naerobic ammonium oxidation (Anammox) refers to the process of oxidizing ammonia to nitrogen with nitrite as an electron acceptor under hypoxic conditions, which is catalyzed by a unique class of obligate anaerobic autotrophs known as "AnAOB".
The discovery of Anammox denitrification technology breaks the traditional heterotrophic denitrification denitrification cognition, which does not require an external organic carbon source as an electron donor, nor does it require a large amount of aeration, and can efficiently carry out sewage denitrification, with a maximum volume nitrogen removal rate of 9.5kg· N/(m³·d), which was much higher than that of the traditional nitrification denitrification process (volume nitrogen removal rate < 0.50kg· N/(m³·d)), according to foreign operation data, its processing cost is 0.75 euros/kg· N, which is far lower than the treatment cost of 2~5 euros/kg· N, due to its advantages such as no need for additional organic carbon sources, high denitrification load, low operating costs, and small footprint, has been recognized as one of the most economical and sustainable biological denitrification processes.
1. Process principle
Broda discovered NH based on chemical free energy exploration4+In hypoxic conditions with NO2-The possibility of direct generation of N2 as a missing part of the natural nitrogen cycle. Mulder and Van de Graffe first experimentally demonstrated this in the mid-90s of the 20th century, and since then there has been great interest in the process. The reaction equation for anaerobic ammonia oxidation is:
NH4++1.32NO2-+0.066HCO3-+0.13H+→
1.2N2+0.26NO3-+ 0.066CH2O0.5N0.15+2.03H2O
Van de Graffe et al. proposed the possible metabolic pathway of Anammox through tracing experiments, which is also the currently recognized possible metabolic pathway of nitrite-type anaerobic ammonia oxidation, which mainly includes two processes: one is decomposition (capacity) metabolism, that is, ammonia is used as the electron donor and nitrite is the electron acceptor, and the two react in a 1:1 ratio to generate nitrogen, and the generated energy is stored in the form of ATP; The second is anabolism, that is, nitrite is used to provide reducing power to electron acceptors, and the carbon source carbon dioxide and ATP produced by catabolism are used to synthesize cellular matter, and nitrate is produced in this process.
2. Progress in engineering application
In terms of practical engineering applications, in 2002, Parker built the world's first productive anaerobic ammonia oxidation reactor at the Dokhaven Wastewater Treatment Plant in Rotterdam, the Netherlands, using the Sharon-Anammox system to treat sludge dehydration. Since then, engineered anammox oxidation projects have continued to emerge around the world, and there are currently more than 200 Anammox projects around the world, most of which are located in Europe. In recent years, the Anammox project in China has also grown rapidly.
The Anammox wastewater treatment plant that has been built or is under construction is mainly aimed at high-ammonia nitrogen wastewater, including sludge digestate, landfill leachate, kitchen biogas slurry, aquaculture wastewater, coking wastewater, fermentation wastewater and semiconductor chip wastewater, etc., although the wastewater in these fields has the engineering application of Anammox, but there are still some problems that need to be optimized and solved, and some other fields of high-ammonia nitrogen wastewater also need to be developed.
01 Progress in engineering application of municipal urban sewage
1. Progress in the mainstream engineering application of municipal urban sewage
In recent years, the process of urbanization has been accelerating, and the pressure on the urban sewage treatment industry is increasing, and there is an urgent need to find a suitable method for sustainable development with good economic and environmental benefits to treat urban sewage. The water volume of urban sewage is large, the ammonia nitrogen content and water temperature are relatively low, and the composition is more complex, so it is difficult to carry out the engineering application of Anammox in the mainstream section of municipal sewage treatment plants.
In terms of municipal mainstream wastewater treatment, the Austrian Strass wastewater treatment plant was the first to start moving towards mainstream anaerobic ammonia oxidation. The daily treatment scale of the sewage treatment plant is 38,000 tons, using AB process, the influent is adsorbed by high-load activated sludge, and most of the suspended solids and dissolved organic matter in the sewage are converted into biogas for the sludge digestion system.
The plant replaces the original SBR process with the DEMON autotrophic denitrification process (a type of anaerobic ammonia oxidation), which uses a hydrocyclone to separate AnAOB by controlling the pH value, and returns the bottom flow of the cyclone to DEMON to enrich AnAOB, while the overflow flows back into the B section process. By supplying the stable enrichment of AnAOB in the lateral flow process to the mainstream process and the formation of sludge granulation in the mainstream process system, the annual removal rate of total nitrogen was higher than 80%, and the effluent TN<5mg/L and ammonia nitrogen < 1.5mg/L. At the same time, the plant is also known worldwide for achieving complete energy self-sufficiency and capacity surplus.
Singapore's Changi Sewage Treatment Plant has achieved the world's first mainstream autotrophic ammonia oxidation project without the need for side-flow inoculation. The plant treats 800,000 t/d of urban sewage, adopts the segmented influent activated sludge process (SFAS), and the volume ratio of the anoxic tank to the aerobic tank is 1:1, of which nitrite accumulation is realized in the aerobic tank, and the anaerobic ammonia oxidation reaction occurs in the anoxic tank, and the mainstream autotrophic denitrification process of the plant contributes 62% to the removal of TN. The high water temperature of the plant is a natural advantage for achieving stable nitrosation accumulation, and the process characteristics of hypoxia, aerobic alternating operation and short mud age are the key reasons for achieving stable ammonia oxidation.
The above two sewage treatment plants are currently the only two sewage treatment plants in the world that have realized the anaerobic ammonia oxidation process in the mainstream section. The application of Anammox technology in the mainstream of wastewater treatment plants requires solving some key issues, such as how to quickly start the Anammox project at low temperature, how to ensure the growth and enrichment of AnAOB in the reactor, and how to ensure the stable operation of the anammox oxidation project at low temperature.
2. Progress in the engineering application of municipal urban sewage side flow
The water volume is usually very small, accounting for only about 1-2% of the total water volume, but the water quality concentration is very high, the ammonia nitrogen concentration can usually reach 1000mg/L, and the high concentration of ammonia nitrogen makes the free ammonia concentration relatively high, which can well inhibit nitrite oxidizing bacteria (NOB). In addition, the carbon source is generally recovered through "anaerobic digestion", which can reduce the carbon-nitrogen ratio, and at the same time, heat will be generated during anaerobic digestion, and the effluent temperature can generally reach 30°C. High ammonia nitrogen, low carbon-nitrogen ratio, and high water temperature are important conditions for realizing anaerobic ammonia oxidation, so more than half of the completed urban sewage anammox oxidation projects are applied to the side flow of urban sewage treatment plants.
The world's first Anammox project Dokhaven sewage treatment plant in Rotterdam, the Netherlands, is used to treat sludge digestate, the sewage treatment plant adopts the AB method, the sludge generated in the main section is transported to the Sluisjesdijk sludge treatment plant 600 meters away for anaerobic digestion, the generated biogas is used for combined heat and power (CHP), and the digestate adopts Paques' SHARON+Anammox process for autotrophic denitrification.
The Sjölunda wastewater treatment plant in Malmö, Sweden is the world's first water plant to use Anammox biofilm, using ANITA™ Mox (a type of anaerobic ammonia oxidation process), which is mainly achieved by attaching different microorganisms to the filler, on the MBBR form of the filler AnAOB grows in the innermost layer, AOB is in the outer layer, and AOB oxidizes ammonia nitrogen to nitrite nitrogen for AnAOB to use. The Sjölunda wastewater treatment plant has also become an important source of bacteria for this process, and the South Durham wastewater treatment plant in the United States has successfully engineered this method, which has also become the source of bacteria for the development of this process in North America.
The above project adopts the anaerobic ammonia oxidation and denitrification technology of high ammonia nitrogen wastewater developed by Beijing Urban Drainage Group, of which the largest sludge digestate treatment plant - Beijing Gaoantun Sewage Plant Sludge Digestate Treatment Plant, with a daily treatment of 4600m of digestate3The total nitrogen concentration of the digestive solution is about 2500mg/L, the ammonia nitrogen concentration is about 2200mg/L, the average total nitrogen concentration of effluent is 300mg/L, the total nitrogen removal rate is more than 85%, and the removal load reaches 0.3kgN/(m).3d), which has been in stable operation since it was put into operation in 17 years.
3. Engineering applications in other municipal sewage treatment directions
Because landfill leachate is characterized by high ammonia nitrogen content (generally about 2000mg/L), high concentration of organic matter, large changes in water quality, and easy to contain toxic substances such as heavy metals, it is a complex sewage composition. In recent years, the research on the treatment of landfill leachate with anaerobic ammonia oxidation process has gradually emerged and matured, and a number of practical projects have been completed around the world.
Some experts and scholars found that controlling free ammonia (FA) and free nitrite (FNA) is the key to realizing Anammox, and our country officially commissioned and launched the first anaerobic ammonia oxidation technology to treat landfill leachate in 2015 - Hubei Shiyan Western Landfill Leachate Treatment Project. The project has a design treatment capacity of 150m3/d, adopts the self-domesticated AnAOB-Reinoka, and the device uses the two-stage uplifting anaerobic sludge bed (UASB) + Anammox + membrane filtration (MBR/RO) combined treatment process, and the effluent water quality fully meets the "Domestic Waste Landfill Pollution Control Standard" (GB16889-2008), which overcomes the engineering application problem of low C/N and becomes the first project in China to use anaerobic ammonia oxidation to treat landfill leachate.
The biogas slurry produced by anaerobic fermentation of food waste has a high temperature and contains a large amount of ammonia nitrogen and COD, etc., and the process of "traditional nitrification-denitrification biological denitrification system" is often used to treat this kind of wastewater in engineering, which has low nitrogen removal efficiency, large sludge yield and high operating cost. However, the treatment of this wastewater with anammox technology can achieve efficient nitrogen removal, without the need to supplement carbon source and alkalinity, and the economic and environmental benefits are obvious.
In 2019, in a comprehensive food waste disposal center built by Wuxi Huilian, the first to use this technology to treat the biogas slurry of food waste after anaerobic fermentation, the design water volume of the project is 650m3/d, using the process of "coagulation air flotation + high-load aeration tank + anammonia oxidation + MBR" process, in which the denitrification efficiency of Anammox is about 84%, and the treated sewage meets the three-level discharge standard in the "Comprehensive Sewage Discharge Standard" (GB8978-1996).
In 2021, the food waste comprehensive disposal center built in Meishan, Sichuan Province also uses the Anammox process to treat the fermented biogas slurry, the treatment water volume of the project is 200m3/d, the use of self-domesticated filler sludge, and the reaction system of "efficient collaborative anaerobic digestion + short-range nitrification (PN) + Aanmmox + Fenton reactor" is built to treat the fermented biogas slurry, and the COD effluent is controlled at 500mg/ L,TN effluent is controlled at 45mg/L, and ammonia nitrogen effluent is controlled at 30mg/L, with obvious economic and environmental benefits.
02 Progress in engineering application of industrial wastewater
In the past 20 years, anaerobic ammonia oxidation processes have been successfully practiced in the fields of high ammonia nitrogen industrial wastewater such as coking, fermentation, pharmaceuticals, tanning, semiconductors, and food processing. However, problems such as how to start quickly, achieve rapid and effective enrichment of AnAOB, and how to make the project run stably still need to be solved.
1. Progress in engineering application in coal chemical wastewater treatment
Coking wastewater contains a large amount of ammonia nitrogen, organic matter, phenols, cyanide, thiocyanide, tar and polycyclic aromatic hydrocarbons and other pollutants, high toxicity, poor biodegradability, traditional biological denitrification methods require a large number of external carbon sources, low nitrogen removal efficiency, high construction and operation costs, and efficient nitrogen removal, anaerobic ammonia oxidation process without external carbon sources can treat such wastewater well.
Toh et al. showed that AnAOB had a certain tolerance to high concentrations of phenols and had the potential to treat coal chemical wastewater. Xue Zhanqiang et al. used short-course nitrification-anaerobic ammonia oxidation-full-process nitrification process to treat coking wastewater, and the effluent was NH under normal operating conditions4+-N concentration less than 15mg/L, NO2--N concentration was less than 1mg/L, and the effluent water quality was significantly better than that of traditional biological nitrogen removal process.
The Inner Mongolia Golden Coal Chemical Wastewater Treatment Project, which was successfully launched in 2018, is the first and only anoxic ammonia oxidation and self-improvement denitrification project of coal chemical wastewater in the world. The project treated water 4000m3/d, the total nitrogen influent was 1000mg/L, and the project was initially commissioned using the anaerobic ammonia oxidation granular sludge method for 1 year, but the final sludge disintegrated and failed to operate successfully. Subsequently, another team took over, using the "PN+Anammox+deep biochemistry" process, inoculating the self-domesticated and cultured filler mud, and finally the effluent TN was stably controlled below 50mg/L, reaching the third-level standard of the "Comprehensive Sewage Discharge Standard" (GB8978-1996), and the project has been running stably for 4 years.
2. Engineering application in semiconductor chip wastewater treatment
In the production process of semiconductor chips, in order to ensure the purity of crystalline silicon, the production process will be cleaned, fleece, etched with strong oxidizing solutions such as chromic acid, nitric acid, hydrofluoric acid, sulfuric acid, etc., and isopropyl alcohol, ethanol and heavy metals should be added as additives, resulting in high nitrogen content, high fluoride ion content, low pH, low biodegradability, heavy metals, etc. This kind of wastewater is difficult to treat and the treatment cost is very high, because the wastewater quality needs to meet the "Battery Industry Pollutant Emission Standard" (GB30484-2013), it is difficult to meet the standard of traditional treatment.
Daverey et al. used CANON process (an anaerobic ammonia oxidation process) to treat optoelectronic industrial wastewater, and the results showed that the ammonia nitrogen removal rate reached 98%, and the process had efficient nitrogen removal performance when the temperature fluctuation range was 17~37°C. A semiconductor factory in the Netherlands has established a "nitrification + Anammox + aeration and denitrification" process to treat the wastewater produced, the plant's wastewater treatment capacity is 550m3, and the wastewater contains 250-400mg/L ammonia. After many process improvements, the plant successfully controlled the ratio of nitrite to ammonia nitrogen, and the nitrogen removal efficiency in the anaerobic ammonia oxidation reactor reached 3.29kgN(m).3/d), and the soluble nitrogen in the effluent was controlled below 8mg/L.
3. Engineering application in fermentation wastewater treatment
The fermentation industry is a processing industry that uses starch from grain or agricultural and sideline products as the main raw material, mainly including winemaking, monosodium glutamate, pharmaceuticals and other industries. The water quality of fermentation wastewater varies greatly, mainly characterized by high wastewater temperature, high content of organic matter and suspended solids, easy to perish, generally non-toxic, but organic matter is mainly organic compounds and nitrogen-containing compounds, which can easily lead to eutrophication of water bodies. Due to the high concentration of ammonia nitrogen in fermentation wastewater, the nitrogen load concentration of traditional anaerobic-aerobic biological treatment is too large, and the operation control is difficult, making it difficult to meet the discharge standards. Anammox technology, which has low energy consumption and high load, has become a hot application technology for the treatment of this type of wastewater, and in recent years, engineering cases have been successfully applied.
Meihua Biotechnology Co., Ltd. in Tongliao City produces more than 18,900m of wastewater per day3In 2009, the plant built the world's largest autotrophic nitrogen removal reactor, with a design capacity of 11,000 kgN/d, and used an integrated CANON process to treat wastewater in the production of monosodium glutamate (monosodium glutamate), with a nitrogen removal efficiency of more than 95%.
Anqi Yeast Company in Binzhou City, Shandong Province used the Anammox process to replace the traditional AO technology to treat high ammonia nitrogen industrial wastewater, compared with the company's original AO process, the Anammox reactor achieved 2.0kgN/(m) on the basis of greatly saving land space3d) High ammonia nitrogen load is stable, which is also the largest sludge load that the anaerobic ammonia oxidation reactor can bear at present, and its industrial scale is much higher than that of traditional processes.
Hebei Yufeng Industrial Group is mainly engaged in the deep processing of grain products, and the types of wastewater produced are mainly VB12 wastewater and fermentation wastewater, and the plant adopts the Anammox process to replace the original AO process, and the water volume of the first phase of the renovation project is 5000m3/d, the water volume of the second phase of the renovation project is 30,000m3/d, using the Anammox process as the core to combine other processes, so that the wastewater denitrification efficiency of the plant reaches 85%, and the two phases of the project have been running stably so far, and the total nitrogen of the effluent from the carbon source has reached the first-class A emission standard.
03 Engineering application in aquaculture wastewater treatment
As of 2018, there are nearly 90,000 intensive large-scale aquaculture in the country, and the breeding wastewater mainly comes from feces, urine and flushing wastewater, and the sewage contains a large amount of nitrogen, phosphorus, organic matter, suspended solids and water quality fluctuates greatly, and there is also a large amount of organic nitrogen, which is difficult to treat. Using traditional methods not only consumes high energy, but also requires additional carbon sources, and the nitrogen removal effect is not ideal. Anammox technology is expected to be an alternative process for treating this type of wastewater.
Xun Fangfei et al. successfully started the anaerobic ammonia oxidation process with aerobic nitrification sludge as seed mud and diluted pig farm wastewater as influent water in ASBR, which lasted for 125 days, and the total nitrogen removal rate of the reactor effluent reached more than 90%. Huang Fangyu et al. studied the performance differences of autotrophic synchronous denitrification process in treating anaerobic digestate in pig farm wastewater at different temperatures, and found that the reactor had the best nitrogen removal performance at 30°C, with a total nitrogen removal rate of 73%. At present, Liuyang Wanfeng Medium-sized Pig Farm and Changsha County Xinguang'an Intersection Pig Farm adopt the improved "AO+Anammox+BAF" process, which has high sewage treatment efficiency and low operating cost after on-site commissioning, and is a new process worthy of promotion and practice.
3. Conclusions and prospects
In actual wastewater treatment, due to the large differences in the water quality of different types of wastewater, in order to ensure that the effluent meets the standards and consider the economy of engineering projects, the anammox process is often not an independent application in the actual project, and needs to be combined with other processes. The combined process is the most common and economical method in practical engineering, and is an important method to realize the transformation of sewage treatment from high energy consumption to low energy consumption.
However, the following issues are also at the core of the large-scale engineering application of anaerobic ammonia oxidation processes:
1. How to maintain the activity of AnAOB under low temperature or temperature change conditions to maintain efficient nitrogen removal performance;
2. How to shorten the generation cycle of AnAOB, make the strains proliferate rapidly, and make the reactor start up quickly;
3. How to effectively control the inhibitory factors of anaerobic ammonia oxidation bacteria in the sewage system, so that anaerobic ammonia oxidation becomes the dominant bacteria in the system.
