Determining biofilm thickness in a membrane supported biofilm reactor

Patent metadata

Field	Value
Publication number	US-9328004-B2
Application number	US-201414188631-A
Country	US
Kind code	B2
Filing date	Feb 24, 2014
Priority date	Nov 27, 2008
Publication date	May 3, 2016
Grant date	May 3, 2016

Abstract

A method of assessing biofilm thickness in a membrane supported biofilm reactor (MSBR) of the type comprising a lumen containing a gas phase, a liquid phase, and a gas permeable membrane providing an interface between the gas and liquid phases, the method comprising the steps of charging the lumen with an inert gas, closing the lumen to establish an initial elevated pressure in the lumen, measuring the rate of change of pressure within the lumen, and correlating the rate of change of pressure (dP/dt) with biofilm thickness. The step of correlating dP/dt with biofilm thickness involves correlating dP/dt with the rate of diffusion of the inert gas (dn/dt), correlating dn/dt with an overall mass transfer coefficient (K), correlating K with the mass transfer coefficient of the biofilm (k B ), and correlating k B with the biofilm thickness. Also described is a membrane supported biofilm reactor (MSBR) of the type comprising a gas permeable membrane providing an interface between a lumen containing a gas phase, and a liquid phase, characterized in that the MSBR comprises means for flushing the lumen with an inert gas, means for closing and re-opening the lumen, and means for detecting intra-membrane pressure within the lumen. The means for detecting intra-membrane pressure is provided by a pressure transducer.

First claim

The invention claimed is:

1. A membrane supported biofilm reactor (MSBR) of the type comprising a gas permeable membrane providing an interface between a lumen containing a gas phase, and a liquid phase, characterised in that the MSBR comprises a gas supply stream coupled to the gas phase of the lumen for flushing the lumen with an inert gas, one or more valves coupled to the lumen for closing and re-opening the lumen, a pressure transducer coupled to a gas phase of the membrane for detecting intra-membrane pressure within the lumen, and a processor programmed to receive pressure readings from the pressure transducer; calculate a rate of change of pressure with time (dP/dt) value; and use the dP/dt value to calculate a biofilm thickness value.

2. The MSBR as claimed in claim 1 , wherein one of said one or more valves is coupled to each end of the lumen.

3. The MSBR as claimed in claim 1 , wherein the gas permeable membrane is in the form of a hollow fibre in which the gas phase is located within the lumen of the fibre.

4. The MSBR as claimed in claim 1 , wherein the processor is programmed to:
compare the biofilm thickness value with a pre-set thickness threshold value; and
actuate a cleaning procedure when the biofilm thickness value is above the pre-set thickness threshold value.

5. The MSBR as claimed in claim 1 , wherein the processor is programmed to:
compare the biofilm thickness value with a pre-set thickness threshold value; and
when the biofilm thickness value is above the pre-set thickness threshold value, provide an indication that a cleaning procedure is required.

6. The MSBR as claimed in claim 5 , further comprising a membrane cleaning apparatus and in which the membrane cleaning apparatus is operatively connected to the processor such that the cleaning apparatus is actuated when the processor detects that the biofilm thickness value is above the pre-set thickness threshold value.

7. A system for assessing biofilm thickness in a membrane supported biofilm reactor (MSBR) of the type comprising a lumen containing a gas phase, a liquid phase, and a gas permeable membrane providing an interface between the gas and liquid phases, the system comprising:
a gas supply stream coupled to the lumen for charging the lumen with an inert gas;
a valve at each end of the lumen for closing the lumen to establish an initial elevated pressure in the lumen;
a pressure transducer for measuring the rate of change of pressure within the lumen; and
a processor programmed to use the rate of change of pressure (dP/dt) to compute biofilm thickness.

8. The system as claimed in claim 7 , wherein computing said biofilm thickness comprises:
applying dP/dt to calculate a rate of diffusion of the inert gas (dn/dt) through equation

ⅆ
n

ⅆ
t

=

ⅆ
P

ⅆ
t

⁢

(

R
⁢

⁢
T

V

)

-
1

;

using dn/dt to calculate an overall mass transfer coefficient (K) through equation

K
=

ⅆ
n

ⅆ
t

A
⁡

(

C
i
*

-

C
i

)

;

using K to calculate a mass transfer coefficient of the biofilm (k B ) through equation

1
K

=

1

k
M

+

1

k
L

+

1

k
B

;

and using k B to calculate the biofilm thickness through equation

L
B

=

D

i
,
B

k
B

,

where:
P is pressure,
T is temperature,
V is the total fixed volume of the membrane lumen,
R is the gas constant,
A is the total membrane area,
C* i is the solubility of the inert gas in the liquid at the prevailing temperature,
C i is the concentration of the inert gas in the bulk liquid,
k M is mass transfer coefficient of the membrane,
k L is mass transfer coefficient of the liquid boundary layer,
k B is mass transfer coefficient of the biofilm,
D i,B is the diffusion coefficient of the inert gas in the biofilm, and
L B is the biofilm thickness.

9. The system as claimed in claim 7 , wherein said processor is further programmed to actuate a biofilm cleaning procedure when the measured biofilm thickness exceeds a biofilm threshold value.

Assignees

• Univ Dublin

Inventors

• Casey Eoin
• Syron Eoin
• Heffernan Barry

Classifications

• B01D61/10

  Accessories; Auxiliary operations · CPC title

• B01D61/12

  Controlling or regulating · CPC title

• B01D2321/40

  Automatic control of cleaning processes · CPC title

• B01D65/10

  Testing of membranes or membrane apparatus; Detecting or repairing leaks · CPC title

• B01D2321/18

  Use of gases · CPC title