In denitrification in wastewater, is often insufficient carbon source denitrification removal rate is low, cause effluent TN to exceed bid, so the only applies to plus carbon source has become the current means of practice, the carbon source generally have methanol, acetic acid sodium, flour, such as glucose, compare to the current application in this paper make a comparison between a wide range of carbon source, let everybody have a preliminary knowledge of 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 yield. When the methanol carbon source is insufficient, the phenomenon of nitrite accumulation exists. The denitrification rate with methanol as carbon source is 3 times faster than that with glucose as carbon source, and the ratio of carbon to nitrogen (COD: ammonia nitrogen) is 2.8 ~ 3.2.
According to the current research, when methanol is used as carbon source, C/N >.5 can achieve a better effect, but there are three disadvantages:
(1) as a chemical agent, the cost is relatively high;
(2) The response time is slow, and methanol can not be used by all microorganisms. When methanol is added, a certain adaptation period is needed until it is fully enriched and gives full play to the effect. When it is used for emergency adding carbon sources in sewage treatment plants, the effect is poor.
Methanol has a certain toxic effect, and long-term use of methanol as a carbon source will also have a certain impact on tailwater emissions.
2. Sodium acetate
The advantage of sodium acetate is that it can respond immediately to the denitrification process and can be used as an emergency treatment during water plant operation.
Because sodium acetate is a small molecular organic acid, denitrifying bacteria are easy to use and the denitrification effect is better. However, due to the high price, high sludge yield, and the current sewage treatment plant sludge disposal problem is also a major problem, so it is almost impossible to apply sodium acetate to the large-scale addition of sewage treatment plants.
3, sugars,
Among sugar substances, flour, sucrose and glucose are the main ones. Because glucose is a simple sugar, there are many researches on glucose at present. When the carbon source is sufficient, the carbon and nitrogen with glucose as the carbon source is much higher than that with methanol as the carbon source, which is 6:1 ~ 7:1. The type of carbon source had little effect on the specific reduction rate of nitrite, but had a great effect on the specific accumulation rate of nitrite. Only glucose had no accumulation in this study.
Represented by glucose sweets as additional carbon source treatment effect is good, but, as a molecular compound, more easy to cause the bacteria multiply, causing sludge bulking, increase the water COD value, affect the water quality, at the same time, compared with the alcohol carbon source, sweets are more likely to produce the phenomenon that the nitrate accumulation.
4, sludge hydrolysis supernatant
Bioconversion VFA is derived from the supernatant of sludge hydrolysis. Due to the high denitrification rate of VFA generated by hydrolysis, the carbon source can be directly provided from the sewage plant, which reduces the sludge capacity and also reduces the problems of carbon source transportation, so it is a relatively advantageous carbon source at present.
At present, there are many different conclusions on the study of sludge hydrolytic utilization as external carbon source, but it is generally considered that it is a valuable method as the carbon source of denitrification and denitrification system. For different sludge, however, different hydrolysis conditions, the composition of VFA in sludge have bigger difference, and because of the different components, and can cause a different rate of denitrification (this is why a lot of study of the causes of inconsistent), so, how will the sludge hydrolysis product of VFA unification research and application, is still a big problem. In addition, if hydrolyzed sludge is directly used as an external carbon source, the release of nitrogen and phosphorus in the process of sludge hydrolysis should be considered. If this part of nitrogen and phosphorus is added to sewage in the form of carbon source, it is bound to increase the load of nitrogen and phosphorus in sewage treatment plant. How to solve this problem is another big problem in the use of sludge hydrolysate.
