Method for treating aqueous sludge, material so produced and the use thereof
View Patent ↗The invention relates to a method for the accelerated dehydration of sludges in sludge disposal areas, especially of sludges from rivers and harbors, by the exclusive use of anionic polymer flocculants and the use of materials obtained according to the inventive method.
1. A method for the dewatering of sludge including negatively charged particles obtained from rivers, harbors, the sea floor, or sandbanks, comprising
adjusting the concentration of the sludge to a pumpable concentration by addition of water,
flushing the sludge through a pipeline to a dewatering field,
mixing the sludge with an aqueous solution of a polymeric flocculating agent while it is being transported,
allowing the sludge to settle in the dewatering field to form a sediment and partly freeing the sludge of supernatant and/or drainage water and then subjecting the sludge to natural evaporative drying,
wherein the polymeric flocculating agent is a water-soluble, anionic, polymeric flocculating agent that contains from 5 to 30 percent by weight of anionic monomer units and has a weight-average molecular weight Mw of higher than 1.0×10 7 .
2. The method according to claim 1 , wherein the anionic polymeric flocculating agent is formed from anionic and nonionic monomers wherein acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, vinylsulfonic acid, acrylamidoalkanesulfonic acids, vinylphosphonic acid and/or their salts with alkalis, ammonia, (alkyl)amines or alkanolamines or mixtures of these monomers are used as the anionic monomers and wherein acrylamide, methacrylamide, acrylonitrile, hydroxyalkyl esters of acrylic and methacrylic acid, vinylpyrrolidone or vinylacetamide or mixtures of these monomers are used as the nonionic monomers.
3. The method according to claim 1 , wherein the polymeric flocculating agent contains 10 to 20% by weight of integrally polymerized anionic monomer constituents.
4. The method according to claim 1 , wherein at least two different anionic flocculating agents are used.
5. The method according to claim 1 , wherein the polymeric flocculating agent is added in a proportion of 0.02 wt % to 2 wt % relative to the solids content of the sludge.
6. The method according to claim 1 , wherein the polymeric flocculating agent is used in the form of an aqueous solution with a concentration of lower than 2 wt %.
7. The method according to claim 6 , wherein the polymer solution is prepared from a powdery polymer.
8. The method according to claim 1 , wherein the sludge to be dewatered contains at least 50 wt % of fine particles in the size range of 0.06 mm or smaller.
9. The method according to claim 1 , wherein the flocculating agent is metered into the pipeline over a section between the outlet to the dewatering field and 150 m ahead of the outlet.
10. The method according to claim 9 , wherein the evaporative drying of the sludge is continued to a density of at least 1.45 metric tons per m 3 .
11. The method according to claim 10 , wherein the sludge has a vane shear strength of greater than 25 kN/m 2 .
12. The method according to claim 1 , wherein a measuring device in the pipeline determines the sludge concentration, calculates the quantity of flocculating agent therefrom and initiates metering of the flocculating-agent solution.
13. The method according to claim 1 , wherein the sludge treated with the flocculating agent has a density of 1.25 to 1.35 metric tons per m 3 after dewatering and before natural evaporative drying.
14. The method according to claim 1 , wherein the natural evaporative drying is accelerated by mechanically turning the sludge.
15. The method according to claim 14 , wherein the mechanical turning is achieved by means of rotary hoes.
16. The method according to claim 1 , wherein the dewatered and dried sludge is mixed with clays and/or slaked lime and/or cement in proportions of 1 to 15 wt % each.
17. A dewatered sludge prepared according to the method as claimed in claim 1 .
18. A building material comprising the dewatered sludge prepared according to the method as claimed in claim 1 .
19. The method according to claim 1 , wherein the anionic polymeric flocculating agent is a copolymer of acrylamide and acrylic acid.