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Nitrogen, phosphorus and other nutrients are an important factor in maintaining the growth and reproduction of microorganisms, if you can not meet the needs of microorganisms for nutrient elements (N, P), microorganisms can not grow and reproduce normally, then the purification function of activated sludge on wastewater will also disappear with the end of microbial life, therefore, for industrial wastewater with a single component, nitrogen and phosphorus nutrients are relatively lacking, the timely and appropriate addition of nitrogen and phosphorus nutrients is particularly important.
1, N, P the necessity of activated sludge
N and P are an important part of the microorganism, the main body of activated sludge, so the basis for understanding microbial nutrition needs is to understand the chemical composition of cells. Chemical analysis of the cells showed that microbial cells contained a lot of water (about 80%), the rest were dry matter (about 20%), and dry matter consisted of organic matter (about 90%) and inorganic matter (about 10%). Carbon occupies the first place in organic matter (about 53.1%), nitrogen ranks third (about 12.4%); phosphorus ranks first among inorganic substances (50%), and the rest are sulfur, sodium, etc. In general, microbial cells can be represented as C60H87O23N12P, which shows that N and P are essential for microorganisms.
On the other hand, most of the wastewater components are complex and can generally provide various nutrients required by microorganisms, but for those industrial wastewater with a relatively single composition, the relative content of N and P in wastewater is very small. According to the law of minimum factors - microbial growth is limited by the lowest relative content rather than the least absolute content of nutrients - it can be seen that when treating industrial wastewater by biological method, N and P are prone to become limiting factors. Therefore, when treating industrial sewage with a single component by the activated sludge method, the addition of nitrogen and phosphorus is necessary.
2. The effect of N and P dosage on activated sludge
Nutrients (N, P) are very important in the cultivation of activated sludge bacteria and normal operation stages, so the amount of nitrogen and phosphorus has an impact on the industrial sewage with a single component of the activated sludge method:
1. Insufficient amount of N and P dosing
In the process of treating sewage by activated sludge method, the impact of insufficient nitrogen and phosphorus on sewage treatment is mainly manifested in the following aspects:
(1) Poor flocculation of activated sludge
Activated sludge in the decomposition of organic matter needs to cooperate with the proportion of nitrogen, phosphorus nutrients added, when the nitrogen, phosphorus is insufficient, can not produce a sufficient amount of microbial decomposition of organic matter. In the state of nutrient deficiency, the active sludge synthesis process can not get a sufficient amount of nitrogen and phosphorus, and the flocculation will then deteriorate.
(2) Poor sedimentation of activated sludge
Due to the poor flocculation of activated sludge, the excessive amount of fine activated sludge flocs can not play a better sedimentation, filamentous bacteria swelling is a manifestation of insufficient nitrogen and phosphorus nutrients, similarly, due to the failure to synthesize enough microorganisms to cope with the relatively high concentration of organic matter in the inflow, the activated sludge is in a high load state, in the state of high sludge load, the occurrence of poor sedimentation of activated sludge has become an inevitable phenomenon. Activated sludge will disintegrate or flocculation poorly, and the resulting liquid surface scum and foam phenomenon will follow.
(3) The efficiency of activated sludge treatment decreased
The decline in processing efficiency is also caused by insufficient nutrients when synthesizing bacterial bodies, and cannot be synthesized effectively and in sufficient quantities. At the same time, the loose structure of activated sludge and the loss due to poor settling properties are another reason for the poor efficiency of activated sludge treatment.
(4) The discharge belt of the second sedimentation pond is brownish yellow
There are many reasons why the discharge water of the second sedimentation pond is brownish yellow, among which the failure of the synthesis and metabolism of the activated sludge due to the lack of sufficient supplementation of nitrogen and phosphorus nutrients in the activated sludge will occur, and the disintegration of the activated sludge will occur when the dissolved activated sludge is dissolved into the water body.
(5) It is difficult to increase the concentration of activated sludge
In the early stage of the activated sludge treatment of sewage, if the nitrogen and phosphorus nutrients are insufficiently added to the culture and domestication stage of the activated sludge, it will seriously affect the increase in the concentration of the activated sludge. The performance is: the concentration of activated sludge is low, and the film is not successful after a long period of time. In the bacteriotic stage of activated sludge, the requirements for the dosing of nutrient elements (N, P) are the same as those of normal culture, which need to be strictly mastered, but relative to the amount of nutrients added during normal operation, it is required to be slightly higher, basically higher than about 15% of the normal value, the purpose is also to provide the necessary peripheral conditions for the rapid initiation of the activated sludge, and also to provide the necessary guarantee for the rapid proliferation of the concentration of activated sludge in the process of cultivating the bacterium of the activated sludge.
2.N, P dosing too much
The excessive addition of nitrogen and phosphorus nutrients is also unfavorable to the sedimentation of activated sludge, and its adverse effects on the system in the process of treating sewage by activated sludge method are mainly manifested in the following aspects:
(1) The second sedimentation pond grows moss or algae
Moss, like algae, reproduces using photosynthesis and requires nutrients (N, P) as necessary elements. When the nutrient is overdosed, it is very easy to cause the growth of moss in the outlet of the second sedimentation tank. Traces of algae can also be found when the water quality treatment is better. The reason is that due to the excessive amount of nitrogen and phosphorus put into the biochemical system, the activated sludge cannot be fully utilized, and there will be a relative eutrophication phenomenon. This also reduces the treatment efficiency of biological filters, usually reducing the removal efficiency by 10%, because the growth of algae does not have the ability to degrade organic matter in wastewater, and only requires nutrients and sunlight as the energy needed for growth and reproduction.
(2) Floating mud appears in the second sinking pool
There are many reasons for the floating of sludge in the second sedimentation tank, but due to the floating of activated sludge caused by excessive addition of nitrogen and phosphorus nutrients, most of them are the presence of excess nitrogen in the activated sludge, which causes the reactive sludge to be denitrified in an anaerobic state. The gas produced during the denitrification process floats up with the activated sludge floc, and its floating state is often snowflake-like.
(3) Changes in the biological phase in the activated sludge system
Excessive addition of nitrogen and phosphorus nutrients can also lead to changes in the biological phase of activated sludge systems. These changes can be confirmed from the observation of protozoan species, mainly in the number of reptile ciliates, such as the change of activated sludge protozoa such as the substitution of bellworms for bell worms. From this aspect, it can be found that too much nitrogen and phosphorus nutrients are added, which has little impact on microorganisms in activated sludge in a certain period of time, but long-term over-addition, the microbial population will change, and the effect of treatment will also have a more serious impact.
(4) The nitrogen and phosphorus content of the effluent is too high
The amount of microorganisms in the activated sludge is a certain amount, and the amount of nutrients (N, P) required for microbial growth is also certain. If the amount of nutrients (N, P) added is too much, there will be a part of the N and P unused, they will be discharged with the treated sewage together with the second sedimentation tank, resulting in the N, P content of the second sedimentation water is too high, will make the treatment effect of the sewage worse, to a certain extent will aggravate the eutrophication of the water body.
3, N, P the calculation of the amount of addition
The determination of the amount of nitrogen and phosphorus nutrients is the premise of reasonable nutrient addition. When confirming the amount of nitrogen and phosphorus nutrients added in the aerobic process, the following empirical ratio is usually used to calculate, that is, organic matter: nitrogen: phosphorus = 100: 5: 1. In the proportional formula, organics can be expressed in C, nitrogen can be expressed in N, phosphorus is expressed in P, and the expression can be changed to: C:N:P=100:5:1. This ratio can be understood as the consumption of 5 g of nitrogen and 1 g of phosphorus for every 100 g of organic matter decomposed, so as to ensure that the need for nutrients when the activated sludge decomposes organic matter is balanced. In the actual engineering applications are often found that the N, P addition calculated by theory is often larger than the actual demand, the main reason for the analysis is: inlet sewage, wastewater or more or less contain nutrient elements, if you ignore the content of this part of the nutrient elements, according to the theoretical amount of addition, there will be discharge of water nitrogen, phosphorus exceeded the standard. Therefore, it is necessary to pay enough attention to the nitrogen and phosphorus values in the inlet sewage and wastewater, calculate the nitrogen and phosphorus content of this part, and deduct it from the theoretical calculation value, so that the nitrogen and phosphorus content added will not be excessive.
1. Calculation method of nitrogen source addition
At present, there is less controversy about N, generally recognized as TKN, in addition to specific industrial sewage, the actual inlet water organic nitrogen is very small, so the addition is mostly calculated according to ammonia nitrogen addition, and the amount of N source is:
N=V*G/Y
where:
N—N source dosing
V—Amount of water in the pond
G—The difference of N needs to be supplemented
Y—The amount of N converted to the N source
1) Urea as an added N source (CH4N2O molecular weight: 60.06 g/mol)
Urea contains 46.7% N, if you need to add 1g N source, you need to add urea Y = 1/ 0.467 = 2.14 g
2) Ammonium sulfate as an added N source ((NH4)2· SO4 molecular weight: 132.14)
Ammonium sulfate contains 21.2% N, if you need to add 1g N source, you need to add ammonium sulfate Y = 1 / 0.212 = 4.72 g
3) Ammonium nitrate as an added N source (NH4NO3 molecular weight 80g/mol)
Ammonium nitrate contains 35% N, if you need to add 1g N source, you need to add ammonium nitrate Y = 1 / 0.35 = 2.86 g
2. Calculation of the amount of phosphate added
Ordinary sludge culture is generally calculated by CNP ratio 100:5:1, the current TP is not controversial generally recognized as phosphate, in addition to specific organophosphorus and phosphorus industrial sewage, the actual addition of phosphate calculation, P source dosage is:
P=V*G/Z
P—P source dosing
The amount of phosphate converted into z—P source
1) Sodium dihydrogen phosphate as an added P source (Na2HPO4.7H2O, molecular weight 268.07 g/mol)
Sodium dihydrogen phosphate contains 11.57% P, if you need to add 1g P source, you need to add sodium dihydrogen phosphate Z=1/ 0.1157=8.64 g
2) Potassium dihydrogen phosphate as a P source (K2HPO4-3H2O, molecular weight 228.22
g/mol）
Potassium dihydrogen phosphate contains 13.6% P, if you need to add 1 g P source, you need to add potassium dihydrogen phosphate Z = 1 / 0.136 = 7.35 g
3) Phosphate fertilizer supercalcium superphosphate as a P source
The available phosphorus in phosphate fertilizer is soluble phosphorus pentoxide (P₂O5, molecular weight 141.94g/mol)
The available phosphorus content in phosphate fertilizer is 12%, the P content of P₂O5 is 43.66%, if 1g P source is added, phosphate fertilizer Z= 1/ (0.12×0.4366) = 19.09 g