CN1323958C - Method for processing urban sewage deeply - Google Patents

Abstract

The invention relates to a method for advanced treatment of urban sewage. The method includes advanced treatment of urban sewage by coagulation filtration, ozone oxidation, and biological oxidation to remove refractory trace organic matter, bacteria, and viruses remaining in the secondary effluent of urban sewage, decolorize and deodorize, and achieve safe reuse. purpose. According to the different requirements for the specific reuse objects of the advanced treated urban sewage, the method also includes reverse osmosis or nanofiltration treatment to further remove residual organic and inorganic substances in the water. This method is a combined technology integrating coagulation filtration, ozone oxidation, biological oxidation and reverse osmosis, which can solve the problems of urban sewage treatment and safe reuse of water quality, and can obtain high-quality effluent at a lower treatment cost, with good performance-price ratio. This has important practical significance for alleviating the contradiction of urban water shortage, improving the utilization rate of water resources, reducing environmental pollution and promoting the sustainable development of social economy.

Description

A method for advanced treatment of urban sewage

technical field

The invention relates to a method for advanced treatment and safe reuse of urban sewage.

Background technique

my country is a country with relatively poor water resources, and the distribution of time and space is uneven, which does not match the local population, cultivated land resources and economic layout of our country. Especially with the rapid development of social economy and the acceleration of urbanization, the problems of urban water shortage and environmental pollution are particularly prominent, and water resources have become an important factor restricting social and economic development. Urban sewage, which is almost equal to the amount of urban water supply, contains about 0.1% of pollutants. It has the characteristics of sufficient water volume and stable water quality. It is a potential water resource and can be used as a reliable second water source for the city after proper treatment. This has become the consensus of all countries in the world today to alleviate the problem of urban water shortage. At present, all countries have carried out the research and implementation of urban sewage advanced treatment and reuse technology. Developed countries such as the United States and Japan have implemented it earlier and are at the forefront of the world. my country has a relatively early start.

After traditional secondary treatment of urban sewage, 70% to 80% of turbidity, 40% to 60% of chroma, 60% to 70% of SS, 25% to 50% of BOD ₅ , and 30% to CODcr can be removed 55%, 30% to 90% of TP, but still contains trace amounts of refractory harmful organic matter, bacteria and viruses, etc., and has high chroma, prominent smell, poor biodegradability, and biological toxicity. These residual microorganisms and chemical safety are the key issues and the biggest obstacles affecting their reuse.

The advanced treatment of urban sewage is to further remove these substances that cannot be completely removed by conventional secondary treatment. The existing technology mainly uses physical and chemical methods, usually coagulation, sedimentation, filtration, activated carbon adsorption, membrane technology, ozone oxidation, land infiltration, etc. It is an optimized combination of unit technologies such as filtration and disinfection to form a multi-level barrier system. At present, the combined processes for the advanced treatment of urban sewage mainly include traditional treatment processes based on coagulation, sedimentation, and filtration, combined processes based on activated carbon and membrane separation, and combined processes based on soil aquifer treatment. These typical technological processes are only different in form, but almost all of them adopt the basic urban sewage advanced treatment technology based on coagulation, sedimentation and filtration, and are equipped with special technical units.

However, these conventional coagulation sedimentation filtration treatment technologies commonly used at present have no effect on the removal of chroma, odor and residual organic matter in the secondary effluent. Chromaticity and odor are sensory indicators that people attach great importance to in the process of using water, and residual organic matter will also affect the biological stability of water. Therefore, the residue of these substances in the effluent will become an important factor that hinders the reuse of sewage. factor. Although the combined process based on activated carbon and membrane separation has a good effect on the removal of organic matter and chroma, the cost is too high due to the high price of activated carbon and membrane, the complicated regeneration of activated carbon and the easy pollution of the membrane. Although soil aquifer treatment has a good removal effect on organic matter and ammonia nitrogen, it occupies a large area and is inconvenient to manage. Therefore, it is very necessary to develop an economical, safe and effective recycling technology.

Contents of the invention

The purpose of the present invention is to overcome the problem that the secondary effluent still contains a small amount of harmful organic matter, bacteria, viruses, etc. when using coagulation sedimentation filtration treatment and recycling technology in the prior art when treating urban sewage, and the chroma is relatively high and the odor is prominent ; The cost is too high when using activated carbon and membrane separation as the main combination process, and the regeneration of activated carbon is complicated, and the membrane is easy to pollute; and the use of soil aquifer treatment occupies a large area and the defects of inconvenient management, thus providing a secondary treatment for urban sewage It is a method of advanced treatment of urban sewage that is designed for the characteristics of effluent water quality, can effectively reduce the content of residual organic matter, color and odor, is low in cost, and is easy to operate.

The purpose of the present invention is achieved through the following technical solutions:

The method for the advanced treatment of urban sewage provided by the present invention, its process flow is shown in Figure 1, including the use of coagulation filtration, ozone oxidation, biological oxidation to carry out advanced treatment of urban sewage, to remove the residual difficult impurities in the secondary effluent of urban sewage Degrade trace organic matter, bacteria, viruses, etc., decolorize and deodorize, and achieve the purpose of safe reuse. The specific steps are as follows:

1) Coagulation filtration: using conventional methods, the effluent from the secondary sedimentation tank of the sewage plant enters the coagulation, sedimentation, sand filtration or micro-flocculation filtration treatment unit to remove turbidity (suspended solids in water) and some organic matter;

Aluminum salts, iron salts, etc. can be used as flocculants when flocculation sedimentation filtration or micro-flocculation filtration is used. When polyaluminum chloride is used, the dosage is 5-15 mg/L Al ₂ O ₃ , which can remove 10-30% of chemical needs. Oxygen COD _Cr (, more than 80% suspended matter SS and more than 70% total phosphorus TP, etc.;

2) Ozone oxidation: The sewage treated in step 1) enters the conventional ozone reaction device from the upper part, and the ozone enters from the lower part through the titanium plate gas distribution, and the gas and water flow countercurrently for ozone oxidation. The ozone consumption can be determined according to the specific water quality and use. The water retention time (HRT) is 2-10mg/L, and the hydraulic retention time (HRT) is 5-15min. The strong oxidizing property of ozone is used to change the molecular structure of organic matter in water, sterilize, decolorize and deodorize, and improve the biodegradability and safety of organic matter in sewage; The ozone reaction device includes peripheral equipment such as raw material gas preparation equipment, an ozone generator, an ozone reactor, and an ozone tail gas destroyer;

3) Biological oxidation: enter the sewage treated in step 2) into the biological contact oxidation tank for biological oxidation reaction to degrade the intermediate products of ozone oxidation, residual ammonia nitrogen and reduce the sludge index (SDI), increase biological stability; biological contact oxidation Activated carbon, ceramsite, and coarse quartz sand with a diameter of more than 2 mm are used as fillers in the pool, and the empty bed residence time (HRT) is 10 to 20 minutes. Finally, water that can be reused after advanced treatment is obtained.

According to different influent water quality and effluent requirements, different reflux ratios can be used between the ozone oxidation and biological oxidation units, and the ratio is between 0 and 0.5 to achieve multi-stage oxidation.

According to the different requirements for the specific reuse objects of advanced treated urban sewage, the method for advanced urban sewage treatment provided by the present invention also includes:

4) Reverse osmosis or nanofiltration treatment: Using conventional methods, reverse osmosis desalination is used to further remove residual organic and inorganic substances from the sewage treated in step 3).

After the effluent of the secondary sedimentation tank of the sewage plant is treated by coagulation filtration, ozone oxidation and biological oxidation, the treated water at this time has a high reuse value and can be used for toilet flushing or various landscape purposes. For some more demanding applications, since the front-stage treatment has greatly reduced the SDI (silt density index) value (an index used to characterize the potential of incoming water to pollute the membrane), the subsequent reverse osmosis or nanofiltration treatment unit can be directly connected. The water quality of the effluent has been further improved in terms of salinity, hardness and organic matter.

The method for the advanced treatment of urban sewage provided by the present invention utilizes ozone (O ₃ ), which is a strong oxidizing agent (E=2.07V), which can selectively decolorize and deodorize, change the molecular size or structure of organic matter, and improve the dustiness of organic matter Compared with chlorine, the harm of disinfection by-products is much smaller. Therefore, the application of ozone oxidation technology to the treatment process of sewage reuse has become a powerful guarantee for improving the quality of effluent water. Ozone oxidation generally cannot completely mineralize organic matter into carbon dioxide and water, but only changes the properties and molecular structure of organic matter, generating many small molecular ozone oxidation intermediate products; therefore, subsequent biological treatment units are required to further mineralize these intermediate products. Another feature of the combined process of ozone oxidation and biological contact oxidation is that this method can significantly reduce the SDI value of incoming water, which provides powerful conditions for the subsequent use of reverse osmosis membranes or nanofiltration membranes. At present, there are also some project cases where the secondary effluent of urban sewage is filtered through coagulation sedimentation sand or directly treated with ultrafiltration membrane or microfiltration membrane as reverse osmosis membrane or nanofiltration membrane. However, the secondary effluent of urban sewage Because the effluent contains some organic molecules derived from organisms, its SDI value is usually above 10. Conventional coagulation sedimentation filtration technology does not contribute much to the reduction of SDI. Membrane filtration technologies such as ultrafiltration and microfiltration and ozone oxidation technology are both It is difficult to make the SDI value of the effluent meet the requirements of the incoming water of the reverse osmosis membrane or the nanofiltration membrane (SDI<5). However, as shown in Table 1, after the combined process of ozone oxidation and biological contact oxidation provided by the present invention, the SDI value of the effluent is stably reduced to below 3, which can fully meet the water requirements of reverse osmosis membrane or nanofiltration membrane.

The method for advanced treatment of urban sewage provided by the invention is a combined technology integrating coagulation filtration, ozone oxidation, biological oxidation and reverse osmosis. Compared with the prior art, its advantages are: (1) Ozone oxidation treatment is adopted, By changing the molecular structure of organic matter, it can not only remove some refractory trace organic matter, environmental endocrine disruptors and priority control substances, but also has the functions of sterilization, disinfection, decolorization and deodorization; Low cost improves the removal rate of organic matter and ammonia nitrogen and reduces the SDI index; (3) the present invention does not need to adjust the pH value of the incoming and outgoing water and add biological nutrient elements, and has a good performance-price ratio; (4) urban sewage is treated by this method After treatment, in addition to conventional water quality indicators meeting the national drinking water indicators, trace organic matter and biological toxicity can reach relevant foreign water quality standards, and can be used as environmental water or industrial process water.

In addition, the urban sewage advanced treatment method provided by the present invention can solve the problems of urban sewage treatment and safe reuse water quality, can obtain high-quality effluent at a relatively low treatment cost, and has a good performance-price ratio. This has important practical significance for alleviating the contradiction of urban water shortage, improving the utilization rate of water resources, reducing environmental pollution and promoting the sustainable development of social economy, especially for my country's water-deficient cities, which has good economic and environmental benefits. Has a good application prospect.

Description of drawings

Fig. 1 is a schematic process flow diagram of the method for the advanced treatment of urban sewage provided by the present invention.

Detailed ways

In this example, a pilot test device for the combined process of coagulation sedimentation filtration, advanced ozone oxidation and biological contact oxidation was built in a sewage treatment plant in Beijing, and the secondary biological treatment effluent of the plant was taken as the research object.

The effluent from the secondary sedimentation tank of the sewage plant is sequentially treated by coagulation filtration, ozone oxidation, and biological oxidation. The effluent water from the secondary sedimentation tank enters the coagulation sedimentation sand filter treatment unit, the dosage of flocculant is 15mg/L Al ₂ O ₃ , and the effluent water is called reclaimed water; then the reclaimed water enters the ozone reactor from the upper part, and the ozone passes through the titanium dioxide reactor from the lower part. The plate cloth gas enters, and the gas and water flow countercurrently for ozone oxidation. The ozone consumption and hydraulic retention time (HRT) are controlled between 3-10mg/L and 5-15min respectively; finally enter the biological contact oxidation tank for biological oxidation reaction to degrade Ozone oxidizes intermediate products, residual ammonia nitrogen and reduces sludge index (SDI) to increase biological stability; biological contact oxidation tanks are filled with activated carbon, and the empty bed residence time (HRT) is 10-20min. used water.

The raw water quality and experimental results are listed in Table 1 and Table 2.

From the average value of water quality changes in each treatment unit of the combined process listed in Table 1, it can be seen that the effluent (raw water) of the secondary sedimentation tank of the sewage plant is treated by the coagulation and filtration unit to obtain reclaimed water, which has no effect on COD _Mn , DOC, NH ₄ ⁺ The removal rates of -N, UV ₂₅₄ and chroma were 21.6%, 23.9%, 35.8%, 8% and 11% respectively: after reclaimed water was oxidized by ozone, DOC decreased from 6.36mg/L to 5.5mg/L, and the removal rate up to 13.5%; COD _Mn decreased from 6.45mg/L to 4.32mg/L, and the removal rate reached 33%; the chromaticity decreased from 40 degrees to 2.5 degrees, and the decolorization rate exceeded 93%, and the decolorization effect was obvious; UV ₂₅₄ decreased from 0.134 to 0.068, the removal rate is 49.3%, which shows that the ozone oxidation destroys the nature and structure of the organic matter, thereby improving the biodegradability of the effluent; it has almost no effect on NH ₄ ⁺ -N, but sometimes it will increase, which is due to the organic nitrogen The result of being oxidized, and the removal of part of NH ₄ ⁺ -N is mainly due to the result of stripping. After biological activated carbon treatment, DOC decreased to 3.4mg/L, with a total removal rate of 46.5%; COD _Mn decreased to 2.92mg/L, with a total removal rate of 54.7%; UV ₂₅₄ decreased to 0.059, with a total removal rate of 56%; NH ₄ ⁺ -N decreased by 1.24mg/L, and the removal rate reached 87.60%. It can be seen from Table 1 and Table 2 (full analysis of the water quality of each unit of the combined process at a certain time) that after the combined process treatment, the effluent water quality is significantly improved, and can reach the drinking water quality standard except for some water quality indicators.

Table 1. The average value of water quality changes in each treatment unit of the combined process Unit mg/L water quality COD _Mn DOC NH ₄ ⁺ -N UV ₂₅₄ Chroma (degrees) SDI raw water 8.23 8.36 15.60 0.146 45 - reclaimed water 6.45 6.36 10.02 0.134 40 7.7 Ozone oxidation 4.32 5.5 9.94 0.068 2.5 5.6 activated carbon oxidation 2.92 3.4 1.24 0.059 2.5 2.3

Table 2. Full analysis of water quality of each unit of combined process at a certain moment mg/L sample name project CODcr COD _Mn TP TN NH ₄ ⁺ -N TDS Volatile phenol Turbidity (degrees) NO ₃ -N DOC Total number of bacteria (pcs/ml) reclaimed water 24.1 6.35 1.64 30.5 18.6 702 0.001 0.30 9.81 5.11 300 Ozone water 30.1 5.34 1.53 30.3 18.3 694 nd 0.08 9.88 4.06 120 Activated carbon effluent 22.6 <5 1.32 28.1 2.07 666 nd 0.19 24.30 1.89 94 pH SP BOD ₅ Chroma (degrees) total hardness Petro Fluoride cyanide Sulfide LAS Escherichia coli (unit/L) reclaimed water 7.46 1.6 1.0 25 357 <5 0.27 0.002 0.097 0.108 130 Ozone water 7.77 1.41 8.79 3 357 <5 0.27 nd 0.078 0.096 nd Activated carbon effluent 7.74 1.16 1.0 3 359 <5 0.27 nd nd 0.099 nd Conductivity Al Fe mn Total Cr Cd Hexavalent chromium Pb Cu Zn Fecal coliform group (unit/L) reclaimed water 1618 0.3 0.13 0.05 0.009 nd 0.004 0.003 0.12 0.35 <20 Ozone water 1605 0.4 0.05 0.029 0.008 nd 0.004 0.004 0.06 0.382 nd Activated carbon effluent 1207 0.2 0.04 0.027 0.008 nd 0.004 0.003 0.03 0.34 nd

Note: nd means not detected, the same below.

The effluent treated with activated carbon is then treated by the subsequent reverse osmosis unit. The effluent water quality is shown in Table 3. The effluent water quality index fully meets the water quality standards of tap water and industrial boiler water, and reuse water with high reuse value can be obtained.

Table 3. Average value of effluent water quality of subsequent reverse osmosis treatment units Unit mg/L Water quality project Reverse osmosis (RO) effluent COD _Mn nd DOC nd TP <0.05 TN 1.50 NO ₃ -N <1.0 NH ₄ -N <1.0 chloride 2.85 Turbidity nd Chroma <2 TDS 18 Conductivity (us/cm) 38.2 total hardness 1.96 Fluoride nd cyanide nd Sulfide <0.175 Sulfate 0.72 Volatile phenol nd Hexavalent chromium nd Cu <0.02 Zn 0.08 Cd nd Pb <0.002 Fe 0.01 mn 0.025 Total Cr <0.004

Using the method of the present invention to treat sewage containing E. coli with different concentrations (10 ⁴ to 10 ⁶ /L at high concentration and 10 ² to 10 ³ /L at low concentration), the results are listed in Table 4, as can be seen , the effluent of the secondary sedimentation tank of the sewage plant is treated by the method provided by the invention, which can effectively remove E. coli to ensure the safety of reuse.

Table 4. Ozone disinfection and sterilization effect Ozone depletion mg/L High concentration E.coli/L E.coli removal rate% Low concentration E.coli/L E.coli removal rate% 0.0 3.50E+05 0.00 9.20E+03 0.00 2.9 1.20E+05 65.71 240E+03 73.91 4.8 3.50E+03 99.00 8.00E+01 99.13 7.0 5.00E+01 99.99 2.00E+01 99.78 9.3 1.30E+02 99.96 2.00E+01 99.78 12.1 1.00E+00 100.00 1.00E+00 99.99

Using tap water filtered by activated carbon, and using the method of the present invention to treat the effluent of the secondary sedimentation tank of the sewage plant, carry out an exposure comparison experiment on crucian carp, that is, to use biological methods to continuously detect the distortion of crucian carp exposed to different water quality conditions for a long time situation, so as to evaluate the safety of the effluent from the treatment process. The experimental method is as follows: the on-site running water dynamic experiment is adopted, the experimental water source directly adopts the on-site process to enter and exit the water, the tap water (treated by activated carbon) treatment group is set as the control group, the reclaimed water group comes from the reclaimed water system (ie ozone inflow), and the ozone activated carbon The group (O ₃ +BAC) came from the ozone activated carbon group (O ₃ +GAC) of the treatment device, and the water was released; the fish used in the experiment were juvenile fish of the same year, 100 juvenile fish in each group, and the exposure experiment period was 2 months. Body weight and average body length were randomly divided into groups, and the distortion was recorded every two weeks; the water temperature was controlled above 20°C (constant temperature heating rod), the natural photoperiod was combined with external light, and bait was fed every day (5-10% of fish body weight). The results of its different exposure time distortions are listed in Table 5. It can be seen that the water treated by the method of the present invention to the effluent of the sewage plant secondary sedimentation tank can be equivalent to the water quality of tap water, and can obviously reduce the mutagenic rate of crucian carp.

Table 5. Effect of exposure on distortion of crucian carp Two-week distortion rate % Peripheral distortion rate% Six-week distortion rate % Distortion rate % at eight weeks Tap water group 0 0.00 1.20 7.69 Second sinking out of water 6.67 12.67 18.00 Zhongshui group 0 3.70 11.11 17.04 Ozone activated carbon group 0 2.00 5.00 8.33

Claims (6)

1, a kind of method of city sewage deep treatment, comprise and adopt coagulation and filtration, ozone oxidation, bio-oxidation, come municipal effluent is carried out advanced treatment, to remove difficult degradation micro-content organism, bacterium, virus remaining in the municipal effluent secondary effluent, and decolouring removes and to smell, obtain can safe reuse water outlet.

2, the method for city sewage deep treatment as claimed in claim 1, it is characterized in that, described coagulation and filtration is to use ordinary method, and the water outlet of Sewage Plant secondary sedimentation basins is entered coagulation, precipitation, sand filtration or micro flocculating filter processing unit, to remove turbidity and partial organic substances; Flocculation agent when adopting flocculation sediment filtration or micro flocculating filter is aluminium salt or molysite.

3, the method for city sewage deep treatment as claimed in claim 1 or 2 is characterized in that, described flocculation agent is a polymerize aluminum chloride, and its consumption is 5～15mg/LAl ₂O ₃

4, the method for city sewage deep treatment as claimed in claim 1, it is characterized in that, described ozone oxidation is that the sewage that will handle through coagulation and filtration enters conventional ozone reaction device from top, ozone enters from the bottom by titanium plate gas distribution, the air water adverse current is carried out ozone oxidation, the ozone-depleting amount is 2～10mg/L, and hydraulic detention time is 5～15min; Described ozone reaction device comprises that unstripped gas prepares equipment, ozonizer, ozone reactor and ozone tail gas destructor.

5, the method for city sewage deep treatment as claimed in claim 1, it is characterized in that, described bio-oxidation is the sewage through ozone Oxidation Treatment to be entered biological contact oxidation pond carry out biooxidation reactions, comes the ammonia nitrogen of degrade ozone intermediate oxidation product, remnants and reduces sludge index; It is the above thick quartz sand of 2mm that the filler of biological contact oxidation pond adopts gac, haydite or diameter, and the empty bed residence time is 10～20min.

6, the method for city sewage deep treatment as claimed in claim 1 is characterized in that, also comprises reverse osmosis or nanofiltration processing.

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