Sludge is an inevitable product of sewage treatment plants and sewage stations. Untreated sludge entering the environment will directly cause secondary pollution to water bodies and the atmosphere, posing a serious threat to the ecological environment and human activities. Therefore, sludge treatment is very cautious, and sludge treatment can be divided into two types: sludge dewatering process and sludge drying process. The following mainly introduces the respective advantages of different types of sludge dewatering machines.

type

The sludge from sewage treatment plants generally includes three types: physical and chemical sludge, biochemical sludge, and mixed sludge of physical, chemical, and biochemical processes.

Various types of sludge have different adaptations to dewatering machines. Currently, the commonly used models of sludge dewatering machines in China include centrifugal, filter belt, spiral ring disc, and plate frame. The selection and proportioning of coagulants are crucial for the dewatering of sedimented sludge. Good flocculation effect ensures relatively smooth dewatering of sludge. Here is a brief introduction to the actual usage of three models for selection:

Centrifugal: All three types of sludge can adapt, but high energy consumption and high rotational speed result in loud noise. Belt filter: Suitable for physical and chemical sludge, with low moisture content in the filter cake, poor adaptability to mixed sludge and biochemical sludge, high reflux sludge, large backwash water consumption, high energy consumption, and complex maintenance. Spiral ring type: The first generation dehydration machine represented by Japanese prototypes has been widely used in China for 3-4 years, but its disadvantage is low production.

Technical principles

New separation technology: The organic combination of spiral pressure and dynamic and static rings forms a new separation technology that integrates concentration and dehydration, adding an advanced dehydration mode selection to China's environmental wastewater treatment field. Energy saving and Water saving: Due to the continuous displacement of the dynamic and static rings, the self-cleaning effect of the cylinder body is achieved, which reduces the clogging of the filtration gap and replaces the high-pressure flushing of the old generation filter cloth and belt filter plate, greatly saving industrial water (single machine water-saving of 13000 tons/year). The low-speed operation of the main screw shaft (3-5 revolutions per minute) reduces mechanical wear and extends the service life of the equipment. The power consumption of the host is ≤ 1.1kw/hr, and the single machine can save up to 50000 kWh/year. Double processing capacity: The processing capacity of the second generation dehydrator has doubled compared to the first generation dehydrator. A 303 unit can solve the sludge generated from 10000 tons of sewage (120-150 tons) and can be equipped with a process for deep dewatering of sludge to 50-40%. A single process can solve a sewage treatment capacity of 10000-30000 tons. Domestic pioneering: The pressure regulating plate adopts elastic automatic adjustment, naturally balancing the internal pressure of the sludge in the dewatering section, and more effectively ensuring the service life of the dynamic and static ring plates. Green and environmentally friendly: The whole machine operates in a sealed manner and can be directly observed. The shell is easy to disassemble and assemble, with no sewage leakage or secondary pollution. The noise level is ≤ 45 decibels, making the sludge treatment room environment beautiful and civilized for production. The ring type sludge dewatering machine has no clogged components such as filter cloth or holes inside: it operates safely and simply, depending on the customer's operating time period. Combined with an automatic control system, program settings can be made to achieve automatic unmanned operation (with a considerable amount of sludge).

Working principle

1. Plate and frame sludge dewatering machine: In a closed state, the sludge pumped in by a high-pressure pump is compressed by the plate and frame, and the water inside the sludge is discharged through the filter cloth to achieve the purpose of dewatering.

2. Belt type sludge dewatering machine: The sludge layer is carried by two tensioned filter belts on top and bottom, and passes through a series of regularly arranged roller drums in an S-shape. By relying on the tension of the filter belt itself, it forms a pressing and shearing force on the sludge layer, squeezing out the capillary water in the sludge layer and achieving sludge dewatering.

3. Centrifugal sludge dewatering machine: composed of a transfer and a screw conveyor with a hollow shaft. The sludge is fed into the rotary drum by the hollow shaft, and under the centrifugal force generated by high-speed rotation, it is immediately thrown into the rotary drum chamber. Due to different densities, solid-liquid separation occurs. Under the push of the screw conveyor, the sludge is transported to the conical end of the drum and continuously discharged from the outlet; The liquid in the liquid ring layer is continuously 'overflowed' from the weir and discharged outside the drum by gravity.

4. Stacked sludge dewatering machine: a filtering body formed by the stacking of fixed rings and moving rings, with a spiral shaft passing through them. Through gravity concentration and the internal pressure formed by the back pressure plate during the propulsion process, the sludge is fully dehydrated. The filtrate is discharged from the filter gap formed by the fixed ring and the movable ring, and the sludge cake is discharged from the end of the dehydration section.

workflow

1. The sludge in the sludge tank is transported to the measuring tank through the sludge conveying pump. The sludge inlet is adjusted by adjusting the liquid level in the measuring tank through the regulating pipe, and excess sludge is returned to the sludge tank through the reflux pipe.

2. Sludge and flocculant are thoroughly mixed in the flocculation mixing tank using a mixer to form alum flowers, with an ideal diameter of around 5mm.

3. Alum flowers undergo gravity concentration in the concentration section, and a large amount of filtrate is discharged from the filter slot in the concentration section.

4. The concentrated sludge continues to move forward in the direction of the spiral axis rotation, and is fully dehydrated under the internal pressure formed by the back pressure plate.

5. The dehydrated mud cake is discharged from the gap formed between the back pressure plate and the spiral body. The sludge treatment capacity and moisture content of the sludge cake can be adjusted by adjusting the rotation speed of the spiral shaft and the clearance of the back pressure plate.

model selection

After sedimentation treatment, sewage will produce a large amount of sludge. Even after concentration and digestion treatment, the moisture content is still as high as 96%, with a large volume that is difficult to digest and dispose of. Dehydration treatment is necessary to increase the solid content of the sludge cake and reduce the footprint of sludge stacking.

Generally, large and medium-sized sewage treatment plants adopt mechanical dehydration. There are many types of dehydrators, which can be divided into three categories according to the dehydration principle: vacuum filtration dehydration, pressure filtration dehydration, and centrifugal dehydration. This article introduces the working principles, key considerations when selecting equipment, and maintenance and operation costs of filter presses (including belt filter presses and plate and frame filter presses) and centrifugal dewatering machines commonly used in domestic sewage treatment plants.

1. Belt filter press is less affected by fluctuations in sludge load, and has the characteristics of low sludge moisture content, stable operation, low start-up consumption, relatively simple management and control, and low requirements for the quality of operating personnel. At the same time, due to the early introduction of belt filter dewatering machines in China, a considerable number of manufacturers can produce this equipment. When making decisions on sewage treatment project construction, belt filter presses can be used to reduce project investment. At present, most of the newly built sewage treatment plants in China use belt filter dewatering machines. For example, all five dewatering machines in the first phase of the Beijing Gaobeidian sewage treatment plant project are belt filter dewatering machines. Since the filter belt and roller press cylinder have been put into operation, they have been in good condition. Therefore, this type of machine was still selected for equipment selection in the second phase.

2. Compared with other types of dewatering machines, the plate and frame filter press has the highest solid content in the sludge cake, up to 35%. If considering the factor of reducing the land occupation of sludge stacking, the plate and frame filter press should be the preferred solution. The movement method of the filter plate. The requirement is that it can be fully or semi automatically completed through hydraulic pneumatic devices, which are inconvenient to operate. The filter cloth oscillation device is used to make the filter cake easy to fall off. Compared with other types of dehydrators, the biggest disadvantage of plate and frame filter press is that it occupies a larger area. Taking the belt filter press used in the first phase of Beijing Gaobeidian Wastewater Treatment Plant and the plate and frame filter press used in Anshan Industrial Wastewater Treatment Plant as examples for comparison: Gaobeidian Wastewater Treatment Plant has a sewage treatment capacity of 500000 t/d, sludge production of 1852.5m3/d, and dry matter of 92.63t/d. It uses five German KLEIN-KS30 belt filter presses, each with a base area of only 2750 * 350mm. Anshan Wastewater Treatment Plant has a water treatment capacity of 22t/d and dry matter of 275t/d. It uses six plate and frame filter presses, each with a base area of 2400 * 1200mm. At the same time, due to the intermittent operation of the plate and frame filter presses, the efficiency is low. The operating environment is poor and there is secondary pollution. Large scale sewage treatment plants in China rarely adopt it.

purpose

1. Industrial wastewater coagulation sedimentation sludge

2. Excess activated sludge from industrial wastewater

3. Excess sludge from urban sewage treatment

4. Community sewage treatment sludge

5. Adding chemicals to the water purification plant to aggregate sludge

6. Water and fertilizer treatment of residual sludge

7. Solid liquid separation during factory manufacturing process