Experimental study on roller sludge dewatering machine

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Author of pilot study on roller sludge dewatering machine: Li Changwei of Shandong Jiahao Group Co., Ltd. 1. Overview 1.1 The significance of sludge dehydration During the sewage treatment process, a large amount of sludge is produced, which accounts for about 0.3% to 0.5% of the treated water (moisture content is about 97%). Of the total construction costs of sewage treatment plants, about 20% to 50%, or even 70%, are used to treat sludge. Therefore, sludge treatment is an important part of the sewage treatment system and must be given full attention. Sludge contains a large amount of harmful and toxic substances, such as parasite eggs, heavy metals, etc. ； Useful substances such as phytonutrients, organic matter and water. The purpose of sludge treatment is to reduce, stabilize, harmless, and comprehensively utilize sludge. Commonly used unit processes are: Concentration, stabilization, sludge conditioning, dehydration. After concentration and digestion, the sludge still has a water content of about 95% to 97%, and the volume is still very large. For comprehensive utilization and final disposal, the sludge needs to be dewatered. The function of dehydration is to remove water existing between and within the sludge particles, thereby changing the physical properties of the liquid sludge into a semi-solid state. The ideal dehydration should remove water to the maximum extent, while all solid particles of the sludge should be retained on the dehydrated mud cake, and this operation requires the lowest investment. 1.2 Types and characteristics of sludge dewatering machine Mechanical sludge dehydration uses the pressure difference on both sides of the filter medium as a driving force to force the sludge water through the filter medium to form filtrate ； The solid particles are trapped on the medium to form a filter cake, thereby achieving the purpose of dehydration. Mechanical sludge dehydration methods include vacuum filtration, filter press and centrifugation. Vacuum filtration and dehydration is currently rarely used. The machine used is called a vacuum filter, which can be used to dewater the pretreated primary sedimentation sludge, chemical sludge and digestion sludge. The characteristics of vacuum filter dehydration are that it can produce continuously, operate stably, the process is complex, and the operating cost is high. Filter press dehydration uses a plate and frame filter press. Its structure is relatively simple, its filtration driving force is large, and it is suitable for all kinds of sludge. But it cannot run continuously. Belt filter press is used for rolling dehydration. Its main feature is to apply pressure on the filter cloth, and use the pressure and tension of the filter cloth to dehydrate the sludge without the need for vacuum or pressurization equipment. It consumes less power and can produce continuously. This dehydration method is currently widely used. The driving force for dehydration in centrifugal dehydration is centrifugal force. The object of push is the solid phase. The size of the centrifugal force can be controlled and is hundreds or even tens of thousands of times greater than gravity, so the dehydration effect is better than concentration. The centrifuge can be operated continuously, the workplace has good sanitary conditions and occupies a small area. But it consumes a lot of power and makes a lot of noise. 1.3 Rolling dewatering machine The research on sludge dehydration of rolling machine was started by Shandong Jiahao Group Company in March 2002. The prototype trial production work was completed in June 2003. The working principle of the rolling press is different from traditional belt machines, plate and frame filter presses and centrifuges. Its working principle is that wet sludge (solid content 0.5% to 5%) enters the sludge channel. There is a circular stainless steel grid with small holes on both sides of the channel. The grid rotates 0.5 to 3 revolutions per minute, bringing the sludge into the dehydrator. The first half of the circular dehydration channel of the roller press, 0-180°, is the concentration area. The sludge water begins to be squeezed out from the outlet holes of the grids on both sides, and is discharged from the sewage tank under the dehydrator. After the water in the sludge is desorbed, it flows slowly and is under increasing pressure, causing more water to be squeezed out to achieve better dehydration effects. The grid screen uses friction to push the solids in the sludge to the outlet gate. The outlet gate is the squeeze area, and the gate opening and closing pressure is controlled by a computer. The sludge solids are squeezed in front of the gate to form a mud cake with low moisture content. 2. Productivity test and result analysis of rolling dewatering machine Dewatering machine and test conditions The rolling sludge dewatering machine used in this test has an external size of 1078×600×974mm, and uses one dehydration channel. The dehydration channel size is 30 (w) × 136 (h) mm, the grid screen diameter is 600mm, the effective filtration area is 0.55m2, the dewatering grid screen speed is 0.5~3r/m, the overall machine weight is 1500kg, and the motor power is 3kw. The test used mixed sludge from Jinan Yuanshou Co., Ltd., and the sludge was fed into the sludge tank intermittently. The flocculant tank is equipped with 0.1% to 0.2% flocculant. The sludge and flocculant are input into the mixing tank at the same time to completely mix and form flocs. After flocculation, the sludge is fed into the dewatering channel for dehydration. The filtrate is discharged into the incoming water of the sewage plant for treatment. 2.1 Mixed sludge dehydration test of Jinan Yuanshou Co., Ltd. Mixed sludge is the main test object of this mixing test. The mixed sludge of Jinan Yuanshou Company comes from the gravity concentration tank, and its properties vary greatly. During the test, the moisture content ranged from 95.74% to 98.06%, and the pH value was approximately 6.0-6.5. The specific dehydration test data are as follows. Mixed sludge experimental data table Sampling time August 5 August 6 August 6 August 6 August 8 August 9 Flocculant PAC PAC PAC PAC PAC PAC Flocculant dosage (‰) 1.57 5.08 15.42 19.03 2.84 9.45 Sludge flow rate (m3/h) 1.983 1.270 0.815 1.820 2.535 Incoming mud moisture content (%) 95.87 96.36 96.11 97.33 98.06 97.55 Incoming mud SS (g/l) 18.64 23.54 Mud cake moisture content (%) 74.49 76.77 78.56 80.50 77.29 80.69 Filtrate TS (%) 0.7826 0.2508 0.3171 0.2273 0.2556 0.4753 Filtrate SS (g/l) 1.498 0.714 2.694 1.329 1.827 Filtrate CODCr (mg/l) 2423 1301 870 875 593 2358 Dry sludge production (kg/hour) 19.3 34.9 57.23 33.1 Solid retention rate (%) 83.6 94.1 93.2 92.6 87.8 96.6 It can be seen from the data in the table: After the mixed sludge is dehydrated by the roller dehydrator, the moisture content of the mud cake can be reduced to a minimum of 74.49% and a maximum of 80.69%, mostly between 76% and 79%. The solid retention rate is a maximum of 96.6% and a minimum of 83.6%, with most of the moisture content above 91%. The sludge dehydration effect is good. 2.2 Dehydration test sampling time of unconcentrated mixed sludge, primary sedimentation sludge, secondary sedimentation sludge, and diluted sludge August 17 August 17 August 19 August 19 August 18 August 19 No. 2 1 1 2 1 3 Sludge type Primary sedimentation tank sludge Secondary sedimentation tank sludge First barrel of unconcentrated secondary sedimentation tank sludge Second barrel of unconcentrated secondary sedimentation tank sludge Mixed sludge (A/O method) The second barrel of 680L sludge (add 4.5kg of wet grass) Flocculant PAC PAC PAC PAC PAC PAC Flocculant dosage (kg/ton dry solid) 2.83 7.77 5.66 5.99 9.95 13.0 Sludge flow rate (m3/h) 2.430 1.620 3.600 3.330 0.99 1.440 Incoming mud moisture content (%) 96.47 99.24 97.56 98.20 96.81 98.20 Mud cake moisture content (%) 73.01 79.44 77.65 76.80 83.66 81.45 Filtrate TS (%) 0.1564 0.1889 0.1538 Filtrate CODCr (mg/l) 0.899 0.8240 2384 Dry sludge production (kg/hour) 181.8 993.8 29.0 Solid retention rate (%) 80.0 95.3 96.1 Fiber content (%) 19.5 64.3 16.72 Solid retention rate (%) 80.0 95.3 Fiber content (%) 52.28 Ash (%) 44.75 The test data table of various sludges shows that due to the high ash content of the primary sedimentation tank sludge, the dehydrability is significantly better than that of the secondary sedimentation tank sludge. The moisture content of the mud cakes of the two is 73.01% and 79.44% respectively, and the flocculant required per unit dry solid is also reduced. This test once again proved that the roller dehydrator has the integrated functions of concentration and dehydration. 2.3 Fecal sludge dehydration test Fecal sludge dehydration test data sampling time September 7 September 7 September 8 September 8 Flocculant PAC PAC PAC PAC Dosage of flocculant (kg/ton dry solid) 3.93 3.47 9.06 5.27 Sludge flow rate (m3/h) 1.695 1.735 3.950 3.290 Moisture content of incoming mud (%) 94.15 93.61 97.98 96.24 Moisture content of mud cake (%) 54.4 52.6 66.5 61.2 Dry sludge production (kg/hour) 99 111 82 124 It can be seen from the data that the roller dehydrator has a good dehydration effect on fecal sludge. The moisture content of the mud cake can reach 52.6% to 66.5%, and the dry solid yield is also high, about 100kg/h. Conclusion 1. The rolling sludge dehydrator can be used to dewater mixed sludge from urban sewage plants. The solid content of the mud cake after dehydration can reach 74.49% to 81.11%. It is especially suitable for dehydrating high fiber content sludge such as fecal sludge and papermaking sludge. The solid content of the sludge after dehydration can reach 52.6% to 66.5%. 2. The rolling sludge dehydrator has the integrated functions of concentration and dehydration. It can dehydrate sludge without concentration (moisture content above 98%) and achieve good dehydration effects. 3. The rolling sludge dehydrator has low power consumption, ranging from 6.65 to 18.84kw·h/ton of dry solids. It can be operated continuously and has good hygienic conditions in the workplace.