with the development of social economy, the contradiction between supply and demand of water resources is becoming more and more serious. the reuse of wastewater after treatment has become an urgent problem to be solved. the existing municipal wastewater treatment plants in china mainly aim at the removal of carbon source pollutants, mainly bod5. the removal rate of nitrogen and phosphorus is very low, and nitrogen and phosphorus are the main nutrients leading to eutrophication of water body. this paper summarizes the mechanism of biological denitrification and phosphorus removal, analyses the research status of biological denitrification and phosphorus removal technology, introduces the sustainable sewage treatment technology and carbon neutralization operation technology, hoping to bring you thinking and help.
i. theory and technology of traditional biological denitrification and phosphorus removal
1. principle of traditional biological denitrification
sewage is treated by secondary biochemical treatment, while removing the carbon source pollutants dominated by bod5 under aerobic conditions, deamination is accomplished with the participation of ammoniating bacteria, nitrification and nitrification are accomplished with the participation of nitrifying and nitrifying bacteria, and denitrification is accomplished with the participation of denitrifying bacteria under anaerobic or anoxic conditions.
2. principle of traditional biological phosphorus removal
under anaerobic conditions, atp in p-accumulating bacteria hydrolyzes and releases h3po4 and energy to form adp; under aerobic conditions, p-accumulating bacteria breathe aerobically and continuously release energy. under the catalysis of membrane permease, p-accumulating bacteria absorb h3po4 from the outside by energy and active transportation. some of them combine with adp to form atp, while others synthesize polyphosphate (phb) and store in cells. excessive phosphorus uptake is now occurring. phosphorus is removed from the system by eliminating excess sludge or enriching anaerobic supernatant by side-stream. in the process of biological phosphorus removal, carbon source microorganisms are also decomposed.
3. common processes and upgrading
representational common processes are a/o process, a2/o process, uct process, sbr process, bardenpho process, biological turntable process, etc. these processes are through adjusting working conditions, using the dominant bacteria in each stage, eliminating the interference among the influencing factors as far as possible, in order to adapt to the growth conditions of bacteria in each stage and achieve the effect of water treatment. in recent years, with the deepening of research, some improvements have been made to the commonly used process. at present, the most widely used and the difficulty of upgrading and transformation of water plants is the sectional water intake process.
compared with traditional a/o process, a2/o process and uct process, segmented water intake process can make full use of carbon source and maintain better aerobic and anaerobic (or anoxic) environment. it has the advantages of high nitrogen and phosphorus removal efficiency, no need of internal circulation, high sludge concentration and long sludge age. segmented water intake process is suitable for upgrading a/o process, a2/o process, uct process, etc. by separating biochemical reaction pool and making the feed water into each section of reaction pool in a certain proportion, the problem of insufficient carbon source and excessive excess sludge in current sewage treatment plants can be solved by making full use of carbon source. although the subsection water intake process has a good effect on improving the quality of effluent, it can not improve the treatment capacity. when the water plant is under overload operation, the subsection water intake transformation can not achieve good treatment effect.
ii. new theory and technology of biological nitrogen and phosphorus removal
in recent years, scientific research has found that the biological nitrogen and phosphorus removal process has exceeded the traditional biological nitrogen and phosphorus removal theory. based on this, some new denitrification and phosphorus removal processes have been proposed, such as short-cut nitrification and denitrification process, synchronous nitrification and denitrification process, anaerobic ammonia oxidation process, denitrification and phosphorus removal process.
1. short-cut nitrification and denitrification process
the traditional biological denitrification theory is the whole process of nitrification and denitrification, i.e. using no3 - as the electron acceptor of denitrification process, while short-cut nitrification and denitrification uses no2 - as the electron acceptor of denitrification process.
short-cut nitrification and denitrification can save 25% of aeration, 40% of organic carbon and shorten reaction time compared with full-course nitrification and denitrification. therefore, it has practical engineering application value to realize and maintain short-cut nitrification and denitrification. the key to realize short-cut nitrification and denitrification is the predominant proliferation of ammonia-oxidizing bacteria relative to nitrite-oxidizing bacteria, i.e. the accumulation of ammonia-oxidizing bacteria. the main influencing factors of shortcut nitrification and denitrification are temperature, ph, dissolved oxygen (do), free ammonia (fa), sludge age (srt), organic matter concentration and so on.
sharon process is a typical short-cut nitrification and denitrification process, which uses high temperature (30-36 c) to inhibit the proliferation of nitrite oxidizing bacteria and realize the accumulation of ammonia oxidizing bacteria, so as to control the nitrification reaction to maintain in the no2-stage, followed by denitrification.
2. simultaneous nitrification and denitrification process
synchronized nitrification and denitrification is a process in which nitrification and denitrification are carried out in the same reactor, and total nitrogen can be removed without obvious anoxic time or anoxic area. using immobilized microbial technology, the microbial carrier embedded with nitrifying bacteria was put into the aerobic tank. the removal rate of ammonia nitrogen was over 90%, and the treatment effect was obviously improved. nitrobacteria carriers have good application prospects because they are easy to add, strong shock load resistance, convenient operation and management, low cost and good treatment effect.
3. anaerobic ammonia oxidation process
anaerobic ammonia oxidation process refers to the process of converting nh3 into n2 under anaerobic conditions, using no2 - as electron acceptor, without the intervention of organic carbon source and o2. from the engineering point of view, anaerobic ammonia oxidation process has obvious advantages over traditional biological denitrification process. this process can get rid of the constraints of traditional electronic donors (organic carbon sources), and can save oxygen demand in nitrification process, thus reducing excess sludge and saving energy. in addition, enriching anaerobic ammonia oxidizing bacteria in the form of granular sludge in the reactor can make full use of the vertical space and reduce the occupation of land. of course, the reactor form of anaerobic ammonia oxidation process can be not only granular sludge form, but also sbr, biological turntable, mobile bed and so on.
although the technology of anaerobic ammonia oxidation has many advantages, its engineering application is limited by the very low growth rate of anaerobic ammonia oxidation bacteria (generation time is about 10 days), and the start-up time of the reactor is very long. at present, the process is mainly aimed at wastewater with high nh4 , low cod and a certain residual temperature, such as anaerobic digestion liquid and landfill leachate.
4. denitrifying phosphorus removal process
the mechanism of denitrifying phosphorus removal is similar to that of traditional biological phosphorus removal. the reaction mainly depends on denitrifying phosphorus removal bacteria. these microorganisms absorb phosphorus with oxygen or no3 - as electron acceptor and store it in cells in the form of polyphosphate. at the same time, no3 - is converted into n2. using denitrifying phosphorus removal bacteria to achieve biological phosphorus removal, nitrogen and phosphorus removal rate is high, while reducing the excess sludge, reducing the demand for organic carbon sources.
sustainable biological denitrification, phosphorus removal and carbon neutralization operation
traditional wastewater treatment theory regards water as the main product, and other substances are discharged in the form of waste gas and sludge. there are some problems such as energy waste and resource waste. at the same time, traditional water treatment technology will occupy a large amount of land. the essence of carbon neutralization and operation of sewage treatment is to realize the self-sufficiency of energy needed in the treatment process, so as to solve the problems of "energy dissipation" and "pollution transfer". in this process, not only the "open source" of energy, but also the "throttling" of treatment process should be considered. sustainability and carbon neutralization of sewage treatment are the general trend.
1. sustainable biological nitrogen and phosphorus removal
the technical basis of sustainable biological nitrogen and phosphorus removal process is denitrification and phosphorus removal technology and anaerobic ammonia oxidation technology. using facultative denitrifying bacteria, denitrifying and biological phosphorus removal were combined to reduce the consumption of organic carbon source and oxygen. compared with traditional aerobic phosphorus removal bacteria, the facultative denitrifying bacteria could save 50% of organic carbon source and 30% of oxygen, and reduce 50% of excess sludge. anaerobic ammonia oxidizing bacteria directly convert nh4 to n2 by using no2 - as electron acceptor. this process does not need organic carbon source and o2. compared with the traditional whole nitrification and denitrification process, the consumption of organic carbon source and o2 is reduced to the greatest extent. by saving organic carbon sources in the process of biological nitrogen and phosphorus removal, it creates conditions for methanation of residual cod without traditional oxidation stabilization (to co2) and energy generation; at the same time, the reduction of consumption of oxygen reduces aeration, indirectly reduces co2 emissions from burning fossil energy to provide energy for sewage treatment.
based on the above technology foundation, a sustainable biological nitrogen and phosphorus removal process is proposed. the process is based on a/b and combines bcfs@process and can on process, which highlights the realization of sustainable goals such as cod methanation (energy), phosphate recovery and treatment water reuse. the influent is pretreated by grille and sediment and enters the a section of ab process. the bacteria increase rapidly with a short sludge age. 70%-80% cod in raw water is called bacterial cells. after separation from the a section sedimentation tank, the supernatant enters the bcfs @ process for nitrogen and phosphorus removal. the high phosphorus content sludge discharged from the bcfs @ process enters the sludge digestion tank together with the sludge discharged from a section, and produces ch4, high phosphorus and high nh4 . sludge digestion liquor, digestion liquor by adding magnesium to form phosphoric acid according to magnesium compound precipitation and recovery of phosphorus; phosphorus recovery digestion liquor using canon process to remove high concentration of nh4 ; canon process effluent and bcfs @ process effluent mixed after discharge. the domestic sewage treated by this process can reach the standard of reclaimed water reuse only after simple advanced treatment.
compared with the traditional biological treatment process, the sustainable biological nitrogen and phosphorus removal process reduces the oxygen consumption by about 45%, saves about 70% of organic carbon sources, reduces 25% of excess sludge, reduces 18% of co2 emissions, and produces 0.28 ka of ch4 per kg of cod and recovers 49% of phosphorus.
2. carbon neutralization and operation
the results show that, due to the low cod in the influent of municipal wastewater treatment plants in china, the ch4 (energy) recovered from anaerobic digestion of excess sludge can only provide 50% of the energy consumption of wastewater treatment plants, and indirectly reduce the co2 emissions by 50%. this restriction determines that carbon neutralization and operation of sewage treatment in china must take the road of "open source" and "throttling". in addition to research and development of new sewage treatment theory and technology, non-traditional energy sources such as water source heat pump, air source heat pump, wind energy, solar energy and microbial fuel cell are also needed.
source: polaris environmental protection network
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