This new environmentally friendly method would allow scientists to purify even heavily polluted water and considerably reduce the consumption of energy required for the purification process.
According to the researchers, millions of tons of dangerous substances, such as oil products, heavy metal and pesticides, find their way into the world water basin through sewage. Discharging this water without preliminary treatment is unacceptable since many polluting components are so detrimental to the environment.
"According to the UN, the scarcity of fresh water around the world is currently estimated at 230 billion cubic meters per year," said Professor Pavel Strizhak, head of the research team and professor at the Tomsk Polytechnic University. "Over 1.8 billion people today are drinking only contaminated water. By 2030, almost half of the world population will face the threat of a water shortage. Given this, the development of processes to purify water from contaminants and industrial waste is of vital importance."
This water treatment method, developed at Tomsk Polytechnic University, includes several stages. First, contaminated water is converted into emulsions and suspensions. To obtain emulsions, researchers add liquids that are insoluble in water. To obtain suspensions, they add solid substances that are distributed in the form of tiny particles. Then these emulsions and suspensions are injected into a special heating chamber where each droplet containing impurities is heated to relatively low temperatures (from 300 to 500 ºC).
Upon heating, a decrease in pressure occurs across the boundary between various components of the droplet (between the two components in emulsions, and between the liquid and solid particles in suspensions). This pressure drop causes an explosive breakup of interphase boundaries. From the initial droplet, an aerosol is formed — a multitude of droplets with some exploding and disintegrating upon the application of heat. These processes follow a chain reaction, thus quickly separate pure water from impurities.
"When heated, water evaporates, and non-combustible impurities precipitate while the combustible ones burn out," Strizhak explained. "Then, water vapor condensates and we obtain purified water that can be later reused for technological needs, for instance. In industry, this treatment can be carried out in chambers of various constructions, such as contact heat exchangers (which look like dryers with spray nozzles). To purify heavily polluted water, the fire method could be used with fuel burners."
Strizhak believes that this new method is highly competitive as it enables the effective removal of toxic and flammable impurities.
"Compared to other known developments by foreign scientists, our method allowed researchers to achieve a stable explosive disintegration of droplets exclusively for a group of fluids that are significantly heterogeneous in composition and structure," Strizhak explained. "These findings will serve as a basis for the development of an advanced water treatment technology that will take less time and energy."
This method can be used to purify water used in processing at industrial sites (chemical, petrochemical, steel, pulp and paper production) since it can efficiently purify water containing a combination of different contaminants. It also allows the use of secondary energy, e.g., heat from flue gases in a boiler house operating within a company can be utilized in the water treatment facility.
Tomsk Polytechnic University is a participant in the Russian federal Project 5-100. This project is aimed at funding relevant scientific researches, stimulating the development of cooperation between university scientists and industry, and increasing the scientific and research potential of Russian universities.