Table 2 Comparison of several aeration methods III. Operating costs The operating costs are mainly determined by the consumption of chemical drugs and total electricity consumption. Equipment depreciation, maintenance and management costs are similar, and the proportion is very low. The chemical consumption and total power consumption of the five processes are summarized in Table 3. Rotary Electric Toothbrush,Kid Electric Toothbrush,Children Electric Toothbrush,Electric Toothbrush Rotary GUANGZHOU WANYUAN INDUSTRIAL CO.,LTD. , https://www.wanyuanfuture.com
First, process flow and characteristics 1 Physical + biochemical treatment Figure 1 Physical + biochemical treatment process (slightly
As shown in Figure 1, this process has a reactive pre-saturation tank pre-treatment, which can increase the removal rate of SS. Because it does not add chemicals, it is a physical process. The removal rate of general pre-sedimentation tank SS is 70%, and the removal rate of SS in this reaction type pre-sedimentation tank can reach more than 90%, which can reduce CODCr by more than 30%.
The design principle is to fully utilize the flocculation characteristics of the fiber without adding flocculants. A large-diameter and low-speed stirrer lifts the sludge that has been deposited in advance and mixes with the sewage 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. Longer, when the suspended solids in the sewage grows into flocs. When the mixed sewage flows out of the reaction chamber, the flow rate of the sewage gradually decreases, thereby providing optimum reaction conditions for the flocs.
The reaction-type pre-settlement tank of this process has been applied to the sewage treatment of Henan Feihe Yinge Paper Mill and Sichuan Ya'an Paper Mill. Since the reaction type pre-settlement tank has no flocculant and the operation cost is low, the one-time investment is higher than that of the general pre-sinking tank.
2 Anaerobic + aerobic treatment The company that proposed this process believes that TMP and DIP have higher concentrations of organic matter in the two wastewaters and are suitable for anaerobic pretreatment. CODCr after anaerobic treatment can be reduced to less than 1000mg/L, CODCr removal rate can reach about 70%, thereby reducing the burden of subsequent aerobic pretreatment (see Figure 2 omitted).
Anaerobic + aerobic treatment process The anaerobic reactor is a relatively mature upflow anaerobic sludge blanket (UASB). This is an empty container with no filler, no power plant, and a certain amount of anaerobic granular sludge. The principle of the process is that a three-phase separator is arranged in the upper half of the reactor. The upper part of the separator is a precipitation area and the lower part is a reaction area. In the reaction zone, according to the distribution of sludge can be divided into sludge layer and suspended layer. When the sewage flows upwards from the bottom into the reactor, the sewage is fully in contact with the granular sludge and biogas is generated after a series of biochemical reactions. As the bubbles rise up to hold up the sludge, the sludge gradually expands and slightly fluidizes as the reaction progresses and the amount of gas increases, and the gas escapes from the sludge layer. The sludge with lower sedimentation performance forms a suspension layer under the agitation of the gas, and the mixture rises into the three-phase separator. When the gas strikes the reflector, it is folded toward the air chamber and is effectively separated and discharged. Sludge and water enter the sedimentation zone. Under gravity, water is separated from the sludge.
The advantages of anaerobic treatment are low energy consumption, small footprint, low sludge production, high removal efficiency, and the ability to degrade some macromolecule organics, which is beneficial to further aerobic treatment. However, the one-time investment for anaerobic treatment is large; there is little experience in domestic operation, especially in the pulping wastewater treatment, there is no anaerobic treatment method in China; anaerobic treatment in the test, the granular sludge is not easy to cultivate, and the cultivation time is longer It is difficult to grasp stable operations; resin, organic chlorine, hydrogen peroxide, and sulfides in pulping wastewater may have inhibitory effects on anaerobic bacteria; in addition, the use of biogas in anaerobic processes must also be considered. Therefore, anaerobic treatment of pulping wastewater is not yet mature and anaerobic treatment is not considered.
3 Materialization and biochemical methods (see Figure 3)
The process features a flocculation tank for pretreatment and dosing of chemicals. This chemical flocculation pretreatment can not only increase the sedimentation performance of suspended solids, but also greatly reduce the insoluble CODCr by increasing the removal rate of SS, and can also remove some macromolecule refractory organic substances such as lignin, cellulose, organic chlorine, and the like. The principle is that after flocculating agent is added, the fine fibers suspended in the water condense into large particles. These various shapes of particles also have a porous surface, which has a certain suction effect on some macromolecule organics.
Compared with anaerobic pretreatment and reactive pretreatment, the investment cost of chemical pretreatment is relatively low, and it is easy to control and manage. However, the amount of added chemicals is large, and the operating cost is greatly increased.
Fig. 3 Process of physicochemical + biochemical treatment (slightly)
4 Two-stage aeration + physicochemical method The process uses two-stage aeration and finally chemical treatment, as shown in Figure 4. Due to the complexity of the process and the large number of construction facilities, the land area is relatively large and the relative investment is also high. At the end of the process, chemicals are also added. Although this can ensure compliance with discharge standards, there is no doubt that the operating costs will increase accordingly, and the viscosity of the sludge after the addition will increase, affecting the dewatering of the sludge.
Figure 4 Two-stage aeration + physicochemical treatment process (slightly)
5 biochemical + physicochemical method shown in Figure 5, the pretreatment is not generally precipitated, and finally air floatation treatment. Because there is no special pretreatment method, the removal rate of pretreated CODCr is low, and the burden of CODCr removal by aerobic organisms is increased. Therefore, the final air flotation treatment must add more flocculants to ensure compliance with the standards.
Figure 5 biochemical + physicochemical treatment process (slightly
Common to these processes is the addition of a selector in front of the aeration tank, and the aeration time is longer, all between 15h and 30h. The selector and delayed aeration are all designed to increase the CODCr removal rate and ensure CODCr compliance.
The addition of the selector is mainly when the returned sludge enters the selector together with the sewage, and the organic matters are consumed without an aeration to cause oxygen deficiency. The first is that some anaerobic bacteria can decompose a small part of refractory organics, followed by aerobic bacteria that have better survivability and better activity under hypoxic conditions. Once these life-threatening species enter the aeration tank, their abilities to remove organic matter are significantly enhanced under aerobic conditions.
With the increase of aeration time, organics and activated sludge have a longer mixing time and can gradually degrade some of the more difficult-to-degrade organics.
Second, aeration method All proposed technical solutions, there are three aeration tank aeration methods, namely surface aeration, blast aeration and jet aeration. Their respective advantages and disadvantages are shown in Table 2.
Through the comparison and analysis of the characteristics of process flow, aeration method, and operating cost in the technical scheme of foreign sewage treatment companies, a technical plan that is more suitable for the wastewater treatment of Nanping Paper Mill's pulping is proposed.
Aeration method Advantages Disadvantages Surface aeration can be adjusted according to the need of dissolved oxygen, mobility; easy to operate and control management; easy maintenance, no need to drain the pool of water power consumption; low oxygenation ability; need to add defoamer eliminate Foam on the water surface, otherwise it is not conducive to the surface air oxygenation blast aeration power consumption is relatively small; oxygenation ability is high, suitable for deep aeration; surface foam does not affect the oxygen blowing blast noise; the bottom of the gas distribution facilities failure When the water in the pool needs to be drained, it is extremely inconvenient to spray and aerate. The power consumption is small; the oxygenation efficiency is highest, and it is also suitable for aeration in deep pools. The surface foam does not affect the oxygenation rate to control a certain injection rate, otherwise the outlet is too low. Mud; When the same facility is repaired, the water in the pool needs to be drained
Treatment Process Chemical Consumption/kg·d-1 Trisodium Phosphate Urea Polyacrylamide Aluminum Sulfate Defoamer Total Power Consumption/kWh·d-1 Physical + Biochemical 500 1050 85 - - 17400 Anaerobic + Aerobic 400 1000 100 - 60 15600 Chemical + Biochemical 125 650 150 12000 100 23000 Two-stage aeration 1200 2400 160
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