The Mengsu Economic Development Zone Zero Carbon Industrial Park, located in Ordos City, Inner Mongolia, has attracted several leading enterprises in the fields of photovoltaics, power batteries, and new energy vehicles to settle in, with an annual installed capacity equivalent to one-fifth of the total installed capacity of the Three Gorges Dam.

However, at the same time, the wastewater generated during the production process of photovoltaic products also poses significant challenges to local ecological environment protection.

In October of this year, the first phase of China's largest photovoltaic wastewater zero discharge project was officially put into operation here, capable of treating 100000 tons of industrial wastewater per day. After the completion of the second phase, this sewage treatment project will cover a total area of 487 acres, equivalent to 45 football fields.

Photovoltaic factories generate a large amount of wastewater during processes such as silicon wafer cutting, debonding, and cleaning. These wastewater have high salt content, high hardness, and are difficult to degrade organic matter. Therefore, how to recycle the wastewater has always been a recognized challenge. But in this sewage treatment plant, the recycling rate of photovoltaic wastewater reaches 95%.

Fluoride removal is a major challenge in photovoltaic wastewater treatment. Researchers at Nanjing University have discovered that fluoride ions have penetrated into the interior of suspended solids in wastewater, which act as a huge lock that traps fluoride inside. So conventional detection methods have always been ineffective.

Zhang Xiaolin, Associate Professor and Doctoral Supervisor at the School of Environment, Nanjing University: We used a special chemical key to open the lock, and after opening it, the undetectable part of fluoride was exposed.

After fluoride ion detection, the next challenge is how to remove fluoride from photovoltaic wastewater. To this end, a research team from Nanjing University has developed a composite nanomaterial with a diameter of less than 1 millimeter, containing billions of nanoparticles with a particle size equivalent to one 60000 times that of a human hair.

With these composite nanomaterials, the research team effectively removed fluorine from photovoltaic wastewater, and this victory is the result of half a century or four generations of researchers' relay efforts to overcome difficulties.

Thanks to more than 50 years of scientific research and exploration by Nanjing University, a defluorination workshop using this new nano material technology and process has been operating for over two months in Ordos, several hundred kilometers away, and the water quality treatment effect has significantly improved.

After treatment, 75% of photovoltaic wastewater can be recycled, the remaining 25% can be further treated and reused by 20%, and the remaining 5% can be distilled into industrial sodium chloride (industrial salt) through evaporation.

Through more than ten processes such as silicon and hardness removal, and nano fluorine removal, photovoltaic wastewater has been transformed from sewage into recyclable reclaimed water, and industrial salt can be extracted, increasing economic value and ultimately achieving zero discharge of photovoltaic wastewater and the recycling of water resources.

Nowadays, the zero discharge photovoltaic wastewater project in Ordos has broken the "three records" in the domestic photovoltaic wastewater treatment field in terms of investment scale, reuse standards, and salt content, becoming a new benchmark in the photovoltaic wastewater treatment field.