Future Judgment of China's Urban Domestic Sewage Nitrogen...

Future Judgment of China's Urban Domestic Sewage Nitrogen Removal Technology

Polaris Water Network Source: JIEI Innovation Lab author: Li Ruiling 2019/7/9 8:52:55

Channel: Water treatment Keywords: sewage nitrogen and nitrogen removal technologynitrogen pollution
Polaris Water Treatment Network News : Beijing, Kunming, Chaohu, Taihu and other key areas and watersheds as environmental promoters, put forward higher and higher requirements for sewage treatment. The TN emission standard is raised from 20mg/L (Grade B), 15 mg/L (Grade A) to 10 mg/L, or even 5 mg/L (Kunming A standard), and gradually moves toward the limit of nitrogen removal. However, in the current denitrification technology route, some denitrification processes have a large increase in the cost of chemicals through the increase of carbon sources, as well as the increase of sites, complex operation and maintenance, etc. With the sustainable development of capital.
Regarding the denitrification of sewage , is the ultimate nitrogen removal a future trend in China's sewage treatment? Under the characteristics of China's unique sewage, how to achieve efficient and stable operation of wastewater denitrification under high emission standards? What is the future direction of China's nitrogen removal technology based on international experience? We hope to clarify the future technical route of nitrogen removal technology and promote the healthy development of industry innovation and environmental protection through the discussion and reflection of history, present and future.
Is China's water body contaminated with nitrogen ?
It is called "human activating nitrogen" or "reactive nitrogen", which is different from natural biological fixed nitrogen, chemically synthesized nitrogen, nitrogen oxides released by burning fossil fuels, and increased biological nitrogen fixation due to rice expansion. Tsinghua University's Research Center for Green Economy and Sustainable Development found that during the 100 years from 1910 to 2010, the net annual production of reactive nitrogen in China increased by more than 6 times, and by 2010 its contribution reached more than 80%. The amount of anthropogenic nitrogen is double that of natural organisms. The amount of nitrogen fixed significantly changes the regional nitrogen cycle, putting more pressure on the ecological environment. The greenhouse effect, sputum and acid rain are all related to changes in the nitrogen cycle under the disturbance of human activities.
So is our country's water body contaminated with nitrogen?
In February 2019, Dr. Yu Chaoqing from Tsinghua University and his colleagues published a paper entitled "Managing nitrogen to restore water quality in China" in Nature. The authors report that the rate of nitrogen emissions into freshwater in China due to human causes is 14.5 million t/a, which is about 2.7 times the safe emission threshold estimate (5.2 million t/a). Before the 1980s, the nitrogen concentration in water was less than 1 mg/L, but after the 1990s, the nitrogen concentration in many catchments rose rapidly to above 15 mg/L. The study found that except for the Tibet region, all provinces in China have pollution problems in the basin, and 95% of the waters have been polluted before 2000, and the accumulation of pollutants has exceeded 20 years. The Beijing-Hangzhou Grand Canal in 1980, Chaohu in 1985, Dianchi in 1981 have begun to appear nitrogen pollution, nitrogen accumulation for nearly 40 years.
China is moving from a "low carbon society" to a "low nitrogen society"
The concept of “low-carbon society” has been deeply rooted in the hearts of the people. However, as mentioned above, human activities may significantly interfere with the nitrogen cycle and may have more serious adverse effects, but it has not attracted the attention of all sectors of society. Faced with the increasing number of active nitrogen production in China and the world, building a “low-nitrogen society” has become an inevitable measure to control environmental pollution and maintain ecosystem health.
In 2016, Tsinghua University's Center for Green Economy and Sustainable Development put forward the idea of “accelerating the construction of a low-nitrogen society and ensuring the health of the ecosystem”. In 2018, at the Sino-Dutch Eco-Environment Technology International Summit Forum, Professor Wang Kaijun from the Environmental College of Tsinghua University also said that people still do not have a fuller understanding of the issue of nitrogen and phosphorus, focusing on “low-carbon society” to “low-nitrogen society”. Development concept.
How to achieve "low nitrogen"? Can be understood as less reactive nitrogen emissions, reducing the environmental impact of nitrogen. On the one hand, it is necessary to control nitrogen pollution from the source and increase the management and regulation of nitrogen pollutants; on the other hand, it is necessary to implement coordinated control in the process of nitrogen transport and conversion. Professor Wang Kaijun also pointed out that “the potential for energy saving and emission reduction of nitrogen is very large. It is possible to pursue the best possible “closed loop of water and matter” in any possible field and possible scale.
What role does a municipal wastewater plant play in nitrogen emissions?
Dr. Yu Zhaoqing's research combines observational data on total nitrogen concentrations in water with simulated nitrogen emissions from agriculture and other sources to estimate China's nitrogen emissions patterns from 1955 to 2014. From the perspective of pollution sources, agricultural and domestic pollutants are the main source of nitrogen in water. Among them, agricultural pollution accounts for 59% of the total nitrogen emissions (35% of farmland, 24% of livestock), and domestic pollution accounts for 39% (13% of urban sewage, 8% of rural sewage, 18% of organic waste), and industrial waste accounts for 2%. .

As of December 2018, China has operated 5,370 domestic sewage treatment plants with a processing capacity of 200 million m3/d. If the TN concentration of the effluent from the sewage treatment plant is reduced from 15 mg/L to 5 mg/L, the nitrogen emissions from the water body can be reduced by 5%-10%. With the improvement of the construction, management and maintenance of China's sewage pipe network, municipal sewage plants will play an increasingly important role in reducing water nitrogen emissions.
Is it economically feasible to denitrify the sewage?
Academicians Qu Jiuhui, Academician Peng Yongzhen, Professor Wang Kaijun, Professor Wang Hongchen and many other experts and scholars have pointed out that for sensitive water bodies such as lakes, local stricter local emission standards should be formulated according to local conditions, and sewage treatment standards should be gradually integrated with surface water quality standards. The continuous improvement of emission standards by wastewater treatment plants must be the eternal theme of China's sewage treatment industry. At present, Kunming has implemented the limit nitrogen removal standard of wastewater treatment plant TN<5mg/L. In the future, more and more water-sensitive areas or watersheds will move toward the limit of nitrogen removal.
Is it economically feasible to limit nitrogen removal? Re-examining and observing the history of water environment governance in developed countries and national policies may provide us with a reference. In the article "America's Water Environment Governance" in this issue, the author elaborates on the US water environment management ideas and investments in the United States that implement TN < 3m / L, TP < 0.1mg / L emission standards. From the experience of the United States, the increase in investment and operating costs of enhanced nutrient removal (ENR) and limit nutrient removal (LOT) has been limited, and some sewage plants have even seen operating cost savings, which can be said to be cost-effective.
Current Status and Countermeasures of China's Sewage Characteristics
Carbon management is the fundamental problem of sewage treatment
In 1914, Arden and Lockett invented the activated sludge method. In 1964, the British Water Pollution Center Downing established the basic rule of nitrification theory. In the 1970s, James Barnard, the father of biological nitrogen and phosphorus removal, created the classic Bardenpho wastewater treatment. Nitrogen technology, since then sewage treatment based on biological methods, has been continuously extended and developed. Mr. Cao Yeshi, the former chief expert of the Singapore Public Utilities Bureau (PUB), once said at the sewage denitrification technology salon held by JIEI that all the nitrogen and phosphorus removal needs carbon. How to realize the rational management and distribution of carbon is the foundation of sewage treatment. problem. It takes 6 CODs to remove one N by biological method, 7-10 CODs to remove one P, and these CODs are all degradable COD. Combined with the characteristics of sewage and the characteristics of microorganisms, it is a systematic project to remove carbon, phosphorus and other nutrients from sewage by carbon management. It is also a fundamental problem of sewage treatment.
Inefficient operation of “sick” sewage plants is widespread
Dr. James Barnard believes that with the deepening of the biological principles of wastewater treatment, it is possible to design a reliable system to achieve high standard effluent, ie TN<3 mg/L, TP<0.1 mg/L, combined with chemical phosphorus removal to achieve TP <0.01 mg/L. The results of the Dutch study also show that the technical limits of the activated sludge process are TN < 2.2 mg / L and TP < 0.15 mg / L under appropriate conditions. The above theory can be said to lay a solid theoretical foundation for optimizing the operation and management to achieve the ultimate nitrogen removal based on the biological nitrogen and phosphorus removal process.
In contrast to the current situation of sewage treatment in China, there are many practical problems. The problem of impaired pipelines, unsatisfactory drainage of rain and sewage, and mixed discharge of industrial wastewater have formed the characteristics of urban sewage in China: complex water intake and insufficient carbon sources.Professor Li Xie of Jiangnan University analyzed the whole process process of 58 sewage treatment plants across the country and found that 85% of the wastewater treatment plants had insufficient carbon sources. This may be the reason why the denitrification filter on the back end of the process is generally used in the provincial and municipal wastewater plants that need to implement the TN<10mg/L effluent standard, which also increases the cost of adding 0.2-0.3 yuan carbon source to the operation of the ton water. , 0.004 degrees / m second-level increase in electricity costs. China's sewage plant “running with disease” and inefficient operation have become the norm.
"Source control, bio-enhancement, optimized operation" - a good strategy for efficient and stable nitrogen removal from wastewater
At present, the stable operation time of domestic high-emission sewage treatment plants is relatively short. Beijing has been a pioneering area. It has been published since the publication of the landmark (DB11/890-2012) for 7 years, but most of the areas are still in the process of upgrading and upgrading, and have less experience in efficient and stable nitrogen removal. In the central control area of Beijing Enterprises Water Management, combined with the management and technical experience of the project, the paper puts forward the experience and suggestions that “the local conditions are the premise, the operation is the foundation, the secondary treatment is the key, the third-level treatment is the guarantee, and the investment cost is the core”. Professor Li Ji put forward operational optimization suggestions for the main influencing factors of denitrification such as carbon source, internal reflux ratio, internal reflux dissolved oxygen, and agitation through the investigation and analysis of 58 sewage treatment plants. It is worthy of readers' tasting and practice. At the same time, for Jiangsu, which is in the process of upgrading, we have invited Zhang Chao, who has participated in the preliminary investigation of the “Standards for the discharge of major water pollutants from urban sewage treatment plants and key industrial industries in Taihu District” (DB32/1072-2018). The system analyzes the problems and countermeasures of the new round of bidding in the Taihu Basin, and hopes to enlighten the readers. Combining the views of many experts, we believe that “source control, bio-enhancement, and optimized operation” are good strategies for achieving efficient and stable nitrogen removal in wastewater in a new round of bidding.
The direction of sewage treatment and denitrification technology in the next 10 years
After entering the 21st century, there has been a major conceptual change in wastewater treatment. Sewage is no longer considered a waste, but a renewable resource.At the beginning of 2014, six experts represented by Academician Qu Jiuhui proposed the “China Urban Wastewater Treatment Concept Factory” and pursued “water quality sustainability, energy self-sufficiency, resource recycling and environmental friendliness”. With the change of ideas, reducing or abandoning the demand for additional carbon sources, reducing aeration energy consumption, and taking up less land, using existing infrastructure to develop new processes has become the current and future 10 years of technical direction and challenges.
More cost-effective carbon source replacement technology and products
At present, in the academic circles and industries, since there is no need to add an organic carbon source, and the nitrogen removal efficiency is high, the operating cost is low, and the autotrophic denitrification technology using inorganic substances such as sulfur as an electron donor has become a research hotspot of technical engineering application. Professor Li Ji believes that compared with the denitrification deep bed filter, the sulfur autotrophic denitrification unit can save at least 20% of the floor space, reduce the operating cost by more than 50%, and stably achieve the effluent TN<10 mg. /L deep denitrification target. Although there is no engineering application for this technology, it is reported that a number of pilot projects are in progress. Carbon source as a universal application of nitrogen removal in wastewater treatment plants, a more cost-effective alternative product is also a hot spot in the current market. A company in Beijing has developed a new high-efficiency bio-carbon source BioC-1M that can replace conventional carbon sources. It not only has high safety, but also can reduce operating costs by 15%-30%. It is currently in Beijing Changping, Datong Pharmaceutical Park and other sewage. The factory got the application.
More energy-efficient and cost-effective technologies and products
Dr. Cao Yeshi once elaborated on the energy consumption of various biological nitrogen removal technologies in the seminar of the technical salon held by JIEI. He pointed out that short-range nitrification and denitrification can save 25% of oxygen and 40% of carbon compared with traditional nitrification and denitrification, and Anammox can save 75% of oxygen and 60% of carbon. Anaerobic ammonium oxidation began in 1977 by the Austrian theoretical chemist Engelbert Broda. After 40 years of development, it has become the focus of attention worldwide. For example, Veolia, a world-renowned water company, has not only developed a one-stage partial nitrosation-anaerobic ammonium oxidation (PNA) denitrification process based on MBBR system-ANITATMMox, and has been exploring the mainstream PNA denitrification process. DC Water, USA, operates the world's largest sidestream anaerobic ammonium oxidation process (DEMON® wastewater treatment plant, Blue Plains, and is also advancing to short-range denitrification coupled anammox technology (PdA). The prestigious University of Cape Town, South Africa, developed the “External Nitrification Activated Sludge Process”, which not only increases the processing capacity by 50%, but also reduces the need for aeration by 75%.
The new biofilm technology is also shining with new innovations based on material innovation, biofilm formation mechanism and structural stability. The world-renowned companies Suez, Fluence, and OxyMem all started to develop aerated membrane bioreactors (MABR) around 2000, and they were introduced to the market around 2015. They have been used in engineering applications abroad. The MABR technology is suitable for the characteristics of low C/N ratio and low VSS in China. It can be directly applied to the anoxic zone of the conventional activated sludge process, and the oxygenation efficiency is 4 times higher than that of the microporous aeration, and the synchronization is brought about. Nitrification and denitrification and partial short-cut nitrification and denitrification can achieve 20%-40% power consumption savings, and can increase water load by 30%-50%, and stably achieve effluent TN<10mg/L. Now the MABR integrated equipment developed by Fluence has been popularized in China's rural domestic sewage treatment, and Suez and OxyMem have begun to carry out the first engineering demonstration in Huzhou and other places in China. In the future, as more and more people pay attention to and develop this technology, KNOW-HOW costs are reduced. It is believed that in China, especially in the absence of space, the scenario of overloaded operation and further TN promotion will be applied faster. .

Finally, I still want to use the summary of Dr. Cao Yeshi's sharing in the denitrification technology salon as a conclusion. China's unique sewage characteristics are our challenge. How can the inefficiently operated wastewater treatment plant be improved? “Optimize existing BNR processes to improve efficiency; explore efficient use of carbon in wastewater, minimize the use of additional carbon sources and chemicals; strengthen engineering research through industry, academic and public utilities; and select breakthroughs in cutting-edge topics” This may be the breakthrough direction of China's BNR program in the next 10 years.

Original title: JIEI | Future judgment of China's urban domestic sewage denitrification technology