With the acceleration of urbanization, the volume of municipal sewage treatment has been increasing year by year, and the problem of sludge treatment has become increasingly severe. Municipal sludge has a high water content and large volume. Deep dewatering has become a key link in sludge reduction treatment. For a long time, lime has been widely used as a traditional sludge conditioner in the deep dewatering of municipal sludge, but the environmental problems that come with it have gradually emerged. The emergence of new sludge conditioning agents has provided a more environmentally friendly solution for the deep dewatering of municipal sludge, demonstrating great potential to replace lime.
I. Limitations of Using Lime for Deep Dewatering of Municipal Sludge
Lime, with its low cost and wide availability, holds an important position in the field of deep dewatering of municipal sludge. Its working principle is to react with the water in the sludge, change the physical and chemical properties of the sludge, increase the particle size of the sludge, reduce the specific resistance of the sludge, and thereby improve the dewatering efficiency. However, the use of lime has many drawbacks, which are contrary to the current strict environmental protection requirements and sustainable development concepts.
(1) The amount of sludge has increased significantly, and the disposal pressure has intensified
Lime itself does not participate in the dewatering reaction. After being added, it will remain in large quantities in the dewatered sludge, resulting in a significant increase in the dry basis weight of the sludge. Relevant data shows that after being conditioned with lime, the dry basis weight of sludge can increase by 30% to 50%. This not only increases the subsequent transportation cost of sludge, but also significantly raises the land resources required for landfill treatment, intensifying the disposal pressure in cities with tight land resources.
(2) The equipment is severely corroded, and the operation and maintenance costs are rising
Lime reacts with water to form a strongly alkaline substance, which causes severe corrosion to metal equipment such as plate and frame filter presses and screw pumps during the sludge dewatering process. According to statistics, for equipment that has been using lime to regulate sludge for a long time, the service life of key components has been shortened by 30% to 40%, and the frequency and cost of equipment maintenance have significantly increased. Frequent equipment failures can also lead to production disruptions and affect the normal operational efficiency of sewage treatment plants.
(3) There is a high risk of secondary pollution, which is harmful to the ecological environment
Lime is highly prone to generating a large amount of dust during storage, transportation and dosing. These lime dusts not only pollute the surrounding atmospheric environment, but also cause damage to the respiratory tract, skin and other parts of the operators. In addition, the residual lime in the dewatered sludge can affect the pH of the sludge. If it is utilized as a resource, it may change the soil properties, affect the growth of crops, and even endanger human health through the food chain.
(4) Hindering the resource utilization of sludge and restricting sustainable development
Municipal sludge contains a large amount of organic matter and nutrients, and has the potential to be made into fertilizers, building materials, etc. for resource utilization. However, the addition of lime will reduce the calorific value of sludge and affect the efficiency of incineration power generation. When making building materials, the physical properties of the building materials will also be changed, the product quality will be reduced, and the process of sludge resource utilization will be seriously hindered, which is contrary to the concept of circular economy development.
Ii. Working Principle and Advantages of the New Sludge Conditioner
The new type of sludge conditioner is a compound agent developed specifically for the characteristics of municipal sludge, mainly composed of high-molecular polymers, surfactants, cell wall disruptors and other components. These components work in synergy to fundamentally improve the dewatering performance of sludge, demonstrating multiple environmental protection advantages.
(1) Efficient dewatering to reduce the total amount of sludge
The new type of sludge conditioner promotes the rapid aggregation of sludge particles into large and dense flocs through the bridging and entrapment effects of high-molecular polymers. Surfactants reduce the surface tension between sludge particles and water molecules, making it easier to separate water. The cell wall disruptor destroys the cellular structure of microorganisms in the sludge and releases intracellular water. The multi-effect integrated mechanism of action enables the moisture content of sludge to be reduced from over 90% to 40% - 60%. Compared with lime, the dewatering effect is more significant, effectively reducing the total amount of sludge treatment.
(2) Environmentally friendly and reduce secondary pollution
The new type of sludge conditioner contains no corrosive or toxic substances. During use, it causes no dust pollution and poses no threat to the health of operators or the surrounding environment. Its components remain stable after sludge dewatering, without altering the sludge's pH value or chemical properties, and will not cause secondary pollution. The dewatered sludge is more likely to meet the environmental protection requirements for subsequent disposal and resource utilization.
(3) Protect the equipment and extend its service life
The new type of sludge conditioner has mild chemical properties and is non-corrosive to dewatering equipment. It can effectively extend the service life of equipment such as plate and frame filter presses and centrifugal dewatering machines, reduce the frequency of equipment maintenance and replacement, and lower the operation and maintenance costs of sewage treatment plants. Meanwhile, the conditioned sludge is less likely to adhere to the surface of the equipment, reducing the frequency of equipment cleaning and improving the operational efficiency of the equipment.
(4) Facilitate resource utilization and promote a circular economy
The sludge dehydrated with the new type of sludge conditioner has better retention of organic matter and nutrients, and its calorific value is not affected, which is more conducive to incineration power generation. When making building materials, the quality and performance of the products can be guaranteed. This provides a solid foundation for the resource utilization of municipal sludge, promotes the transformation of sludge from waste to resource, and contributes to the development of a circular economy.
Iii. Practical Application Cases of New Sludge Conditioning Agents
A sewage treatment plant in a first-tier city has a daily sewage treatment capacity of 800,000 tons, and the task of sludge treatment is arduous. This factory originally used lime to regulate sludge, but it faced problems such as high moisture content in the sludge cake (about 75%), severe equipment corrosion, and low resource utilization rate of sludge. After introducing the new type of sludge conditioner and optimizing the process, the moisture content of the sludge was reduced to 50%, and the volume of the mud cake was decreased by 60%, effectively lowering the transportation and disposal costs. Meanwhile, the phenomenon of equipment corrosion disappeared and the maintenance cost was reduced by 40%. The dehydrated sludge was successfully used to make eco-friendly bricks, achieving resource utilization and bringing a win-win situation of economic and environmental benefits to the enterprise.
Four. Conclusion
In the field of deep dewatering of municipal sludge, the new type of sludge conditioner, with its significant environmental protection advantages, is gradually becoming the ideal alternative to lime. It not only resolves the problems such as sludge increment, equipment corrosion, secondary pollution and limited resource utilization brought about during the use of lime, but also promotes the development of municipal sludge treatment towards green, efficient and sustainable directions through its features of efficient dewatering, environmental friendliness, equipment protection and resource utilization assistance. With the continuous improvement of environmental protection requirements and the continuous innovation of technology, the new type of sludge conditioner is expected to be widely applied in more municipal sewage treatment plants, playing an important role in improving the ecological environment and achieving sustainable urban development.