Membrane separation technology for purifying water

Clean and safe drinking water is the primary necessity of life. But with the fast depleting fresh water resources and the rising amount of industrial waste contaminating the remaining water resources, the necessity for recycling water to make it fit for consumption is becoming more and more important. Among various methods and technologies, membrane separation technology is rising as a reliable and safe way to purify water today.

By Debarati Das

Water scarcity is an issue that every nation is battling with today. If numbers were to be believed, then by 2025, 60 percent of the world population will live with water scarcity while more than 90 percent of available fresh water resources will be consumed in the next fifteen years. Emerging pollutants from various industries have been poisoning the remaining water resources. The need to recycle and make pure and safe water fit for consumption is increasing day by day.

Various chemical and biological methods are currently being used to treat industrial wastewater. However, biological treatments have been proved more economical and safe while adhering to strict legal regulations.

Membrane separation technology has gained momentum in the current scenario because it works without the addition of chemicals, with a relatively low energy use and with easy and well-arranged process conductions. Membrane separation processes can be in the form of electrodialysis, microfiltration, nanofiltration, ultrafiltration, reverse osmosis etc, all of which use selective membranes to separate a contaminant from a liquid phase.

All membrane separation technologies are capable of separating contaminants from a liquid as the principle remains the same - a membrane which acts as a filter that allows water to flow through and catches suspended solids and other substances. However, each method utilises a different separation mechanism suitable for the treatment of different waste streams. Membrane filtration is used as an alternative for flocculation, sediment purification techniques, adsorption, extraction and distillation.

Market Outlook

Growing environmental concerns, stringent government regulations, rising population, rising production activities and fast depleting fresh water resources are some of the key factors that is driving membrane separation market. Governments and municipal authorities are increasingly waking up to the effects of environmental degradation on the economy.

Membrane separation is being recognised as an ideal solution to re-use waste water and simultaneously reduce water footprint. Among various water-purification techniques available in the market today, membrane separation technology offers high filtration efficiency at minimum operation area. Properties of membranes, like durability, porosity, permeability, stability and selectivity, give them a further edge over other purification methods in various industrial applications.

This technology is increasingly being used in not just water & wastewater treatment but also in industrial, laboratory, medical, food & beverage and research applications to purify, concentrate, sterilize, or separate samples.

According to MarketsandMarkets report, the global membranes market is projected to grow at a CAGR of 9.47 percent from 2015 to become a $32.14 billion market by 2020. The BRIC countries are expected to be the key growth markets due to rapid industrialisation coupled with alarming water-shortage issues in these regions.

With exponential rise in population, growing chemical, pharmaceutical and other industries, Asia-Pacific is projected to generate a huge demand for membranes and have an expected growth rate of 12.20 percent, followed by MEA at 10.40 percent between 2015 and 2020. The North American market is will be driven by advancements and development initiatives undertaken to enhance and upgrade existing membrane separation systems.

Microfiltration dominates the global market whereas water & wastewater dominates the end-user market globally. Among the various membrane separation technologies sprouting in the market, ceramic membranes segment is projected to grow at the highest CAGR of 11.96 percent between 2015 and 2020 due to its superior performance, less fouling and easily to clean properties. However, high cost associated with this process is expected to be a hindrance in the growth. Other membranes such as liquid, ion-exchange membranes along with carbon membranes are also expected to witness fastest-growth in the overall membranes market. The nanofiltration technology is expected to see a growth rate of 12.55 percent between 2015 and 2020, according to MarketsandMarkets.

Processes

Membrane separation technology is broadly segregated into four major processes: microfiltration, ultrafiltration, nanofiltration and reverse osmosis. When membrane filtration is used for the removal of larger particles, micro filtration and ultra filtration are applied. Because in these membranes, the productivity is high while the pressure differences are low. When salts need to be removed from water, nano filtration and reverse osmosis are applied here the separation takes place by diffusion through the membrane and the pressure required is much higher than the pressure required for micro and ultra-filtration.

Microfiltration: Microfiltration membranes are used across diverse applications including water & waste-water treatment, semiconductor & electronics manufacturing, food & beverage processing and pharmaceuticals & bio-pharmaceuticals production. The separated components are 0.1 to 1μm in diametre, mainly are fine microparticles, submicroparticles and nanoparticles. Increasing use of microfiltration membranes as pre-filters to reverse osmosis and ultrafiltration processes is expected to drive membrane separation growth.

Ultrafiltration: Ultrafiltration is similar to reverse osmosis, separating fractions with a diameter of 0.005~10μm, which is between the reverse osmosis and microfiltration.

Nanofiltration: Desalination is one of the major forces driving nanofiltration demand. It has a high retention performance for organic materials and high price, low price inorganic materials with molecular weight between 200 and 1000. Nanofiltration membranes typically have a pore size between 1 to 5 nm and is widely used for water softening, organic bio active substances and dechlorination, purification, concentration, wastewater decoloration.

Reverse Osmosis: In a reverse osmosis device, water is pumped by high pressure booster, with the choice of semipermeable membrane interception function to remove inorganic ions in the water. Due to the reverse osmosis membrane in high pressure situations, it only allows water molecules to pass through and does not allow the potassium, the sodium, calcium, zinc ion and viruses, bacteria, so as to obtain high quality water.

Recently, BASF launched its new water treatment solutions including Sokalan® AF-X – a water soluble and readily biodegradable antifoam for thermal desalination processes that provides foam control properties at low dosage rates; Sokalan® RO 3500 – a multifunctional antiscalant for reverse osmosis membrane treatment with proven performance on various scales; and Zetag® ULTRA – a cationic ultra-high molecular weight powder flocculants for superior sludge dewatering performance at lower dosage rates.

“BASF is committed to providing sustainable and high-performing products to address the world’s rising water demand. Secure water supply is one of the biggest challenges especially for the arid region of the Middle East,” said Marcus Fuest, global marketing, water chemicals, BASF. “Our portfolio of differentiating water treatment chemicals, investments in product innovations and the collective expertise of our globally operating team are helping our customers meet their needs for reliable and cost-efficient water treatment.”

Lanxess developed an iron oxide, called Bayoxide® E33, which is designed specifically for the removal of arsenic from water. The water treatment system is built on a solid bed of iron oxide beads. The specially-engineered beads have finely structured surfaces that adsorb pollutants when contaminated water flows over them.

For reverse osmosis (RO) elements from its Lewabrane® product line, Lanxess developed a market-ready, novel feed spacer used in the membrane element. It provides for optimised flow in the RO element and thus lowers energy consumption.

“With the introduction of new products from Lewabrane® and the new software module for LewaPlus®, we are well positioned to make the most of the opportunities that the market provides,” said Prakash Shanmugam, head, business unit, liquid purification technologies, Lanxess India.

Benefits and Challenges

Membrane separation technologies have numerous benefits when compared to various other water treatment processes such as:

• The process can take place in low temperatures and enables the treatment of the heat-sensitive matter. Hence, it is widely used in food production.
• Process with low energy cost. The total amount of energy required is to pump liquids through the membrane which is very less compared to alternative techniques, such as evaporation.
• The process can easily be expanded.

However, no process comes without certain challenges. Despite being a cost effective process, factors such as membrane fouling, chemical corrosion such as oxidation and faulty installation & maintenance are issues that the industry is battling with.

Membrane fouling is inevitable in this process even with sufficient pre-treatment. Particles, biofouling and scaling are the three main types of fouling on a membrane. However, the type and amount of fouling depend on factors, such as feed water quality, membrane type, membrane materials and process design & control.

Also, while developing countries offer significant growth opportunities due to the rising need for waste-water treatment, high installation & operational costs associated with this technology hamper the membrane separation market in developing nations.  However, emerging processes and applications like forwarding osmosis and hybrid forward osmosis for waste-water recycling and water desalination can provide avenues for membrane separation market growth.

However, mandatory government regulations and increasing demand for clean and safe drinking water will constantly propel the membrane separation technology to reign over the water processing industry in the times to come.

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