Saving millions of lives by using an inexpensive paper filter made by algae

Paper filter made from Pithophora algae. Photograph: Albert Mihranyan

The problem of access to safe drinking water in most parts of Bangladesh is a persistent challenge. Now, a team of scientists from Uppsala University, Sweden, and Dhaka University, Bangladesh, shows that a locally growing and previously unexploited green macroalgae species could be used to extract cellulose nanofibers, which can then be formed into paper sheets with tailored pore size that are utilized for point-of-use water treatment.

The paper filter has demonstrated excellent virus and bacteria removal capacity both in the lab and in real-life tests. The scientists believe that with further development, the paper filter produced from Pithophora algae, could be an affordable and efficient remedy to prevent numerous potentially deadly water-borne infections.

“Pithophora algae have been largely overlooked in the past as a valuable raw material. It is with great satisfaction that we can now document excellent pathogen removal clearance for both water-borne bacteria and viruses with efficiency above 99.999 percent. It can purify even the smallest virus particles of 27-28 nanometers”, says Albert Mihranyan, Professor of Nanotechnology at Uppsala University, who heads the study.

Bangladesh is a country with a population of over 168 million people, which is larger than that of Russia (144.5 million). By 2050, the projected growth rates suggest that the population of Bangladesh may reach the mark of 200-225 million people. In parts of the biggest cities in Bangladesh, such as Dhaka or Chittagong, the density of population is as high as 205,000 inhabitants/km2, which is almost 58 times more than that in Stockholm and nearly 20 times more than that in New York city.

In 2018, about 15 million people lived below the extreme poverty line of USD 1.90 (18 SEK) per day. Hyper-high density of population, poor hygiene, and lack of clean water increase the risk of spreading water-borne infections. The cities of Dhaka and Chittagong are the only cities with extensive piped water and sewage system, but even there the water is available at most a few hours per day and may still be contaminated with infectious pathogens due to leakage in pipelines. With Dhaka population growing over 300,000 persons/year, access to clean water is critical for sustainable life.

To prevent the spread of water-borne infections, affordable point-of-use water treatment strategies that can be effective against all kinds of water-borne pathogens are needed. Boiling, sunlight pasteurization, or chemical disinfection are some of the methods that are currently used for point-of-use water treatment. An excellent way of treating water to physically remove all kinds of pathogens is filtration. Thus, new types of affordable point-of-use filters that can remove all kinds of pathogenic bacteria, spores, and viruses are highly in demand. Now, thanks to the joint efforts by the Swedish and Bangladeshi teams a new source of locally growing raw material has been discovered that can be used for manufacturing paper filter for water treatment applications.

“Access to clean water will contribute strongly to improved health thus reducing poverty. We are optimistic that through future development of devices the filter paper produced from the locally growing algae will be useful to prevent potentially deadly water-borne diseases and improve the quality of life for millions of people” says Khondkar Siddique-e-Rabbani, Honorary Professor at University of Dhaka and project coordinator in Bangladesh.

Learn more: Paper filter made from algae can save millions of lives in Bangladesh

 

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New technology can clean water twice as fast as commercially available ultrafiltration membranes

Using bacteria to create a water filter that kills bacteria

More than one in 10 people in the world lack basic drinking water access, and by 2025, half of the world’s population will be living in water-stressed areas, which is why access to clean water is one of the National Academy of Engineering’s Grand Challenges. Engineers at Washington University in St. Louis have designed a novel membrane technology that purifies water while preventing biofouling, or buildup of bacteria and other harmful microorganisms that reduce the flow of water.

And they used bacteria to build such filtering membranes.

Srikanth Singamaneni, professor of mechanical engineering & materials science, and Young-Shin Jun, professor of energy, environmental & chemical engineering, and their teams blended their expertise to develop an ultrafiltration membrane using graphene oxide and bacterial nanocellulose that they found to be highly efficient, long-lasting and environmentally friendly. If their technique were to be scaled up to a large size, it could benefit many developing countries where clean water is scarce.

The results of their work were published as the cover story in the Jan. 2 issue of EnvironmentalScience & Technology.

Biofouling accounts for nearly half of all membrane fouling and is highly challenging to eradicate completely. Singamaneni and Jun have been tackling this challenge together for nearly five years. They previously developed other membranes using gold nanostars, but wanted to design one that used less expensive materials.

Their new membrane begins with feeding Gluconacetobacter hansenii bacteria a sugary substance so that they form cellulose nanofibers when in water. The team then incorporated graphene oxide (GO) flakes into the bacterial nanocellulose while it was growing, essentially trapping GO in the membrane to make it stable and durable.

After GO is incorporated, the membrane is treated with base solution to kill Gluconacetobacter. During this process, the oxygen groups of GO are eliminated, making it reduced GO.  When the team shone sunlight onto the membrane, the reduced GO flakes immediately generated heat, which is dissipated into the surrounding water and bacteria nanocellulose.

Ironically, the membrane created from bacteria also can kill bacteria.

“If you want to purify water with microorganisms in it, the reduced graphene oxide in the membrane can absorb the sunlight, heat the membrane and kill the bacteria,” Singamaneni said.

Singamaneni and Jun and their team exposed the membrane to E. coli bacteria, then shone light on the membrane’s surface. After being irradiated with light for just 3 minutes, the E. coli bacteria died. The team determined that the membrane quickly heated to above the 70 degrees Celsius required to deteriorate the cell walls of E. coli bacteria.

While the bacteria are killed, the researchers had a pristine membrane with a high quality of nanocellulose fibers that was able to filter water twice as fast as commercially available ultrafiltration membranes under a high operating pressure.

When they did the same experiment on a membrane made from bacterial nanocellulose without the reduced GO, the E. coli bacteria stayed alive.

“This is like 3-D printing with microorganisms,” Jun said. “We can add whatever we like to the bacteria nanocellulose during its growth. We looked at it under different pH conditions similar to what we encounter in the environment, and these membranes are much more stable compared to membranes prepared by vacuum filtration or spin-coating of graphene oxide.”

While Singamaneni and Jun acknowledge that implementing this process in conventional reverse osmosis systems is taxing, they propose a spiral-wound module system, similar to a roll of towels. It could be equipped with LEDs or a type of nanogenerator that harnesses mechanical energy from the fluid flow to produce light and heat, which would reduce the overall cost.

Learn more: Using bacteria to create a water filter that kills bacteria

 

 

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Saving electricity and costs by filtering liquids with liquids

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Liquid-gated membrane filtration system improves industrial wastewater purification and saves energy

Filtering and treating water, both for human consumption and to clean industrial and municipal wastewater, accounts for about 13% of all electricity consumed in the US every year and releases about 290 million metric tons of CO2 into the atmosphere annually – roughly equivalent to the combined weight of every human on Earth.

One of the most common methods of processing water is passing it through a membrane with pores that are sized to filter out particles that are larger than water molecules. However, these membranes are susceptible to “fouling,” or clogging by the very materials they are designed to filter out, necessitating more electricity to force the water through a partially clogged membrane and frequent membrane replacement, both of which increase water treatment costs.

New research from the Wyss Institute for Biologically Inspired Engineering at Harvard University and collaborators at Northeastern University and the University of Waterloo demonstrates that the Wyss’ liquid-gated membranes (LGMs) filter nanoclay particles out of water with twofold higher efficiency, nearly threefold longer time-to-foul, and a reduction in the pressure required for filtration over conventional membranes, offering a solution that could reduce the cost and electricity consumption of high-impact industrial processes such as oil and gas drilling. The study is reported in APL Materials.

“This is the first study to demonstrate that LGMs can achieve sustained filtration in settings similar to those found in heavy industry, and it provides insight into how LGMs resist different types of fouling, which could lead to their use in a variety of water processing settings,” said first author Jack Alvarenga, a Research Scientist at the Wyss Institute.

LGMs mimic nature’s use of liquid-filled pores to control the movement of liquids, gases and particles through biological filters using the lowest possible amount of energy, much like the small stomata openings in plants’ leaves allow gases to pass through. Each LGM is coated with a liquid that acts as a reversible gate, filling and sealing its pores in the “closed” state. When pressure is applied to the membrane, the liquid inside the pores is pulled to the sides, creating open, liquid-lined pores that can be tuned to allow the passage of specific liquids or gases, and resist fouling due to the liquid layer’s slippery surface. The use of fluid-lined pores also enables the separation of a target compound from a mixture of different substances, which is common in industrial liquid processing.

The research team decided to test their LGMs on a suspension of bentonite clay in water, as such “nanoclay” solutions mimic the wastewater produced by drilling activities in the oil and gas industry. They infused 25-mm discs of a standard filter membrane with perfluoropolyether, a type of liquid lubricant that has been used in the aerospace industry for over 30 years, to convert them into LGMs. They then placed the membranes under pressure to draw water through the pores but leave the nanoclay particles behind, and compared the performance of untreated membranes to LGMs.

The untreated membranes displayed signs of nanoclay fouling much more quickly than the LGMs, and the LGMs were able to filter water three times longer than the standard membranes before requiring a “backwash” procedure to remove particles that had accumulated on the membrane. Less frequent backwashing could translate to a reduction in the use of cleaning chemicals and energy required to pump backwash water, and improve the filtration rate in industrial water treatment settings.

While the LGMs did eventually experience fouling, they displayed a 60% reduction in the amount of nanoclay that accumulated within their structure during filtration, which is known as “irreversible fouling” because it is not removed by backwashing. This advantage gives LGMs a longer lifespan and makes more of the filtrate recoverable for alternate uses. Additionally, the LGMs required 16% less pressure to initiate the filtration process, reflecting further energy savings.

“LGMs have the potential for use in industries as diverse as food and beverage processing, biopharmaceutical manufacturing, textiles, paper, pulp, chemical, and petrochemical, and could offer improvements in energy use and efficiency across a wide swath of industrial applications,” said corresponding author Joanna Aizenberg, Ph.D., who is a Founding Core Faculty member of the Wyss Institute and the Amy Smith Berylson Professor of Material Sciences at Harvard’s John A. Paulson School of Engineering and Applied Sciences (SEAS).

The team’s next steps for the research include larger-scale pilot studies with industry partners, longer-term operation of the LGMs, and filtering even more complex mixtures of substances. These studies will provide insight into the commercial viability of LGMs for different applications, and how long they would last in a number of use cases.

“The concept of using a liquid to help filter other liquids, while perhaps not obvious to us, is prevalent in nature. It’s wonderful to see how leveraging nature’s innovation in this manner can potentially lead to huge energy savings,” said Wyss Founding Director Donald Ingber, M.D., Ph.D., who is also the Judah Folkman Professor of Vascular Biology at Harvard Medical School and the Vascular Biology Program at Boston Children’s Hospital, as well as Professor of Bioengineering at SEAS.

Learn more: Filtering liquids with liquids saves electricity

 

 

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A better water filtration system that could even deal with the emerging threat from microplastics pollution?

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Manta rays strain their tiny food from mouthfuls of seawater in a novel way that could hold the key to better filtration in a variety of commercial applications, new research by Oregon State University shows.

Published today in Science Advances, the findings explain that manta rays filter zooplankton, mesoplankton and microcrustaceans with an apparatus different from anything previously seen in any biological or industrial system.

“The most common type of filter is a sieve filter, where a particle-containing fluid is passed through a membrane with pores smaller than the particles,” said study co-author Jim Strother, assistant professor of integrative biology in the OSU College of Science.

Sieve filters include everything from a kitchen colander that strains pasta to membrane filters that produce ultrapure water. Other filter mechanisms are hydrosol filtration, such as the fiber filters in HVAC systems, and cyclonic filtration, used in bagless vacuum cleaners.

“There are lots of different types of filters used for many purposes worldwide, but they’re all based on just a few fundamental mechanisms,” said Strother, who collaborated with corresponding author Misty Paig-Tran and Raj Divi of Cal State Fullerton.

Manta rays, close relatives of sharks that can measure more than 20 feet across, eat by bringing plankton-rich water into their mouths as they swim. They filter and ingest the plankton and then flush the remaining water out their gill slits.

Many filtration systems are prone to clogging as they collect whatever they’re filtering out, but manta rays use arrays of leaf-like lobes to bounce food particles away from the filter.

Water passing over the lobes creates a complex pattern of swirling eddies, and food particles in the flow hit the lobes and move away. The setup allows the fish to retain food organisms much smaller than the pores.

“Manta rays appear to utilize a novel mechanism for filtering particles out of fluids,” Strother said. “Their filtering apparatus has a special structure that causes plankton particles to ricochet off the filter and become concentrated in the mouth cavity, so the fish can then ingest them.”

Since the particles are repelled by the filter but not captured, the filter has several highly desirable properties, including that it can be operated at high flow rates and is extremely resistant to clogging.

“This paper establishes the basic mechanism, and we are currently looking at whether we can adapt this mechanism for engineered systems,” Strother said. “For example, one future direction is exploring whether this can be applied to wastewater treatment in order to address the emerging threat from microplastics pollution.”

Learn more: Manta rays’ food-capturing mechanism may hold key to better filtration systems

 

 

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Carbon nanotube sponge shows improved water clean-up

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Carbon nanotube sponge shows improved water clean-up

The CNT sponges were also shown to absorb vegetable oil up to 150 times of its initial weight

A carbon nanotube sponge capable of soaking up water contaminants, such as fertilisers, pesticides and pharmaceuticals, more than three times more efficiently than previous efforts has been presented in a new study published today.

The carbon nanotube (CNT) sponges, uniquely doped with sulphur, also demonstrated a high capacity to absorb oil, potentially opening up the possibility of using the material in industrial accidents and oil spill clean-ups.

The results have been published today, 17 January, in IOP Publishing’s journal Nanotechnology.

CNTs are hollow cylindrical structures composed of a single sheet of carbon. Owing to their structure, CNTs have extraordinary thermal, chemical and mechanical properties that have led to an array of applications from body armour to solar panels.

They have been touted as excellent candidates for wastewater clean-up; however, problems have arisen when trying to handle the fine powders and eventually retrieve them from the water.

Lead author of the research Luca Camilli, from the University of Roma, said: “It is quite tricky using CNT powders to remove oil spilled in the ocean. They are hard to handle and can eventually get lost or dispersed in the ocean after they are released.

“However, millimetre- or centimetre-scale CNTs, as we’ve synthesised in this study, are much easier to handle. They float on water because of their porous structure and, once saturated with oil, can be easily removed. By simply squeezing them and releasing the oil, they can then be re-used.”

In the new study, the researchers, from the University of Roma, University of Nantes and University of L’Aquila, bulked up the CNTs to the necessary size by adding sulphur during the production process?the resulting sponge had an average length of 20 mm.

The addition of sulphur caused defects to form on the surface of the CNT sponges which then enabled ferrocene, which was also added during the production process, to deposit iron into tiny capsules within the carbon shells.

The presence of iron meant the sponges could be magnetically controlled and driven without any direct contact, easing the existing problem of trying to control CNTs when added onto the water’s surface.

The researchers demonstrated how the constructed CNT sponges could successfully remove a toxic organic solvent?dichlorobenzene?from water, showing that it could absorb a mass that was 3.5 times higher than previously achieved.

The CNT sponges were also shown to absorb vegetable oil up to 150 times of its initial weight and absorb engine oil to a slightly higher capacity than previous reported.

Read more . . .

 

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