Abstract: Despite good performance in conditioning dredging sludge, conventional chemicals generate highly alkaline tail water and mud cake from plate and frame pressure filtration dehydration. Based on laboratory sludge conditioning test, we researched the process of plate and frame pressure filtration dehydration of sludge conditioned with low-alkaline environmental modifier, PAC and PAM, and further analyzed the characteristics of tail water and mud cake. Results demonstrate that low-alkaline modifier combined with PAC and PAM could reduce the dosage of PAC and APAM while achieving an equivalent conditioning effect. With 0.12% APAM, 2.5% PAC and 2.5% low-alkaline modifier, the pH value of tail water and mud cake is 7.4 and 7.6, respectively, and the dehydration efficiency is 42.2% higher than that without dosing. Particle size analysis shows that the low-alkaline modifier increases the proportion of large particles in mud cake and improves the dehydration performance. EDS and XRD analysis reveals that low-alkaline modifier reacts with clay minerals in sludge and generates silicate mineral skeleton, which is favourable to reducing the specific resistance and the dewaterability. The pH value of the mud cake treated from the modifier declines slowly until finally stablizes, and such decline gets more intensive in the presence of high dosage. The research findings provide a scientific basis for exploring the sludge conditioning performance of new agents and the technical features of plate and frame filter press equipment.

Key words: sludge treatment, plate and frame filter pressing, low-alkaline environmental modifier, dehydration and solidification, sludge conditioning