Modern sewage treatment technology, according to the degree of treatment, can be divided into primary, secondary and tertiary treatment.
Primary treatment, the main removal of sewage in a suspended state of solid pollutants, most of the physical treatment method can only complete the requirements of primary treatment. After primary treatment of sewage, BOD can generally remove about 30%, not up to discharge standards. Primary treatment belongs to the pretreatment of secondary treatment.
Secondary treatment, the main removal of sewage in the colloidal and dissolved state of organic pollutants (BOD, COD substances), the removal rate of up to 90% or more, so that organic pollutants to meet the discharge standards.
Tertiary treatment, further treatment of difficult to degrade organic matter, nitrogen and phosphorus can lead to eutrophication of the water body, such as soluble inorganic substances. The main methods include biological nitrogen and phosphorus removal, coagulation and precipitation, sand filtration, activated carbon adsorption, ion exchange and electro-osmosis analysis.
The whole process is through the coarse grating of raw sewage through the sewage lifting pump, after lifting, through the grating or sand filter, and then into the sand sedimentation tank, after the sand and water separation of sewage into the initial sedimentation tank, the above for the first level of treatment (i.e., physical treatment), the primary sedimentation tank of the effluent into the biological treatment equipment, there are activated sludge and biofilm method, (which activated sludge method of the reactor aeration tank, oxidation ditch, etc.), biofilm method includes biofilter, and biofilm method includes biofilter. (The reactors of activated sludge method are aeration tank, oxidation ditch, etc., and biofilm method includes biofilter, bio-turntable, bio-contact oxidation and bio-fluidized bed), the effluent of the biological treatment equipment enters into the secondary sedimentation tank, and the effluent of the secondary sedimentation tank is disinfected and discharged or enters into the tertiary treatment, which is the end of the primary treatment to the secondary treatment, and the tertiary treatment includes the biological denitrification and removal of phosphorus, coagulation and sedimentation, sand filtration, activated carbon adsorption, ion-exchange and electrodialysis. Part of the sludge from the secondary sedimentation tank is returned to the primary sedimentation tank or biological treatment equipment, part of it enters the sludge thickening tank, and then it enters the sludge digesting tank, and after dewatering and drying equipment, the sludge is finally utilized. Process flow
Raw water→grid→regulation tank→lifting pump→bioreactor→circulation pump→membrane module→disinfection device→medium water storage tank→medium water system
MBR wastewater treatment process
Wastewater enters the regulation tank through the grid and then enters into the bioreactor through the lifting pump, and then the oxygenation is turned on by the aeration machine via the PLC controller, and the effluent of bioreactor enters into the membrane separation treatment unit through the circulating pump. The water from the bioreactor enters the membrane separation treatment unit through the circulation pump, the concentrated water returns to the regulating pool, and the water separated from the membrane is chlorinated and disinfected by the rapid mixing method (sodium hypochlorite, bleach, chlorine tablets), and then it enters the medium water storage tank. The backwash pump utilizes the treated water in the cleaning tank to backwash the membrane treatment equipment, and the backwash effluent returns to the conditioning tank. The opening and closing of the lifting pump is controlled by the water level in the bioreactor. The membrane unit's filtration operation and backwash operation can be automatically or manually controlled. When the membrane unit needs chemical cleaning operation, close the water inlet valve and sewage circulating valve, open the medicinal washing valve and medicament circulating valve, start the medicinal liquid circulating pump, and carry out chemical cleaning operation. Membrane biological treatment technology applied to wastewater reuse, has the following characteristics:
(1) can efficiently solid-liquid separation, the wastewater in the suspended substances, colloidal substances, biological unit loss of microbial flora and has been purified water separate. Separation process is simple, covers an area of small, good quality of effluent water, generally can be reused without three-stage treatment.
(2) can make biological treatment unit biomass to maintain a high concentration, so that the volumetric load is greatly improved, while the high efficiency of the membrane separation, so that the treatment unit hydraulic retention time is greatly shortened, and the footprint of the bioreactor is reduced accordingly.
(3) As it can prevent the loss of various microbial flora, it is conducive to the growth of slow-growing bacteria (nitrifying bacteria, etc.), so that the system of various metabolic processes are carried out smoothly.
(4) It makes the residence time of some large molecules of difficult-to-biodegrade organic matter longer, which is favorable to their decomposition.
[5] Membrane treatment technology and other filtration and separation technology, in the long-term operation process, the membrane as a filtration medium clogging, membrane through the amount of water through the running time and gradually decline in effective backwashing and chemical cleaning can slow down the decline in the membrane flux, to maintain the effective service life of the MBR system.
(6) MBR technology used in municipal wastewater treatment, due to its simple process, easy to operate, can realize the fully automatic operation and management. Outline
SBR wastewater treatment process is the sequencing batch activated sludge method, the full name: Sequencing Batch Reactor Activated Sludge Process (Sequencing Batch Reactor Activated Sludge Process).
Abbreviation (SBR-Sequencing Batch Reactor) batch activated sludge sewage treatment process, SBR process.
It is based on the suspended growth of microorganisms in aerobic conditions on the degradation of organic matter, ammonia and nitrogen and other pollutants in the sewage wastewater biological treatment activated sludge process. It is a wastewater treatment technology that is widely recognized and adopted around the world, which operates by intermittent aeration and changes the growth environment of activated sludge according to the time sequence.
Process
A representative SBR process is: pre-treatment of wastewater through the grid, into the collection well, elevated by the submersible pumps into the SBR reaction tank, the use of water flow aerator oxygenation, the treated water is discharged from the drain, the residual sludge hydrostatic pressure, discharged into the sludge well from the SBR tank, the sludge is used as fertilizer.
Batch operation: time-divided operation instead of space-divided operation, such as the SBR operation cycle by the water intake time, reaction time, settling time, decanting time, sludge discharge time and idle time, which can be appropriately and flexibly adjusted.
Calculation method:
Sedimentation and drainage time ( Ts + D ) is generally designed according to 2 ~ 4h. Idle time ( Tx) is generally designed according to 0.5~1h. Set the reaction time ( Tf). The time required for a cycle T ≥ Tf + Ts + D + Tx.[1]
Example of time allocation, such as: operation cycle 12h, in which the intake of water 2h, aeration 4 ~ 8h, sedimentation 2h, drainage 1h. SBR process as a kind of activated sludge process, but also the advantages and disadvantages of the activated sludge process, such as activated sludge process Advantages: sewage adaptability, construction costs are lower.
Disadvantages of activated sludge process: poor operational stability, prone to sludge expansion and sludge loss, separation effect is not ideal.
SBR process also has unique characteristics. Its total advantages and disadvantages see the following:
Advantages
The treatment process is simple:
Five stages of the process: water intake, aeration, sedimentation, drainage, standby.
Intermittent aeration, non-stable biochemical reaction instead of steady-state biochemical reaction,
Static ideal precipitation Static ideal precipitation instead of the traditional dynamic precipitation.
Low number of structures, low cost:
No need to set up the primary sedimentation site, there is no need for the second sedimentation site, sludge reflux facilities, regulating tanks, primary sedimentation tanks can also be omitted.
Easy to operate and maintain management. It avoids the shortcomings of traditional anaerobic reactor, such as low processing efficiency and large area.
Simple structure
Combined construction method, conducive to the expansion and transformation of wastewater treatment plant.
Good quality of treated effluent.
Good self-control system, good denitrification and phosphorus removal effect, wastewater discharge, some data say that the average removal rate of CODCr can reach more than 94%, stronger than the single-stage aerobic treatment process.
Operation of orderly and intermittent operation.
Specially suitable for the treatment of wastewater that is difficult to biochemical degradation.
Solve the problem of UASB and other high-efficiency anaerobic reactors, which are prone to acid accumulation in the hydrolysis acidification stage and thus inhibit the treatment efficiency of the methane production section.
Small footprint, low energy consumption, investment, easy operation and management
Disadvantages
Severe reliance on modern automation control technology.
The degree of automation requires a high degree of operation, management, maintenance, the quality of the operation and management personnel required.
If manual operation, there will be due to the in and out of the water process operation of cumbersome, aeration plate is easy to clog.
Scope of application
Small and medium-sized towns and industrial sewage and industrial sewage of factories and mining enterprises, especially intermittent discharge and flow changes. Places that need higher water quality, such as scenic tour areas, lakes and harbors, etc., not only to remove organic matter, but also require the effluent water to remove phosphorus and denitrogen to prevent eutrophication of rivers and lakes. Where water resources are scarce, the SBR system can carry out physical treatment after biological treatment, without the need to increase facilities for water recycling. Where land is tight. Retrofitting of established continuous flow sewage treatment plants, etc. Very suitable for the treatment of small amounts of water, intermittent discharge of industrial wastewater and decentralized point source pollution management.
SBR design points
1, the operating cycle (T) to determine the operating cycle of the SBR by the filling time, reaction time, settling time, drainage time and idle time to determine. The filling time (tv) should have an optimal value. As mentioned above, the filling time should be determined according to the specific water quality and the aeration method used during operation. When using limited aeration and the concentration of pollutants in the feed water is higher, the filling time should be appropriately longer; when using non-limited aeration and the concentration of pollutants in the feed water is lower, the filling time can be appropriately shorter. Charging time is generally taken 1 ~ 4 h. Reaction time (tR) is to determine the volume of the SBR reactor is a very important process design parameters, the determination of its value also depends on the nature of the sewage in the operation process, the concentration of sludge in the reactor and aeration and other factors. For domestic sewage class easy to deal with sewage, the reaction time can be taken shorter, on the contrary, the sewage containing difficult to degrade substances or toxic substances, the reaction time can be appropriately taken longer. Generally in 2 ~ 8h. precipitation drainage time (tS + D) is generally designed according to 2 ~ 4h. Idle time (tE) is generally designed according to 2h. A cycle of time tC ≥ tR "tS" tD number of cycles n﹦24/tC 2, the calculation of the volume of the reaction tank assuming that the volume of sewage for each series of q, the volume of sewage in each cycle into the reaction tank q/n-N. The volume of the reaction tank for: V: the capacity of the reaction tank 1/m: discharge ratio n: the number of cycles (cycle/d) N: the number of the series of the reaction tank q: the volume of the reaction tank of each series of Sewage intake (design maximum daily sewage volume) (m3/d) 3, aeration system In the sequential batch activated sludge method, the capacity of the aeration device should be the oxygen demand that can be supplied in the specified aeration time, and in the design, the BOD per unit of influent water is 0.5-1.5kgO2/kgBOD in high load operation, and it is 1.5-2.5kgO2/kgBOD in low load operation.
In sequential batch activated sludge method, due to the aeration and sedimentation of activated sludge in the same reaction tank, the aeration device must be not easily clogged, while taking into account the mixing performance of the reaction tank. Commonly used aeration systems are gas-liquid mixing jet, mechanical mixing, perforated aeration pipe, microporous aerator, generally selected jet aeration, because it is not aeration fashion has a mixing effect, while avoiding clogging. 4, drainage system
1) supernatant discharge device should be able to set the drainage time, the activated sludge does not occur in the case of floating supernatant discharge, discharge mode gravity discharge and pump discharge. (2) In order to prevent the failure of the supernatant discharge device, a drainage device for accidents shall be provided. (3) The supernatant discharge device shall be equipped with a mechanism for preventing the outflow of scum. The discharge device for sequential batch activated sludge shall discharge supernatant separated from activated sludge during the settling drainage period and shall have the following characteristics: 1) It shall be possible to discharge supernatant at a specified flow rate without either disturbing the settled sludge or causing the sludge to float. (Quantitative Drainage) 2) To obtain clear treated water after separation, the collecting mechanism shall be located as close to the water surface as possible and shall be capable of draining in response to changes in the water level after the supernatant has been discharged. (Performance of following the water level) 3) Drainage and stopping of drainage should be carried out smoothly with accurate, long-lasting and reliable operation. (Reliability) The structural form of the drainage device has float type, mechanical type and fixed type without lifting according to the different ways of lifting. 5、Discharge equipment Design sludge dry solid volume = design sewage volume × design influent SS concentration × sludge yield/1000 Sludge yield is calculated by producing 1 kg for every 1 kg of SS inflow during high load operation (0.1～0.4 kg-BOD/kg-ss-d), and is calculated by producing 0.75 kg for every 1 kg of SS inflow during low load operation (0.03～0.1 kg-BOD/kg-ss-d). In low load operation (0.03 to 0.1 kg-BOD/kg-ss-d), 0.75 kg is generated per 1 kgSS inflow. A simple sludge thickening tank is installed in the reactor to obtain 2 to 3% thickened sludge. Because the sequential batch activated sludge method does not have a primary sedimentation tank, easy to inflow more debris, sludge pumps should be used to prevent clogging of the pump type.
SBR design main parameters
Sequencing batch activated sludge design parameters, must take into account the geographical characteristics of the treatment plant and design conditions (land area, maintenance management, treatment of water quality indicators, etc.) to determine the appropriate. Design parameters for facility design should be based on the following values: Item Parameter BOD-SS loading (kg-BOD/kg-ss-d) 0.03～0.4 MLSS (mg/l) 1500～5000 Discharge ratio (1/m) 1/2～1/6 Safe height ε (cm) (minimum water depth above the activated sludge interface) 50 or more Sequencing batch activated sludge method is a kind of method which, according to the different organic loads, starts from the low load and then goes to the low load. The sequencing batch activated sludge method is a method that can be operated from low load (equivalent to the oxidation ditch method) to high load (equivalent to the standard activated sludge method) depending on the organic load. The BOD-SS loading of the sequencing batch activated sludge method, due to the consideration of the aeration time as the reaction time, is defined by the following formula: QS: sewage intake (m3/d) CS: average BOD5 of the influent water (mg/l) CA: average MLSS concentration of the mixture in the aeration tank (mg/l) V: volume of the aeration tank e: ratio of the aeration time e=n-TA/24 n: number of cycles TA. Aeration time of one cycle The loading conditions of the sequential batch activated sludge method are determined based on the ratio of the reactor tank volume to the sewage influent volume and the number of cycles per day in each cycle; moreover, in the sequential batch activated sludge method, the organic load can also be adjusted by the change of MLSS concentration because it is easy to maintain a good MLSS concentration in the tank. Further, since the aeration time is easily adjustable, the organic matter load can also be adjusted by changing the aeration time. When denitrification and desulfurization are the targets, in addition to the organic matter load, the discharge ratio, the number of cycles, the daily aeration time, etc., must also be studied. High load operation is appropriate in facilities with restricted site area, and low load operation is preferable in small-scale facilities with small influent flows and large load variations. Therefore, it is effective to operate at a low load at the beginning of operation and at a high load as the water volume increases. Characteristics under different loading conditions Organic loading conditions (influent conditions) High loading operation Low loading operation Intermittent influent Intermittent influent, continuous Operating conditions BOD-SS loading (kg-BOD/kg-ss-d) 0.1-0.4 0.03-0.1 Number of cycles Large (3-4) Small (2-3) Discharge ratio Large Small Processing Characteristics Organic matter removal Treated water BOD<20mg The removal rate is relatively high Nitrogen removal is low High Phosphorus removal is high Low Sludge production is more or less Maintenance and management The resistance to load change is poorer than the low load The adaptability to load change is strong, and the flexibility of operation is strong Land area Reactor volume is small, saving land Reactor volume is large Scope of application It is able to effectively treat sewage above the medium scale, and is applicable to the facilities with a scale of treatment of more than about 2,000m3/d. It is applicable to the small-scale sewage treatment plant, and the scale of treatment of about 2,000m3/d is about 2,000m3/d or more. The treatment scale is about 2000m3/d or less, applicable to facilities that do not require nitrogen removal.