The impact of carbonation intensity on sludge dewatering

I. Core Mechanism of Carbonization Intensity in Improving Sludge Dewatering Carbonization intensity is primarily manifested through parameters such as temperature, time, and heating rate. Its positive effect on dewatering stems from the following three points: Disrupting the colloidal structure of sludge: Moderate carbonization (typically at temperatures ranging from 150-300°C) causes the microbial cells in the sludge to rupture and the organic matter to decompose, releasing the bound water encapsulated within. This transforms the difficult-to-remove "bound water" into easily removable "free water". Reducing the hydrophilicity of sludge: The carbonization process decomposes the hydrophilic groups (such as hydroxyl and carboxyl groups) in the sludge, while simultaneously generating a hydrophobic carbonaceous structure. This reduces the adsorption capacity of sludge particles for water, making it easier for water to detach from the particle surface. Enhancing the rigidity of sludge particles: After carbonization, the sludge particles form a denser and harder carbon skeleton, reducing "sludge particle compression deformation" caused by pressure during the dewatering process. This prevents the filter cake from blocking the filter cloth and enhances the permeability of the filter cake. II. Negative Impacts of Excessively High Carbonization Intensity When the carbonization intensity exceeds the optimal range (such as temperature > 350°C and excessive time), it can actually weaken the dewatering effect, specifically manifested as follows: Excessive Fragmentation of Sludge Particles: Excessively high temperatures can lead to the embrittlement and fragmentation of the carbonaceous structure, producing a large amount of fine powder. This powder can clog the pores of the filter cloth, forming a dense "cake layer" that hinders water infiltration, thereby reducing the dewatering rate. Reverse Enhancement of Adsorption Capacity: Extreme carbonization can produce highly porous activated carbon-like substances, which can re-adsorb the water released during the dewatering process, leading to an increase in the moisture content of the filter cake. Soaring Energy Consumption and Costs: Higher carbonization temperatures and longer durations require more energy consumption, while the improvement in dewatering performance is far less than the increase in energy consumption, resulting in a significant decrease in cost-effectiveness. III. Limitations of Excessively Low Carbonization Intensity If the carbonization intensity is insufficient (such as temperature < 120°C and too short a duration), it cannot achieve the goal of improving dewatering: Insufficient Destruction of Colloidal Structure: The cells and organic matter in the sludge are not effectively decomposed, and the bound water is still encapsulated within the colloids. After dewatering, the moisture content of the filter cake remains high (usually > 80%), failing to meet the requirements for subsequent disposal (such as landfilling and incineration). High Sludge Viscosity: The hydrophilic groups have not significantly decreased, and the sludge particles still maintain strong hydrophilicity and viscosity. During the dewatering process, they are prone to adhering to the filter cloth, which not only affects the dewatering efficiency but also increases the frequency of filter cloth cleaning.