Urban treatment plants produce a large amount of sludge every day, which is difficult to treat due to its high moisture content (over 80%), large volume, and easy to decompose and stink.
With the increasing production of municipal and industrial sludge, many countries in the European Union have formulated and implemented relevant environmental laws, prohibiting sludge containing biodegradable organic substances from being landfilled and encouraging incineration treatment.
The "Guidelines for the Best Feasible Techniques for Pollution Prevention and Control in the Treatment and Disposal of Sludge from Urban Sewage Treatment Plants" and "Guidelines for the Best Feasible Techniques in the Treatment and Disposal of Sludge from Sewage Treatment Plants" issued by the Ministry of Environmental Protection of China clearly consider sludge incineration as one of the feasible technologies for sludge treatment and disposal in China. This method is a sludge disposal technology with advantages such as reduction, harmless treatment, resource utilization, and energy recovery, However, at present, the moisture content of sludge after various types of mechanical dewatering is relatively high, which makes it difficult to implement mixed burning of sludge.
In order to effectively and deeply dehydrate sludge, physical and chemical conditioning methods are often used for sludge pretreatment. The chemical conditioning method has become one of the most commonly used methods due to its simple operation, low cost, and significant effectiveness. Among them, commonly used chemical conditioning agents include inorganic coagulants (such as FeCl3, CaO, AlCl3, etc., with an addition amount of 5% to 20% of the sludge dry solids), organic polymer coagulants (PAM, etc., with an addition amount of 0.1% to 0.3% of the sludge dry solids), and microbial coagulants.
Due to the difficulty of achieving ideal sludge dewatering results with a single chemical conditioner, in recent years, domestic and foreign scholars have attempted to use composite conditioners or combine multiple conditioners to improve the deep dewatering performance of sludge. Among them, the most common is the use of CaO in combination with iron and aluminum salts. It can be seen that the application of conditioners can effectively reduce the moisture content of sludge, which means that in the future, the target of sludge treatment will mostly be sludge after deep dehydration.
