Pay more attention to the public account: environmental protection water treatment
The main advantages of UASB are:
1. The sludge concentration in UASB is high, and the average sludge concentration is 20-40gVSS/1;
2. The organic load is high, the hydraulic retention time is long, and the volume load is generally about 10kgCOD/m3.d when medium-temperature fermentation is adopted;
3. Without mixing and stirring equipment, the sludge in the upper part of the sludge bed is in a suspended state by the rising movement of the biogas generated in the fermentation process, and the sludge layer in the lower part is also stirred to a certain extent;
4. The sludge bed is not filled with carriers, which saves costs and avoids blockage due to fillers;
5. The UASB is equipped with a three-phase separator, usually without a sedimentation tank, and the sludge separated from the sedimentation area is returned to the sludge bed reaction area, and the sludge reflux equipment is usually not provided.
The main disadvantages are:
1. The suspended solids in the inlet water need to be properly controlled, not too high, and generally controlled below 100mg/l;
2. There is a short flow phenomenon in the sludge bed, which affects the treatment capacity;
3. It is sensitive to sudden changes in water quality and load, and the impact resistance is slightly poor.
The main advantages of SBR are:
1. The ideal flow pushing process increases the driving force of the biochemical reaction, improves the efficiency, and the anaerobic and aerobic in the pool are in an alternating state, and the purification effect is good.
2. The operation effect is stable, the sewage is precipitated in an ideal static state, the time required is short, the efficiency is high, and the effluent quality is good.
3. Resistant to impact load, there is retained treated water in the pool, which has the effect of dilution and buffering on sewage, and effectively resists the impact of water volume and organic dirt.
4. Each process in the process can be adjusted according to the water quality and quantity, and the operation is flexible.
5. Less processing equipment, simple structure, easy to operate and maintain management.
6. There is a concentration gradient of DO and BOD5 in the reaction tank, which can effectively control the expansion of activated sludge.
7. The SBR system itself is also suitable for the combined construction method, which is conducive to the expansion and transformation of the wastewater treatment plant.
8. Denitrification and phosphorus removal, properly control the operation mode, realize the alternation of aerobic, anoxic and anaerobic states, and have a good effect of denitrification and phosphorus removal.
9. The process flow is simple and the cost is low. The main equipment has only one sequential batch reactor, no secondary sedimentation tank, sludge return system, regulating tank and primary sedimentation tank can also be omitted, compact layout, and saving floor space.
shortcoming
1. High requirements for automatic control.
2. The drainage time is short (intermittent drainage), and the sedimentation sludge layer is not stirred during drainage, so special drainage equipment (decanter) is required, and the requirements for the decanter are very high.
3. The requirements for post-treatment equipment are large: such as the disinfection equipment is large, the volume of the contact pool is also large, and the drainage facilities such as drainage pipes are also very large.
4. The decanting depth is generally 1~2m, and this part of the head loss is wasted in vain, increasing the total head.
5. Because there is no primary sedimentation tank, scum is easy to be generated, and the scum problem has not been properly solved.
A/O process
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1. Basic principle
A/O is the abbreviation of Anoxic/Oxic, its advantage is that in addition to the degradation of organic pollutants, it also has a certain function of denitrification and phosphorus removal, and it is the use of anaerobic hydrolysis technology as the pretreatment of activated sludge, so the A/O method is an improved activated sludge method.
The A/O process connects the anterior anoxic section and the posterior aerobic section in series, with the DO of the A section not more than 0.2mg/L and the O section DO=2~4mg/L. In the anoxic section, heterotrophic bacteria hydrolyze suspended pollutants such as starch, fiber, carbohydrates and soluble organic matter in sewage into organic acids, so that macromolecular organic matter is decomposed into small molecule organic matter, and insoluble organic matter is converted into soluble organic matter, when these products hydrolyzed by anoxic hydrolysis enter the aerobic pond for aerobic treatment, the biodegradability of sewage and the efficiency of oxygen can be improved; NH4+), under the condition of sufficient oxygen supply, the nitrification of autotrophic bacteria oxidizes NH3-N (NH4+) to NO3-, and returns to pool A through reflux control, and under anoxic conditions, the denitrification of isotrophic bacteria reduces NO3- to molecular nitrogen (N2) to complete the circulation of C, N and O in the ecology, and realize the harmless treatment of sewage.
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2. Characteristics of A/O internal circulation biological denitrification process
Based on the above description of the basic process of biological denitrification, combined with years of experience in denitrification of coking wastewater, we have concluded that the (A/O) biological denitrification process has the following advantages:
(1) High efficiency. The process has a high removal effect on organic matter and ammonia nitrogen in wastewater. When the total residence time is greater than 54h, the effluent after biological denitrification can be coagulation and precipitation, which can reduce the COD value to below 100mg/L, and other indicators also meet the emission standards, and the total nitrogen removal rate is more than 70%.
(2) The process is simple, the investment is low, and the operation cost is low. The process uses organic matter in wastewater as a carbon source for denitrification, so there is no need for an additional expensive carbon source such as methanol. In particular, after the ammonia distillation tower is equipped with a device for defixing ammonia, the carbon-nitrogen ratio is improved, and the alkalinity generated in the denitrification process correspondingly reduces the alkali consumption required in the nitrification process.
(3) The anoxic denitrification process has a high degradation efficiency for pollutants. For example, the removal rates of COD, BOD5 and SCN- in the anoxic section are 67%, 38% and 59%, and the removal rates of phenol and organic matter are 62% and 36%, respectively, so denitrification is the most economical and energy-saving degradation process.
(4) High volumetric load. Due to the use of enhanced biochemistry in the nitrification stage and the membrane technology of high-concentration sludge in the denitrification stage, the concentration of nitrification and denitrification sludge is effectively increased, and it has a higher volumetric load compared with similar foreign processes.
(5) The anoxic/aerobic process has strong load impact resistance. When the influent water quality fluctuates greatly or the pollutant concentration is high, the process can maintain normal operation, so the operation and management are also simple. Through the comparison of the above processes, it is not difficult to see that the biological denitrification process itself is not only denitrification, but also degrades organic substances such as phenol, cyanide, and COD. Combined with the characteristics of water quantity and water quality, we recommend the use of anoxic/aerobic (A/O) biological denitrification (internal circulation) process, so that the sewage treatment plant can not only meet the requirements of denitrification, but also meet the discharge standards of other indicators.
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3. Disadvantages of the A/O process
1. Because there is no independent sludge reflux system, sludge with unique functions cannot be cultivated, and the degradation rate of refractory substances is low;
2. In order to improve the efficiency of denitrification, it is necessary to increase the internal circulation ratio, thus increasing the operating cost. In addition, the internal circulating liquid comes from the aeration tank and contains a certain amount of DO, which makes it difficult for section A to maintain an ideal anoxic state, which affects the denitrification effect, and the denitrification rate is difficult to reach 90%.
3. Influencing factors
水力停留时间 （硝化＞6h ，反硝化＜2h ）污泥浓度MLSS（＞3000mg/L）污泥龄