brackish water reverse osmosis models integrate the L feed spacer: BW 400 R G2, BW 400 R Dura, BW 400 AFR G2, BW 400 UES, BW 400 ES L.
Official distributor of NanoH2O RO membrane in VietnamATS Water Technology Co., Ltd is the official distributor of LG Chem’s NanoH2O™ RO membrane in Vietnam since 2016
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