desalination of seawater

Desalination of seawater, converting salt water into fresh water is important in water-scarce countries. For that process, certain charged particles – known as ions – have to be removed from the water. However, some ions are difficult to remove from water due to their chemical properties. Recent research by scientists from Israel and the Netherlands is helping to improve this ion-removal process.

The researchers were able to predict the behaviour of boron ions during water processing and thus simplify their removal. The study is available on-line at the Proceedings of the National Academy of Sciences (PNAS). Many harmful or valuable ions in seawater, brackish water or freshwater are amphoteric: their properties vary with the pH. “It is difficult to remove these particles from the water with standard membrane technologies,” says Jouke Dykstra, Assistant Professor at the Department of Environmental Technology at Wageningen University & Research. “You then have to add certain chemicals to control the pH. But we want to avoid that as much as possible: there is a strong trend to use fewer chemicals.”

Desalination of seawater

As an example of this ion removal process, Dykstra refers to the desalination of seawater. This is happening worldwide at locations with a shortage of fresh water. For example, many countries around the Mediterranean use desalinated seawater for irrigation. “But seawater also contains boron, which is toxic in high concentrations and it inhibits plant growth. Obviously, this is a problem for irrigation, and that is why we are looking for new ways to remove boron and other ions from sea water.” Desalination is becoming increasingly important due to drought in many regions. Dykstra: “New technologies are needed to continue to meet the demand for fresh water, not only in the Mediterranean and the Middle East, but also in the Netherlands.”

Wageningen researchers are working on this challenge together with colleagues from Technion – the Israel Institute of Technology, and from Wetsus – the European Centre of Excellence for Sustainable Water Technology in Leeuwarden. Together they have developed a new theoretical model of the behaviour of boron during a process known as capacitive deionisation. This is an emerging, membraneless technique for water treatment and desalination using microporous, flow-through electrodes When an electric current is applied, ions are adsorbed to the electrodes and hence removed from the water. Dykstra: “We are the first in science to develop a theoretical model that enables us to predict this behaviour and use it to our advantage.”

Entirely new design

The Israeli and Dutch researchers discovered that such systems require a completely new design. For example, they demonstrated both theoretically and experimentally that the water has to flow from the positive to the negative electrode, and not the other way around, as is now customary. “Our research has shown that a good theoretical model is essential to effectively control such complex chemical processes,” concludes Dykstra. “This approach offers many interesting possibilities. You could also use this model for other challenges in waste water treatment, including removing arsenic or small organic molecules, such as drug residues or herbicides.”

PNAS summarizes the process: Water treatment is required for a sustainable potable water supply and can be leveraged to harvest valuable elements. Crucial to these processes is the removal of charge pH-dependent species from polluted water, such as boron, ammonia, and phosphate. These species can be challenging for conventional technologies. Currently, boron removal requires several reverse-osmosis stages, combined with dosing a caustic agent. Capacitive deionization (CDI) promises to enable effective removal of such species without chemical additives but requires a deep understanding of the coupled interplay of pH dynamics, ion electrosorption, and transport phenomena. Here, we provide a detailed theory tackling this topic and show both theoretically and experimentally highly counterintuitive design rules governing pH-dependent ion removal by CDI.

Photo by Lance Cheung on Foter

starch from co2

Creating starch from co2 is not a new process. Plants do it all the time. But Chinese researches now discovered a way to do it much more efficiently in a lab. That would potentially save up to 90% of farm land, water, fertiliser and pesticides, they claim.

Chinese scientists recently reported a new technology for artificial starch synthesis from carbon dioxide (CO2). The results were published in Science on September 24.

The new route makes it possible to shift the mode of starch production from traditional agricultural planting to industrial manufacturing, and opens up a new technical route for synthesizing complex molecules from CO2, reports Eurekalert.

Starch is the major component of grain as well as an important industrial raw material. At present, it is mainly produced by crops such as maize by fixing CO2 through photosynthesis. This process involves about 60 biochemical reactions as well as complex physiological regulation. The theoretical energy conversion efficiency of this process is only about 2%.

A sustainable production of starch and use of CO2 are urgently needed to solve the food crisis and climate change. Designing new ways to replace plant photosynthesis for converting CO2 to starch can contribute to achieve that.

To address this issue, scientists at the Tianjin Institute of Industrial Biotechnology (TIB) of the Chinese Academy of Sciences (CAS) designed a chemoenzymatic system as well as an artificial starch anabolic route consisting of only 11 core reactions to convert CO2 into starch.

The abstract of the research says: “Starches, a storage form of carbohydrates, are a major source of calories in the human diet and a primary feedstock for bioindustry. We report a chemical-biochemical hybrid pathway for starch synthesis from carbon dioxide (CO2) and hydrogen in a cell-free system. The artificial starch anabolic pathway (ASAP), consisting of 11 core reactions, was drafted by computational pathway design, established through modular assembly and substitution, and optimized by protein engineering of three bottleneck-associated enzymes. In a chemoenzymatic system with spatial and temporal segregation, ASAP, driven by hydrogen, converts CO2 to starch at a rate of 22 nanomoles of CO2 per minute per milligram of total catalyst, an ~8.5-fold higher rate than starch synthesis in maize. This approach opens the way toward future chemo-biohybrid starch synthesis from CO2.”

Starch from co2 can be 8.5 times more efficient

The artificial route can produce starch from CO2 with an efficiency 8.5-fold higher than starch biosynthesis in maize, suggesting a big step towards going beyond nature. It provides a new scientific basis for creating biological systems with unprecedented functions.

The research is a first step towards industrial manufacturing of starch from CO2. From the moment the total cost of the process will become comparable with agricultural planting, this technology is expected to save more than 90% of cultivated land and freshwater resources.

In addition, it would help to prevent the negative environmental impact of pesticides and fertilizers, improve human food security and facilitate a carbon-neutral bioeconomy.