Denitrification deep bed filter brick

As the name implies, the denitrification filter is a biological filter with denitrification and denitrification function, which is developed on the basis of the traditional biological filter. Because of its good nitrate removal effect, small footprint, high treatment efficiency, and low project investment costs, it has received extensive attention in the upgrading and transformation of sewage treatment plants in recent years. The author will mainly introduce Denitrification filter sewage treatment principle, composition structure, and introduce several typical denitrification filter products.

2. Principles and key factors

Most of the denitrification reactions carried out in the denitrification filter process are heterooxy denitrifying bacteria using organic carbon sources (common carbon sources such as methanol, acetic acid and ethanol) as electron donors, and nitrate or nitrite as electron donors. The redox process of the electron acceptor. Some autotrophic denitrifying bacteria use inorganic carbon (such as CO2, H2CO3, etc.) as a carbon source, and hydrogen, iron, sulfur and other compounds as electron donors.

This process is a complex biochemical reaction process involving multiple enzymes and multiple intermediate products accompanied by electron transfer and energy production. The process involves 4 enzymes: nitrate reductase, nitrite reductase, and nitric oxide. Enzymes and nitrous oxide enzymes are involved in the 4-step reaction of nitrate conversion: NO3--N→NO2--N→NO→N2O→N2

The enzymes involved in the reaction have certain requirements on the reaction conditions: pH (7~8), dissolved oxygen concentration (≤0.5mg/L), water temperature (20~35℃), carbon to nitrogen ratio (generally required in engineering ≥5: 1) etc. Therefore, as far as the denitrification filter is concerned, ensuring the above conditions is a prerequisite for ensuring the denitrification effect. In actual on-site engineering, the sewage treatment plant has relatively stable control of water temperature and pH. However, due to changes in the quality and quantity of influent water, the influent organic matter content is insufficient, which makes the denitrifying bacteria in the filter unable to obtain sufficient carbon source. Causes low denitrification efficiency.

In addition, the hydraulic load of the designed filter, the general hydraulic load design experience value is 0.5~3m3. m-2﹒ Around h-1 [4], low hydraulic load is likely to cause problems such as clogging and difficulty in flushing and maintenance. High hydraulic load will lead to insufficient contact time between sewage and biofilm, and insufficient response will also result in low order removal efficiency.

Third, the frequency and intensity of flushing. The denitrification biological filter belongs to the biofilm method, so it needs to be flushed within a certain period of use to restore the lost water head. At the same time, a part of the aging and shedding biofilm is discharged out of the entire filter to promote the formation of new biofilms, just like the excess sludge is discharged from the system in the activated sludge method, so the denitrification biological filter needs to be changed according to the water quality and quantity As well as the growth of the biofilm, find out the appropriate washing frequency and washing intensity.

3. Structure composition

According to the hydraulic flow regime, the denitrification filter can be divided into two forms: upflow and downflow. The shape of the upflow denitrification filter is similar to the structure of the traditional biological filter. The sewage flows from the bottom to the top, and the filter is divided into a water distribution layer, a supporting layer, a filling layer, and a clear water layer from bottom to top. The downflow denitrification filter is similar in structure to the V-type filter. The sewage enters the filter area from the water distribution tank on the upper part of the filter. The filter is divided into water distribution area, filling area, supporting layer, and effluent collection area from top to bottom. .

Compared with the biological aerated filter, the denitrification filter does not need to add aeration equipment in the filter, and is only designed for the backflushing equipment of air washing and combined washing. In order to ensure the normal operation of the denitrification filter, it is often equipped with air-water combined backwash equipment.

The supporting layer of the filter is generally composed of a filter plate, a filter head, and a supporting layer filter material. The backwashing system (flushing water pipe, flushing air pipe) is also arranged under the filter plate of the supporting layer. The new filter brick that is convenient for water and air distribution, optimizes the air and water distribution.

The filter material has also changed from ordinary pebbles, gravel, etc. to ceramsite, anthracite, volcanic stone, and polymer inert carriers, which have large specific surface areas and strong dirt interception capabilities. The flushing direction of the upstream filter and the direction of the inlet water flow are the same, so there is often a flushing wastewater collection tank/tank in the outlet area of ​​the filter, and the flushed wastewater flows back to the inlet water distribution area.