1. The nitrification solution is refluxed for the pre-denitrification process.
The nitrification solution is refluxed to the front-end anoxic zone, and at the same time, a carbon source is added to denitrify the nitrogen-based nitrogen through denitrifying bacteria to convert it into nitrogen, without the need for new treatment facilities and new land occupation, only an internal reflux pump needs to be installed at the end of the existing aerobic section to return the nitrified liquid to the pre-denitrification zone. This scenario is theoretically possible, but there are problems such as the following:
1) If the total nitrogen needs to reach the first class A standard, the nitro nitrogen needs to be reduced to less than 10mg L, and by calculation, the nitrification solution reflux ratio will be 150-200%, that is, the nitrification solution rich in dissolved oxygen (DO about 4mg L) will flow back to the anoxic section at twice the amount of influent water to the anoxic section will directly change the dissolved oxygen environment of the anoxic section (02mg/l≤do≤0.5mg l), an important indicator affecting the denitrification efficiency is the strict anoxic environment, the increase of dissolved oxygen and the decrease of anoxic residence time caused by such a large reflux ratio will seriously affect the denitrification efficiency and reaction time, and then the total nitrogen in the effluent can not reach a very low level, but the reduction of the reflux ratio can not complete the amount of total nitrogen denitrification, and will also affect the total nitrogen in the effluent to meet the standard.
2) If the denitrification reaction is carried out, the denitrifying bacteria will definitely use a certain carbon source, from the analysis of the influent C n ratio and the C n ratio of the effluent water, if the plant needs to add a carbon source for denitrification, if methanol is supplemented at the front end as a carbon source, there is a competition between denitrifying bacteria and other strains, from the perspective of microbiology, denitrification is not the dominant strain under this condition, so a large number of carbon sources added at the front end will be wasted, resulting in an increase in operating costs, and if excessive supplementation will lead to an increase in the back-end treatment load.
2. Post-denitrification process.
The denitrification system is connected to the back end of the existing biochemical system, such as the denitrification filter is connected to the back end, the conditions for post-denitrification are optimized, and the carbon source is added at the same time, and the nitro nitrogen is denitrified into nitrogen through denitrifying bacteria, so as to achieve the total nitrogen of the effluent is less than 10mg l, this scheme is absolutely feasible in theory, but there are the following problems:
1) The new land is too large, the new back-end denitrification filter, according to the drawings provided by the owner and our technical personnel on-site survey, such as the completion of the denitrification reaction, the main body of the denitrification filter covers an area of about 500 square meters.
2) The addition of carbon source will lead to an increase in the COD concentration of the effluent, a low carbon source utilization efficiency, and a decrease in the denitrification efficiency when the water temperature decreases in winter, which directly affects the total nitrogen of the effluent.
3) Not resistant to shock loads. The sudden change of incoming water quality has a great impact on the total nitrogen of the effluent.
3. Membrane process.
The membrane process is mainly MBR process, which improves the efficiency of denitrification by adding MBR to the existing tank to maintain a higher sludge concentration and reflux sludge concentration in the system (the reflux sludge concentration can supplement a certain carbon source).
1) The installation of MBR requires the existing treatment facility to stop water for installation, and the existing aeration system also needs to be redesigned and installed because the aeration required for the operation of the MBR system is larger than that of the general biochemical process.
2) The operation and management requirements of MBR are high, in addition to daily cleaning, regular off-line chemical cleaning is also required, and the membrane filament is easy to break, so the maintenance and replacement cost of the membrane is high, and the MBR operation power cost is high, so the total operating cost of MBR is higher.
3) MBR operation maintains a high sludge concentration and has a certain anti-shock load capacity, but in view of the characteristics of low BOD TKN in the range of 2 3, the denitrification carbon source is insufficient, and whether it can maintain a high phosphorus removal and denitrification efficiency still has a great impact on the quality of the incoming water.
4) MBR itself cannot intercept nitronitrogen, and it is still a kind of biological denitrification process, so water temperature, water quality, carbon source, dissolved oxygen and other factors have an impact on the operation of MBR.
4. Targeted macroporous resin denitrification system.
The targeted macroporous resin denitrification system uses the principle of ion exchange to adsorb nitrate ions in water with resin. The system operates unaffected by temperature changes and changes in feed water concentration. Compared with conventional denitrification biological denitrification, the system has good resistance to shock loads and adaptability. According to the long-term monitoring data, 90% of the total nitrogen in the effluent of the sewage plant is nitrate nitrogen, and the removal efficiency of the total nitrogen can reach more than 80% by using this system. Therefore, the "Targeted Macroporous Resin Nitrogen Removal System" is more targeted and technically advantageous for the removal of total nitrogen in this project.
At the same time, it is found that the concentration of phosphate ions in the effluent treated by the system can also be greatly reduced, and the COD and suspended solids in the effluent can be further removed. It also has a 5% and 30% adsorption efficiency for yellow humic acid organic compounds in wastewater.
To sum up, the simple biochemical denitrification process, whether it is the traditional pre-denitrification, post-denitrification, and membrane process, is affected by factors such as land occupation, carbon source, dissolved oxygen, and inlet water impact load to varying degrees, especially when the water temperature is low in winter, the influence of the above factors will be more significant. The deep denitrification process effectively solves the various deficiencies of a single biochemical denitrification process, and on the basis of giving full play to biological denitrification, the deep denitrification process is used for advanced treatment, which effectively ensures the stability of the total nitrogen index under various unfavorable conditionsThe concentrated high-concentration nitrate wastewater has a higher utilization rate of carbon sources during denitrification, saving operating costs. Therefore, the "deep denitrification process" is used to remove nitrate from the water.
The deep denitrification process can effectively remove the total nitrogen in the wastewater, but the concentrated water produced is difficult to treat, and the following solutions are proposed to solve this problem
Establishment of a denitrification reactor.
For the purpose of mainly treating nitrate nitrogen, a separate denitrification system is established to save land space, improve denitrification efficiency and reduce carbon source addition. Main process flow:
1) Adjust the pH value of the concentrated water to about neutral
2) The adjusted high nitrate nitrogen wastewater enters the denitrification reactor to supplement the carbon source, monitor the pH value, redox potential (ORP) and dissolved oxygen (DO) in the denitrification tower, and add acid to adjust the pH value 7 8 and increase or decrease the aeration amount to control the dissolved oxygen 02mg l or so. The total nitrogen can be reduced to about 20 mg l for denitrification reaction by adding a carbon source.
3) Because the denitrification material adsorbs a small amount of COD organic matter, the elution increases the COD and has a light yellow color during regeneration, a small amount of powdered activated carbon is added to the denitrification tank to adsorb and decolorize and enhance the sedimentation of the sludge in the denitrification tank, and then the effluent is mixed with the inlet water of the high-density sedimentation tank, and the sludge is mixed with the physicochemical sludge in the sludge thickening tank of the high-density sedimentation tank and dewatered together.