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A New Method of Water Treatment

Apr. 29, 2019

1. Basic knowledge


1.1 Basic knowledge of sewage treatment


1.1.1 Wastewater Treatment Method


The main treatment methods of sewage are the physical method, physical-chemical method, biological method, and combination method.


Pretreatment of 1.1.2 Wastewater


The pretreatment of wastewater is aimed at removing large particle pollutants and suspended matter from wastewater.


Common pretreatment methods include grille, and settling, oil isolation and regulation.

Johnson screen (wedge wire screen) is widely used in water treatment pretreatment for the following reasons:


1. Not easily blocked

V-shaped wire structure, not easy to plug, Johnson mesh can work in harsh filtering environment.

2. easy to clean

3. pressure reduction


In water treatment, flow control is very important, and the main factor affecting flow is the opening rate of wedge wire screen. Please check the relevant technical information: Wedge Wire Screen Open Area.

The main methods of oil removal are: adding partitions and inclined plates.


Water quality and quantity can be regulated by regulating the pool.

1.1.3 Sewage Treatment Level


Primary treatment: water after simple physical treatment of sewage; secondary treatment: effluent after primary treatment and biochemical treatment. Third-level treatment: also known as an advanced treatment, the effluent of second-level treatment is then treated by adding medicine, filtering, disinfection lamp, and other technologies so that the effluent meets higher standards.


Among them, the metal filter element is mainly used in the primary treatment process. At present, the most widely used metal filter elements in water treatment are:


A. Johnson screen(wedge wire screen filter)

B. Pleated filter element

C. Sintered filter element

D. Stainless steel filter basket


If you are interested in these stainless steel filter element, you can also visit our home page.

1.1.4 Grade of Drainage Water Quality


In GB3838-88, water is classified into five categories, i.e. Class I, Class II, Class III, Class IV, and Class V.


Category I is mainly applicable to source water and national nature reserves.


Category II is mainly applicable to the first-level protection area of centralized drinking water sources, precious fish and shrimp spawning grounds, etc.


Class III is mainly applicable to secondary protection zones, general fish protection zones and swimming zones concentrated in drinking water sources.


Category IV is mainly applicable to agricultural water use areas and waters with general landscape requirements.


Category V is mainly applicable to agricultural water use and waters with general landscape requirements.


1.1 Basic terms and nouns


SS: Suspended solids refer to the pollutants of inorganic substances, organic substances, organisms and microorganisms whose diameter is less than 0.45um.


COD: Chemical oxygen demand (COD) refers to the elimination of water samples treated with strong oxidants under certain conditions.


The amount of oxidant consumed. COD reflects the pollution degree of reducing substances in water, and also reflects the number of organic substances in water. The reducing substances in water include organic substances, nitrite, ferrous sulfide and so on.


CODcr: Chemical oxygen demand (COD) measured in a strongly acidic solution with potassium dichromate as oxidant.


CODmn: Potassium permanganate index is the chemical oxygen demand measured by using potassium permanganate solution as oxidant.


TOC: Total organic carbon (TOC) is a comprehensive indicator of the total amount of organic matter in water expressed by the content of carbon.


TOD: Total oxygen demand refers to substances that can be oxidized in water, mainly organic substances in combustion.


The amount of oxygen required to become a temperature oxide is expressed in mg/L of O2.


BOD: Biochemical oxygen demand, refers to the value of aerobic microorganisms in the decomposition of organic matter in water under the condition of dissolved oxygen.


BOD5: Five-day BOD, i.e. the change of dissolved oxygen in water before and after incubation for five days at (20 +1)degrees Celsius.


NH3-N: Ammonia nitrogen refers to nitrogen in the form of free ammonia (NH3) and free ammonia (NH4+).


Transparency refers to the transparency of water samples.


Turbidity: The degree of obstruction of suspended matter in water to light transmission.


Chromaticity: Using the dilution method, the color intensity of the sample is determined by visual comparison with the sample under test.


DO Dissolved oxygen, molecule oxygen dissolved in water.


PH: The negative logarithm of hydrogen ion activity in solution. Characterize the acidity and alkalinity of water.


SV: Sludge settling ratio refers to the percentage of sludge volume in the mixed liquid volume after 30 minutes of settling in the oxidation tank.


SVI: It refers to the wet sludge volume of 1 g dry sludge after 30 minutes precipitation of the mixed liquor in the oxidation tank.


MLSS: The weight of dry sludge contained in the sludge mixture of 1-liter oxidation tank. Expressed as mg/L or g/L.


1. A2/O process


A2/O process for nitrogen and phosphorus removal (anaerobic-anoxic-aerobic activated sludge process, also known as A-A-O process), which is in the process of Ap/O phosphorus removal added an anoxic tank, and the aerobic tank outflow part of the mixed liquid back to the anoxic tank, has the function of simultaneous nitrogen and phosphorus removal.


After pretreatment and primary treatment, the wastewater first enters the anaerobic tank, and the reaction process in the anaerobic tank is the same as that in the Ap/O biological phosphorus removal process; the reaction process in the anaerobic tank is the same as that in the An/O biological nitrogen removal process; the reaction process in the aerobic tank includes both the reaction and function in the Ap/O biological phosphorus removal process and the AN/O biological nitrogen removal process. 。


Therefore, A2/O process can achieve simultaneous removal of organic matter, nitrification, and phosphorus.


A2/O process is suitable for municipal wastewater treatment, which has strict requirements for nitrogen and phosphorus emission indicators. Its advantages and disadvantages are as follows:


(1) This process is the simplest one for simultaneous nitrogen and phosphorus removal. The total hydraulic retention time and total output area are less than those of other processes.




(2) Under the condition of alternating anaerobic and aerobic operation, filamentous bacteria could not proliferate in large quantities, and there was no risk of sludge bulking. SVI values were generally less than 100.


(3) The sludge has high phosphorus concentration and high fertilizer efficiency.


(4) There is no need to administer drugs in operation. Only gentle stirring is used in the two A sections to avoid the concentration of dissolved oxygen and the running cost is low.



(1) The phosphorus removal effect is difficult to improve again, sludge growth has a certain limit, not easy to improve, especially when the P/BOD value is high.

(2) The denitrification effect is also difficult to further improve. The internal circulation is generally limited to 2Q, which should not be too high, otherwise, the operation cost will be increased.

(3) To maintain a certain concentration of dissolved oxygen in the sedimentation tank, reduce the residence time and prevent the occurrence of anaerobic state and phosphorus release from sludge, but the dissolution concentration should not be too high. To prevent the disturbance of circulating mixtures to the reactor.


2. Oxidation ditch process


Oxidation ditch, also known as circulating aeration tank, is a deformation of activated sludge process.


Oxidation ditch, also known as circulating aeration tank, is a modification and development of conventional activated sludge process. The circulating flow of sewage and activated sludge mixture in the annular aeration channel is a kind of deformation of the activated sludge process. The hydraulic retention time of oxidation ditch can reach 10-30 hours, and the organic load is very low, which is essentially equivalent to the delayed aeration activated sludge system. Because of its low operation cost, simple structure, easy maintenance and management, good effluent quality, shock load resistance, stable operation, and nitrogen and phosphorus removal, it can be used in large and medium-sized water plants.




(1) The oxidation ditch has unique hydraulic flow characteristics, which is conducive to the biological flocculation of activated sludge, and can be divided into the oxygen-enriched zone and anoxic zone for digestion and reverses digestion, thus achieving the effect of nitrogen removal.


(2) Organic suspended solids can reach aerobic stability in oxidation ditch without using primary sedimentation tank.


(4) Only the aerator and the propeller in the oxidation ditch can maintain the normal operation of the ditch. The power consumption is small and the operation cost is low.






(1) Sludge bulking. When there are more carbohydrates in wastewater, the amount of N and P is not balanced, the pH value is low, the sludge load in oxidation ditch is too high, the concentration of dissolved oxygen is insufficient, and sludge discharge is not smooth, filamentous bacterial sludge bulking is easily caused.


(2) bubble problem.

(3) Sludge floatation.

(4) The problem of uneven flow rate and sludge deposition.

(5) The oxidation ditch covers a large area.




CASS is the abbreviation of Cyclic Activated Sludge System, which combines a well-nourished biological selector with a traditional continuous influent SBR reactor. CASS process is a new simple sewage treatment process based on the principle of bio-reaction kinetics and reasonable hydraulic conditions.


At present, the CASS process has been widely used in Europe, America and other countries. From the operation effect, the treatment effect is good, and the effect of phosphorus and nitrogen removal is also good.




The process is especially suitable for municipal wastewater containing more industrial wastewater and wastewater requiring phosphorus and nitrogen removal.


Handle. Its advantages and disadvantages are as follows:


(1) The process flow is simple, the management is convenient and the cost is low. CASS process has only one reactor, no secondary sedimentation tank, no sludge confluence equipment and no regulating tank in general. Therefore, it saves more than 30% of the capital investment than the activated sludge process and has a compact layout, which can reduce the area by 35%.


The treatment effect is good. Activated sludge in the reactor is in a process of alternate adsorption, absorption, biodegradation, and activation, so the treatment effect is good.


(3) It has a better effect of nitrogen and phosphorus removal. CASS process can easily alternate aerobic, anoxic and anaerobic environments, and create conditions to improve the effect of nitrogen and phosphorus removal by changing aeration rate and reaction time.


(5) Sludge sedimentation performance is good. The special operating environment of CASS process inhibits the growth of filamentous bacteria in sludge and reduces the possibility of sludge bulking. At the same time, because the precipitation stage of the CASS process is carried out in a static state, the precipitation effect is better.


(6) The unique operating conditions of CASS process determine that it can well adapt to the fluctuation of influent water quantity and quality.




Because the water intake runs through the whole operation cycle, the water intake in the sedimentation stage is at the bottom of the mainstream, causing hydraulic turbulence, affecting the sludge separation time, the water intake is limited to a certain extent, and the hydraulic retention time is longer.


Here I need to talk about the equipment of sludge treatment - solid liquid separator. This equipment is used in the treatment of farm excrement, but after our improvement, it also has a good effect on sludge in water treatment.

2. SBR process


SBR is the abbreviation of Sequencing Batch Reactor Activated Sludge Process. SBR is an activated sludge sewage treatment technology operated by intermittent aeration, also known as sequencing batch activated sludge process.


Different from the traditional sewage treatment process, SBR technology uses time-division operation instead of a space-division operation, unstable biochemical reaction instead of steady-state biochemical reaction, and static ideal precipitation instead of traditional dynamic precipitation.


Its main characteristics are orderly and intermittent operation in operation. The core of SBR technology is SBR reaction tank, which integrates homogenization, initial sedimentation, biodegradation, secondary sedimentation, and other functions into one tank, without sludge reflux system.


SBR has the following advantages:


(1) The ideal push-flow process enhances the driving force and efficiency of a biochemical reaction. The anaerobic and aerobic conditions in the pond are in alternate state, and the purification effect is good.

(2) The operation effect is stable. Sewage is deposited in an ideal static state, which requires a short time, high efficiency and good effluent quality.


(3) Shock load resistance, retention of treated water in the tank, dilution, and buffer of sewage, effective resistance to water and organic pollutants impact.


(4) Each process in the process can be adjusted according to the water quality and quantity, and the operation is flexible.


(6) The processing equipment is few, the structure is simple, easy to operate and maintain and manage.


(7) There are DO and BOD5 concentration gradients in the reaction tank, which can effectively control activated sludge bulking.


(8) The SBR system itself is also suitable for the combined construction method, which is conducive to the expansion and transformation of wastewater treatment plants.


(9) Nitrogen and phosphorus removal, proper control of operation mode, alternation of aerobic, anoxic and anaerobic conditions, has a good effect of nitrogen and phosphorus removal.


(10) The process is simple and the cost is low. The main equipment has only one sequencing batch reactor, no secondary sedimentation tank, and sludge reflux system. The regulating tank and primary sedimentation tank can also be omitted, and the layout is compact and the area is saved.


Scope of application of the SBR system




(1) Domestic sewage from small and medium-sized cities and towns and industrial wastewater from factories and mining enterprises, especially in places where intermittent discharge and flow rate change greatly.


(2) Where higher effluent quality is needed, such as scenic spots, lakes, and harbors, it is necessary not only to remove organic matter but also to remove phosphorus and nitrogen from effluent to prevent eutrophication of rivers and lakes.


(3) Where water resources are scarce. SBR system can be physicochemically treated after biological treatment without additional facilities, which is convenient for water recycling.


(4) Where land is scarce.


(5) Renovation of the existing continuous-flow sewage treatment plant, etc.


It is very suitable for the treatment of industrial wastewater with small water volume and intermittent discharge and the treatment of dispersed point source pollution.


5. UASB( Up-flow Anaerobic Sludge Bed)


Because of its dual characteristics of anaerobic filtration and anaerobic activated sludge process, it is a technology that can convert pollutants in sewage into renewable clean energy - biogas.


It has strong adaptability to sewage with different solid content, and its structure, operation, maintenance, and management are relatively simple, and its cost is relatively low. The technology has matured, and is increasingly valued by the sewage treatment industry, and is widely welcomed and applied.


UASB consists of the sludge reaction zone, gas-liquid-solid three-phase separator (including sedimentation zone) and gas chamber. A large amount of anaerobic sludge is retained in the bottom reaction zone, and sludge with good sedimentation and coagulation properties forms a sludge layer in the bottom. The sewage to be treated flows from the bottom of the anaerobic sludge bed to mix with the sludge in the sludge layer, and the microorganisms in the sludge decompose the organic matter in the sewage and convert it into biogas.


Biogas emits continuously in the form of micro-bubbles. During the rising process, micro-bubbles merge and gradually form larger bubbles. In the upper part of the sludge bed, due to the stirring of biogas, a sludge with thinner sludge concentration and water rise together into the three-phase separator. When biogas meets the reflecting plate at the lower part of the separator, it bends around the reflecting plate and then enters the gas chamber through the water layer. Focusing on methane in the gas chamber, the mixture of solid and liquid is reflected into the sedimentation zone of the three-phase separator. The sludge in the sewage flocculates, and the particles gradually increase, and then settle under the action of gravity.


The sludge deposited on the inclined wall slides back to the anaerobic reaction zone along the inclined wall, which accumulates a large amount of sludge in the reaction zone. After separation with the sludge, the treated effluent overflows from the upper part of the overflow weir in the sedimentation zone and then discharges the sludge bed. The basic requirements are:


It provides favorable physical, chemical and mechanical conditions for sludge flocculation so that anaerobic sludge can obtain and maintain good sedimentation performance.


A good sludge bed can often form a relatively stable biological phase, maintain a specific micro-ecological environment, can resist strong disturbance, larger flocs have good sedimentation performance, thus improving the sludge concentration in the equipment; through setting a sedimentation zone in the equipment of the sludge bed, the fine particles of the sludge can flocculate and precipitate further in the sludge layer of the sedimentation zone, and then flow back into the sludge layer of the sedimentation zone. 污泥床内。


The main advantages of UASB are:


The sludge concentration in UASB is high, and the average sludge concentration is 20-40 gVSS/1.


The organic load is high and the hydraulic retention time is short. When medium temperature fermentation is used, the volume load is generally about 5-10 kg COD/m3.d.


Without mixing equipment, the sludge on the upper part of the sludge bed is suspended and stirred to a certain extent on the lower part of the sludge bed by the rising motion of biogas generated during fermentation process; the sludge bed does not fill the carrier, which saves the cost and avoids the problem of blocking competition due to the filler.


UASB has a built-in three-phase separator, usually, no sedimentation tank, sludge separated from the sedimentation zone can be returned to the sludge bed reaction zone, usually without sludge reflux equipment;


When UASB operates at low temperature in winter, steam pipes are added to the pool, and the system is heated by the waste heat of boiler steam to ensure a good operating environment.


The methane gas generated by the system can be introduced into the boiler room for retention.


Finally, in water treatment, the choice of metal filter element is very important. I personally suggest that if there is no need to go to the filter area, the wedge wire screen filter is the most suitable.



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