(1) due to the burden of the drainage area is small, the amount of sewage is small, the water quantity and quality of water within a day, the frequency of large changes;
(2) generally constructed in towns and cities within the community or enterprise, due to the location of the area is generally not large, and the sewage conveyance pipeline outside the plant will not be too long. Therefore, its footprint is often limited, the treatment unit should be arranged as compact as possible.
(3) generally require a high degree of automation to reduce staffing and reduce operating costs.
(4) sewage plant is often located in the district or industrial enterprises, the layout may be subject to practical constraints, sometimes * near residential areas or ground undulation and so on, the layout should be appropriate to the location, change the shelter for the benefit.
(5) Due to the small scale, generally not set up sludge digestion, should be used low load, delayed aeration process to minimize the amount of sludge while making the sludge partially aerobic stabilization.
In view of the above characteristics, for small municipal wastewater plants, SBR and oxidation ditch method for the first consideration of the process plan. These two processes have the following advantages:
(1) are completely mixed, with high shock load resistance;
(2) generally do not set up a primary sedimentation tank, process simplification, saving space;
(3) generally low load delayed aeration mode operation, treatment effect is good, the sludge is aerobically stabilized, and at the same time reduce the production of sludge (if the sludge can be*, can also be appropriate to increase the load);
(4) the sludge can be used to reduce the production of sludge (if the sludge can be*, can also be appropriate to increase the load). (If the sludge outlet can be *, can also be appropriate to increase the load);
Oxidation ditch is currently commonly used Carrousel oxidation ditch, Aubert oxidation ditch, three ditch and double ditch and other alternating oxidation ditch and other forms, of which the previous two are more commonly used. Oxidation ditch *** with the same characteristics of sewage flow in the circulating pool, the aeration method is mainly used in the surface aeration method (in recent years, there are also blower aeration method of oxidation ditch, also known as oxidation ditch pool type of Pu aeration, combining the oxidation ditch and the advantages of micropore aeration).SBR process including the traditional SBR method, the ICEAS process, the DAT-IAT process, the CAST process, the UNITANK process and so on. Different methods. From a strict sense, the alternating operation of the oxidation ditch is actually also a kind of SBR process.
SBR method compared with the oxidation ditch has the following advantages:
(1) SBR process eliminates the second sedimentation tank and reflux sludge pumping room, so that the arrangement is more compact;
(2) oxidation ditch aeration device - table aeration machine in operation, splashing water is larger, the surrounding environment has an adverse impact. Some special circumstances, the sewage plant has high environmental protection requirements, the upper part of the reaction pool needs to be covered or additional upper building to isolate the odor, which will affect the aeration efficiency of the table aeration.
(3) As the SBR pool is intermittent operation, a very strong regulating capacity, for water quality and quantity changes in the case, there is no need for a high regulating pool (in fact, the SBR pool itself has the role of regulating pool).
(4) in the northern cold regions, winter outdoor temperature is low, oxidation ditch surface aeration aeration is not suitable.
(5) SBR pool depth is not limited, if necessary, can be appropriately deepened.
The above factors, in the design of small sewage treatment plant, SBR process is more widely used than oxidation ditch. The characteristics and scope of application of various SBR methods are shown in the following table:
Process name
Reactor compartment
Water intake
Whether reflux
Applicable Scale
Project Examples
Traditional SBR
Single pool, not compartmentalized
An intermittent alternating feed
No
Small
Hundreds of small wastewater plants in China
ICEAS
Has medium compartment wall divided into pre-reaction area and main reaction area
Continuous influent
Needs to reflux
Large and medium
Kunming No.3 Wastewater Plant
DAT-IAT
Middle Diaphragm wall is divided into DAT tank and IAT tank
Continuous water intake
Return ratio 200-300%
Large and medium
Tianjin Development Area Wastewater Plant
Fushun Sanbotun Wastewater Plant
CAST
Divided into selective area and main reaction area
Intermittent alternating water intake
Reflow ratio 20-35%
Medium and small-sized
Zhenjiang New District Wastewater Treatment Plant
UNITANK
Divided into three tanks with partition wall
Intermittent alternate water intake
No
Medium and small-sized
Shanghai Shidongkou Wastewater Treatment Plant
The major small-scale wastewater treatment plant Requirements are simple to operate, compact layout, from the table above comparison, no return or very little return of the traditional SBR and CAST process has become the first choice of design, while the large sewage treatment plant requires continuous water intake, otherwise the intake pipelines and valves of the design of the flow rate will increase exponentially. From the point of view of the domestic sewage treatment plant has been built, large and medium-sized sewage treatment plants such as Fushun Sanbotun sewage treatment plant (250,000 tons / day), Tianjin Development Area sewage treatment plant (100,000 tons / day), Kunming, the third sewage treatment plant (150,000 tons / day), Kunming, the fourth sewage treatment plant are used in the DAT - IAT process or ICEAS, such as the treatment of continuous water intake process. On the contrary, small wastewater treatment plants overwhelmingly use the traditional SBR process, and in recent years the use of CAST process is also gradually increasing. For UNITANK and the recent rise of similar MSBR (Modified SBR) process, the current application is not much, but soon likely to become a popular process for small wastewater treatment plants.
CAST process review
CAST process is in recent years in the traditional SBR process on the hair up a new type of process, it is the use of different microorganisms in different loading conditions under the growth rate differences and sewage biological phosphorus denitrification mechanism, will be the biological selector and the traditional SBR reactor combination of products. This process combines the initial reaction conditions of push-flow activated sludge method (with substrate concentration gradient and higher floc load) and the advantages of complete activated sludge method (stronger shock load resistance), which is an effective method for both municipal and industrial wastewater, effectively preventing sludge expansion. In addition, if the anaerobic mode of operation of the selector, it has a biological phosphorus removal effect.
Some information: CAST process introduced an anaerobic selector, so that the system has a strong ability to remove phosphorus denitrogenation. In fact, this statement is not entirely correct. Because in terms of nitrogen removal, CAST system and the traditional SBR is not much different, static precipitation denitrification and denitrification denitrification at the same time in the process of nitrogen removal plays a major role. As for phosphorus removal, only 20-30% of the reflux ratio, the sludge concentration in the selection area can not be guaranteed, for example, if the sludge concentration in the reactor is 6g/L (generally not so high), the reflux ratio of 20%, the sludge concentration of the selection of only 1g/L. Such a low concentration of sludge is very difficult to ensure that a good phosphorus removal effect. Moreover, the reflux is carried out at the same time as the water inlet, which is in the aeration stage, the reflux mixture contains a large amount of dissolved oxygen and nitrate oxygen, also unfavorable phosphorus removal. Thirdly, biological phosphorus removal is realized by excluding phosphorus-rich sludge, and the system of long sludge age and low load operation, the sludge production rate is very low, the same can't guarantee the good effect of phosphorus removal. In fact, many actual engineering design, CAST process is often supplemented with chemical phosphorus removal to ensure that the treatment standard. Therefore, many of the information introduced by the CAST process of good phosphorus de-nitrogen capacity is necessary to further explore and research.
In summary, for small wastewater treatment plants, the traditional SBR process and CAST process is the preferred process for small wastewater treatment plants. Comparison of these two processes, CAST process has a certain biological phosphorus removal effect, and in the case of low concentration of pollutants in the influent, CAST process can effectively prevent sludge expansion. The traditional SBR process is simplified by the lack of internal reflux.
Levels of treatment unit
Pre-treatment
Generally speaking, the temperature, PH value, such as not too high or too low, there can be no special adjusting tank. Because the SBR pool itself is actually equal to a regulating pool. This is the SBR process used in small sewage plants in a very important superiority.
Grid
Because the design flow is small, resulting in a smaller grid. For example, the size of 5000 tons / day sewage plant, set up coarse and fine grating each set of two, parallel settings, the calculated size of the grating is as follows:
Size of sewage plant (tons / day)
5000
The total coefficient of variation is taken as
1.7
Design Parameters
Fine grating
Coarse grating
The gap between bars is as follows
Grate gap (mm)
20
5
Water depth in front of the grille (mm)
300
500
Flow rate through the grille (mm)
0.8
0.8
Mounting angle (°)
60
60
Grid width (mm)
300
350
From the above table, the treatment scale of 5000 tons / day treatment plant, the total coefficient of variation of Kz = 1.7, the calculation of coarse and fine grating size are very small. In this case if the use of mechanical grating, the drive part of the upper part of the channel and slag conveyor space required are generally more than 2m, resulting in a large waste of space, for small wastewater treatment plants, grating often have upper buildings, then increased civil investment. So in the case of slag volume is not a lot, if the calculation of the grille is small, you can use artificial grille instead of mechanical grille.
Sand sedimentation tank
Sand sedimentation tank is generally used bell-type sand sedimentation tank or similar products. If the bell-type sand sedimentation tank pool diameter is not too, sand sedimentation tank can be made of carbon steel sets of equipment. In addition, the sand sedimentation tank inlet and outlet channels can also use the corresponding carbon steel production. This not only increases the convenience of construction and installation, and because of the smaller size, the cost does not have to be much higher than the reinforced concrete pool.
Aeration system
Activated sludge method of aeration can be divided into two categories: blast aeration and mechanical aeration of two categories. The main equipment of the aeration system is the blower and diffusion system. Small sewage plant blowers generally use Roots fans and small centrifugal fans. Dispersal system generally use microporous aerator. But it must be adapted to the operation of intermittent aeration. The blower is often installed next to the SBR tank to reduce the cost of the piping system. Due to the small sewage plant, generally do not set up the blower room, only in the blower on the canopy. This applies mainly to sewage treatment plants within factories and mines that do not strictly control noise. If the sewage plant adjacent to the living community, if the use of blower aeration must be built blower room, but also have the corresponding noise reduction measures, so that it is appropriate to use mechanical aeration.
Mechanical aeration relative to the blower aeration, with low noise, simple installation and other advantages, especially for small sewage plants. The principle of the main mechanical aeration equipment, applicable conditions and reference production equipment manufacturers see the following table.
No.
Equipment name
Oxygen supply
Depth
Working principle
Reference manufacturers
1
Centrifugal submersible aeration machine
2-90kgO2/hr
3-6m
Submersible motor drives the impeller rotation
Taiwan Chuan Yuan Co., Ltd's AR series products;
Nanjing Lanshen QXB series products;
2
Jet Submersible Aerator
0.5-8kgO2/hr
2-4m
Using the principle of the water injector to the reaction pool of sewage as a medium, through the water pump Pressurized, high-speed through the throat, the formation of negative pressure, inhalation of air, and fully mixed with sewage, through the diffusion tube spray. Can also be used in the reaction tank outside the dry pump combined with the water jet work
Taiwan Chuan Yuan Co., Ltd. of the GR series; Guangzhou Green Blue Environmental Protection Company QPJ series products; Nanjing Blue Deep QSB series products;
3
Vertical Shaft Pusher Aerator
7.5-24 kg of CO2 / hr
3- 6m
Aerator* floats on the surface of the water, the drive shaft is perpendicular to the water surface, the drive shaft drives the impeller high-speed rotation in the center of the impeller front area to generate strong negative pressure, the air from the hollow spindle into the turbulence chamber, stirring and then diffused into the sewage
Zhejiang Zhuji Hongyu Environmental Protection Equipment Factory O2BG-type equipment;
4
Inclined-axis push-flow type aerator
5-30kgO2/hr
1-5.5m
Principle is the same as 3, except that the drive shaft is at an angle of 0-45° with the water surface, which has the function of aeration as well as push flow.
Shanghai wise environmental protection company agent of the United States AIRE-O2 series of products; Zhejiang Zhuji Hongyu Environmental Protection Equipment Factory O2JBG-type equipment;
The above table 1, 2 types of equipment for the submersible motor, with a compact structure, easy to install, low noise, aeration efficiency and other advantages, but the submersible motor on the equipment processing capacity and equipment for the self-protection ability of the requirements of a higher. And 3, 4 types of motors on the water surface, running safety, relatively long life, but the noise is slightly larger than 1, 2, installation requires a zip line, less beautiful.
In many cases, the aerator is the preferred equipment. In recent years, the construction of small sewage plants, the above four types of aerators are widely used. But relative to the blower aeration power efficiency is low.
Dewatering machine
Generally can be used belt dewatering machine. Because the domestic equipment is more over, the equipment cost is not high, do not have to run continuously. Although the sanitary conditions are poor, but also can take corresponding measures to improve, such as forced ventilation or deodorization mentioned later. Under the conditions, can also be used centrifugal dewatering machine, in order to improve the working environment, reduce the dosage.
Deodorization measures
Wastewater treatment plant in the sewage treatment at the same time, the by-products with odor. The main components of the odor is hydrogen sulfide (H2S), ammonia, tetrathiols, etc., mainly from the decay of sewage and sludge. H2S in the air will be part of the oxidation of SO2, generally 30% of the SO2 in the air is converted from H2S. These odors inevitably affect the surrounding environment, in order to reduce the adverse effects of odor on the surrounding environment, in many of the more stringent requirements of small sewage treatment plants, set up biological deodorization measures. Commonly used methods are: chemical absorption method, biological method, soil method three categories.
(1) chemical absorption method is through the chemicals (mainly lye) to absorb H2S and other pollutants in the air. Deodorization device by the deodorization tanks and regeneration tower. Tank diameter and height ratio is generally: 1:5 or so, odor collected by the ventilation equipment, through the duct from the lower part of the tank into the deodorant tank. With a concentration of 2% -3% of sodium carbonate solution as an odor absorber. The advantages of this method are: good treatment effect, stable operation, strong shock load resistance; the disadvantage is that the agent needs to be replaced regularly, the operating costs are high.
(2) biological method is through the biofilm attached to the filler to degrade the odor in the air, biofilm growth, maturity and biodegradation ability to achieve biodegradation process is a biological culture process. Biofilm microorganisms need nutrients from the sewage organic matter, for sewage treatment plants generally use raw sewage on the filler spray. Deodorization tank empty pool residence time of 1-3min (depending on the odor concentration changes), the inlet flow rate of 2-3m/s. The advantage of this method is to strengthen the management of the case, the treatment effect is good, the operating costs are very low (compared to the other two methods), the disadvantage is: the treatment effect is affected by the concentration of the inlet gas, not very stable, for the spraying of the sewage in the concentration of organic matter has certain requirements.
(3) soil deodorization method is the collection of gas through the pipeline into the bottom of the deodorization tank and diffuse in the soil (soil to natural soil, humus is appropriate), odor in the process of passing through the soil by the adsorption on the surface of the soil particles, a variety of odorous substances are retained. After a period of time, microorganisms can be gradually cultivated on the surface of soil particles for odor-causing substances, and can continuously decompose odor-causing substances to complete deodorization. At the same time, the surface of the soil deodorization tank can be naturally grown or artificially planted with flowers and plants, forming a good environmental effect. The advantage of soil deodorization is that the investment is small, the operation cost is low, and can be combined with the greening of the plant, without any by-products. The disadvantage is susceptible to the influence of groundwater and low temperature in winter, deodorization effect is general.