Figure 1 Physical+Biochemical Treatment Process
Sewage → regulating tank → reaction pre-sedimentation tank → jet cooling tank → selector → jet aeration → secondary sedimentation tank → sludge dewatering.
↑ ↓↓
└-reflux-discharge
As shown in figure 1, the process is equipped with reactive pre-settling tank pretreatment, which can improve the removal rate of ss. Because no chemicals are added, it is a physical process. The removal rate of SS in common pre-sedimentation tank is 70%, while the removal rate of SS in this reactive pre-sedimentation tank can reach more than 90%, thus reducing CODcr by more than 30%.
Its design principle is to make full use of the flocculation characteristics of fiber without adding flocculant. The agitator with larger diameter and lower rotation speed lifts the pre-precipitated sludge and contacts and mixes it with the sewage entering from the bottom of the pre-sedimentation tank in the central conduit. The mixed sewage enters the conical reaction chamber and stays in the conical reaction chamber for a long time, at which time the suspended solids in the sewage grow into flocs. When the mixed sewage flows out of the reaction chamber, the velocity of sewage gradually decreases, thus providing the best reaction conditions for flocs.
The reactive pre-settling tank of this process has been applied to the sewage treatment of Yin Ge Paper Mill in Luohe, Henan Province and Ya 'an Paper Mill in Sichuan Province. Because no flocculant is added into the reaction pre-sedimentation tank, the operation cost is low, but the one-time investment is higher than the general pre-sedimentation tank.
2 Anaerobic+Aerobic Treatment
The company that proposed the process thought that TMP and DIP wastewater had high organic concentration and were suitable for anaerobic pretreatment. After anaerobic treatment, the CODCr can be reduced to below 1000mg/L, and the CODCr removal rate can reach about 70%, thus reducing the burden of aerobic pretreatment (see Figure 2).
Anaerobic+aerobic treatment process
other
Sewage ┌ ┌ ┐ ┐ ┐
↓ ↓ ↑
TMP/DIP wastewater → pretreatment → cooling tower → anaerobic treatment → pre-sedimentation tank → selector → blast aeration → secondary sedimentation tank → concentration tank → sludge dewatering.
↓
avoid
Anaerobic reactor is a mature upflow anaerobic sludge bed abroad, namely UASB. This is an empty container with no filler, no power device and a certain amount of anaerobic granular sludge. The process principle is that the upper half of the reactor is equipped with a 1 three-phase separator, the upper part is a precipitation zone and the lower part is a reaction zone.
In the reaction zone, it can be divided into sludge layer and suspended layer according to the distribution of sludge. When sewage enters the reactor from bottom to top, it fully contacts with granular sludge and produces biogas through a series of biochemical reactions.
With the rise of bubbles, the sludge is lifted up. With the progress of the reaction and the increase of gas volume, the sludge gradually expands and slightly presents a fluidized state, and the gas escapes from the sludge layer. Sludge with poor settling performance forms a suspended layer under the stirring of gas, and the mixed liquid rises into the three-phase separator. When the gas hits the reflector, it turns to the gas chamber and is effectively separated and discharged. Sludge and water enter the sedimentation area, and under the action of gravity, water and sludge are separated.
The advantages of anaerobic treatment are low energy consumption, less land occupation, less sludge output and high removal efficiency, which can degrade some macromolecular organic substances and is conducive to further aerobic treatment. But the one-time investment of anaerobic treatment is large; There is little experience in domestic operation, especially in pulping wastewater treatment, and there is no anaerobic treatment method in China. In the trial operation of anaerobic treatment, granular sludge is difficult to cultivate and takes a long time. Stable operation is difficult to grasp; Resin, organic chlorine, hydrogen peroxide and sulfide in pulping wastewater may inhibit anaerobic bacteria; In addition, the utilization of biogas in anaerobic process should also be considered. Therefore, the anaerobic treatment of pulping wastewater is not mature at present, and anaerobic treatment is not considered for the time being.
3 Physicochemical+Biochemical Method (see Figure 3)
The process is characterized by setting flocculation tank for pretreatment and adding chemicals. This chemical flocculation pretreatment can not only improve the settling performance of suspended solids, but also greatly reduce insoluble CODCr by increasing the removal rate of SS, and can also remove some macromolecular refractory organic substances such as lignin, cellulose and organochlorine. Its principle is that after adding flocculant, fine fibers suspended in water condense into large particles, and these particles with different shapes also have porous specific surfaces, which have certain adsorption effect on some macromolecular organic substances.
Compared with anaerobic pretreatment and reactive pretreatment, chemical pretreatment has lower investment cost and is easy to control and manage, but the chemical dosage is more and the operation cost is greatly increased.
Fig. 3 Process flow of physicochemical and biochemical treatment
┌ ──────────┐
│ │
↓ ↑
Sewage → flocculation tank → pre-sedimentation tank → regulating tank → cooling tower → selector → surface aeration tank → secondary sedimentation tank → sludge dewatering.
↓
avoid
4 Two-stage aeration+physicochemical method
The process adopts two-stage aeration and finally chemical treatment, as shown in Figure 4. Because of the complex technology and many facilities, it occupies a relatively large area and has a relatively high investment. Chemicals need to be added at the end of the process. Although this can ensure the discharge standard, there is no doubt that the operating cost will increase accordingly, and the viscosity of sludge will increase after dosing, which will affect the dehydration of sludge.
Figure 4 Two-stage Aeration+Physicochemical Treatment Process
┌ ── backflow ── ┐ ┌ backflow ┐
↓ ↑ ↓ ↑
Adjust the surface flocculation of the cooling surface.
Sewage → pond → pre-settling pond → tower → selector → aeration pond → intermediate pond → aeration pond → sedimentation pond → concentration pond → sludge dewatering.
↓
avoid
5 biochemical+physicochemical method
As shown in figure 5, pretreatment generally does not precipitate, and finally air flotation treatment is added. Because there is no special pretreatment method, the CODCr removal rate of pretreatment is low, which increases the burden of CODCr removal by aerobic organisms. Therefore, more flocculants must be added in the final air flotation treatment to ensure the discharge standard.
Fig. 5 Process flow of biochemical+physicochemical treatment
sludge dewatering
┌-----reply
↓ │
Sewage → pre-sedimentation tank → regulating tank → cooling tower → selector → jet aeration → secondary sedimentation tank → air flotation device → discharge.
The similarity of these processes is that a selector is added in front of the aeration tank, and the aeration time is longer, ranging from 15h to 30h. Adding selector and prolonging aeration can improve the removal rate of CODCr and ensure the discharge of CODCr up to standard.
With the increase of aeration time, the mixed residence time of organic matter and activated sludge is longer, and some refractory organic matter can be gradually degraded.
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