Bio-catalytic calcium carbonate cementation
The present invention is directed to methods of preparing biocement. The methods disclosed herein employ microbial or enzymatic means first to generate acid which dissolves CaCO 3 , and then to degrade urea, producing CO 3 − ions which increase the pH and lead to the reprecipitation of CaCO 3 . The precipitation of CaCO 3 acts as a cementation process which can bind together particulate materials to yield mortars, concretes and suchlike. The invention further provides construction materials formed by the methods of the invention, and bacterial strains which can be used in the methods of the invention to generate organic acids.
1 . A method of forming a construction material from CaCO 3 and a particulate starting material, comprising:
(i) providing a combined mixture that includes a combination of the CaCO 3 and the particulate starting material;
(ii) enzymatically generating an acid in a first portion of the combined mixture, wherein the acid generation causes a local pH decrease in the first portion of the combined mixture, thereby locally dissolving at least a first portion of the CaCO 3 in the first portion of the combined mixture; and
(iii) enzymatically generating a local pH increase in a second portion of the combined mixture while enzymatically generating the acid in the first portion of the combined mixture thereby causing at least a second portion of the CaCO 3 to precipitate and to bind together at least part of the particulate starting material and the precipitated CaCO 3;
wherein one or more reagents for enzymatically generating the local pH increase are present in the combined mixture.
2 . The method of claim 1 , wherein the enzymatic generation of the local pH increase is performed using a microorganism or a microbial extract which contains enzymes.
3 . The method of claim 2 , wherein the microorganism is a bacterium or the microbial extract is a bacterial extract.
4 . The method of claim 1 , wherein the enzymatic generation of the local pH decrease is performed under aerobic conditions.
5 . The method of claim 1 , wherein the acid is a carboxylic acid and the particulate starting material comprises aggregate.
6 . The method of claim 5 , wherein the carboxylic acid is lactic acid or acetic acid.
7 . The method of claim 1 , wherein all the reagents for enzymatically generating the local pH increase and for enzymatically generating the acid are present in the combined mixture.
8 . The method of claim 3 , wherein both the pH decrease of (ii) and the pH increase of (iii) are performed using the same microorganism or microbial extract.
9 . The method of claim 3 , wherein the bacterium is of the strain having NCIMB accession number 42600, or a mutant or derivative thereof.
10 . The method of claim 2 , wherein the pH decrease of (ii) is performed using a different microorganism or extract thereof than the microorganism.
11 . The method of claim 1 , wherein:
the one or more reagents include urea; and
the particulate starting material comprises a plurality of aggregate particles.
12 . The method of claim 1 , wherein:
the enzymatically generating the local pH increase includes adjusting at least one of an amount of oxygen or an amount of sugar provided to the combined mixture.
13 . The method of claim 1 , wherein:
the enzymatically generating the local pH increase includes reducing an amount of sugar or reducing an amount of oxygen provided to the combined mixture.
14 . A method of forming a construction material, comprising:
(i) providing a combined mixture that includes a combination of CaCO 3 and a particulate starting material;
(ii) enzymatically generating an acid in the combined mixture during a first time period, wherein the acid generation causes a pH decrease in the combined mixture, thereby dissolving at least a first portion of the CaCO 3 in the combined mixture; and
(iii) enzymatically generating a pH increase in the combined mixture during a second time period thereby causing at least some of the first portion of the CaCO 3 to precipitate and to bind together at least part of the particulate starting material and the precipitated CaCO 3 , wherein one or more reagents for enzymatically generating the pH increase or for enzymatically generating the acid are present in the combined mixture prior to enzymatically generating the acid in the combined mixture.
15 . A method of manufacturing a construction material, comprising:
acquiring a combined mixture that includes a combination of CaCO 3 and a particulate starting material;
enzymatically generating an acid in a first portion of the combined mixture, wherein the acid generation causes a local pH decrease in the first portion of the combined mixture and causes at least a first portion of the CaCO 3 to be locally dissolved in the first portion of the combined mixture; and
enzymatically generating a local pH increase in a second portion of the combined mixture while enzymatically generating the acid in the first portion of the combined mixture thereby causing at least a second portion of the CaCO 3 to precipitate and to bind together at least part of the particulate starting material and the precipitated CaCO 3 , wherein one or more reagents for enzymatically generating the local pH increase are present in the combined mixture prior to enzymatically generating the acid in the first portion of the combined mixture.
16 . The method of claim 15 , wherein the enzymatic generation of the local pH increase is performed using a microorganism or a microbial extract which contains enzymes.
17 . The method of claim 16 , wherein the microorganism is a bacterium or the microbial extract is a bacterial extract.
18 . The method of claim 15 , wherein the acid is a carboxylic acid and the particulate starting material comprises aggregate.
19 . The method of claim 18 , wherein the carboxylic acid is lactic acid or acetic acid.
20 . The method of claim 14 , wherein the enzymatic generation of the pH increase is performed using a microorganism or a microbial extract which contains enzymes.
21 . The method of claim 20 , wherein the microorganism is a bacterium or the microbial extract is a bacterial extract.
22 . The method of claim 14 , wherein the acid is a carboxylic acid and the particulate starting material comprises aggregate.
23 . The method of claim 22 , wherein the carboxylic acid is lactic acid or acetic acid.
24 . The method of claim 14 , wherein the enzymatic generation of the pH decrease is performed under aerobic conditions.
25 . The method of claim 14 , wherein all the reagents for enzymatically generating the pH increase and for enzymatically generating the acid are present in the combined mixture.
26 . The method of claim 14 , wherein the pH increase of (iii) is generated by metabolizing the acid.
27 . The method of claim 14 , wherein the pH increase of (iii) is generated by enzymatically producing ammonia.
28 . The method of claim 14 , wherein the pH increase of (iii) is generated bu urea hydrolysis.
29 . The method of claim 14 , wherein the microorganism is able to produce acid at a pH of at least 8.5.
30 . The method of claim 14 , wherein the microorganism is a facultative anaerobe or an obligate anaerobe.
31 . The method of claim 14 , wherein both the pH decreases of (ii) and the pH increase of (iii) are performed using the same microorganism or microbial extract.
32 . The method of claim 14 , wherein the pH decrease of (ii) is performed using a different microorganism or extract thereof than the microorganism or extract thereof of (iii).
33 . The method of claim 14 , wherein the pH decrease of (ii) or the pH increase of (iii) is performed using an isolated and purified or commercially acquired enzyme.
34 . The method of claim 14 , wherein the one or more reagents for enzymatically generating the pH increase and the one or more reagents for enzymatically generating the acid are present in the combined mixture prior to enzymatically generating the acid in the combined mixture.
35 . The method of claim 14 , wherein the acid is acetic acid.
36 . A method of forming a construction material, comprising:
(i) providing a combined mixture that includes a combination of CaCO 3 and a particulate starting material;
(ii) enzymatically generating an acid in the combined mixture during a first time period, wherein the acid generation causes a local pH decrease in the combined mixture, thereby locally dissolving at least a first portion of the CaCO 3 in the combined mixture; and
iii) enzymatically generating a local pH increase in the combined mixture during a second time period thereby causing at least some of the first portion of the CaCO 3 to precipitate and to bind together at least part of the particulate starting material and the precipitated CaCO 3 , wherein one or more reagents for enzymatically generating the local pH increase and for enzymatically generating the acid are present in the combined mixture prior to enzymatically generating the acid in the combined mixture.