The Organic Polymer Flocculants For Sludge Dewatering Preliminary Study

Dehydration characteristic of flocculants with different ionic property and intrinsicviscosity in the dehydration processes of sludge from six different representative areas inJiangsu province and the evaluating method on decomposing of PDA flocculants insludge dehydrated were studied in this paper.By using synthetic and commercial copoly acrylamide (PAM) with the cationic,non-ionic and anionic property and different intrinsic viscosity, the effects of theirdifferent dosages on the sizes of flocculates, water-containing rates in cakes, COD_Crvalues and transmittion of supper leakage were investigated in detail. At the same time,by using turbidity value, transmittion of supper leakage and microscope photograph, thedecomposing possibility and speed of flocculant residua in sludge were studied.The experimental results indicated: Flocculants with different ionic property andintrinsic viscosity, which were applied treating the sludge from different representativeareas all effective, but the dosages used and the water-containing rates in cakes offorming optimum size of flocculate were different.When the sludge containing low water, such as 90%, was flocculated, the dosagesused in optimum size of flocculate and the water-containing rates of cakes for the sludgefrom rivers and lakes were in the range of 350mg·L^-1～640mg·L^-1and 47.0%～74.0%respectively, but the dosages and the rates for from those harbors were 850mg·L^-1～1200mg·L^-1 and 41.0%～57.0% respectively. When the sludge containing higher water,such as 95%, was flocculated the dosages used in optimum size of flocculated and thewater-containing rates of cakes for the sludge from rivers and lakes were in the range of52.8mg·L^-1～316.8mg·L^-1and 47.8%～71.1% respectively, but the dosages and the ratesfor those from harbors were 26.4mg.·L^-1～158.4mg·L^-1and 41.2%～57.1 respectively.After flocculation by different ionic property and intrinsic viscosity; COD_Cr values ofsupper leakage decreased first, then increased as increasing of the different flocculantsdosages. But the transmission of supper leakage increased first and then decreased,correspondingly. The COD_Cr value of forming optimum size of flocculate was more thanthe lowest value in the curve of COD_Cr value. Zeta potential of the supper leakageincreased after flocculated by CPAM and NPAM, but decreased by APAM. In general,for CPAM, APAM and NPAM, they all could be used in sludge dehydration. For the purposes of forming optimum size of flocculate and for obtaining lowestwater-containing rates of cakes, APAM and CPAM had their superiority better than theothers, respectively. Specially, the low water-containing rates of cakes played animportant role in decreasing the cost of transport and the stacking volume.The results from the research on processes of flocculant decomposing in sludgeflocculated and on its evaluating method indicated that: turbidity of the suspension liquidcontaining 1% by weight of flocculated sludge which had degraded at room temperaturefor several days increased, while its transmission rate fell down. phenomena inphotomicrograph showed that large particles of sludge after flocculated was surroundedby water and then turned into a kind of paste after degraded. When under the samedegrading condition, turbidity and transmission rate for the suspension liquid of thesludge from rivers and lakes change a little at first, then the turbidity reduced graduallywhile the transmission rate increased with the time increasing. But for the sludge fromharbors areas, the turbidity and transmission rate changed inapparently. It can beconcluded that all of the flocculants which were used for the treatment of sludge fromsuch six typical areas could degrade. The flocculants used in sludge from rivers and lakesdegraded quickly, and under room temperature, three weeks were needed for fullydegradation. However, flocculants used for sludge from harbors degraded slowly and thewhole process would cost for more than three weeks.These research results could give out some proposes on process of sludgedehydration, and be helpful to select proper flocculants and to use sludge as a resource inmodern sludge cleaning-up project.