Note: (This manual and the calculation methods and experimental data provided are for reference only: based on the actual experimental data of the school.)
First, the purpose of the experiment:
Sludge specific resistance (or specific impedance) is a comprehensive indicator of sludge dewatering performance. The larger the sludge specific resistance, the worse the dewatering performance, and the better the dewatering performance. In this experiment, the specific resistance of activated sludge was determined by using FeCl3 and Al2(SO4)3 as coagulants.
I hope to achieve the following objectives through experiments:
Master the experimental method for determining the specific resistance of sludge;
Master the choice of coagulant using the Buchner funnel test;
Master the method of determining the dosage of coagulant.
Second, the experimental principle:
The sludge specific resistance is the resistance of the unit dry weight filter cake per unit filtration area. When the value is equal to the viscosity, the pressure difference required for the filtrate to produce the unit filtrate flow rate per unit weight of the mud cake is
Factors affecting the dewatering performance of sludge include: the nature of the sludge, the concentration of the sludge, the viscosity of the sludge and filtrate, the type of coagulant and the dosage. Usually, the Buchner funnel test is used to determine the specific resistance of the sludge by measuring the speed of the sludge filtrate filtration medium, and the filtration performance of different sludges is compared to determine the optimum coagulant and its dosage.
Sludge dewatering relies on the pressure difference between the two sides of the filter medium (porous material) as a driving force to force the water to pass through the filter medium, and the solid particles are trapped on the medium to achieve the purpose of dehydration. There are four ways to create a pressure difference:
Relying on the static pressure of the thickness of the sludge itself (such as the osmotic dehydration of the sludge natural drying field);
One side of the filter medium causes a negative pressure (such as vacuum filtration dehydration);
Pressurized sludge to filter the moisture (such as dewatering by pressure filtration);
Cause centrifugal force as a driving force (such as centrifugal dehydration).
According to the evolution of the driving force in the dehydration process, it can be divided into two types: constant pressure filtration and constant vertical filtration. The former remains unchanged in the filtration process; the latter remains unchanged during the filtration process.
In this experiment, the pressure difference is caused by vacuuming, and the pressure is adjusted by the regulating valve to make the pressure difference constant throughout the experimental process.
At the beginning of the filtration, the filtrate only needs to overcome the resistance of the filter medium. When the filter cake is gradually formed, the filtrate also needs to overcome the resistance of the filter cake itself. The filter cake is made up of particles of sludge and can also be regarded as a porous filter medium. The pores belong to the capillary. Therefore, the true filter layer includes filter cake and filter media. Since the pore size of the filter medium is much larger than the particle size of the sludge particles, only the initial stage of filtration, the filtrate tends to be turbid. As the filter cake is formed, the resistance becomes large and the filtrate becomes clear.
Due to the different nature of sludge suspended particles, the properties of filter cake can be divided into two categories: one is incompressible filter cake, such as grit, primary sediment sludge or other inorganic sediment, under pressure, the particles will not be deformed. Therefore, the passage of the filtrate in the filter cake (such as capillary pore size and length) is not changed by the change of pressure; the other type is a compressible filter cake, such as activated sludge, under the action of pressure, the particles will be deformed, with As the pressure increases, the particles are compressed and squeezed into the channels, causing the passage of the filtrate to become smaller and the resistance to increase.
When filtering, the volume V of the filtrate is proportional to the pressure drop P, the filtration area A, and the filtration time t, and is proportional to the filtration resistance R and the viscosity u of the filtrate, that is, when filtering: V = Par uR (ml) (14-1) )
Where: V - filtrate volume (ml);
P——pressure during filtration (Pa)
A——Filter area (cm2)
t——Filter time (s)
U——filtrate viscosity (Pa·s)
R——The filtration resistance per unit volume of filtrate per unit filtration area is determined by the nature of the filter cake (cm-1)
The filtration resistance R includes two parts of the filter cake resistance Rz and the filter medium resistance Rg. The resistance R increases as the thickness of the filter cake increases, and the filtration speed increases with the thickness of the filter cake.
The increase is reduced, so the formula (14-1) is rewritten into a differential form: dV dt = PA uR = RA u (δRz + Rg) (14-2)
Where: δ - thickness of the mud cake
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It is assumed that the filtrate volume per unit volume is filtered, and the volume of the filter cake trapped on the filter medium is υ. When the volume of the filtrate is V, the volume of the filter cake is υ·V, so δA=υV
δ=υV A(14-3)
Substituting equation (14-3) into equation (14-2) gives dV dr=PA2u(Ï…VRz+RgA)(14-4)
If the filtered filtrate is removed on the filter medium to remove the solid weight of the filter biscuit C instead of Ï…, and the resistance r is replaced by Rz per unit weight, then the formula (14-4) can be rewritten as dV dr=PA2u (CVr+RgA). )(14-5)
Where: r - sludge specific resistance
For constant pressure filtration, formula (14-5) integrates with time: ∫ ̇0dt=∫v0 (uCVr PA2+Ur0PA)dV (14-6)
t=uCrV2r 2PA2+uR0V PA
t V=uCrV 2PA2+ uRgPA(14-7)
Formula (14-7) Description: Filter under constant pressure, t/V and V are in a linear relationship, namely: y-bx+a
Slope b=uCr 2PA2 intercept a=uRgPA so the specific resistance formula is r=2PA2u·b C(14-8)
r unit is cm/g, b is s/cm6, and C is g/cm3
It can be seen from the formula (14-8) that the sludge specific resistance r is required, and the slope b and C0b need to be obtained under the experimental conditions: the series can be determined under constant pressure (the vacuum degree remains unchanged) The r-V data is obtained by graphical method, as shown in Figure 14-1. The method of C is:
Figure 14-1 illustrates the schematic diagram of b
C=(V0-Vy)Cb(g mud biscuit weight/ml filtrate)(14-9)
Where: V0 - original sludge volume (ml)
Vy - filtrate volume (ml)
Cb - filter cake solids concentration (g / ml)
V0C0=VyCy+VbCbVb=V0Vy
Vy=V0(C0-Cb)Cy-Cb(14-10)
Where: C0 - raw sludge solids concentration (g / ml)
Cy - solid concentration in the filtrate (g / ml)
Vb - filter cake volume (ml)
Substituting formula (14-10) into (14-9) gives C=Cb(C0-Cy)Cb-C0(g/ml)(14-11)
Since the solid concentration of the filtrate Cy is much smaller than the sludge solid concentration C0, it is negligible, so C=CbC0Cb-C0(g/ml)(14-12)
Adding coagulant can improve the dewatering property of the sludge and reduce the specific resistance of the sludge. For inorganic coagulants, such as FeCl3, Al2(SO4)3, etc., the dry weight of the sludge is generally 5 -10%; polymer coagulant, such as polyacrylamide, basic aluminum chloride, etc., the dosage is generally 1% of the dry weight of the sludge.
It is generally considered that the specific impedance is 1012-1013 cm/g for difficult filtration of sludge; for (0.5-0.9)×1012 cm/g is medium, and less than 0.4××1012 cm/g is easy to filter sludge.
The specific resistance of activated sludge is generally (2.74-2.94)×1013cm/g; the specific resistance of digested sludge is (1.17-1.37)×1013cm/g; the specific resistance of primary sludge is (3.9-5.8)×1012cm /g.
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Third, experimental equipment and equipment:
(1) Experimental device:
The experimental device consists of a vacuum pump, a suction filter cartridge, a metering cylinder, a suction nozzle, a Buchner funnel, and the like.
Figure 14-2 Comparative impedance test device diagram
Stainless steel holder 2, metering cylinder 3, suction nozzle 4, Buchner funnel 5, suction filter cartridge 6, vacuum pump
7. Vacuum gauge 8, regulating valve 9, venting valve 10, hard plastic tube 11, hard rubber tube
The measuring cylinder is a stoppered glass measuring cylinder, which is clamped by a stainless steel frame, and is connected with a suction nozzle and a Buchner funnel. The suction filter cartridge is used as a vacuum chamber and for water, and is made of plexiglass. It has a vacuum gauge and a regulating valve, and has a venting valve underneath; one end is connected with a suction tube by a hard plastic tube, and the other end is connected to a vacuum pump by a hard rubber tube. The vacuum pump sucks the air in the suction filter cylinder to form a certain degree of vacuum inside the cylinder.
(2) Experimental equipment and instrumentation: (purchased by the user):
1, stopwatch 1 block
2, 1 oven
3. Analytical balance 1
Fourth, the experimental steps:
The solid concentration C0 of the sludge was measured.
FeCl3 (10 g/l) and Al2(SO4)3 (10 g/l) coagulant solutions were prepared.
The sludge was adjusted with FeCl3 (10g/l) coagulant (each group added a coagulating dose, the added amount is 5%, 6%, 7%, 8%, 9%, 10% of the dry weight of the sludge) .
Place a quick filter paper (larger than the funnel, preferably more than double the diameter) on the Buchner funnel, wet with water, and stick to the bottom of the week.
Start the vacuum pump and adjust the vacuum pressure to about 1/3 of the experimental pressure with the regulating valve. The experimental pressure is 35.5 kPa (vacuum degree 266 mmHg) or 70.9 kPa (vacuum degree 532 mmHg), so that the filter paper is close to the bottom of the funnel and the vacuum pump is turned off.
Put 50-100ml adjusted sludge in the funnel, (the sludge height does not exceed the filter paper height), let it rely on gravity filtration for 1 minute, start the vacuum pump, adjust the vacuum pressure to the experimental pressure, and record the filtrate in the measuring cylinder at this time. Volume V0. Start the stopwatch. During the entire experiment, the vacuum regulator was carefully adjusted to keep the experimental pressure constant.
At regular intervals (every 10s or 15s at the beginning of filtration, every 30s or 1min after the filtration rate is slowed down), record the corresponding filtrate volume V1 in the measuring cylinder.
The filter cake is smashed under constant pressure and the vacuum cake is broken. If the vacuum is not destroyed for a long time, it can be stopped by filtration for 20 minutes (also 30-40 min, until the mud cake is formed).
The thickness and solid concentration of the filter cake after constant pressure filtration were measured.
10. Take the sludge with Al2(SO4)3 coagulant (the same amount of coagulant plus FeCl3) and the sludge without coagulant. Experiments are carried out according to experimental steps 4-9.
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Precautions:
After adding the coagulant to the sludge, it should be thoroughly mixed.
The vacuum should be consistent throughout the filtration process.
During the experiment, the joints of the vacuuming device should not leak.
Fifth, the results of the experiment:
Determine and record the basic parameters of the experiment:
Experiment date, year, month, day, experimental vacuum kPa
Adding coagulation dose and mud cake thickness
1 plus Al2 (SO4) 3mg / l, mud cake thickness δ2 = mm.
2 plus FeCl3 mg / l, mud cake thickness δ2 = mm.
3 mud cake without coagulant thickness δ2 = mm.
The sludge solids concentration C0 = g / ml.
The mud cake solid concentration Cb = g / ml.
The experimentally measured data was recorded and calculated according to Table 14-1.
Taking t/V as the ordinate and V as the abscissa, find b.
C was determined from the mud cake and sludge solids concentration.
Calculate the specific resistance r under experimental conditions.
Taking the specific resistance r as the ordinate, the dosage of the coagulant is plotted on the abscissa to obtain the optimal dosage.
Sludge without coagulant
FeCl3 added sludge
Adding Al2(SO4)3 sludge
t
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Metering cylinder
Internal filtrate
V1 (ml)
Amount of filtrate
V=V1
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Metering cylinder
Internal filtrate
V1 (ml)
Amount of filtrate
V=V1
-V0(ml)
t V
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t
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Metering cylinder
Internal filtrate
V1 (ml)
Amount of filtrate
V=V1
-V0(ml)
t V
(s/ml)
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Sixth, the experimental results are discussed:
Is the relationship between the specific impedance and the solids concentration of the sludge? What is the relationship?
When the activated sludge is vacuum filtered, can it be said that the greater the degree of vacuum, the greater the solid concentration of the mud cake? Why?
Discuss the problems found in the experiment.
Fourth, the composition and specifications of the equipment:
1. Make 1 set of suction filter tube with plexiglass tube (Φ150mm×250mm, 2, with 2 sets of 300ml metering cylinder, 3, 2 ceramic Buchner funnels, 4, 1 pipe with suction pipe, 5, connecting pipe 1 piece, 6, 1 vacuum table, 7, 1 vacuum pump, 8, 1 vent valve, 9, 1 leak valve, 10 sets, 1 set of stainless steel stands with moving wheels, etc.
17, the total size of the experimental device: 500mm × 300mm × 1300mm
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Eight, regular inspection items
First, check the project regularly
1. suction pipe, Buchner funnel, hard plastic pipe, hard rubber hose;
2. Whether the vacuum gauge and other equipment are normal;
3. Whether the suction filter cartridge and vacuum pump are in normal operation;
Second, regular maintenance work:
1. When not in use, the filter cartridge must discharge water.
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