Industry News » American Air Liquide Inc. Patent Issued for Aluminum Hydroxide Coagulant Recovery From Water/Wastewa...


American Air Liquide Inc. Patent Issued for Aluminum Hydroxide Coagulant Recovery From Water/Wastewater Treatment Sludge (USPTO 10,358,355)

2019 AUG 8 (VerticalNews) -- By a News Reporter-Staff News Editor at Politics & Government Week -- According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventors Mahmudov, Rovshan (Newark, DE); Zuttah, Sylvester (Bear, DE), filed on December 14, 2017, was published online on August 5, 2019.

The assignee for this patent, patent number 10,358,355, is American Air Liquide Inc. (Fremont, California, United States).

Reporters obtained the following quote from the background information supplied by the inventors: "Aluminum hydroxide (alum) is the most common coagulant used in water and wastewater treatment. The main purpose of alum in these applications is to improve the settling of suspended solids and color removal. Alum is also used to remove phosphate from wastewater treatment effluent. In all these applications, aluminum enriched sludge is generated. Alum in the sludge generated during these processes causes difficulties with sludge dewatering and disposal because alum traps water. Therefore, aluminum recovery from water and wastewater treatment sludge has several significant advantages: (1) improving sludge dewaterability, (2) reducing sludge mass or weight by dewatering the sludge, and (3) cutting down the cost of alum by reusing the recovered alum.

"There are limited options for recovery of alum from sludge containing high concentration of CaCO.sub.3, CaSO.sub.4, and Mg(OH).sub.2. The most widely accepted method for aluminum recovery is acidulation of the sludge. Exemplary examples of aluminum recovery under acidic circumstance include CN105948442, TW201226577, KR20040088093, U.S. Pat. Nos. 5,304,309, 6,495,047, US2013319941, JP2002113472, RU2133225, U.S. Pat. Nos. 4,130,627, 3,959,133, etc.

"Attempts have been made to recover aluminum hydroxide under alkaline conditions. For example, EP2017225 to Olsson et al. discloses a process for production of an aluminum hydroxide containing filter cake from aluminum containing waste waters, in which acidic and alkaline waste waters containing aluminum are mixed in a ratio resulting in a pH of 9-11 to obtain mixed waste waters. The mixed waste waters are allowed to react with each other during a retention time of at least 5 hours resulting in an aluminum hydroxide containing slurry, which is dewatered to obtain an aluminum hydroxide containing filter cake.

"EP2452924 to Rossi et al. discloses a method for the treatment of waste liquids originating from plants for the treatment of aluminum that includes mixing a first alkaline eluate (B) that contains sodium hydroxide (NaOH) and sodium aluminate (NaAlO.sub.2), and a second acid eluate (A) which contains sulfuric acid (H.sub.2SO.sub.4) and aluminum sulfate (Al.sub.2(SO.sub.4).sub.3) to achieve the forming of an aluminum hydroxide precipitate (Al(OH).sub.3) on the bottom of a reactor upon reaching a pH value of the content of the reactor between 7.5 and 9.0.

"Masschelein et al. (W. J. Masschelein, R. Devleminck and J. Genot, 'The Feasibility of Coagulant Recycling by Alkaline Reaction of Aluminum Hydroxide Sludges', Water Research, vol. 19, No. 11, 1985, p 1363-1368) disclose recovery of aluminum from a waterworks sludge by alkalization with NaOH or Ca(OH).sub.2 under laboratory conditions. Even though it was possible to recover 80% of the aluminum the authors recommended recycling less than 50% of the total dosing rate because of impurity problems. Lime was more effective than sodium hydroxide for removing heavy metals from the recovered coagulant.

"In addition, cost is also an issue to be considered for aluminum hydroxide coagulant recovery industry.

"Thus, a need remains for effective recovery of aluminum hydroxide from wastewater treatment sludge."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "There is disclosed a method for recovery of aluminum hydroxide Al(OH).sub.3 from an aluminum enriched water/wastewater treatment sludge, the method comprising the steps of: a) adding a hydrated lime slurry to the aluminum enriched water/wastewater treatment sludge to form an alkaline sludge; b) adding sodium carbonate Na.sub.2CO.sub.3 to the alkaline sludge to form a Na.sub.2CO.sub.3 treated sludge; c) forming a supernatant from the Na.sub.2CO.sub.3 treated sludge of step b) containing NaAl(OH).sub.4; d) introducing CO.sub.2 to the supernatant to form a precipitate of Al(OH).sub.3 and a supernatant containing NaHCO.sub.3; and e) recycling at least a portion of the NaHCO.sub.3 from the supernatant back to the alkaline sludge of step a).

"In some embodiments the pH of the aluminum enriched water/wastewater treatment sludge is approximately 7.

"In some embodiments the pH of the alkaline sludge ranges from approximately 11.5 to 12.

"In some embodiments the pH of the supernatant ranges from approximately 6.5 to 7.5.

"In some embodiments the pH of the supernatant is approximately 7.

"In some embodiments the method further comprises a step of retaining the aluminum enriched water/wastewater treatment sludge for a contact time with the hydrated lime slurry sufficient in length to inactivate at least a portion of bacteria and viruses present in the sludge during the step a) of forming the alkaline sludge.

"In some embodiments the contact time is about 2 to 5 hours.

"In some embodiments the aluminum enriched water/wastewater treatment sludge contains up to 5% solids.

"In some embodiments the solids include aluminum hydroxide.

"In some embodiments the method further comprises a step of thickening the aluminum enriched water/wastewater treatment sludge to increase a solid content of the sludge.

"In some embodiments the thickened aluminum enriched water/wastewater treatment sludge contains up to 5% solid content.

"In some embodiments the solid content in the thickened aluminum enriched water/wastewater treatment sludge includes aluminum hydroxide.

"In some embodiments the pH of the thickened aluminum enriched water/wastewater treatment sludge is approximately 7.

"In some embodiments the method further comprises the steps of: recycling a slurry phase of the alkaline sludge; dewatering a waste sludge from the slurry phase to form a dilution water with a high pH value, preferably pH 11.5 or greater; and mixing the dilution water with a hydrated lime to form the hydrated lime slurry.

"In some embodiments the method further comprises a step of adding Mg(OH).sub.2 to the alkaline sludge to purify the alkaline sludge.

"In some embodiments the method further comprises a step of adding Mg(OH).sub.2 to the alkaline sludge in an amount sufficient to coagulate natural organic matter present in the alkaline sludge.

"In some embodiments the hydrated lime slurry contains 5-10% Ca(OH).sub.2.

"In some embodiments the alkaline sludge contains calcium aluminate CaAl.sub.2(OH).sub.8 according the reaction: 2Al(OH).sub.3+Ca(OH).sub.2.fwdarw.CaAl.sub.2(OH).sub.8.

"In some embodiments NaAl(OH).sub.4 in the supernatant is formed by the following reactions: CaAl.sub.2(OH).sub.8+Na.sub.2CO.sub.3.fwdarw.2NaAl(OH).sub.4+CaCO.sub.3 a) Ca(OH).sub.2+Na.sub.2CO.sub.3.fwdarw.2NaOH+CaCO.sub.3 b) 2NaOH+CaAl.sub.2(OH).sub.8.fwdarw.2NaAl(OH).sub.4+Ca(OH).sub.2 c)

"In some embodiments NaHCO.sub.3 in the supernatant is formed by the following reactions: CO.sub.2+H.sub.2O.fwdarw.H.sub.2CO.sub.3* a) H.sub.2CO.sub.3.fwdarw.H.sup.++HCO.sub.3.sup.- b) HCO.sub.3.fwdarw.H.sup.++CO.sub.3.sup.2- c) NaAl(OH).sub.4+H.sub.2CO.sub.3*.fwdarw.NaHCO.sub.3+Al(OH).sub.3(s)+H.sub.- 2O. d)

"In some embodiments NaHCO.sub.3 recycled back to the alkaline sludge forms NaAl(OH).sub.4 by the following reactions: Ca(OH).sub.2+NaHCO.sub.3.fwdarw.NaOH+CaCO.sub.3+H.sub.2O 2NaOH+CaAl.sub.2(OH).sub.8.fwdarw.2NaAl(OH).sub.4+Ca(OH).sub.2."

The claims supplied by the inventors are:

"We claim:

"1. A method for recovery of aluminum hydroxide Al(OH).sub.3 coagulant from an aluminum enriched water/wastewater treatment sludge, the method comprising the steps of: a) adding a hydrated lime slurry to the aluminum enriched water/wastewater treatment sludge to form an alkaline sludge; b) adding sodium carbonate Na.sub.2CO.sub.3 to the alkaline sludge to form a Na.sub.2CO.sub.3 treated sludge; c) forming a first supernatant from the Na.sub.2CO.sub.3 treated sludge of step b) containing NaAl(OH).sub.4; d) introducing CO.sub.2 to the first supernatant to form a precipitate of Al(OH).sub.3 and a second supernatant containing NaHCO.sub.3; and e) recycling at least a portion of the NaHCO.sub.3 from the second supernatant back to the alkaline sludge of step a).

"2. The method of claim 1, wherein the pH of the aluminum enriched water/wastewater treatment sludge is approximately 7.

"3. The method of claim 1, wherein the pH of the alkaline sludge ranges from approximately 11.5 to 12.

"4. The method of claim 1, wherein the pH of the second supernatant ranges from approximately 6.5 to 7.5.

"5. The method of claim 1, wherein the pH of the second supernatant is approximately 7.

"6. The method of claim 1, further comprising the step of: a1) retaining the aluminum enriched water/wastewater treatment sludge for a contact time with the hydrated lime slurry sufficient in length to inactivate at least a portion of bacteria and viruses present in the aluminum enriched water/wastewater treatment sludge during the step a) of forming the alkaline sludge.

"7. The method of claim 6, wherein the contact time is about 2 to 5 hours.

"8. The method of claim 1, wherein the aluminum enriched water/wastewater treatment sludge contains up to 5% solids.

"9. The method of claim 8, wherein the solids include aluminum hydroxide.

"10. The method of claim 1, further comprising the step of thickening the aluminum enriched water/wastewater treatment sludge to increase a solid content of the sludge.

"11. The method of claim 10, wherein the thickened aluminum enriched water/wastewater treatment sludge contains up to 5% solid content.

"12. The method of claim 11, wherein the solid content in the thickened aluminum enriched water/wastewater treatment sludge includes aluminum hydroxide.

"13. The method of claim 12, wherein the pH of the thickened aluminum enriched water/wastewater treatment sludge is approximately 7.

"14. The method of claim 1, further comprising the steps of: recycling a slurry phase of the alkaline sludge; dewatering a waste sludge from the slurry phase to form a dilution water with a pH value of 11.5 or greater; and mixing the dilution water with a hydrated lime to form the hydrated lime slurry.

"15. The method of claim 1, further comprising the step of adding Mg(OH).sub.2 to the alkaline sludge in an amount sufficient to coagulate natural organic matter present in the alkaline sludge.

"16. The method of claim 1, wherein the hydrated lime slurry contains 5-10% Ca(OH).sub.2.

"17. The method of claim 1, wherein the alkaline sludge contains calcium aluminate CaAl.sub.2(OH).sub.8 according to the reaction: 2Al(OH).sub.3+Ca(OH).sub.2.fwdarw.CaAl.sub.2(OH).sub.8.

"18. The method of claim 17, wherein NaAl(OH).sub.4 in the first supernatant is formed by the following reactions: CaAl.sub.2(OH).sub.8+Na.sub.2CO.sub.3.fwdarw.2NaAl(OH).sub.4+CaCO.sub.3 Ca(OH).sub.2+Na.sub.2CO.sub.3.fwdarw.2NaOH+CaCO.sub.3 2NaOH+CaAl.sub.2(OH).sub.8.fwdarw.2NaAl(OH).sub.4+Ca(OH).sub.2.

"19. The method of claim 18, wherein NaHCO.sub.3 in the second supernatant is formed by the following reactions: CO.sub.2+H.sub.2O.fwdarw.H.sub.2CO.sub.3* H.sub.2CO.sub.3*.fwdarw.H.sup.++HCO.sub.3.sup.- HCO.sub.3.sup.-.fwdarw.H.sup.++CO.sub.3.sup.2- NaAl(OH).sub.4+H.sub.2CO.sub.3*.fwdarw.NaHCO.sub.3+Al(OH).sub.3(s)+H.sub.- 2O, wherein H.sub.2CO.sub.3* denotes the sum of CO.sub.2 and H.sub.2CO.sub.3 present in the second supernatant.

"20. The method of claim 17, wherein NaHCO.sub.3 recycled back to the alkaline sludge forms NaAl(OH).sub.4 by the following reactions: Ca(OH).sub.2+NaHCO.sub.3.fwdarw.NaOH+CaCO.sub.3+H.sub.2O 2NaOH+CaAl.sub.2(OH).sub.8.fwdarw.2NaAl(OH).sub.4+Ca(OH).sub.2."

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