In the process of municipal sewage treatment, sludge treatment is a crucial link. Sludge deep dewatering, as a key step to reduce sludge volume and facilitate subsequent disposal, has always attracted much attention. Traditionally, lime has often been used in the conditioning stage of deep sludge dewatering. However, with increasingly strict environmental protection requirements and continuous technological progress, its drawbacks have gradually become prominent. Meanwhile, sludge enhancer, as a new type of conditioning agent, is demonstrating great potential to replace lime with its significant environmental advantages.
The current situation and problems of using lime for deep dewatering of Municipal sludge
Lime, due to its wide availability and relatively low price, has been widely used in the deep dewatering process of municipal sludge for a long time in the past. During the sludge conditioning stage, lime is mixed with the sludge. Its main function is to change the physical and chemical properties of the sludge, increase the particle size and density of the sludge particles, and reduce the specific resistance of the sludge, thereby improving the dewatering efficiency of subsequent dewatering equipment (such as plate and frame filter presses).
However, the use of lime has brought about many problems that cannot be ignored. Firstly, the addition of lime will significantly increase the dry basis weight of the sludge. This is because lime itself does not participate in the dehydration reaction but only plays an auxiliary role in dehydration. A large amount of lime remains in the dehydrated mud cake, resulting in a significant increase in the weight of the mud cake. For instance, after a certain sewage treatment plant used lime to conditioning the sludge, the dry basis weight of the sludge cake increased by approximately 30% to 50%, which undoubtedly raised the subsequent costs of sludge transportation and disposal. Moreover, as the dry basis weight of sludge increases, the land resources required for landfill disposal also increase accordingly. This issue is particularly prominent in cities with tight land resources.
Secondly, lime can cause severe corrosion to equipment. During the mixing of lime with sludge and the subsequent dewatering process, it reacts with water to form alkaline substances. The strongly alkaline environment has a strong corrosive effect on the metal parts of dewatering equipment. According to relevant data, for dewatering equipment that has been using lime to adjust sludge for a long time, the service life of key components (such as filter plates of plate and frame filter presses and screw pumps, etc.) has been shortened by approximately 30% to 40%. This not only increases the frequency and cost of equipment maintenance but also may lead to production disruptions due to equipment failures, affecting the normal operation of sewage treatment plants.
Thirdly, the use of lime is not conducive to the resource utilization of sludge. If the dehydrated sludge is to be incinerated for power generation or used to make building materials and other resource treatments, the presence of lime will reduce the calorific value of the sludge, affect the incineration effect, and may also change the physical properties of the building materials, reducing their quality. For instance, during the sludge incineration process, due to the dilution effect of lime, the calorific value of the sludge decreases, which leads to the need to add additional auxiliary fuel during incineration, thereby increasing energy consumption and operating costs. In the production of building materials, the residue of lime may reduce the strength, durability and other properties of building materials, which limits the wide application of sludge in this field.
In addition, lime can also cause dust pollution during its use. Lime powder is prone to drift into the air during storage, transportation and addition, posing a threat to the surrounding environment and the health of operators. According to occupational health monitoring data, employees who have been working in sewage treatment plants that use lime for a long time have a significantly higher probability of suffering from respiratory diseases than workers in other industries.
The working principle and advantages of sludge enhancers
Sludge enhancer is a new type of conditioning agent specially developed for the deep dewatering of municipal sludge. Its main components include various functional compounds, such as surfactants, cell wall disruptors, and flocculants. These components work in synergy to exert a unique sludge conditioning effect.
Surfactants can reduce the surface tension between sludge particles and water, making it easier for water molecules to detach from the surface of sludge particles, thereby enhancing the dewatering performance of sludge. Cell wall disruptors can destroy the cell walls and cell membranes of microorganisms in sludge, releasing the bound water within the cells and further increasing the reduction in the moisture content of the sludge. Flocculants can promote the aggregation of sludge particles to form larger flocs, which is conducive to the solid-liquid separation of subsequent dewatering equipment.
Compared with lime, sludge enhancers have multiple environmental protection advantages. Firstly, the dosage of sludge enhancer is small, yet it can achieve efficient dewatering. Generally speaking, the dosage of sludge enhancer is only 0.5% - 2% of the dry weight of the sludge, which is much lower than the usage of lime. For instance, in the practical application of a certain municipal sewage treatment plant, when using lime for conditioning, 200 to 300 kilograms of lime need to be added per ton of dry sludge. However, after switching to a sludge enhancer, only 5 to 10 kilograms of enhancer need to be added per ton of dry sludge to achieve the same or even better dewatering effect. Reduce the moisture content of sludge from over 90% to below 60%. This not only reduces the cost of the chemicals themselves, but more importantly, significantly lowers the increase in sludge caused by the addition of chemicals.
Secondly, the sludge enhancer has no corrosive effect on the equipment. Due to its mild chemical properties and the absence of strong corrosive components, it will not cause corrosive damage to dehydration equipment like lime does. This means that the use of sludge enhancers can extend the service life of equipment, reduce the frequency of equipment maintenance and replacement, and thereby lower the operating costs of sewage treatment plants. Take a set of plate and frame filter press worth 1 million yuan as an example. When using lime, the equipment needs to undergo large-scale maintenance or replace key components every 3 to 5 years. However, after using sludge efficiency enhancers, the normal service life of the equipment can be extended to 8 to 10 years, saving a large amount of equipment investment and maintenance costs.
Furthermore, sludge enhancers are conducive to the resource utilization of sludge. After being treated with sludge enhancers, the properties of the sludge remain basically unchanged. It will not reduce the calorific value of the sludge, nor will it have a negative impact on subsequent resource utilization processes such as the production of building materials. On the contrary, due to the effective reduction of the moisture content of the sludge, the calorific value of the sludge relatively increases, which is more conducive to incineration power generation. Meanwhile, the dehydrated sludge can better ensure the quality and performance of building materials when they are used in the production of building materials. For instance, the bricks made from sludge treated with sludge enhancers all meet national standards in terms of strength, impermeability and other indicators, thus opening up a broader path for the resource utilization of sludge.
In addition, the sludge enhancer causes no dust pollution during its application, which is friendly to the health of the operators and the surrounding environment. It is usually in liquid or granular form, easy to store, transport and add. During the addition process, no dust is generated, effectively avoiding the harm of lime dust to the environment and human health, and improving the working environment of the sewage treatment plant.
Practical application cases of sludge enhancers
A large urban sewage treatment plant can treat 500,000 tons of sewage per day and generates a huge amount of sludge. In the past, this factory treated the sludge by adding lime and iron salts, and then dehydrated it through a plate and frame filter press. During the operation process, the factory is confronted with numerous problems, such as the high moisture content of the mud cake, which makes it difficult to meet the landfill standards. The equipment is severely corroded and the maintenance cost remains high. Lime dust causes serious pollution and has aroused strong reactions from employees, etc.
To solve these problems, the factory introduced sludge enhancers for experiments. In practical applications, an appropriate amount of sludge enhancer is added to the sludge. After thorough stirring and mixing, it is sent to a plate and frame filter press for dewatering. The results show that after the use of the sludge enhancer, the moisture content of the sludge cake has stably decreased to about 55%, fully meeting the landfill requirements. Meanwhile, as the sludge enhancer has no corrosive effect on the equipment, the operational stability of the equipment has been significantly enhanced, and the frequency of maintenance has been greatly reduced. In addition, the on-site working environment has been greatly improved. There is no longer any lime dust spreading, and the work enthusiasm of the employees has also significantly increased.
From a cost perspective, although the unit price of sludge enhancers is relatively high, due to their small dosage, the overall cost of sludge treatment has been reduced by approximately 20% to 30% compared to the previous use of lime. Moreover, the sludge after dewatering, due to its low water content and stable properties, is more convenient for subsequent disposal processes such as landfill and incineration, further reducing the disposal cost.
Conclusion
In the field of deep dewatering of municipal sludge, sludge synergism shows a broad prospect of replacing lime because of its significant environmental advantages. It can not only effectively solve the problems such as sludge increment, equipment corrosion, limited resource utilization and dust pollution caused by the use of lime, but also bring tangible economic benefits to sewage treatment plants by improving dewatering efficiency and reducing treatment costs. With the continuous development of environmental protection technology and the increasing awareness of environmental protection among people, sludge efficiency enhancers are expected to be widely applied in more municipal sewage treatment plants, promoting the municipal sludge treatment industry to develop in a greener, more efficient and sustainable direction. Whether from the current environmental protection demands or the long-term development of the industry, the replacement of lime by sludge enhancers will be an important transformation in the field of deep dewatering of municipal sludge.