For industrial wastewater with a single component and a lack of nitrogen and phosphorus nutrients, the timely and appropriate addition of nitrogen and phosphorus nutrients is particularly important.
Nitrogen, phosphorus and other nutrients are important factors in maintaining the growth and reproduction of microorganisms. If the needs of microorganisms for nutrients (N, P) cannot be met, the microorganisms cannot grow and reproduce normally, and the purification function of activated sludge for wastewater will also disappear with the end of the life of the microorganisms. Therefore, for industrial wastewater with a single component and a lack of nitrogen and phosphorus nutrients, the timely and appropriate addition of nitrogen and phosphorus nutrients is particularly important.
1. The necessity of N and P for activated sludge
N and P are important components of the main body of activated sludge-microorganisms. Therefore, the basis for understanding the nutritional needs of microorganisms is to understand the chemical composition of cells. Chemical analysis of cells shows that microbial cells contain a large amount of water (about 80%), and the rest is dry matter (about 20%), and the dry matter is composed of organic matter (about 90%) and inorganic matter (about 10%). Among organic substances, carbon ranks first (about 53.1%), and nitrogen ranks third (about 12.4%); among inorganic substances, phosphorus ranks first (50%), and the rest are sulfur, sodium, etc. Usually, microbial cells can be expressed as C60H87O23N12P, which shows that N and P are indispensable to microorganisms.
On the other hand, most wastewater components are complex and generally provide various nutrients required by microorganisms, but for those industrial wastewaters with relatively simple components, the relative content of N and P in wastewater is very small. According to the law of minimum factor – microbial growth is limited by the nutrient with the lowest relative content rather than the lowest absolute content – it can be seen that when using biological methods to treat industrial wastewater, N and P are likely to become limiting factors. Therefore, when using activated sludge method to treat industrial wastewater with simple components, the addition of nitrogen and phosphorus is necessary.
2. Effect of N and P dosage on activated sludge
Nutrient elements (N and P) are very important in the activated sludge culture and normal operation stages. Therefore, the effect of nitrogen and phosphorus dosage on the treatment of industrial wastewater with a single component by activated sludge method is as follows:
1. Insufficient N and P dosage
During the activated sludge method, the effect of insufficient nitrogen and phosphorus dosage on wastewater treatment is mainly manifested in the following aspects:
(1) Poor flocculation of activated sludge
Activated sludge needs to add nitrogen and phosphorus nutrients in a proportion when decomposing organic matter. When nitrogen and phosphorus are insufficient, it cannot produce enough microorganisms to decompose organic matter. In the absence of nutrients, nitrogen and phosphorus cannot be matched in sufficient quantities during the activated sludge synthesis process, and the flocculation property immediately deteriorates.
(2) Poor settling of activated sludge
Due to the poor flocculation of activated sludge, excessive fine activated sludge flocs cannot play a good settling performance. The swelling of filamentous bacteria is a manifestation of insufficient nitrogen and phosphorus nutrient elements. Similarly, due to the inability 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. Under the condition of high sludge load, the poor settling of activated sludge is inevitable. The activated sludge will disintegrate or flocculate poorly, resulting in scum and foam on the liquid surface.
(3) Decreased efficiency of activated sludge treatment
The decline in treatment efficiency is also caused by the lack of nutrients when synthesizing bacterial bodies, which cannot be effectively and sufficiently synthesized. At the same time, the loose structure of activated sludge and loss due to poor settling performance are another reason for the poor efficiency of activated sludge treatment.
(4) The effluent from the secondary sedimentation tank is brownish yellow
There are many reasons why the effluent from the secondary sedimentation tank is brownish yellow. Among them, the activated sludge lacks sufficient nitrogen and phosphorus nutrients, which leads to the failure of activated sludge synthesis and metabolism, resulting in the disintegration of activated sludge. When the disintegrated activated sludge dissolves into the water body, the abnormality of the effluent from the secondary sedimentation tank is found.
(5) It is difficult to increase the concentration of activated sludge
In the early stage of activated sludge treatment of sewage, if the nitrogen and phosphorus nutrients are not added enough during the cultivation and acclimatization stage of activated sludge, it will seriously affect the increase of activated sludge concentration. It manifests as: the concentration of activated sludge is low, and biofilm formation fails after a long time. During the activated sludge cultivation stage, the requirements for the addition of nutrients (N, P) are the same as those for normal cultivation, and need to be strictly controlled. However, compared with the amount of nutrients added during normal operation, it needs to be slightly higher, basically about 15% higher than the normal value. The purpose is to provide the necessary peripheral conditions for the successful rapid start-up of activated sludge cultivation, and also to provide the necessary guarantee for the rapid proliferation of activated sludge concentration during the activated sludge cultivation process.
2. Excessive addition of N and P
Excessive addition of nitrogen and phosphorus nutrients is also detrimental to the sedimentation of activated sludge. Its adverse effects on the system during the activated sludge method of treating sewage are mainly manifested in the following aspects:
(1) Growth of moss or algae in the secondary sedimentation tank
Like algae, moss reproduces by photosynthesis and requires nutrients (N, P) as necessary elements. When the nutrient agent is added in excess, it is very easy to cause moss to grow at the outlet weir of the secondary sedimentation tank. Traces of algae can also be found when the water quality is well treated. The reason is that due to excessive nitrogen and phosphorus input into the biochemical system, the activated sludge cannot be fully utilized, and relative eutrophication will occur. This will also reduce the treatment efficiency of the biological filter, usually reducing the removal efficiency by 10%. The reason is that the algae that grow do not have the ability to degrade organic matter in the wastewater, and they only need nutrients and sunlight as the energy required for growth and reproduction.
(2) Floating sludge appears in the secondary sedimentation tank
There are many reasons for the floating of sludge in the secondary sedimentation tank, but the floating of activated sludge caused by excessive addition of nitrogen and phosphorus nutrients is mostly due to the excessive nitrogen in the activated sludge, which causes the denitrification of activated sludge under anaerobic conditions. The gas generated during the denitrification process carries the activated sludge flocs to float, and its floating state is often in the form of snowflakes.
(3) Changes in the biological phase in the activated sludge system
Excessive addition of nitrogen and phosphorus nutrients will also lead to changes in the biological phase in the activated sludge system. These changes can be confirmed by observing the protozoan species, mainly manifested in the changes in the number of reptile ciliates, such as: the dominant species of ciliates instead of bell-shaped worms and other changes in the activated sludge protozoa. From this aspect, it can be found that excessive addition of nitrogen and phosphorus nutrients will have little effect on the microorganisms in the activated sludge in a certain period of time, but long-term excessive addition will change the microbial population and have a relatively serious impact on the treatment effect.
(4) Excessive nitrogen and phosphorus content in effluent
The amount of microorganisms in the activated sludge is certain, 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, some of the N and P will not be used. They will be discharged from the secondary sedimentation tank together with the treated sewage, resulting in excessively high N and P content in the secondary sedimentation effluent, which will make the sewage treatment effect worse and aggravate the eutrophication of the water body to a certain extent.
III. Calculation of N and P dosage
Determining the amount of nitrogen and phosphorus nutrients to be added is the premise for reasonable addition of nutrients. When confirming the amount of nitrogen and phosphorus nutrients to be added during the aerobic process, the following empirical ratio is usually used for calculation, that is, organic matter: nitrogen: phosphorus = 100:5:1. In the ratio formula, organic matter can be represented by C, nitrogen can be represented by N, and phosphorus can be represented by P. The expression can be transformed into: C:N:P=100:5:1. This ratio can be understood as 5g of nitrogen and 1g of phosphorus are required for every 100g of organic matter decomposed to ensure that the demand for nutrients when the activated sludge decomposes organic matter is balanced.
In actual engineering applications, it is often found that the amount of N and P added by theoretical calculation is often larger than the actual demand. The main reason for this is that the influent sewage and wastewater still contain more or less nutrients. If the content of these nutrients is ignored and added according to the theoretical amount, the nitrogen and phosphorus in the discharged water will exceed the standard. Therefore, it is necessary to pay enough attention to the nitrogen and phosphorus values in the influent 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
Currently, there is relatively little controversy about N, and it is generally recognized as TKN. Except for specific industrial sewage, there is very little organic nitrogen in the actual influent, so the addition is mostly calculated based on ammonia nitrogen addition. The amount of N source added is: N=V*G/Y.
Where:
N—N source addition
V—water volume in the pool
G—difference in N to be supplemented
Y—N amount converted from N source
(1) Urea as an added N source (CH4N2O molecular weight: 60.06 g/mol)
Urea contains 46.7% N. If 1g of N source needs to be added, urea Y=1/0.467=2.14 g needs to be added. (2) Ammonium sulfate as a nitrogen source ((NH4)2·SO4 molecular weight: 132.14)
Ammonium sulfate contains 21.2% nitrogen. If 1g of nitrogen source is needed, then ammonium sulfate Y=1/0.212=4.72 g needs to be added.
(3) Ammonium nitrate as a nitrogen source (NH4NO3 molecular weight 80g/mol)
Ammonium nitrate contains 35% nitrogen. If 1g of nitrogen source is needed, then ammonium nitrate Y=1/0.35=2.86 g needs to be added.
2. Calculation of phosphate addition
General sludge culture is generally calculated based on a CNP ratio of 100:5:1. Currently, there is no dispute about TP, which is generally recognized as phosphate. Except for specific organic phosphorus and hypophosphorus industrial wastewater, the actual addition is calculated based on phosphate. The amount of P source added is: P=V*G/Z.
In the formula:
P—dosage of P source
V—water volume in the pool
G—difference in N required to be supplemented
Z—amount of phosphate converted from P source
(1) Sodium dihydrogen phosphate is used as the added P source (Na2HPO4.7H2O, molecular weight 268.07 g/mol). The P content of sodium dihydrogen phosphate is 11.57%. If 1g of P source needs to be added, sodium dihydrogen phosphate Z=1/ 0.1157=8.64 g needs to be added.
(2) Potassium dihydrogen phosphate is used as the added P source (K2HPO4-3H2O, molecular weight 228.22 g/mol). The P content of potassium dihydrogen phosphate is 13.6%. If 1g of P source needs to be added, potassium dihydrogen phosphate Z=1/ 0.136 =7.35 g needs to be added.
(3) Phosphate fertilizer superphosphate is used as a P source. The effective phosphorus in phosphate fertilizer is soluble phosphorus pentoxide (P2O5, molecular weight 141.94g/mol). The effective phosphorus content in phosphate fertilizer is 12%, and the P content of P2O5 is 43.66%. If 1g of P source is needed, phosphate fertilizer Z=1/(0.12×0.4366)=19.09 g needs to be added.
The above is the process in wastewater treatment. In modern wastewater treatment, wastewater testing also accounts for a large proportion. To monitor the effect and process of water treatment, water quality testing instruments are indispensable. Lianhua Technology is a manufacturer with 42 years of experience in producing water quality testing instruments. In 1982, it developed the COD rapid digestion spectrophotometry method, which can detect the COD value in wastewater within 15 minutes. Later, it successively developed ammonia nitrogen rapid tester, total phosphorus rapid tester, total nitrogen rapid tester, and BOD tester. Lianhua believes that it can provide safe, reliable and intelligent testing equipment for the environmental testing industry.
Lianhua Technology’s total phosphorus testing instrument uses the molybdenum antimony anti-spectrophotometric method. Potassium persulfate is added to the sample, digested at 120° for 30 minutes, and then a color developer is added for colorimetry. Lianhua Technology’s total phosphorus determination instrument has set up a curve. After the sample is put in, the instrument can automatically calculate the result and print the result. The measured value is accurate.
Lianhua Technology’s total nitrogen determination instrument uses ultraviolet spectrophotometry. Alkaline potassium persulfate is added to the sample, digested at 122° for 40 minutes, and then taken out and added with dilute hydrochloric acid. In ultraviolet mode, a quartz cuvette is used for colorimetry. The instrument automatically calculates and prints the results. Easy to operate.
Post time: Nov-22-2024
