Synthesis, Characterization Of A Novel Compound Flocculant Starch And Its Sludge Dewatering Performance

In the process of urban sewage treatment, it often can produce a large amount of sludge, containing a high water content of 95% to 99.5%. The volume of sludge is very large that difficult to disposal or transport, and easy to stink of corruption, which must be dehydration. How to handle the sludge safely and effectively has been an important problem in the current environment field, for never cause secondary pollution to environment, and can reduce the cost of sludge treatment.This article use starch as main raw material to prepare a novel combined silicon-aluminum-iron-starch flocculant (CSiAFS) and study its characterization, next to investigate its sludge dewatering performance and mechanisms. The main research results are as follow:1. The optimum reaction conditions for synthesis were:1) 1.2/1 for the ratio of Al/starch (mass ratio),2) 0.375% for the SiO2 mass fraction,3) 3.0 for the pH value, and 4) 0.1/1 for the ratio of Fe/starch (mass ratio).FTIR analysis results showed that the combined silicon-aluminum-iron-starch flocculant (CSiAFS) not only had its new characteristics, also retained the original starch carbon chain structure. XRD analysis results showed that the original starch crystalline region was damaged. Compared to the angle of original starch that appeared peaks, it did not appear on the same curve angle, which implied that the addition of ferric chloride, aluminium sulphate and sodium silicate had changed the original state of the crystallization of starch and generated new crystal material. Thermogravimetric analysis results showed that the crystallinity of starch was reduced in the process of synthesis, instead of increasing thermal stability. SEM images also indicated CSiAFS possessed a discontinuous surface with larger particle size, which helped to promote sludge dewatering. All the characterization showed that silicon, aluminum and iron had been successfully grafted on the skeleton of starch.2. The best reaction conditions for sludge dewatering were:1) 7.0 for the pH value, and 2) 300mg/L for flocculant dosage. Compared with the blank sample, CSiAFS had cut down 97.9% of sludge specific resistance and reduced 78.5% of capillary suction time. With CST, SV30 and SRF value for evaluation indexes, the sludge dewatering performance of CSiAFS was superior to PAC, PAM, FeCl3 and a combined aluminum-ferrous-starch flocculant (CAFS). CSiAFS exhibited a good dewatering efficiency over a wide range of pH (3.0-11.0), especially in the neutral condition, which could save the consumption of acid and alkali.3. The results of protein content analysis were consistent with the CST, SV30 and SRF value. Compared to other flocculants, CSiAFS could thoroughly destroy the hydrated shell of sludge colloid, reducing protein content and aggregating dispersed particles, so as to increase the efficiency of sludge dewatering. The addition of silicon lead CSiAFS to build a poriferous structure, which could circulate the impervious layer during the process of pressure filtration. Its corresponding mud cake also contained a poriferous structure, having large surface area, pore volume and aperture than other flocculants, which meant CSiAFS contained greater adsorption performance. The strong adsorption performance helped CSiAFS to destroy sludge colloid, and then settled with extracellular polymer, thereby improved sludge dewatering efficiency. The compression coefficient of sludge conditioned by CSiAFS was 0.72, having a reduction of 40.5% compared to original sludge, which indicated that the sludge dewatering performance of CSiAFS was much better than the other four kinds of flocculants. The addition of silicon lead CSiAFS to form a porous structure with larger specific surface area, having "metal" framework and could remain well cake porosity and permeability in the filter process.