Aluminum hydroxide coagulant recovery from water/wastewater treatment sludge

Patent metadata

Field	Value
Publication number	US-10358355-B2
Application number	US-201715841533-A
Country	US
Kind code	B2
Filing date	Dec 14, 2017
Priority date	Dec 14, 2017
Publication date	Jul 23, 2019
Grant date	Jul 23, 2019

Abstract

A method for recovery of aluminum hydroxide Al(OH)3 from an aluminum enriched water/wastewater treatment sludge is disclosed. The method includes the steps of: adding a hydrated lime slurry to the aluminum enriched water/wastewater treatment sludge to form an alkaline sludge; adding sodium carbonate Na2CO3 to the alkaline sludge to form a Na2CO3 treated sludge; forming a first supernatant from the Na2CO3 treated sludge of step b) containing NaAl(OH)4; introducing CO2 to the first supernatant to form a precipitate of Al(OH)3 and a second supernatant containing NaHCO3; and recycling at least a portion of the NaHCO3 from the second supernatant back to the alkaline sludge of step a).

First claim

We claim:

1. A method for recovery of aluminum hydroxide Al(OH) 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 2 CO 3 to the alkaline sludge to form a Na 2 CO 3 treated sludge;
c) forming a first supernatant from the Na 2 CO 3 treated sludge of step b) containing NaAl(OH) 4 ;
d) introducing CO 2 to the first supernatant to form a precipitate of Al(OH) 3 and a second supernatant containing NaHCO 3 ; and
e) recycling at least a portion of the NaHCO 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) 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) 2 .

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

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

Ca(OH) 2 +Na 2 CO 3 →2NaOH+CaCO 3

2NaOH+CaAl 2 (OH) 8 →2NaAl(OH) 4 +Ca(OH) 2 .

19. The method of claim 18 , wherein NaHCO 3 in the second supernatant is formed by the following reactions:
CO 2 +H 2 O→H 2 CO 3 *

H 2 CO 3 *→H + +HCO 3 −

HCO 3 − →H + +CO 3 2−

NaAl(OH) 4 +H 2 CO 3 *→NaHCO 3 +Al(OH) 3 ( s )+H 2 O,

wherein H 2 CO 3 * denotes the sum of CO 2 and H 2 CO 3 present in the second supernatant.

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

2NaOH+CaAl 2 (OH) 8 →2NaAl(OH) 4 +Ca(OH) 2 .

Assignees

• Air Liquide American

Inventors

• Mahmudov Rovshan
• Zuttah Sylvester

Classifications

• C02F11/14

  with addition of chemical agents · CPC title

• C02F2303/04

  Disinfection · CPC title

• C02F1/5236

  using inorganic agents · CPC title

• C01F7/46 Primary

  Purification of aluminium oxide, aluminium hydroxide or aluminates (C01F7/028 takes precedence) · CPC title

• C02F11/145

  using calcium compounds · CPC title