Upflow Anaerobic Sludge Bed Reactor for Domestic Sewage Treatment

It is imperative to improve the efficiency of sewage treatment, strengthen the treatment efficiency of sewage treatment plants and reduce the energy consumption of sewage treatment. The development trend of sewage treatment technology is simplicity, high efficiency and low energy consumption.

Upflow Anaerobic Sludge Bed Reactor (UASB), as an efficient anaerobic reactor, has the advantages of low energy consumption, small sludge output, and good effluent organic matter treatment effect. It is widely used in anaerobic treatment of sewage. .

The following briefly introduces the development history, technical advantages, influencing factors, and application and prospect of anaerobic membrane bioreactors in the treatment of low-concentration domestic sewage.

Development History of Upflow Anaerobic Sludge Bed Reactor

Second, the technical advantages of the up-flow anaerobic sludge bed reactor

Compared with the traditional aerobic treatment of domestic sewage, the up-flow anaerobic sludge bed reactor has the following advantages:

①The energy consumption of the reactor treatment is small, and the amount of sludge is greatly reduced compared with aerobic biological treatment.

②Anaerobic treatment can produce biogas, which can combine environmental protection and energy recovery. There are better environmental benefits.

③ The treatment cost is lower than that of aerobic, and it has better economic benefits. Without considering the benefits of the generated biogas, the cost of anaerobic treatment is only 1/3 of that of anaerobic treatment.

④The anaerobic treatment load is high and the land occupation is small. Today’s cities are expensive, saving more land not only reduces costs, but also optimizes the structure of the entire city. In the case of the same amount of treated water, the area of anaerobic treatment is only half of that of aerobic treatment.

⑤ The scale of the anaerobic system is more flexible and changeable, which can be large or small. Moreover, the processing facility is simple, easy to manufacture, and does not require expensive equipment, and can be suitable for more different occasions. Anaerobic biological treatment is in line with the development direction of urban domestic sewage treatment in my country in the future.

Influencing factors of upflow anaerobic sludge bed reactor

Granular sludge

The efficient and stable operation of the UASB system depends on the formation of granular sludge with good settling effect, high methanogenic activity and abundant microorganisms. Granular sludge is the basis for the operation of the UASB reactor, and the granular sludge with good sedimentation is not easy to be lost, which determines the treatment efficiency of the reactor and the resistance to water quality fluctuations.

Organic load

With the correct control of organic load, granular sludge can be formed as quickly as possible. Practice has proved that controlling the organic load of the reactor and improving the sedimentation of the sludge are the main means to control the excess sludge loss.

Temperature

Temperature has an important effect on the startup of UASB and maintaining the stability of the system.

The reactor can be successfully started at normal temperature (20-30°C), medium temperature (33-41°C) and high temperature (50-55°C) to form granular sludge.

For different treatment processes, different temperature ranges can be selected according to actual needs.

Water distribution

Influent water is very important to the operation of UASB. It is necessary to use the influent form of uniform water distribution and good stirring effect, which can increase the height of the activated sludge zone, which is beneficial to improve the anaerobic efficiency and impact resistance.

Alkalinity

Alkalinity mainly affects sludge granulation in two aspects:

One is the effect on the granulation process, and the other is the effect on the activity of granular sludge. NaHCO3 can be added to adjust the alkalinity of the influent water. Some reactors increase the alkalinity of the influent water by refluxing the treated water, and at the same time increase the influent water load.

Toxic substances

Like other biological systems, anaerobic treatment systems should also avoid the entry of toxic substances.

Since the adaptability of microorganisms to various substrates is limited to a certain extent, some chemical substances exceeding a certain concentration will inhibit anaerobic fermentation and even completely destroy the anaerobic process.

Application and Prospect of Upflow Anaerobic Sludge Bed Reactor in Treatment of Low-concentration Domestic Sewage

In the 1980s, Lettinga et al. conducted experiments on the UASB reactor to treat urban domestic sewage.

The volume of the reactor is 120L, the inoculated sludge is granular sludge, the temperature of the influent water is 8~20℃, the COD of the influent water is 300mg/L~500mg/L, and when HRT=12h, the COD removal rate is 50%~70% , the output of methane is 7.1~7.3m3/yr, and the output of sludge is 5.0~8.6kg/yr.

Since then, domestic and foreign experts and scholars have also begun to study the UASB reactor for domestic sewage treatment.

Under the normal temperature of 20~21℃, when the hydraulic retention time is , the system has a good effect on domestic sewage treatment, and the COD removal rate is 69.5%~78.0%.

The effluent is less than 120mg/L, which meets the secondary standard of the national “Integrated Wastewater Discharge Standard” (GB8978-1996).

In the study, Chen Xuemin and others used a UASB reactor with an effective volume of 8m3 to treat domestic sewage with an average COD of 492.0mg/L.

It took 35 days for the successful start-up, the COD removal rate was 65% to 80%, and the average removal rate of BOD and SS reached 80%. The temperature was between 10 and 23 °C, and the change of temperature had no obvious effect on the removal rate of COD, BOD and SS.

The sludge was least granulated, but the flocculent sludge also made the UASB work well. In the experiment, Luo Wensheng directly used granular sludge for inoculation and carried out a second start, and the start-up speed was faster. When the water temperature is 20°C, the startup can be completed in 5 days.

The domestic sewage used in the test has a COD of 100-500 mg/L, and the COD removal rate is 40%-80%. When the COD concentration of the influent is lower than 100mg/L, the granular sludge of the reactor will decompose, that is, the limit concentration of the granular sludge is maintained when COD=100mg/L.

The use of anaerobic reactor alone has too many restrictions, and it has little effect on the removal of nitrogen and phosphorus, and the effluent quality is difficult to meet the discharge standard. Therefore, more scholars study the combination of UASB reactor with other processes to make up for the deficiency of anaerobic reactor.

UASB has various combined processes, including activated sludge post-treatment processes, such as UASB-AS (activated sludge process), the UASB reactor replaces the primary settling tank in the original AS process; UASBSBR (sequencing batch activated sludge process) ), SBR can complete the nitrogen and phosphorus removal that UASB is not good at.

Biofilm post-treatment such as UASB-TF (biofilter), UASB-RBC (biological turntable), UASB-DHS (suspension reactor), etc.

V. Conclusion

In summary, it is feasible and effective to use the up-flow anaerobic sludge bed reactor to treat low-concentration domestic sewage. If it is successfully applied in the early stage of the sewage process, it will not only save energy and reduce consumption, but also realize the removal of nutrients. The energy in wastewater can be recovered in the form of biogas, making the sewage treatment process an energy generator.

Although there are still some shortcomings in the application of up-flow anaerobic sludge bed reactors in domestic sewage treatment, with the continuous deepening of research, the problems have been solved. Up-flow anaerobic sludge bed reactors and related post-treatment systems The application in domestic sewage treatment will have broad prospects.

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