How to choose carbon source for denitrification?
The problem of insufficient carbon source for denitrification is common in urban sewage in my country. Insufficient carbon source has become an important factor restricting the efficiency of biological denitrification. It is necessary for sewage treatment plants to choose an external carbon source.
1. Principles of selection of denitrifying carbon sources
1. The external carbon source is easily degraded by microorganisms and easily utilized by denitrifying bacteria, and there is no problem that residues will adversely affect the subsequent effluent compliance;
2. The reaction speed is fast enough to ensure that the added carbon source is exhausted in the anaerobic and anoxic functional areas as much as possible, so as to avoid increasing the burden and operating cost of the subsequent aeration system;
3. It will not affect the type and content of microbial populations in the system, and avoid short-term adaptation problems of microorganisms before and after adding carbon sources;
4. The price is cheap, the safety is good, and it is easy to add, store and transport, and can be obtained nearby.
Second, the advantages and disadvantages of commonly used denitrifying carbon sources
Commonly used carbon sources on the market: methanol, sodium acetate, flour, glucose, biological carbon sources, etc. In the process of use, it is necessary to select an appropriate carbon source according to the actual engineering situation. Now compare various commonly used carbon sources and analyze the advantages and disadvantages of various carbon sources:
1. Methanol
It is generally believed that methanol as an external carbon source has the advantages of low operating cost and small sludge output. When methanol is used as a carbon source, C/N>5 can achieve better results.
But its disadvantages are:
①As a chemical agent, the cost is relatively high;
②The response time is slow, and methanol cannot be utilized by all microorganisms. When methanol is added, it needs a certain adaptation period until it is fully enriched and fully effective. When used for emergency carbon source addition in sewage treatment plants, the effect is not good. ;
③Methanol has a certain toxic effect. Long-term use of methanol as a carbon source will also have a certain impact on the discharge of tail water.
2. Sodium acetate
The advantage of sodium acetate is that it can immediately respond to the denitrification process and can be used as emergency disposal in water plants.
It is generally believed that the denitrification rate of sodium acetate is not as high as that of methanol, but since it is not toxic and the sludge yield is similar to that of methanol, it is considered that it can be used as an alternative carbon source for methanol. When sodium acetate is used as carbon source and nitrate is used as electron acceptor, the optimal C/N=5, the lack of carbon source will cause nitrite accumulation.
There are three points to consider when using sodium acetate:
① Sodium acetate is mostly a liquid of 20%, 25%, and 30%. Due to its low equivalent COD and high transportation costs, it cannot be transported over long distances.
② The amount of sludge produced is large, and the cost of sludge treatment increases;
③ The price is relatively expensive, and the cost of large-scale dosing of sodium acetate in the sewage treatment plant is too high.
3. Sugars
Saccharides represented by glucose have a good effect as an external carbon source. However, as a multi-molecular compound, it is easy to cause a large number of bacteria to multiply, cause sludge expansion, increase the value of COD in the effluent, and affect the quality of the effluent. , compared with alcohol carbon sources, sugars are more likely to accumulate nitrite nitrogen, so it is not recommended to use glucose as an external carbon source.
shortcoming:
① It needs to be configured into a solution on site, which is labor-intensive, and the dosing accuracy is poor, and large-scale sewage treatment plants cannot be used.
② Industrial glucose contains many impurities, and food glucose is expensive.
4. Biomass carbon source
With the improvement of sewage denitrification requirements, new enterprises specializing in the production of carbon sources have emerged. They ferment some sugars and agricultural wastes through bioengineering principles to produce non-toxic and harmless biological products. The main components are small molecules. Organic acids, alcohols, sugars. It is easier to be utilized by microorganisms than a single chemical, and its use cost is cheaper than a single chemical, and it has a very high cost performance.
Disadvantages:
① The stability of the product needs to be improved, and the equivalent COD of each batch of products should be tested before use.
3. HJT high-efficiency composite carbon source
HJT high-efficiency composite carbon source is a new type of biological carbon supplementation and denitrification product. This product uses sodium acetate as the main raw material and adds special biological preparations. It is mainly used to optimize the water quality of the influent and improve the total nitrogen removal efficiency of the biochemical system. After use, the small molecular substances in the carbon source are rapidly hydrolyzed and absorbed and utilized by microorganisms. At the same time, the filler components in the product will also dissolve in water, improving the decolorization effect, and finally realizing the economical, practical and efficient removal of total nitrogen. Harmonize.
