CN108423880B

CN108423880B - Sewage pretreatment process

Info

Publication number: CN108423880B
Application number: CN201810427665.9A
Authority: CN
Inventors: 景江; 纪福林; 毛朝玉; 许洋; 汪栋春; 罗怀清
Original assignee: Chengdu Technological University CDTU
Current assignee: Chengdu Technological University CDTU
Priority date: 2018-05-07
Filing date: 2018-05-07
Publication date: 2020-08-11
Anticipated expiration: 2038-05-07
Also published as: CN108423880A

Abstract

The invention relates to a sewage pretreatment process. The sewage pretreatment process comprises the steps of adding an inorganic flocculant into flowing sewage, then carrying out primary filtration, adding an organic flocculant into the sewage after the primary filtration, and then carrying out secondary filtration to obtain pretreated sewage. The sewage pretreatment process can effectively solve the problem of wide occupied area of the existing sewage pretreatment, simultaneously improves the pretreatment effect of the sewage, effectively reduces the total amount of COD, BOD and SS in the sewage, and does not affect the use of a filter screen.

Description

Sewage pretreatment process

Technical Field

The invention relates to a sewage pretreatment process.

Background

The traditional sewage pretreatment usually adopts a standing mode or adds biological fermentation and the like to promote impurities in the sewage to be separated out in a precipitate mode, so that the impurities are removed through a filtering step; however, the traditional sewage pretreatment method not only takes a long time, but also expands the transverse area of the sewage to be still because of the need of still standing, accelerates the sedimentation process, and leads to a wider occupied area.

The existing sewage purification usually adopts a membrane treatment process, but the sewage needs to be pretreated before membrane treatment, the pretreatment aims at filtering and removing impurities which can be converted into precipitates in an impurity form, and then the purification aim is achieved by adopting the membrane treatment technology. The current membrane applicable to sewage purification has low requirements, and the main reason is that after sewage is subjected to conventional standing filtration in a pretreatment stage, the total COD (chemical oxygen demand) of the obtained pretreated sewage is still high, usually more than 150mg/L, the quality of the membrane capable of treating the sewage with the total COD of more than 150mg/L is low, the purification effect is not ideal, and the membrane with the high purification effect generally requires the total COD, the total BOD and the total SS in the sewage to be below specific values, such as MBR (membrane bioreactor) soft sheet membranes.

In addition, the existing method of adding a flocculating agent and then intercepting and precipitating is applied to pretreatment of flowing sewage, and the method can better solve the problem of larger floor area of sewage pretreatment. However, in the practical application process, the mode is found to have a small floor area, but the precipitation and filtration effects are not ideal, so that the filter screen is easy to block in a short time in the flowing process of the sewage, the effect of sewage pretreatment is affected, the total COD (chemical oxygen demand), the total BOD (biochemical oxygen demand) and the total SS (suspended substance) cannot reach specific required values, and the limitation on the subsequently adopted purification membrane is large.

Disclosure of Invention

The inventor of the invention finds that the reason that the filter screen is easy to be blocked after the flocculating agent is added into the sewage is mainly that the generated precipitate has high viscosity and low looseness after the flocculating agent is added, so that the pore diameter of the filter screen is easy to be blocked, especially under the condition that an inorganic flocculating agent and an organic flocculating agent are added before filtration, regardless of the sequence.

The invention provides a sewage pretreatment process which can effectively solve the problem of wide occupied area of the existing sewage pretreatment, simultaneously improve the pretreatment effect of sewage, effectively reduce the total amount of COD, BOD and SS in the sewage and avoid influencing the use of a filter screen.

In order to solve the above technical problems, the present invention provides a sewage pretreatment process, including a first filtration step of adding an inorganic flocculant to flowing sewage, and a second filtration step of adding an organic flocculant to the once-filtered sewage to obtain pretreated sewage.

Preferably, before the inorganic flocculant is added, the flow rate of the sewage is 1.1-2 m/s; the flow rate of the sewage is 1.9 mm/s-3.5 mm/s during the primary filtration and the secondary filtration.

Preferably, the sewage flows upward after one filtration and flows downward during one filtration.

Preferably, the downward flow of the sewage in the primary filtration is realized by pushing a propeller to rotate by the flowing sewage and simultaneously pushing the sewage to flow downwards by the rotating propeller; the rotating speed of the propeller is 35-64 r/min, and the included angle between the propeller and the vertical direction is 30-60 degrees.

Preferably, one end of the propeller close to the secondary filtering is provided with a hairbrush.

Preferably, the inorganic flocculant is polyaluminium chloride and the organic flocculant is polyacrylamide.

Preferably, the addition amount of the inorganic flocculant is 120mg/L, and the addition amount of the organic flocculant is 2 mg/L.

Preferably, the pore size of the filter for the first filtration is 100-150 μm, and the pore size of the filter for the second filtration is 50-100 μm.

Preferably, the sewage after the primary filtration firstly flows through an electric field area, and then is subjected to secondary filtration after an organic flocculant is added to obtain pretreated sewage.

Preferably, the sewage after primary filtration sequentially flows through a settling zone and an electric field area, and then is subjected to secondary filtration after an organic flocculant is added to obtain pretreated sewage.

Preferably, the height of the electric field region is 80% to 100% of the height of the settling zone.

According to the sewage pretreatment process, different flocculants are added into flowing sewage step by step, and sewage pretreatment is carried out in a step intercepting and filtering mode; meanwhile, due to the fact that different flocculating agents are added in different modes, the viscosity of the sediment is reduced, even if a large amount of sediment is generated or the sewage pretreatment time is long, the sediment is still high in looseness after gathering, and large in porosity, and therefore the influence of the sediment on the blockage of the filter screen is reduced, the sewage pretreatment effect is effectively improved, and the total amount of COD (chemical oxygen demand), BOD (biochemical oxygen demand) and SS (suspended substance) in the sewage is effectively reduced.

Drawings

Fig. 1 is a schematic view of a sewage pretreatment apparatus that may be employed in the sewage pretreatment process of the present application.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention. In the present invention, the embodiments and the features of the embodiments may be arbitrarily combined with each other without conflict.

The following is pretreated sewage obtained by the sewage pretreatment process described in the present application, and various parameters thereof can be detected.

Implementation mode one

1) Adding an inorganic flocculant, such as polyaluminium chloride, into the sewage at a flow speed of m1m/s, and then performing primary filtration, wherein the adding amount of the inorganic flocculant is n1mg/L (taking the sewage volume as a reference, namely the mass of the inorganic flocculant which needs to be added into each liter of sewage);

2) adding an organic flocculant, such as polyacrylamide, into the sewage subjected to primary filtration, and then performing secondary filtration to obtain pretreated sewage; the adding amount of the organic flocculant is n2mg/L (taking the volume of the sewage as a reference, namely the mass of the organic flocculant to be added in each liter of sewage), and the flow rate of the sewage is m2mm/s during the primary filtration and the secondary filtration.

In the above step, the sewage flows in the same direction throughout the process, for example, in a transverse direction, the screens for the primary filtration and the secondary filtration are preferably perpendicular to the sewage flow direction, the screen aperture for the primary filtration is l1 μm, and the screen aperture for the secondary filtration is l2 μm.

The pretreated sewage obtained according to the sewage pretreatment process and the parameters of the following steps 1 has various detection knotsThe results are shown in Table 2, for example: total COD L1mg/L, total BOD L2mg/L, total SS L3mg/L, volume of pretreated sewage V m in 30min³The ratio of the sum of the pore areas of the filter screen and the sediment on the filter screen after the sewage is pretreated for 30min to the pore area of the filter screen before the sewage is treated (after treatment/before treatment) D1, and the ratio of the sum of the pore areas of the filter screen and the sediment on the filter screen after the sewage is pretreated for 30min to the pore area of the filter screen before the sewage is treated (after treatment/before treatment) D2.

TABLE 1

Examples	m1	n1	n2	m2	l1	l2
								1	1.1	120	2	3.5	100	50
2	2	120	2	3.0	150	100
							3	1.3	120	2	2.5	115	60
4	1.8	120	2	2.2	135	90
							5	1.5	120	2	1.9	120	75

TABLE 2

Second embodiment

2) the sewage after primary filtration sequentially flows through a settling zone and an electric field area, and then is subjected to secondary filtration after organic flocculant, such as polyacrylamide, is added to obtain pretreated sewage; the adding amount of the organic flocculant is n2mg/L (taking the volume of the sewage as a reference, namely the mass of the organic flocculant to be added in each liter of sewage), and the flow rate of the sewage is m2mm/s during the primary filtration and the secondary filtration.

In the steps, before primary filtration, the flowing sewage pushes the propeller to rotate, and the propeller with the rotating speed of R rad/s reversely pushes the sewage to flow downwards so as to promote the sewage to flow downwards in the primary filtration, and the sewage flows upwards after the primary filtration, and the sewage can be intercepted simply and physically, the included angle between the propeller and the vertical direction is alpha degrees, and one end of the propeller, which is close to the secondary filtration, is provided with a hairbrush; the brush carries out rotary motion, can further break up the deposit on the secondary filter's filter screen better, increases its porosity. The screens for the primary filtration and the secondary filtration are preferably perpendicular to the direction of flow of the wastewater, the screen aperture for the primary filtration being l1 μm and the screen aperture for the secondary filtration being l2 μm. The height of the electric field region is d% of the height of the settling zone.

The pretreated sewage obtained according to the sewage pretreatment process and the parameters of the following steps 3 has the following detection results as shown in the following table 4, for example: total COD L1mg/L, total BOD L2mg/L, total SS L3mg/L, volume of pretreated sewage V m in 30min³The ratio of the sum of the pore areas of the filter screen and the sediment on the filter screen after the sewage is pretreated for 30min to the pore area of the filter screen before the sewage is treated (after treatment/before treatment) D1, and the ratio of the sum of the pore areas of the filter screen and the sediment on the filter screen after the sewage is pretreated for 30min to the pore area of the filter screen before the sewage is treated (after treatment/before treatment) D2.

TABLE 3

TABLE 4

In the second embodiment, the sewage pretreatment apparatus shown in fig. 1 can be used to pretreat sewage, and fig. 1 is a schematic view of the sewage pretreatment apparatus that can be used in the sewage pretreatment process of the present application. As shown in fig. 1, the sewage pretreatment apparatus shown in fig. 1 includes a drug reservoir 1, a delivery pipe 8, a filter; the filter is internally provided with a filter screen 3 for primary filtration, a pipeline inlet 9, a propeller 10, an electrode field 6, a brush 11, a filter screen 7 for secondary filtration and a filter outlet 12 from bottom to top in sequence;

wherein, the pipeline inlet 9 is connected with the conveying pipeline 8 to convey sewage; before the sewage enters the filter, the medicine storage device 1 adds an inorganic flocculant, such as polyaluminium chloride (PAC), to the flowing sewage in the conveying pipeline 8;

a filler 2 is arranged below the filter screen 3 for primary filtration so as to better filter sewage; the aperture of the filter 3 for the primary filtration is preferably 100-150 μm;

one end of the propeller 10 close to the filter screen 3 for primary filtration is provided with a helical blade 4, and the included angle between the helical blade 4 and the vertical direction is alpha degrees, preferably alpha is 30-60 degrees;

one end of the propeller 10 close to the filter screen 7 for secondary filtration is provided with a brush 11;

an electrode field 6, namely an electric field area, is arranged in the filter between the helical blade 4 and the brush 11, and a settling area 5 is arranged in the filter between the electric field area and the filter screen 3 for primary filtration; after the electric field area, the medicine reservoir 1 feeds an organic flocculant, such as Polyacrylamide (PAM);

the outlet 12 of the filter is provided at the rear end of the secondary-filtered screen 7, and the pore size of the secondary-filtered screen 7 is preferably 50-100 μm.

As can be seen from the above table data, in the first embodiment, the sewage pretreatment effects obtained in examples 3 to 5 are better, and the second embodiment is similar; in addition, the second embodiment has better sewage pretreatment effect than the first embodiment.

The above is only a preferred embodiment of the present invention, and it should be noted that the above preferred embodiment should not be considered as limiting the present invention, and the protection scope of the present invention should be subject to the scope defined by the claims. It will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the spirit and scope of the invention, and these modifications and adaptations should be considered within the scope of the invention.

Claims

1. The sewage pretreatment process is characterized by adopting the following sewage pretreatment equipment and steps; the sewage pretreatment equipment comprises a medicine storage device (1), a conveying pipeline (8) and a filter; a filter screen (3) for primary filtration, a pipeline inlet (9), a propeller (10), an electrode field (6), a brush (11), a filter screen (7) for secondary filtration and a filter outlet (12) are sequentially arranged in the filter from bottom to top;

wherein, the pipeline inlet (9) is connected with the conveying pipeline (8) to convey sewage; before the sewage enters the filter, the chemical storage device (1) adds an inorganic flocculant to the flowing sewage in the conveying pipeline (8); a filler (2) is arranged below the filter screen (3) for primary filtration; one end of the propeller (10) close to the filter screen (3) for primary filtration is provided with a helical blade (4), and the included angle between the helical blade (4) and the vertical direction is alpha degrees; one end of the propeller (10) close to the filter screen (7) for secondary filtration is provided with a brush (11);

an electrode field (6), namely an electric field area, is arranged in the filter between the helical blade (4) and the brush (11), and a settling area (5) is arranged in the filter between the electric field area and the filter screen (3) for primary filtration; after the electric field area, the medicine storage device (1) inputs organic flocculant to the sewage in the filter; the outlet (12) of the filter is arranged at the rear end of the filter screen (7) of the secondary filtration;

adding an inorganic flocculant into flowing sewage, then carrying out primary filtration, enabling the sewage after primary filtration to flow through an electric field area, adding an organic flocculant, and then carrying out secondary filtration to obtain pretreated sewage;

before the inorganic flocculant is added, the flow velocity of the sewage is 1.1-2 m/s; during primary filtration and secondary filtration, the flow velocity of the sewage is 1.9 mm/s-3.5 mm/s;

the sewage flows upwards after the primary filtration, and flows downwards during the primary filtration; the pore size of the filter screen for the first filtration is 100-150 μm, and the pore size of the filter screen for the second filtration is 50-100 μm.

2. The wastewater pretreatment process of claim 1, wherein: the downward flow of the sewage during the primary filtration is realized by pushing the propeller to rotate by the flowing sewage and reversely pushing the sewage to flow downwards by the rotating propeller; the rotating speed of the propeller is 35-64 r/min, and the included angle between the helical blades of the propeller and the vertical direction is 30-60 degrees.

3. The wastewater pretreatment process of claim 1, wherein: and the sewage after primary filtration sequentially flows through a settling zone and an electric field area, and is added with an organic flocculant and then is subjected to secondary filtration to obtain pretreated sewage.

4. The wastewater pretreatment process of claim 3, wherein: the height of the electric field region is 80% -100% of the height of the settling zone.