Application and mechanism of a novel flocculation reagent for mechanical dewatering: A case study on slurry separation in a large-diameter slurry shield

Abstract

A novel C-type flocculation reagent was developed to address the high water content of sludge and the environmental pollution caused by wastewater discharge during mechanical dewatering in the Zhanjiang Bay undersea tunnel. Microscopic parameters, such as particle size and zeta potential, were analyzed to elucidate the flocculation and dewatering mechanisms of the C-type reagent. The applicability of the C-type reagent was further validated in a field test and compared to that of conventional reagents. The results showed that the C-type reagent reduced the water content of the sludge by approximately 20 % and decreased the turbidity of the supernatant by approximately 79 %. The C-type reagent demonstrated enhanced bridging and charge neutralization activity, which facilitated the aggregation of fine particles (<10 μm) into larger particles (>50 μm), ultimately enhancing the efficiency of flocculation. The C-type reagent also facilitated the formation of a calcium drainage channel skeleton with enhanced water permeability and reduced the slurry viscosity to improve the efficiency of mechanical dewatering. These effects enhanced the pore size distribution of the slurry to a range of 346 to 8656 nm, which was approximately 15 % to 41 % greater than the overall pore size of the original slurry. Onsite utilization of 0.5 % C-type reagent enhanced the solid content of the sludge by 35.7 % compared with that obtained with the original reagent, resulting in a 20 % reduction in cost. Moreover, the sludge meets the sewage standards for indicators such as pH and thus qualifies for direct discharge. The findings of this study offer valuable insights for the selection of environmentally friendly and efficient reagents in the context of combined flocculation–mechanical dewatering.