Study On Sludge Chemical Conditioning And Dewatering Enhancement In Hydrocyclone

The construction of sewage treatment facilities underwent rapid development given the continuous urbanization of China. The number of urban sewage treatment plants in China has exceeded 3900. The country's total annual sludge production is estimated to exceed 40 million tons. More than 80% of the sludge produced in the country is not effectively and safely handled. Thus, sludge is a main secondary source of pollution in the water environment. This problem urgently requires the rapid and effective treatment of sludge. Reduction, which is the most basic step in sludge treatment, involves reducing sludge content and volume in water. Sludge dewatering technology is a combination of single and multiple technologies. Multi-technology combination is a combination of the functionalities of multiple fields. The theoretical core of sludge dewatering process is the interaction between the reaction field and the sludge. This study aims to achieve a thorough understanding of the direct interaction between the reaction field and the sludge given the lack of coupling effect of multiple fields in the sludge dewatering process.This study used sludge reduction as basis in proposing enhancement to sludge dewatering. Such an enhancement can be achieved through surfactant treatment and hydrocyclone shearing during sludge conditioning and dewatering to achieve sludge reduction and thereby reduce the cost of sludge disposal. We synthesized gemini surfactants and studied the relationship between activated sludge and surfactants through experimental and molecular dynamic simulations. This process enabled us to understand the molecular mechanism of surfactant application in sludge treatment at the ficroscale. We also explored the process of breaking down sludge in a shear force field. The mechanism of sludge breakage in hydrocyclone shear field was examined through quantitative characterization of the variation regularity of sludge. The flow field in the hydrocyclone was measured by PIV technique. The rotation characteristics of the particles in the rotating flow field were measured by high-speed digital imaging technique. The distribution characteristics of flow and pressure drop of the large-scale parallel enlargement of the hydrocyclone were also studied. The completed research and findings are shown below.(1) Gemini surfactants 12-3-12,2Br were synthesized and compared with single-chain surfactant DTAB. Two kinds of surfactants were added to adjust the activated sludge. The conditioning effects of surfactant left a significant impact on the characteristics of sludge flocculation, macroscopic index of sludge dewatering, and sludge sedimentation index. The impact of 12-3-12,2Br" on the characteristics of sludge flocculation is more significant than that of DTAB. The performance of sludge filtration and cake moisture content improved after 12-3-12,2Br- conditioning. The addition of DTAB can continuously reduce sludge volume. Settling performance improved significantly with the addition of 12-3-12,2Br" at low dosage. By contrast, the effect of sludge settling worsened with the addition of 12-3-12,2Br"at high dosage.(2) The interaction process between the gemini surfactant and polyelectrolyte chain and the structure of compound combined by the gemini surfactant and the polyelectrolyte chain was studied by means of coarse-grained molecular dynamics simulation. Results show that the number of surfactants and hydrophobicity of polyelectrolyte chains directly influence the interaction process and the final formation of complex structure. The adsorption process contains "bottle brush," "beads," "beads grow," and "compound micelles," which formed relatively stable compound micelles. Electrostatic attraction is the main driving force of the adsorption of hydrophilic polyelectrolyte chains. These chains finally formed the rod-like micelle. The synergistic interaction between electrostatic attraction and hydrophobic association is the main driving force of hydrophobic polyelectrolyte chain, which formed a spherical micelle. The length of surfactant-binding group on the adsorption process did not leave a significant effect. Charge density had a synergistic effect on the adsorption of hydrophilic polyelectrolyte chains, whereas the adsorption of hydrophobic polyelectrolyte chains is almost independent of charge density. The strong interaction between the surfactant and the polyelectrolyte material can disrupt the structure of the sludge floes and release free water to increase the rate of sludge dewatering.(3) We studied the cracking process of sludge under the shearing force field of hydrocyclone. The effects of hydrocyclone shear on sludge dewatering were investigated in three aspects, namely, sludge flocculation, sludge dewatering, and sludge settling. Results show strong shear stresses attributed to velocity gradients in the hydrocyclone. We also observed strong turbulent flow and local pressure pulsation, which will significantly affect floe characteristics of the sludge. Sludge floe structure will crack in the swirling effect. Impurities in the floe surface impurities are then removed to ensure smooth appearance. The release of organic matter from sludge floes into the water and the polysaccharide and protein concentration in the supernatant increased significantly with the increase of shear time. By contrast, the increase rate of polysaccharide and protein concentration slowed down. The flocculation performance of the sludge was significantly reduced because of the cracking of floes. The filtration performance of sludge then deteriorates. The shearing action also decreases the moisture content of the cake. Hydrocyclone is a power source of sludge cracking and also provides shear action and facilitates the solid-liquid separation of sludge and particle size classification. Sludge without surfactant conditioning is sensitive to shearing. Sludge dewatering effect improves after conditioning. Combining the effect of surfactant conditioning with hydrocyclone shearing improves dewatering performance.(4) The flow field and particle rotation characteristics of the hydrocyclone were measured by PIV and a high-speed digital camera. Flow field and particle motion studies showed that the internal flow field depends on the parameters of hydrocyclone structure. Axial velocity distribution was not the fully of axial symmetrical structure because of the influences of single inlet and air column of the hydrocyclone. The radial velocity distribution along the axial direction shows regular alternation. In addition to the revolution around the central axis of the hydrocyclone, the dispersed phase particles are rotated around their own axis and random inversion movements. Particle revolution, rotation, and inversion were significantly affected by inlet flow rates. Linear velocity, angular velocity, and separation factor increased with increased inlet flow. The regularity of revolution and rotation of particles became obvious and the randomness of inversion increased. The angular velocity of particle rotation is significantly larger than the revolution and inversion angular velocity. The rotation separation factor is 10 to 15 times higher than the revolution separation factor. Results show that the intensity of particle rotation in the hydrocyclone is stronger than the strength of revolution. This result was not explored in previous studies.(5) The UU-type parallel hydrocyclone group was used as the object of study. A pilot plant and an industrial plant were used to study the flow and pressure distribution characteristics of large-scale hydrocyclone equipment. In the 12 times large-scale pilot plant, the distributions of flow and pressure drop were the most uniform at P= 0.10 MPa with the maximum fluctuation values of 3.6% and 7.2%, respectively. The experimental measurement of flow rate and pressure drop was consistent with theoretical calculations. The trend of flow distribution decreased in the 300 times large-scale industrial device along the axial direction from bottom to top. Flow distribution was relatively uniform along the circumferential. At low inlet pressure, the relative error of flow and pressure drop distribution is 11.0% and 8.5%. The measured values of flow rate and pressure drop are consistent with the calculated results of the increase of inlet pressure. This finding indicates that the distribution of flow and pressure drop can reach the target level.