Nangong University academician team cracks the world's problem of zero discharge of paper pulping wastewater

"This water is already equivalent to pure water, harmless to the human body, and quenching thirst is not a problem."

As I said, I barely held the treated paper pulping wastewater by hand and even drank two big mouths.

In late May, Jiangsu, although it has entered the early summer season, but in the Nantong Economic and Technological Development Zone, the water company's ultrafiltration system operation area, the reporter did not smell the unpleasant smell, but the director of the management committee reluctantly This move is a big surprise.

Just three years ago, the pulping wastewater of the Prince’s Paper Company of the development zone was originally planned to build a line of more than 100 kilometers of straight water, which is the traditional fishery that Qidong fishermen have been living for generations. Pipeline engineering was caught in the center of the whirlpool of public opinion overnight, and it also made this big project with billions of investment become fate.

Now, the black and odorous paper pulping wastewater in the eyes has undergone processes such as pretreatment, membrane filtration, and evaporation crystallization, and it has become a recyclable water, industrial salt and dry mud. Not only does the entire process achieve zero emissions, but Zhongshui has also become a sought-after scent for companies in the development zone. The behind-the-scenes hero of all this is the more than 40 researchers of the academician Xu Nanping of Nanjing University of Technology and the magical membrane technology they have shown.

The paradox of environmental protection behind "rules"

Qidong is a county-level city located on the north side of the estuary of the Yangtze River. It is surrounded by water on three sides and is shaped like a peninsula with abundant aquatic products.

Three years ago, when the total investment of 1.98 billion US dollars, the design of an annual output of 800,000 tons of high-grade paper, 714,000 tons of wood pulp, Jiangsu Oji Paper Co., Ltd., will be a construction of a paper pulping wastewater pipeline to the Qidong, Local people who have been fishing for a generation have begun to worry that paper pulping wastewater will affect ecological and offshore fish farming.

Qidong people believe that papermaking wastewater flows directly into the sea, pollutes the environment, endangers ecology, and destroys fishery resources. In the industry, paper pulping wastewater is treated as an international “custom”. The Prince is the third largest paper company in the world and the largest papermaking company in Asia. It uses the same process and treatment in Japan and other developed countries. method. This is a conflict between development and protection, economic interests and ecological benefits.

The technical dilemma of "dead chess"

Due to the government's "permanent stop construction" commitment, this unfinished sea-discharging pipeline has become a step-by-step "dead chess", leaving a huge dilemma:

——Without the sea, Japan’s largest investment project in China, Prince’s paper-making pulp tail water, has nowhere to be discharged. Nantong faces huge compensation for breach of contract that may exceed 10 billion yuan. Economic and diplomatic negative chain reactions are difficult to estimate;

——On-site treatment, there is no precedent for “zero emission” of papermaking pulp wastewater at home and abroad. Experts have demonstrated that under the existing technical conditions, zero emissions should be realized. Only the initial investment will cost 3 billion yuan. More than double the amount of 1.2 billion yuan required for the drainage of the sea, and local finance is difficult to sustain.

“The zero discharge of pulp tail water was generally considered impossible at home and abroad at the time,” said project implementer Yang Gang, professor of the Institute of Membrane Science and Technology, Nanjing University of Technology.

The reporter was informed that there are three technical obstacles in the treatment of paper pulping wastewater that cannot be overcome: First, the composition is complex, there are 300-600 substances, especially containing a large amount of colloidal substances, lignin, short fibers, etc., which is easy to cause nano-scale filtration. Membrane pollution is blocked, it must be replaced in 3 months, and the cost is extremely high. Second, it contains high concentration of organic matter, which makes the dehydration incomplete, and the by-product salt cannot crystallize. Third, the odor in the pretreatment process is difficult to control and affect the environment.

At the crucial moment, Xu Nanping, assistant to the governor of Jiangsu Province and director of the Science and Technology Department, academician of the Chinese Academy of Engineering, and chief scientist of the China Membrane Science 973 project, took the initiative to lead more than 40 R&D personnel from the Institute of Membrane Science, Nanjing University of Technology. The world's technical problems of “zero emission” of paper pulping wastewater.

The task they will accomplish is to operate the 24/7 unconditional process, turning the pulping wastewater into recyclable water, industrial salt and dry mud to achieve full recycling of the wastewater.

At this time, there is basically no scientific research time reserved for them.

The innovation of “membrane method”

“To achieve 'zero emissions', it is very important to scientifically lock the components of pulping wastewater.” Yang Gang introduced that due to the complex composition of pulping wastewater, the water quality is worse than the imagination of the research group. Even the Japanese Prince Company is constantly correcting the indicators. From the water quality parameters provided each time, it is worse than once.

"We don't have any retreat, we can only fight back!" Academician Xu Nanping told reporters. In order to obtain experimental data as soon as possible, the original Japanese wastewater was airlifted to Nantong for research.

On the basis of multiple scientific analyses of water samples, the project team proposed a complete set of design techniques.

The process of this device is three processes of pretreatment, membrane integration and evaporation crystallization. Each process contains many complicated technologies and processes, which are interlocking and indispensable. For example, in the pretreatment, researchers use biofilm degradation technology to not only remove the odor, but also effectively solve the pollution clogging problem of the filter membrane.

"This is the most advanced and reasonable technology in the world." Yang Gang said.

Membrane integration is a key link, accounting for more than 90% of the treated water. Through the special "screen" of membrane material, most of the good water is filtered out, which is an important guarantee for achieving zero emissions.

In the end, the pure water filtered by the membrane integration process designed by the researchers of Nanjing University of Technology has a water quality index of less than 3 and a conductivity of less than 150, which is better than tap water.

At this time, several hundred tons of high salt water left in the tens of thousands of tons of wastewater needs to be treated. How to make the salt crystallize and smoothly extract it, which is both effective and energy-saving, is the last process of the whole process. However, there are no examples available at home and abroad. A foreign paper-making enterprise used evaporation technology, but eventually it came out with a paste, and the salt could not be extracted at all.

To this end, the researchers adopted a mechanical recompression evaporation crystallization technology, combined with appropriate water inlet conditions and process conditions control, to achieve effective crystallization. The fine chemical plants that came to purchase could not believe that the industrial salt of white flowers actually produced homemade pulp wastewater.

The last remaining dry mud, containing calcium, magnesium and other ingredients, is used in construction projects and is an affordable and safe material.

The design was completed in 3 months, construction and installation were completed in 6 months, and trial operation was completed in one year. Before the prince's pulp production line was completed and put into production, the wastewater treatment project was completed and the Chinese side fully fulfilled the agreement signed by both parties.

A world-class puzzle that looks like "Arabian Nights", it has been overcome!

At present, the world's only water reuse equipment for pulping wastewater has been successfully operated in the Nantong Economic and Technological Development Zone “Nengda Water Co., Ltd.” for more than a year.

Wang Chaohui, director of the Environmental Protection Bureau of the Development Zone, said that the company is the main body of the reclaimed water reuse project. The daily processing capacity of the pulping wastewater is designed to reach a peak of 40,000 tons, with an average of 36,500 tons. The Prince's Nissan pulping wastewater is 32,000-3.6. Ten thousand tons, all of which are concentrated here. The monitoring data show that the water quality produced after treatment is good, and the main water quality indicators such as COD, turbidity, hardness and pH value are superior to Yangtze River water and even tap water.

It is estimated that the current operating cost per ton of water is about 5 yuan, the price is 2 yuan, and the local finance only needs to subsidize the operating cost of 3 yuan. Compared with the drainage pipeline project, construction funds and operating costs have been significantly reduced. After adaptive operation, it will be possible to further reduce operating costs.

Due to the low price and good water quality, these recycled waters have become the scent of enterprises in the development zone. Only the prince company uses 12,000 tons of water every day for papermaking, and Jiangshan Agrochemical uses 5,000 tons per day. Used for boiler make-up water or circulating cooling water. The park can save 20 million tons of water per year and reduce COD and BOD emissions to water bodies by 1,500 tons and 400 tons respectively. A technology has released a large number of environmental capacity indicators, "freeing up" a huge space for local economic development.

Relevant experts said that a number of industrial projects, including the paper industry, although the discharge is up to standard, the damage to the water environment is still not small, and in the long run will inevitably cause the water body to be overwhelmed.

“The reclaimed water reuse project has great scientific and technological value.” Xu Nanping said that this successful practice has given them confidence to solve almost all industrial wastewater treatment problems. As long as the scientific analysis of the relevant industrial wastewater components, targeted membrane material integration, can achieve all water reuse, that is, zero emissions. If local governments can make up their minds to promote, this technology will play an invaluable role in water conservation and water environment management in China and the world.

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