AFFILIATE SPOTLIGHT

JAPAN DESALINATION ASSOCIATION IS SEEKING FOR CHALLENGES IN ADVANCED HIGHPERFORMANCE MEMBRANES & INNOVATIVE MEMBRANE PROCESS By Dr. Hideo Iwahashi

Improving hygiene is essential around the world to protect our lives from the threat of Covid-19, and the importance of clean water will increase. In order to solve the shortage of water resources and to further spread the reverse osmosis process that can obtain clean water at a low price, the development of membranes and membrane processes that can stably exhibit good performance is an eternal theme. We at JDA are working hard every day to pursue this theme.

Examples of JDA's challenges

We introduce two challenges in the development of membranes and membrane processes that JDA is working on. The first one we will introduce is the “Mega-ton Water System” (1,000,000 m3/d of product water) Project, which has been developed and demonstrated in Japan for more than 10 years. Currently the age of Mega-ton Seawater Reverse Osmosis (SWRO) has arrived mainly in the Middle East.

With these trends in the global market, the requirements of sustainable SWRO desalination as green desalination for the 21st century are summarized under three subjects: 1) Energy resources: Renewable energy, 2) Seawater RO system: Advanced membrane and membrane system, 3) Desalination drainage (brine) to reduce marine pollution: Green desalination.

The core of the above requirements is the improvement of RO membrane performance, that is, the realization of high salt rejection and highwater permeability at low pressure. The specific development target is over 99.8% Rejection at 5.0 Mpa. This is equivalent to achieving the same salt removal performance at 15% lower pressure compared as conventional membrane, and various improvements have been achieved. As a result, in standard salt concentration seawater including RO membrane part, Specific Energy Consumption achieved a low value of 2.8 kWh / m3 in the whole process.

In addition, in the Membrane Process, we have developed Biofouling Monitoring Technology that is friendly to the marine environment, without using chlorine or dechlorinating agent, for Biofouling on the RO membrane surface, which is one of the biggest trouble factors. The key to its realization was the establishment of indicators that accurately determine the occurrence of biofouling. The establishment of this indicator is so important that it is presented in a little more detail as follows. The membrane biofilm formation rate (mBFR) was established to provide a simple and reliable biofouling potential quantification tool that can easily be conducted in a RO plant. Its container is composed of consecutivelyconnected separable opaque plastic short columns and a RO membrane cut piece is installed in each short column as a biofilm formation base to prepare the exact same physicochemical property and the roughness of the surface of the RO element within the desalination plant

for accurate biofilm development monitoring. The biofilm is quantified by measuring the amount of adenosine triphosphate (ATP). mBFR is measured as pictograms of ATP per square centimeter per day. A guideline on the RO chemical cleaning frequency for RO plants was established based on the accumulation of mBFR data of RO feedwater together with RO operation data. From our experience, a higher mBFR value always results in earlier biofouling (increase in pressure drop). A mBFR value below 10 pg-ATP/ cm2/d seems to be an appropriate target of RO feedwater quality to assist plant operators in preventing biofouling.

Based on the above results, we conducted a verification test at Al-Jubail (SWCC), Saudi Arabia. We are currently considering the construction / operation of a commercial scale plant in Ummluji, Saudi Arabia.

Another challenge is the Project by ‘Global Aqua Innovation Center', which is the development of new RO membranes with excellent robustness, by full use of Japan's most advanced nano-carbon technologies. The specific aims are the following three items. 1) Energy saving by low resistance and high flux of membrane by applying carbon nanotubes. 2) Robust material on operating temperature range, pH and cleaning condition, etc. 3) Anti-fouling features to prevent adhesion of impurities such as protein. The membrane design is newly developed by applying carbon nanotubes (CNT) to polyamide, which can achieve the higher permeability, while water molecules smoothly move through the specific channel region formed around CNT in the active layer, which is named Multi-walled Carbon NanotubesPolyamide Nanocomposite RO (MWCNT-PA RO). The most significant feature of this membrane is that with same ability to produce water and eliminate salt as the common Polyamide (PA) membrane in the market the significant improving on the anti-fouling performance has been obtained. For example, in the conventional PA membrane, when feed water containing a large amount of protein is flowed, the mesh portion of the membrane’s spacer will be fouled in about

one week, but this MWCNT-PA RO membrane does not accumulate such fouling matters. Labscale development has already been completed, and verification tests on the modules by real sea water are currently underway. When it is put into practical use, it is expected to be useful for raw water with severe contamination.

Summary

We introduced two examples of Japanese efforts to develop stable and high-performance membranes and membrane processes. This is an eternal theme, not an end, and in this respect the JDA will continue to play a leading role in the new world after Covid-19.

About the Author

Dr. Hideo Iwahashi i s a S e n i o r A d v i s e r o f t h e W a t e r B u s i n e s s D i v i s i o n o f M i t s u b i s h i C o r p o r a t i o n a n d a f o r m e r C h i e f E n g i n e e r ( D e s a l i n a t i o n ) o f M i t s u b i s h i H e a v y I n d u s t r i e s , L t d . H e h a s b e e n t h e C h a i r m a n o f t h e J a p a n D e s a l i n a t i o n A s s o c i a t i o n o f N P O s s i n c e 2 0 1 7 a n d w a s a l s o o n t h e I D A B o a r d o f D i r e c t o r s f r o m 2011 to 2015.