Chinese scientists develop 'weapon of mass destruction' as last resort in fight against harmful algal blooms
Scientists in China have used “cold plasma” to attack and destroy a dominant species of algae that causes widespread problems in the seas, lakes or waterways of numerous countries, including poisoning sources of drinking water and killing fish and other marine life on a large scale.
Researchers at the Key Laboratory of Ion Beam Bio-engineering, at the Hefei Institute of Physical Science in East China’s Anhui province, discharged cold plasma, also known as non-thermal plasma, on the harmful cyanobacterial bloom, which resulted in it dying or losing its ability to reproduce within eight hours, they said.
Cyanobacteria takes its name from the Greek word for the colour of the bacteria, which is usually blue-green. It thrives in calm, nutrient-rich waters and can produce toxins that affect humans and animals, causing symptoms including skin irritation, vomiting, diarrhoea and even liver damage.
Other algal blooms, or groupings of aquatic microorganisms, are referred to as “red tides”, and they can be as deadly as an oil spill. At least some algal blooms are human-induced, with seaweed farming, untreated sewage and industrial plant discharges among the potential culprits in China.
China saw a record algal bloom in Shandong’s Qingdao in 2013, with officials in the city using bulldozers to get rid of a reported 7,335 tonnes of growth from nearby beaches as the algae turned the Yellow Sea green.
The algae, Enteromorpha prolifera, was said to cover an area roughly twice the size of the previous record bloom there in 2008.
The Chinese government has at times responded to such outbreaks by deploying legions of PLA personnel to wade in and fish out the algae by hand, but the new research-based discovery could render such measures unnecessary in the future.
It paves the way for a more widespread application of the technology as a form of emergency response to such blooms, the researchers said in their paper published in the journal Scientific Reports on Tuesday.
Unlike other methods that attempted to kill the algae on the spot, the plasma beams allow those pulling the trigger to effectively "fire and forget", leaving the plasma to work its magic unaided, they said.
The researchers, led by China’s professor Huang Qing, said the brief plasma radiation, which lasts from two to four minutes, could significantly increase the speed of treatment for algae contaminating large bodies of water.
It would also require less energy than other methods because this form of plasma can easily be generated at room temperature using a small device that can be mounted on a boat, Huang added.
In a favourable environment, such as being overly nourished and given the most suitable temperature, certain species of algae can multiply at a rapid rate until they dye their host water source green, yellow, brown or red.
Algal colonies absorb lots of oxygen and release harmful chemicals at the same time – often signalling a death knoll for animals and plants inhabiting the same water.
Scientists have been searching for countermeasures to remove excessive algae from large bodies of water for decades, but none have until now been ready for mass application.
Further setting back research, however, some solutions have been found to create new problems.
"The chemical methods [of treating algae], such as the excessive use of algaecides, can lead to secondary pollution,” the authors reported.
Other methods like ultraviolet radiation, sonication – using ultrasonic frequencies to interfere with how particles and molecules function - and electron-beam irradiation are limited and inefficient on a large scale, they added.
The plasma treatment could surmount these problems.
The new algae clean-up solution effectively acts like a death chamber, using high-voltage electrodes to generate cold plasma beams.
As the water containing the algae cells flows through the chamber, the cells are chemically poisoned by hydrogen peroxide and other chemicals created during the “plasma strikes”.
However, the latest find is not alone in its sphere. Rather, it joins a list of competing treatments now being explored, according to Zhang Yangguo, an associate professor of environmental science with the Ocean University of China in Qingdao.
"Numerous methods are under development, with promising results,” he said.
“For instance, bacteria that can kill and eat up the algae is being cultured and explored in some laboratories. In the future, this could also be deployed to remove algae from water in a fast and safe way.”
All of the methods are costly and may have some unexpected, potentially damaging, environmental consequences, so they should be approached with caution, Zhang said.
"An algal bloom often occurs on a massive scale and it can be more difficult to deal with than an oil spill," he added.
"Stop dumping pollutants in water, especially nitrogen and phosphorus. The authorities should enforce a ‘birth control’ policy on algae."