Improved Resource Recovery from Zero Liquid Discharge (ZLD) Processes Using Novel Forward Osmosis (FO) Membranes

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COVER STORY GLOBAL RISE OF ZERO LIQUID DISCHARGE Improved Resource Recovery from Zero Liquid Discharge (ZLD) Processes Using Novel Forward Osmosis (FO) Membranes Since the industries account for around 20% of global freshwater consumption, and tend to be cash-rich in comparison to other freshwater consumers, the governments are increasingly tightening regulations on industrial wastewater disposal. Besides augmenting water supplies, wastewater disposal limitations have the added benefit of protecting aquatic environments. By Mark Perry

ration and are therefore ex- ceedingly energy-intensive. Typically, Mechanical Vapor Compression (MVP) evaporators use 20-25 kWh/m3 of high-grade electric energy to reach brine concentrations of 250,000ppm. In the last stage of ZLD, brine crystallizers use upwards of 70 kWh/m3. Te final stage of evapo- ration is largely unavoidable hence strategies for lowering the operating cost of ZLD focus on brine pre-concentration to reduce capacity demand for evaporators and crystallizers. In comparison, Why are ZLD Processes Zero Liquid Discharge membrane-based Reverse on the Rise? (ZLD) is the ultimate waste- Osmosis (RO) processes con- Water is no longer a giv- water management that sume 2-3kWh/m3 and, there- en. Under great publicity, eliminates any liquid waste fore, represent an excellent the ‘Day Zero’ was narrowly leaving an industrial plant, option for energy reduction avoided in Cape Town during and - as such - also carries the of ZLD processes. Having 2018 and now Chennai in highest price tag in terms of said that, RO processes are India and many towns in capital and operational costs. limited by brine concentra- Australia face the same crisis. According to the work by tion and become less feasible • Makeup Water: 8m3/d When economic growth and Elimelech and co-workers above 70,000 ppm. • Makeup Salt (NaCl): 930kg/d public health face systemic in “Te Global Rise of Zero Hence, a window of op- • Draw Replenishment (MgSO4): 344kg/d risks, the economic burden of Liquid Discharge for Waste- portunity exists for low-en- imposing stricter water treat- water Management: Drivers, ergy technologies capable of System Summary: • Total Wash Water Demand: 350m3/d ment and water recycling Technologies, and Future concentrating brines from • Total Dye Bath Water Demand: 30m3/d regulations is dwarfed by the Directions”, countries at the 70,000 ppm to 250,000 ppm. • Total Salt Demand in Dye Bath: 2900kg/d consequences of the status forefront of imposing ZLD A variety of membrane-based • Total Salt Demand in Wash Water: 0kg/d quo. regulations include the Unit- technologies have shown • Recycled Wash Water: 342m3/d Since the industries ac- ed States, China, and India. potential in this ppm-range, • Recycled Dye Bath Water: 30m3/d count for around 20% of Whereas the power sectors including Osmotically Assist- • Recycled Dye Bath Salt: 1970kg/d global freshwater consump- are the main contributor ed Reverse Osmosis (OARO), • Volume to be Treated by MEE: 39m3/d tion, and tend to be cash- to the ZLD markets in the Membrane Distillation (MD), favorite among membrane in Developing Commercially rich in comparison to other United States and China, the Electro-Dialysis (ED), and researchers. But it is fair to Viable Desalination Technol- freshwater consumers, the textile industry is one of the Forward Osmosis (FO). Te say, that the commercial FO ogies” aptly describes how governments are increasingly main drivers in India’s ZLD remainder of this article will field took a hit - and experi- the use of forward osmosis tightening regulations on in- adoption. focus on how FO can be uti- enced some disillusionment for seawater desalination has dustrial wastewater disposal. lized to improve ZLD ROI. - when it became clear the followed Garner’s hype circle Besides augmenting water The Potential for technology would likely nev- and currently resides some- supplies, wastewater disposal Lowering the Operating The Slope of er revolutionize seawater de- where in the region between limitations have the added Cost of ZLD Enlightenment salination. the “Trough of Disillusion- benefit of protecting aquatic Traditional ZLD processes Forward osmosis technol- Jefrey R. McCutcheon’s re- ment” and the “Slope of En- environments. are based on water evapo- ogies have always been a cent work “Avoiding the Hype lightenment”.

32 August 2019 BEYOND EXPECTATIONS SMART WATER & WASTE WORLD COVER STORY GLOBAL RISE OF ZERO LIQUID DISCHARGE

Economical Parameters NF/RO/MEE FO/NF/RO/MEE FO membranes. Challenge Total System Cost (USD) 447000 671000 (+50%) accepted? Daily CAPEX Cost (USD) 123 184 About the Author Daily O&M Cost (USD) 502 427 (-15%) Mark Perry currently Countries at works at the Royal Danish the forefront Daily Cost of Draw Solution (USD) 0 72 Embassy in Singapore as Daily Water Revenue (USD) 584 677 Commercial Advisor where of imposing Daily Salt Revenue (USD) 169 413 he mainly assists Danish ZLD regulations CleanTech companies in include the Yearly Total Profit (USD) 47000 149000 their eforts towards captur- United States, Payback Period (Years) 9,5 4,5 ing new business opportuni- ties in Singapore. China, and India. Table 1 He has a CleanTech back- Whereas the Tese days, surviving com- tions. However, the low-en- water streams while simulta- ground from heading BD mercial FO players are now ergy ZLD argument only neously recovering monova- & Sales in Aquaporin Asia power sectors largely looking to occupy holds in the case where the lent salts (e.g. NaCl). Pte Ltd, a Singapore-based are the main spaces where convention- engineered draw solution is In addition, the NF-type CleanTech company. In ad- contributor to al RO is not applicable and of a sufciently high osmo- FO membrane would likely dition, he has worked as a where incumbent - and typi- larity (above 300,000ppm enjoy a higher water flux and Membrane Developer, Project the ZLD markets cally thermal based - technol- NaCl equivalent) and can less concentration polariza- Manager, and Business De- in the United ogies are much easier to beat. be regenerated through pro- tion. veloper for Aquaporin A/S in States and Hence, commercialization cesses with low energy re- Everything else equal, the Denmark. of forward osmosis technol- quirements (e.g. thermolytic added value from the recov- He holds a Master’s De- China, the textile ogies is gravitating towards regeneration using low-grade ered salt should improve gree in Physics and Cellular/ industry is one niche applications, which thermal energy). overall system ROI. But how Molecular Biology from the of the main makes much more sense than In order to decouple the much improvement can po- Southern University of Den- aiming for the competitive value proposition of FO from tentially be gained? mark and an Executive MBA drivers in India’s and - from a membrane point engineered draw solutions I recently published a desk- from DTU Business. ZLD adoption. of view - commoditized de- and regeneration methods, top study on ForwardOsmo- He shares his years of ex- salination sector. which may or may not turn sisTech.com based on the perience in forward osmosis sion is to become the leading out to be commercially viable work by Vishnu and co-work- membrane development & independent branch specific How Can Forward on industrial scale, my sug- ers (“Assessment of Field commercialization on For- portal in the FO field with Osmosis Improve ZLD gestion is to start exploring Scale Zero Liquid Discharge wardOsmosisTech.com - the a clear commercial and ap- Processes? the potential of FO to selec- Treatment Systems for Re- Contrary to traditional tively recover valuable sol- covery of Water and Salt from pressure-driven membrane utes from waste streams. Textile Efuents.” Journal of technologies, forward osmo- Cleaner Production 16.10 sis uses chemical energy in NF-Type FO Membrane (2008): 1081-1089.). the form of osmotic pressure Concept Te desktop study demon- to drive water transport across Conventional FO mem- strates clear operational and a semi-permeable membrane branes are designed to ex- economic benefits of includ- along the osmotic pressure tract water from feed streams ing an NF-type FO sub-sys- gradient between feed (im- while rejecting virtually all tem in ZLD treatment of paired water source with low other compounds. However, wastewater from textile dye- solute concentration = low os- by tweaking the pore size of ing processes. motic pressure) and draw (en- the FO rejection layer using In conclusion, FO mem- gineered solution with high the same piperazine-based branes capable of extracting solute concentration = high chemistry known from Na- both water and monovalent osmotic pressure) streams. no-Filtration (NF) membrane salts, hold potential for im- Being powered by an os- technologies, it should be proving ZLD ROI. motic gradient, the energy fairly straightforward to requirement of water trans- achieve FO rejection layers Challenge Accepted? port across a forward osmosis with high rejection for diva- Within today’s conserva- membrane is up to 90% less lent salts (e.g. MgSO4) and tive water industry, commer- than that of reverse osmosis. low rejection for monovalent cializing the forward osmosis Hence, FO has traditionally salts (e.g. NaCl). technologies is very much been viewed as a potential What we end up with then, an exercise in identifying low-energy pre-concentration is an NF-type FO membrane applications with huge cus- technology in ZLD applica- capable of de-watering waste- tomer pains (the low hanging fruits), where current technologies are either not applica- A window of opportunity exists for low-energy ble, massively inefcient, or technologies capable of concentrating brines from extremely expensive. 70,000 ppm to 250,000 ppm. A variety of mem- Te use of forward osmosis brane-based technologies have shown potential for combined dewatering and in this ppm-range, including Osmotically Assisted resource recovery definitely go-to portal for general infor- plication-driven focus and a Reverse Osmosis (OARO), Membrane Distillation seems to fit the bill. What re- mation on forward osmosis strong passion for promoting (MD), Electro-Dialysis (ED), and Forward Osmo- mains to be done is for com- membranes, systems, tech- and facilitating open innova- sis (FO). Tis article focuses on how FO can be mercial players to start de- nologies, and applications. tion, collaborations, partner- utilized to improve ZLD ROI. veloping industrial NF-type Forward Osmosis Tech’s vi- ships, and co-developments.