Status and development of ammonia nitrogen wastewater treatment technology
Guoqiang Xu#, Guangming Zeng#, Zhiwei Yin! , Jianfeng Zhang!
Department of Environmental Science and Engineering, Hunan University, Changsha, Hunan Province Hunan Nonferrous Metals Research Institute, Changsha, Hunan Province Abstract) A systematic overview of the current status of ammonia-nitrogen wastewater treatment technology and its application in industry is presented, and its development trend is discussed on the basis of analysis and evaluation.
Keywords) ammonia-nitrogen wastewater; biological nitrification; ion exchange; ammonia blow-off; folding-point chlorination
Central
Hunan Institute of Nonferrous Metals
/# Preface
In recent years, with the increasing expansion of the urban population and the continuous development of industry and agriculture, the water environment pollution accidents have occurred time and time again, which constitute a serious danger to people and animals. Many lakes and reservoirs cause eutrophication of water bodies due to the discharge of nitrogen and phosphorus, which seriously threatens the production and life of human beings and the ecological balance. Ammonia nitrogen is one of the main factors causing eutrophication of water bodies, in order to meet the public's requirements for environmental quality continues to improve, the state of nitrogen has formulated more and more stringent emission standards, research and development of economic and efficient nitrogen treatment technology has become the focus of the field of water pollution control engineering research and hot spots. This paper systematically describes the status and development of ammonia nitrogen wastewater treatment.
! Treatment technology status
Ammonia nitrogen exists in many industrial wastewater, especially iron and steel, fertilizer, inorganic chemicals, ferroalloys, glass manufacturing, meat processing and feed production processes, are discharged ammonia nitrogen wastewater, the concentration depends on the nature of the raw materials, process, water consumption and water reuse. For a given waste
water, the choice of technical solutions depends mainly on: (#) the nature of the water; (!) treatment effect; (,) economic efficiency. and the final disposal method of the treated effluent, etc.
Although there are many methods are effective in removing ammonia, such as physical methods of reverse osmosis, distillation, soil irrigation; chemical methods of ion exchange, ammonia blow-off, chemical precipitation, folding-point chlorination, electrodialysis, electrochemical treatment, catalytic cracking; biological methods of nitrification and algal aquaculture, but its application to the treatment of industrial wastewater, it must be easy to apply, treatment performance is stable, adapted to the quality of wastewater and more economic and other advantages, therefore, the current ammonia nitrogen treatment of practicality better technology for: (#) biological denitrification; (!) Ammonia blowing off, vapor extraction method; (,) folding point chlorination method; (%) ion exchange
method; # < , =.! $ # Biological denitrification
Biological denitrification usually includes biological nitrification and biological denitrification.
Biological nitrification is the process of oxidizing ammonia and nitrogen to nitrite and nitrate by the action of nitrite and nitrate bacteria under aerobic conditions. If the reaction is complete, the oxidation of ammonia into nitrate is completed in two stages: the beginning, under the action of nitrite bacteria to oxidize ammonia into nitrite, nitrite bacteria belong to the strong aerobic autotrophic bacteria, the use of ammonia as its only energy source, the equation (#) for this reaction equation. The second stage, under the action of nitrate bacteria, make nitrite into nitrate, nitrate bacteria are special autotrophic bacteria that use nitrite as their only energy source, equation (!) is the relational equation for this reaction. The whole nitrification reaction can be expressed by the total equation (,). From this relational equation it can be seen that to achieve complete nitrification, #$ & >? >? @1/, 1 A B 9 (in terms of nitrogen) would require %$ C >? B 9 of dissolved oxygen.
! Although some heterotrophic organisms are also capable of nitrification, the predominant organisms in nitrification are Nitrobacter spp. and Nitrobacter spp. The optimum E/ value for nitrification is '$ %, and when E/ is in the +$ ' < '$ " range, it is the optimum rate of "&F. The rate of nitrification continues to increase as the temperature is raised from ( G to ,& G, and a residual dissolved oxygen greater than #$ & >? B 9 is sufficient to sustain the reaction.
Denitrification is the process by which, under anoxic conditions, and
due to denitrifying bacteria. The process of reduction to. Its process of electron donor is a variety of carbon sources, if the methanol as a carbon source, for example, the reaction formula is:
For the nitrification reaction, the temperature on its impact than other biological processes to be greater, the general temperature should be maintained at the appropriate.
When treating wastewater containing ammonia nitrogen with biological method, the relative concentration of organic carbon is the main factor to be considered, and the maintenance of the optimal carbon to nitrogen ratio is one of the keys to the success of the biological treatment method. If the nature of the wastewater is not suitable for direct biological treatment, the use of physical and chemical methods or physical and chemical. If the nature of the wastewater is not suitable for direct biological treatment, it is more economical to use the physical-chemical method or the combined physical-chemical.
Biological denitrification can remove a variety of nitrogen-containing compounds, its treatment effect is stable, does not produce secondary pollution, and more economical, but has a large footprint, low efficiency at low temperatures, susceptible to the influence of toxic substances and operation and management of the more troublesome shortcomings.
Ammonia blowing off, steam extraction method
Blowing off, steam extraction method is used to remove dissolved gases in water and some volatile substances. The gas will be passed into the water, so that the gas and water are in full contact with each other, so that the dissolved gases in water and volatile solutes through the gas-liquid interface, to the gas phase transfer, so as to achieve the purpose of removing pollutants. Commonly used air or water vapor as a carrier gas, the former is called blowing off, the latter is called vapor extraction. Ammonia blowing off, stripping is a mass transfer process, that is, at high 0 *, so that the wastewater and air in close contact with the process of reducing the concentration of ammonia in wastewater, the driving force from the partial pressure of ammonia in the air and the wastewater ammonia concentration of equivalent equilibrium between the difference in partial pressure.
Blowing off the general use of blowing off the pool (also known as aeration pool) and blowing off the tower of two types of equipment, but blowing off the pool covers an area of large, but also easy to pollute the surrounding environment, so the blowing off of toxic gases are used in tower equipment. Vapor extraction is carried out in the tower equipment.
Natural blowing off method relies on the water surface and air natural contact with the removal of dissolved gases, it is used in the dissolved gases are extremely easy to desorption, water temperature is high, wind speed is greater, there is an open area and does not produce secondary pollution occasions. Such pools also have the role of water storage. Tower equipment in the packing blowing tower is mainly characterized by a certain height in the tower device packing layer, so that has a large surface area of the filling tower to achieve gas. Full contact between the water, conducive to gas. Water mass transfer process. Commonly used fillers are wood lattice plate, paper honeycomb, Lassie ring, polypropylene Bauer ring, polypropylene multi-surface hollow ball and so on. Wastewater is lifted to the top of the filled tower, and distributed to the entire surface of the packing, the water flows down through the packing, and the air flow in the opposite direction, wastewater before leaving the tower, the ammonia component is partially vaporized, but need to keep the 0* value of the incoming water unchanged. The partial pressure of ammonia in the air increases with the degree of ammonia removal and decreases with the increase in the air-to-water ratio, and there is a minimum air-to-water ratio for any degree of ammonia removal required to be achieved, the inlet concentration, 0*, and the tower temperature profile. Since the ammonia blow-off, vapor stripping at the same time play the role of a cooling tower, the gas-water ratio increases will simultaneously reduce the temperature of the outlet cold water, if 0* is lower than 1"/ 2, it will reduce the blow-off effect.
Ammonia blowing off, stripping process has a simple process, stable treatment effect, infrastructure costs and operating costs are low, but its disadvantage is the generation of scale, in large-scale ammonia blowing off, stripping tower, the generation of scale is a serious operational problem. If the generation of soft scale, you can install a water spray system; and if the generation of hard scale, regardless of spray or scraper can not eliminate this problem.
(/ ! Folding Point Chlorination
Folding Point Chlorination is a method of adding excess chlorine or sodium hypochlorite to completely oxidize ammonia in wastewater to $(. The reaction can be expressed as follows
$When chlorine is introduced into the wastewater, it reaches a point where the free chlorine content in the water is at its lowest and the ammonia concentration falls to zero. When )3( the flux exceeds that point, the free chlorine in the water increases. Therefore, this point is the breaking point. The actual amount of chlorine required for treatment depends on temperature, 0* value
and ammonia concentration. The effluent from the fold point chlorination process generally requires counterchlorination with activated carbon or with %( to remove residual chlorine from the water before discharge. The drop in 0* value caused by hydrogen ions produced during the counterchlorination is generally negligible, since the removal of 1 45 residual chlorine consumes only ( 45 or so
base (in )6)%! ). Activated carbon has the advantage of removing residual chlorine as well as other organic matter.
This method has the best effect, is not affected by the water temperature, easy to operate, investment is provincial, but for the treatment of high concentration of ammonia nitrogen wastewater running costs are very high.
(/ + Ion exchange method
Zeolite is a kind of silica-aluminate with strong selectivity to ammonia ions, generally used as an ion exchange resin to remove ammonia and nitrogen for the oblique hair zeolite, and its order of selection of ions in order.
This method has the advantages of investment, process simplicity, operation is more convenient, but for high concentrations of ammonia wastewater, will make the resin regeneration frequently and cause operational difficulties, and the regeneration fluid is still high concentrations of ammonia wastewater, need to be reprocessed. There are three types of ion exchange systems in common use: (1) fixed bed;
(() mixed bed; (!) Moving bed A ! B.
(/ +/ 1 Fixed bed
In this system, the deionization of the solution is a two-stage intermittent
process. The solution passes through a cationic resin bed where cations are exchanged with hydrogen ions to form an acid solution, which then passes through an anionic resin bed to remove the anions
. Exchange capacity will be exhausted, the resin in situ regeneration, often
downstream regeneration method, the operation of this method is reliable and convenient, but its chemical efficiency is
relatively low, the volume is larger, in connection with the resin dosage is large, and sometimes in order to adapt to the requirements of the continuous flow, but also need to have a reserve device, and thus the investment costs
higher.
#$ %$ # Mixed bed
Mixed bed systems use a one-step process to remove ions from solution. The solution
flows through a mixed bed where the anode and cathode resins are well mixed. Regeneration of a mixed bed
is somewhat more complicated than regeneration of two monogenetic beds because the two resins must be
separated before regeneration. Hydraulically the difference in specific
gravity of the two resins can be utilized to stratify them by hydraulic backwashing. While mixed beds are
chemically more efficient, they require a large amount of wash water. This is detrimental to water conservation,
in addition to the fact that when the exchange ions are collected as a recycled product, the recycled liquid is dilute and its
concentration is expensive.
#$ %$ ! Moving Bed
The moving bed system removes ions
from solution through a two-stage process. In both processes, while the water actually treated by the working fluid
is intermittent, its effect is continuous. First the solution and cationic
resin flow in opposite directions, the cationic resin pulsating through the vessel, fresh resin replenished from one end
and used resin drained from the other, completing the ion
exchange and resin regeneration in the process. The solution then swims through an anion moving bed similar to the one above
to complete the anion exchange.
#$ & Chemical precipitation' % (
Chemical precipitation has been used in wastewater
treatment since the #) century*) era, and with continued research into chemical precipitation, it has been found that chemical
precipitation is best accomplished using +! ,-% and . /-. The basic principle is to throw into the 0+%
1
wastewater . /# 1 and ,-%
! 2, which is then combined with 0+%
1 to form the insoluble complex
salt. /0+%,-%-*+#-3 abbreviated as .4,5 crystallized, and then by gravity
precipitation to make .4, separated from the wastewater. This prevents the introduction of other harmful ions into the wastewater, and . /- also plays a certain degree of
neutralization +1 role, saving the amount of alkali. After chemical precipitation, if
0+%
1 60 and,-%
! 2 residual concentrations are still high, it has been suggested
that the chemical precipitation be placed before biological treatment and that the levels of 0 and
, be further reduced after biological treatment. The product .4, is cylindrical crystal,
non-hygroscopic, dries quickly in air, absorbs little
toxic substances during the precipitation process, and does not absorb heavy metals and organic matter. In addition, .4, solubility
decreases with increasing 7+; the lower the temperature, the lower the .4, solubility also
decreases.
Chemical precipitation can treat wastewater with various concentrations of ammonia nitrogen. Its combination with
biological method to deal with high concentrations of ammonia wastewater, the aeration tank does not need to reach
nitrification stage, the aeration tank volume than the nitrification2 denitrification method can be reduced
about double.0+%
1 60 in the chemical precipitation method is removed by sedimentation, and nitrification
chemistry6 denitrification compared to the method, the energy consumption is greatly saved, and the reaction is not subject to the temperature < / p>
limitations, and the reaction is not a good idea. /p>
Limited by temperature, not interfered with by toxic substances, and the product, .4, can also be used as a
fertilizer, which reduces the cost of treatment to some extent. Therefore, .4, precipitation
precipitation method is a technically feasible and economically reasonable method, very promising development
scenario, but to be widely used in industrial wastewater treatment, it is necessary to solve the following two
problems: (") to find inexpensive and highly efficient precipitant; (#) to develop the value of .4,
as a fertilizer.
! Industrial applications
The choice of ammonia nitrogen treatment technology is closely related to ammonia nitrogen concentration. For
the low concentration of ammonia nitrogen wastewater treatment, the more applied methods are air blowing
dehydration method, ion exchange method, biological nitrification and denitrification method, etc., of which
for the treatment of inorganic ammonia nitrogen wastewater, the previous two methods are applied more
many; and for the treatment of organic ammonia nitrogen wastewater, biological nitrification
and denitrification methods are are mainly used.
! $ " Low concentration of ammonia nitrogen wastewater
! $ "$ " natural zeolite ion exchange method ' & (
Natural zeolite is a skeleton aluminum silicate, with ion
exchange characteristics, especially for 0+%
1 has a special selectivity; also has
good thermal stability and acid resistance, in high temperature or strong acid conditions,
lattice can still be used in the water.
The crystal lattice can still remain stable. Natural zeolite ion exchange method of ammonia nitrogen
wastewater treatment has a simple process, easy to operate, less investment and other characteristics, generally
speaking, for ammonia-alkali plant and some of the more advanced technology, management level
higher United Alkali Plant, part of the high concentration of ammonia-containing regeneration solution can be returned to the production
production system, which not only simplifies the entire sewage treatment This can not only simplify the entire sewage treatment process,
can also greatly reduce the cost of sewage treatment. However, ammonia and other
ammonia processing industry can not return to the process of high concentration of ammonia-containing regeneration fluid,
must be blown off the air (blowing off the gas by the +#8-% absorption after the exhaust),
distillation and other methods of treatment to make it recycled. Air blowing off low cost,
but subject to environmental constraints, while the distillation method is not affected by the environment, but the cost
higher, sulfuric acid absorption of ammonia in the blowing off gas ammonium sulfate can be used as a raw material for the production of composite
fertilizers, and distillation of ammonia recovered can be returned to
production system.
! $ "$ # Biological nitrogen removal
! $ "$ #$ " in coking wastewater
Ammonia nitrogen is one of the main pollutants in coking wastewater, and at present to
say that the basic process of biological nitrogen removal is the 4-4- - process' * (, coking wastewater
water contains a high concentration of 0+!60 and Organic matter, many of which have
strong biological toxicity, thus inhibiting nitrification and denitrification processes
. Therefore, the nitrifying bacteria should be domesticated, so that it gradually adapted to the high concentration of
coking wastewater environment, to prevent the wastewater organic matter and 0+! Inhibition of nitrifying bacteria
. Considering the removal of 0+!60 and 9-:, the anaerobic treatment
processing part can change the composition of organic matter in the wastewater
through the action of anaerobic hydrolysis and acidification flora to improve the biochemistry of wastewater, which is convenient for the good operation of the subsequent work
procedure. General nitrite bacteria than nitrate bacteria have a stronger ability to adapt to the environment
and the ability to tolerate poisons, prone to accumulation phenomenon, so
in general should be prevented from large fluctuations in water quality and a long time of impact. As %&!
' is also harmful to the environment, it can cause eutrophication of the water body
, so it is important to prevent %&!
' discharge for some control, can be
step denitrification treatment, so that %&!
' into %". For the treatment effect of the (-(-&
process, the reflux ratio, carbon to nitrogen ratio, dissolved oxygen, )* and temperature
degree are the main factors, which should depend on the quality of the wastewater and
determine.
! + #+"+ " in the application of refinery wastewater
Some domestic refinery wastewater treatment using grease trap - air flotation tank
-biofilter tower-activated sludge tank treatment, in fact, this process for
,&-,,%,. &-, petroleum, volatile phenols, suspended solids removal effect
better, but the degradation of ammonia nitrogen is very poor, resulting in the effluent water %*! /%
Can not meet the national emission standards. After the pilot study, the proposed & 0 &
and ( 0 & biochemical treatment process, the results show that both processes can
make the treated effluent %*! /% and other control indicators to meet national
discharge standards. & 0 & The process flow is as follows: refinery grease trap effluent - air flotation
tank - oxygen tank - primary sedimentation tank - nitrification tank - secondary sedimentation tank - treated wastewater
water (external discharge).
Water (discharged), the main biochemical system includes an oxygen tank and nitrification tank. The dominant bacteria in the primary
oxygen pool are heterotrophic bacteria, which degrade organic
matter through metabolic activities, while the dominant bacteria in the nitrification pool are nitrifying bacteria, which mainly reduce %*! /%
into %&!
'. ( 0 & The process flow is: refinery grease trap effluent - gas
floatation tank - regulating tank - anoxic tank - a sinking tank - nitrification tank - two sinking tank
-treated wastewater (discharged), of which part of the treated wastewater is returned to the
regulating tank and mixed with the air floatation effluent. The biochemical system mainly includes nitrification
pond and anoxic tank, nitrification tank in the dominant strain of nitrifying bacteria, mainly
ammoniacal nitrogen into nitrate nitrogen; anoxic tank in the dominant strain of denitrifying
bacteria, so that part of the nitrification tank reflux water and air floatation effluent mixing of nitrate
nitrogen is converted to %", and the degradation of organic matter. These two processes are relatively
operationally stable and impact resistant.
! + " High concentration of ammonia nitrogen wastewater
For higher concentration of ammonia nitrogen wastewater with a method of treatment, it is difficult
to meet the national emission standards, so for high concentration of ammonia nitrogen wastewater can be used
combined method of treatment in order to meet the requirements of the discharge.
! + "+ # Blow-off method 1 biological method application
Some pharmaceutical factories due to process reasons for some of the high concentration of ammonia
nitrogen wastewater, is not suitable for direct biological nitrification treatment, treatment is very difficult to
to meet the emission standards, but based on the various methods of comparative study, if the ammonia
nitrogen wastewater first blow-off, greatly reducing the % *! /% concentration, after mixing with other
wastewater into the biochemical treatment system for further treatment, the effluent water
quality will be greatly improved, but the wastewater ammonia nitrogen is usually ammonia ions and
free ammonia form of balanced each other,)* value of the neutral is mainly to
%*2
1 exist, alkaline is mainly in the form of %*! in alkaline condition. Blowing efficiency
is directly related to )* value and temperature, and should be tested to determine the best blowing
delivery conditions to achieve the best results.
! + "+ " Blow-off method 1 folding point chlorination application
For a material plant %*2,3 industrial wastewater research comparison,
a single blow-off method of treatment can not meet the requirements of the discharge, the use of closed-circuit blowing
desalination of acid absorption recovery %*2,3 and folding point chlorination method 4 $ 5 joint use
use, both to achieve a better treatment effect, but also to recover the Liquid or solid
Amines chloride can be returned to the process or exported, greatly reducing the cost of treatment
Costs. The chemical reaction formula of the folding point chlorination method is as follows:
%*2
1 1 *&,3*%*",3 (monochloramine) 1 *"& 1 *1
%*",3 1 *&,3*%*,3"
(dichloramine) 1 *"&
%*,3" 1 *&, 3*%,3!6 trichloramine). 3*%,3! 6 trichloramine or nitrogen trichloride)1 *"&
Monochloramine is further oxidized to nitrogen:
"%*",3 1 *&,3*%" 1 *"& 1 ! *1 1 ! ,3 '
Dichloramine produces nitrate by the following reaction:
%*,3" 1 *"&*%*(&*)1 *1 1 ",3 '
%*(&*),3 1"*&,3*%&!
' 1 ! ,3 ' 1 2*1
Trichloramine is in a stable state in water. The blown nitrogen-containing gas
Body is absorbed in a two-stage cycle with a hydrochloric acid solution, and the reaction is:
%*! 1 *,3*%*2,3
This method not only recovers valuable substances, but also eliminates secondary pollution,
The process is an ideal method for removing ammonia and nitrogen.
In summary, the main methods of ammonia-nitrogen wastewater treatment technology are biological
material denitrogenation and blow-off method and their joint application, the authors believe that: ammonia
nitrogen wastewater treatment technology development focuses on the improvement of the existing process conditions, lower
low cost, while developing new treatment methods. It has been pointed out that 4 7 5, given
in consideration of the possible carbon source insufficiency
in the biological denitrification denitrification process and the possible accumulation of %&"
' in the nitrification process, if artificially
guided so that %*! to %*! %&"
' %" denitrification
pathway, that is, %&"
' as the end point of the nitrification reaction, then the non-coagulation
can reduce the energy consumption, and if you need to add an additional source of carbon, you can also reduce the denitrification
on the amount of organic carbon source The requirement for the number of organic carbon sources. Of course, biological denitrification is a very
complex biochemical process, it is not easy to control, for %&"
' as the nitrification
endpoint of the denitrification process to be further studied. In addition, in the aeration tank
the use of suspended filler 4 #8 5 is also now the direction of research and development, but also less
applied to industrial wastewater, its density is close to water, the use of
added directly to the aeration tank, in the aeration of the suspension in the water and the uniform whole pool
fluidization, so that the solid, liquid, gas three-phase full contact, the pollutants are very quickly degraded
decomposition of nitrogen.
Decomposition, suspended packing biofilm ( 0 & process can improve the impact resistance and only
need to reflux the nitrification water in the secondary sedimentation tank, without sludge reflux, power consumption
low, easy to operate and manage.
2 Conclusion
The treatment of ammonia wastewater, so far, has not found a general
use of effective methods. At present, the correct choice of treatment technology for wastewater treatment, whether by physical-chemical, biological or combined physical-chemicalT biological methods,
should be based on a combination of the following:
1 Providing the opportunity to improve the production technology and to change the raw materials used in production in order to reduce the amount of wastewater and to lower the concentration of ammonia-nitrogen;
2 Combined with an optimized water-use plan, good plant management, and the possible by-products recovery;
2 Combined with the optimized water-use plan, good plant management, and possible byproducts recovery;
3 substitution of other methods, including physical and biological methods;
4 the ability to treat ammonia nitrogen in wastewater economically.