Description
Method and Apparatus for controlling loading of waste water
into a biological treatment system
The present invention relates to a method and apparatus for
controlling loading of waste water into a biological
treatment system comprising an attached growth bioreactor.
Biological treatment system involves allowing the waste water
to come in contact with a surface of an attached growth
bioreactor suitable for growth of microorganisms in order to
remove pollutants from the waste water. Microorganisms grow
on the surface of the attached growth bioreactor where
biological degradation of the pollutants in the waste water
takes place. The layer of microorganism on the surface of the
attached growth bioreactor is herein after referred to as a
microbial biofilm.
The thickness of the microbial biofilm increases with the
increase in the pollutants in the waste water. This affects
the performance of the biological treatment systems as the
degree of wastewater treatment is related to the amount of
the area of the surface in contact with the waste water and
the quality and volume of the inflowing waste water into the
system. Increase in the thickness of the microbial biofilm
signifies that the level of pollutants in the waste water is
high. Accordingly, for the proper degradation of the
pollutants in the waste water, the loading of waste water
into the biological treatment system is to be controlled as
per the thickness of the microbial biofilm of the surface of
the attached growth bioreactor.
It is an object of the invention to control loading of waste
water into a biological treatment system based on a thickness
of a microbial biofilm.

The above object is achieved according to the method of claim
1 and the apparatus of claim 11.
The computing of the thickness of the microbial biofilm using
a laser triangulation method enables controlling the loading
of waste water into a biological treatment system at varying
instances of time. Additionally, the use of the laser
triangulation method enables computing the thickness of the
microbial biofilm without making any physical contact with
the surface of the attached growth bioreactor. Moreover, the
thickness of the microbial biofilm may be computed without
bringing the biological treatment system to halt.
According to an embodiment, the laser triangulation method
includes projecting a laser light onto the surface and
detecting an image of a reflected laser light reflected from
the surface. Projecting the laser light -onto the surface and
detecting the image of the reflected laser light enables in
obtaining images of the reflected laser light from the
surface at varying instances of time.
According to yet another embodiment, the thickness is
computed as a distance between a reference position of the
reflected laser light reflected from the surface and an
offset position of the reflected laser light from the surface
in the image. Computing the distance between the offset
position and the reference position of the reflected laser
light provides the thickness of the microbial biofilm as the
offset position of the reflected laser light is due to the
microbial biofilm.
According to yet another embodiment, the thickness is
computed by dividing a difference in length of a reflected
offset laser line and a reflected reference laser line by
two. Dividing the difference in length of the reflected
offset laser line and the reflected reference laser line by
two provides the thickness of the microbial biofilm as the

microorganisms grow uniformly at the portion of the surface
in contact with the waste water.
According to yet another embodiment, the laser light is one
of a laser spot and a laser line. Both laser spot and laser
line can easily and accurately be detected.
According to yet another embodiment, the surface is a surface
of a disk of a rotating biological contactor (RBC). These
disks contain big flat surfaces on which laser triangulation
can easily be used without complicated computations due to
uneven surfaces. Laser triangulation can also be used on the
outer rim of the turning disks, which are easily accessible
for laser triangulation.
According to yet another embodiment, the disk is proximal to
a side of loading waste water into a trough of the biological
treatment system. Computing the thickness of the microbial
biofilm over the disk proximal to the side of loading waste
water into the biological treatment system enables efficient
control of loading of waste water into the system. This is
due to the rate of increase of the thickness of the microbial
biofilm over the surface of the disk proximal to the side of
loading waste water is more than the. rate of increase of the
thickness of the microbial biofilm over the surface of the
disk distal from the side of loading waste water into the
system.
According to yet another embodiment, the controlling of
loading of waste water into the biological treatment system
based on the thickness of the microbial biofilm includes
controlling a flow rate of a pump loading waste water into
the biological treatment system based on the thickness of the
microbial bioflim. Controlling the flow rate of the pump
enables the controlling of loading of waste water into the
biological treatment system.

According to yet another embodiment, the flow rate of the
pump is decreased on increase of the thickness of the
microbial biofilm. Decreasing the flow rate of the pump on
increase of the thickness of the microbial biofilm increases
the efficiency of the biological treatment system as increase
in the thickness of the microbial biofilm indicates that the
level of pollutants present in the waste water is high.
According to yet another embodiment, the flow rate of the
pump is increased on decrease of the thickness of the
microbial biofilm. Increasing the flow rate of the pump on
decrease of the thickness of the microbial biofilm increases
the efficiency of the biological treatment system as decrease
in the thickness of the microbial biofilm indicates that the
level of pollutants present in the waste water is low.
Another embodiment includes an apparatus for controlling
loading of waste water into a biological treatment system
comprising an attached growth bioreactor, wherein the
apparatus comprises a laser triangulation device for
projecting a laser light onto a surface of the attached
growth bioreactor, and for detecting an image of a reflected
laser light reflected from the surface, and a processor
adapted to compute a thickness of a microbial biofilm on the
surface of the attached growth bioreactor by using a laser
triangulation method and provide a corresponding output based
on the thickness of the microbial biofilm for controlling
loading of waste water into the biological treatment system.
The present invention is further described hereinafter with
reference to illustrated embodiments shown in the
accompanying drawings, in which:
FIG 1 illustrates an apparatus for measuring
thickness of a microbial biofilm on a surface
of an attached growth bioreactor for a

biological treatment system according to an
embodiment herein,
FIG 2 illustrates a biological treatment system
comprising the apparatus 10 of FIG 1 for
controlling the loading of waste water into
the biological treatment system based on a
thickness of a microbial biofilm according to
an embodiment herein,
FIG 3 illustrates a portion of a surface of a disk
that comes in contact with the waste water in
the trough 28 of FIG 2,
FIG 4 illustrates the. incidence and the reflection
of a laser light onto a surface of a disk
according to an embodiment herein,
FIGS 5a-5b illustrates detection of a reference position
and an offset position of a reflected laser
light for computing a thickness of a microbial
biofilm on a surface of a disk according to an
embodiment herein,
FIG 5c illustrates a distance between a reference
position and an offset position of a reflected
laser light,
FIG 5d illustrates a reference position and an offset
position of a reflected laser light according
to an embodiment herein,
FIGS 6a-6b illustrates detection of a reference reflected
laser line and an offset reflected laser line
of a reflected laser light for computing a
thickness of a microbial biofilm on a

surface of a disk according to an embodiment
herein, and
FIG 7 illustrates the difference in length of a
reference reflected laser line and an
offset reflected laser line of a
reflected laser light according to an
embodiment herein.
Various embodiments are described with reference to the
drawings, wherein like reference numerals are used to refer
to like elements throughout. In the following description,
for purpose of explanation, numerous specific details are set
forth in order to provide a thorough understanding of one or
more embodiments. It may be evident that such embodiments may
be practiced without these specific details.
FIG 1 illustrates an apparatus for measuring thickness of a
microbial biofilm on a surface of an attached growth
bioreactor for a biological treatment system according to an
embodiment herein. The apparatus 10 comprises a laser
triangulation device 12, and a processor 14. The laser
triangulation device typically comprises a laser source 16 to
project a laser light onto the surface of the attached growth
bioreactor and a photodetector 18 to detect an image of the
reflected laser light from the surface of the attached growth
bioreactor.
The laser source 16 may project a laser spot or a laser line.
The photodetector 18 may be a charge couple device sensor
camera, a Complementary Metal Oxide Semiconductor (CMOS)
sensor camera and the like.
In an embodiment, the position of the detected laser light
reflected by the surface of the attached growth bioreactor at
the photodetector 18 prior to the growth of any
microorganisms on the surface is considered as a reference

position of the laser light reflected from the surface. The
microorganisms may be either autotrophic or heterotrophic or
both. The position of the laser light reflected from the
surface is offset due to the growth of microorganisms on the
surface of the attached growth bioreactor. This position of
the reflected laser light detected at the photodetector 18 is
considered as the offset position of the reflected laser
light. The laser light in the present embodiment may be a
laser spot or a laser line. The processor 14 electronically
connected to the photodetector 18, in an embodiment computes
a distance between the reference position and the offset
position of the laser light reflected by the surface of the
attached growth bioreactor. The distance between the
reference position and the offset position of the laser light
reflected from the surface of the attached growth bioreactor
provides the thickness of the microbial biofilm on the
surface of the attached growth bioreactor.
In an alternate embodiment, where the laser light projected
onto the surface is a laser line, the detected laser line
reflected by the surface of the attached growth bioreactor at
the photodetector 18 prior to the growth of any
microorganisms on the surface is considered as a reference
reflected laser line. The length of the laser line reflected
from the surface increases due to the growth of
microorganisms on the surface of the attached growth
bioreactor, and, therefore the length of the reflected laser
line is larger than the length of the reference reflected
laser line. This reflected laser line detected at the
photodetector 18 is considered as an offset reflected laser
line. The processor 14 may determine the length of the
reference reflected laser line and the length of the offset
reflected laser line. The thickness of the microbial biofilm
may be computed by the processor 14 by dividing the
difference of the length of the reflected offset laser line
and the reflected reference laser line by two.

FIG 2 illustrates a biological treatment system comprising
the apparatus 10 of FIG 1 for controlling the loading of
waste water into the biological treatment system based on a
thickness of a microbial biofilm according to an embodiment
herein. The biological treatment system 20 comprises an
attached growth bioreactor comprising a surface suitable for
the growth of microorganisms. The attached growth bioreactor
in the present embodiment is a rotating biological contactor
(RBC) 22 comprising a plurality of disks 24 mounted on a
rotating shaft 26. However, the biological treatment system
20 may comprise other attached growth bioreactors such as, a
trickling filter, a baffled bioreactor, a fixed bed
bioreactor, a fluidized bed bioreactor and the like. The
disks 24 are contained in a trough 28. Waste water is loaded
or fed into the trough 28 using a pump 30 from a side 29. For
example, waste water is fed into the trough 28 by the pump 30
from a sewage tank 27. The loading or feeding of waste water
into the trough 28 includes organic and hydraulic loading of
waste water into the trough 28.
The treated waste water is drained out from the trough 28 so
that the same may be discharged into the environment.
Typically, the treated water is drained out from a side 31
opposite to the side 29. This enables the flow of waste water
to be at right angles to the rotation of the disks 24. The
microorganisms grow on the portion of the surface 32 of the
disk 24 in contact with the waste water, thereby forming a
microbial biofilm.
FIG 3 illustrates a portion of the surface 32 of the disk 24
that comes in contact with the waste water in the trough 28
of FIG 2. The portion 34 extends inwardly form the outer
periphery of the disk 24. Typically, the microorganisms grow
uniformly at the portion 34 of the surface 32 of the disk 24
as the portion 34 comes in contact with the waste water in
the trough 28 of FIG 2. Typically, forty percent of the
surface 32 of the disk 24 is immersed into the waste water.

However, the surface 32 of the disk 24 immersed into the
waste water may be more or less than forty percent of the
surface 32.
Referring again to FIG 2, the rotating shaft 26 is rotated
using a motor 36. A gear arrangement 38 may be provided
between the rotating shaft 26 and the motor 36 so that the
rotation of the shaft 26 may be controlled. Preferably, the
shaft 26 is rotated such that the disks 24 rotate at right
angles to the flow of the waste water.
Initially, there is no microbial biofilm on the surface 32 of
the disk 24 as there is no growth of microorganisms on the
surface 32. Microorganisms grow on the portion 34 of FIG 2 of
the surface 32 forming the microbial biofilm when the disk 24
comes in contact with the waste water. In order to measure a
thickness of a microbial biofilm, the laser source 16 of the
laser triangulation device 12 projects a laser light 40 onto
the surface 32 of at least one disk 24. The reflected laser
light 44 from the surface 32 of the disk 24 is detected as an
image at the photodetector 18. In an preferred embodiment,
the laser light 40 is projected onto a disk 24 proximal to
the side 29 of the trough 28 through which waste water is
loaded into the biological treatment system 20. Typically,
the rate of increase of the thickness of the microbial
biofilm over the surface 32 of a disk 24 proximal to the side
29 is more than the rate of increase of the thickness of the
microbial biofilm over the surface 32 of a disk 24 distal
from the side 29. This is due to the disks 24 proximal to the
side 29 comes into contact with the waste water earlier than
the disks 24 distal from the side 29.
FIG 4 illustrates the incidence and the reflection of the
laser light onto the surface 32 of the disk according to an
embodiment herein. The laser light 40 in the present
embodiment is a laser spot. The laser light 40 is projected
from the laser source 16 such that the laser light 40 is

incident on the surface 32 at a non-orthogonal angle a to a
tangent 42 to the surface 32 of the disk 24. The reflected
laser light 44 is detected by the photodetector 18.
Preferably, the laser light 40 is projected on the outer rim
of the disk 24. In an alternate embodiment, the laser light
40 may be projected onto any side of the disk 24 within the
portion 34 of FIG 3 of the surface 32. The non-orthogonal
angle a may be increased to achieve an increase in accuracy
of measurement of the thickness of the microbial biofilm. In
an alternative embodiment, the laser light 40 projected may
be a laser line.
FIGS 5a and 5b illustrates detection of a reference position
and an offset position of a reflected laser light for
computing a thickness of a microbial biofilm on the surface
32 of the disk 24 according to an embodiment herein. In the
illustrated example of FIG 5a, there is no microbial biofilm
on the surface 32 of the disk 24. The laser light 40
projected from the laser source 16 in the present example is
a laser spot 41. The laser light 40 is incident on the
surface 32 at a non-orthogonal angle a to the tangent 42 to
the surface 32 of the disk 24. The laser light 40 is
reflected by the surface 32 of the disk 24. The reflected
laser light 44 is detected at the photodetector 18. The
position of the reflected laser light 44 reflected by the
surface 32 not having a microbial biofilm detected at the
photodetector 18 is the reference position 46 of the
reflected laser light 44.
Referring now to FIG 5b, there is shown a microbial biofilm
48 on the surface 32 of the disk 24. The microbial biofilm 48
is due to the growth of microorganism when the surface 24 of
the disk 24 comes into contact with the waste water. The
laser light 40 in the present example will be reflected by
the microbial biofilm 48 on the surface 32. This creates an
offset in the position of the reflected laser light 44 with
respect to the reference position 46. The position of the

reflected laser light 44 reflected by the microbial biofilm
48 is the offset position 50 of the reflected laser light 44.
FIG 5c illustrates a distance D between the reference
position 46 and the offset position 50 of the reflected laser
light 44. In the shown example of FIG 5c, the reference
position 46 and the offset position 50 of the reflected laser
light 4 4 are shown in the same image for the purpose of
illustration only. However, in actual implementation the
reference position 46 and the offset position 50 of the
reflected laser light 44 are captured as different images at
the photodetector 18. The distance D between the reference
position 46 and the offset position 50 of the reflected laser
light 44 provides the thickness of the microbial biofilm 48.
Referring now to FIG 5a and Fig 5b, in embodiments wherein
the laser light 40 is a laser line 43, the reflected laser
light 44 detected at the photodetector 18 shall be an image
of the laser line 43 reflected by the surface 32. FIG 5d
illustrates a reference position and an offset position of a
reflected laser line. The distance D between the reference
position 46 and the offset position 50 of the laser line 43
is the thickness of the microbial biofilm 48.
Referring now to FIG 1, FIG 2, FIG 5a, FIG 5b, FIG 5c and FIG
5d the photodetector 18 converts the detected reflected laser
light 44 into electronic signals corresponding to an
electronic image. The processor 14 includes instructions to
compute the distance D between the reference position 4 6 and
the offset position 50 of the reflected laser light 44. In an
The distance D corresponds to the thickness of the microbial
biofilm 48. In an embodiment, the reference position 46 of
the reflected laser light 44 may be stored in a memory so
that the same may be retrieved for computing the distance at
varying instances of time. Based on the computed thickness of
the microbial biofilm 48, the processor 14 may provide output
to control the flow rate of the pump 30. By controlling the

flow rate of the pump 30, the organic loading of waste water
into the biological treatment system 20 is controlled as the
chemical oxygen demand (COD) or the biological oxygen demand
(BOD) is constant for a particular type of waste water.
FIG 6a and FIG 6b illustrates detection of a reference
reflected laser line and an offset reflected laser line of a
reflected laser light for computing a thickness of a
microbial biofilm on the surface 32 of the disk 24 according
to an embodiment herein. In the present embodiment, the laser-
light 40 is a laser line 52. In the illustrated example of
FIG 6a, there is no microbial biofilm on the surface 32 of
the disk 24. The laser light 40 is incident on the surface 32
at a non-orthogonal angle a to the tangent 42 to the surface
32 of the disk 24. The laser light 40 is reflected by the
surface 32 of the disk 24. The reflected laser light 44 is
detected at the photodetector 18. The reflected laser light
44 reflected by the surface 32 not having a microbial biofilm
detected at the photodetector 18 is the reference reflected
laser line 54.
Referring now to FIG 6b, there is shown a microbial biofilm
48 on the surface 32 of the disk 24. The microbial biofilm 48
is due to the growth of microorganism when the surface 24 of
the disk 24 comes into contact with the waste water. The
laser light 40 in the present example will be reflected by
the microbial biofilm 48 on the surface 32. As the laser
light 40 is projected such that the laser line 52 is incident
in a horizontal position on the surface 32, the length of the
laser line 52 increases with the increase in the thickness of
the microbial biofilm 48 due to the growth of microorganisms.
This reflected laser light 44 detected at the photodetector
18 is considered as an offset reflected laser line 56.
The length of the reference reflected laser line 54 depicts
the thickness of the disk 24 without the microbial biofilm 48
and the length of the offset reflected laser line 56 depicts

the thickness of the disk 24 with the microbial biofilm 48.
Accordingly, to capture the thickness of the disk 24 without
and with the microbial biofilm 48, the length of the laser
line 52 is such that the laser line 52 is reflected by the
edges of the rim of the disk 24, i.e., the laser line 52
should extend from one edge of the rim to the other edge of
the rim of the disk 24.
Referring now to FIG 1, FIG 2, FIG 6a and FIG 6b, the
photodetector 18 converts the detected reflected laser light
44 into electronic signals corresponding to an electronic
image. The processor 14 includes instructions to compute the
thickness of the microbial biofilm 48 by dividing the
difference of the length of the reflected offset laser line
56 and the reflected reference laser line 54 by two. In an
embodiment, the length of the reflected laser line 54 may be
stored in a memory so that the same may be retrieved for
computing the difference in length at varying instances of
time.
FIG 7 illustrates the difference in length of the reference
reflected laser line 54 and the offset reflected laser line
56 of the reflected laser light 44. In the shown example of
FIG 7, reference reflected laser line 54 and the offset
reflected laser line 56 are shown in the same image for the
purpose of illustration only. However, in actual
implementation the reference reflected laser line 54 and the
offset reflected laser line 56 of the reflected laser light
44 are captured as different images at the photodetector 18.
Based on the computed thickness of the microbial biofilm 48,
the processor 14 may provide output to control the flow rate
of the pump 30. Based on the computed thickness of the
microbial biofilm 48, the processor 14 may provide output to
control the flow rate of the pump 30.
Computing the thickness of the microbial biofilm using a
laser triangulation method enables controlling the flow rate

of the pump 30 so that the loading of waste water into the
trough 28 of the biological treatment system 20 may be
controlled at a real time. For example, if there is an
increase in the thickness of the microbial biofilm 48, the
flow rate of the pump 30 may be reduced so that loading of
waste water into the biological treatment system 20 is
reduced. Similarly, if there is a decrease in the thickness
of the microbial biofilm 48, the flow rate of the pump 30 may
be increased so that loading of waste water into the
biological treatment system 20 is increased. This enables
increasing the efficiency of the biological treatment system
20 as the organic matter present in the waste water is
degraded irrespective of the thickness of the microbial
biofilm. Additionally, the use of the laser triangulation
method enables computing the thickness of the microbial
biofilm without making any physical contact with the surface
of the attached growth bioreactor.
While this invention has been described in detail with
reference to certain preferred embodiments, it should be
appreciated that the present invention is not limited to
those precise embodiments. Rather, in view of the present
disclosure which describes the current best mode for
practicing the invention, many modifications and variations
would present themselves, to those of skill in the art
without departing from the scope and spirit of this
invention. The scope of the invention is, therefore,
indicated by the following claims rather than by the
foregoing description. All changes, modifications, and
variations coming within the meaning and range of equivalency
of the claims are to be considered within their scope.

WE CLAIM
1. A method of controlling loading of waste water into a biological treatment
system (20) comprising an attached growth bioreactor, said method
comprising:
- computing a thickness of a microbial biofilm (48) on a surface (32) of
said attached growth bioreactor by using a laser triangulation method,
and
- controlling loading of waste water into said biological treatment system
(20) based on said thickness of said microbial biofilm (48), wherein the
controlling of loading of waste water into said biological treatment system
(20) based on said thickness of said microbial biofilm (48) includes
controlling a flow rate of a pump (30) loading waste water into said
biological treatment system (20) based on said thickness of said microbial
bioflim (48).
2. The method as claimed in claim 1, wherein said laser triangulation method
includes:
- projecting a laser light (40) onto said surface (32), and
- detecting an image of a reflected laser light (44) reflected from said
surface (32).
3. The method as claimed in claim 1 or 2, wherein said thickness is
computed as a distance (D) between a reference position (46) of said
reflected laser light (44) reflected from said surface (32) and an offset
position (50) of said reflected laser light (44) from said surface (32) in
said image.

4. The method as claimed in any of claims 1 to 3, wherein said thickness is
computed by dividing a difference in length of a reflected offset laser line
(56) and a reflected reference laser line (54) by two.
5. The method as claimed in claim 2 or 3, wherein said laser light (40) is one
of a laser spot (41) and a laser line (52).
6. The method as claimed in any of claims 1 to 5, wherein said surface (32)
is a surface of a disk (24) of a rotating biological contactor (22).
7. The method as claimed in claim 6, wherein said disk (24) is proximal to a
side (29) of loading waste water into a trough (28) of said biological
treatment system (20).
8. The method as claimed in any of claims 1 to 7, wherein said flow rate of
said pump (30) is decreased on increase of said thickness of said microbial
biofilm (48).
9. The method as claimed in any of claims 1 to 7, wherein said flow rate of
said pump (30) is increased on decrease of said thickness of said microbial
biofilm (48).
10. An apparatus (10) for controlling loading of waste water into a biological
treatment system (20) comprising an attached growth bioreactor, wherein
waste water is loaded into the biological treatment system using a pump,
said apparatus comprising:
- a laser triangulation device (12) for projecting a laser (40) light onto a
surface (32) of said attached growth bioreactor, and for detecting an
image of a reflected laser light (44) reflected from said surface (32), and

- a processor (14) adapted to:
- compute a thickness of a microbial biofilm (48) on said surface (32) of
said attached growth bioreactor by using a laser triangulation method,
wherein said thickness is computed as a distance D between a reference
position (46) of said reflected laser light (44) reflected from said surface
(32) and an offset position (50) of said reflected laser light (50) reflected
from said surface (32) in said image, and
- provide a corresponding output based on said thickness of said microbial
biofilm (48) for controlling loading of waste water into said biological
treatment system (20), wherein said corresponding output controls a flow
rate of the pump (30) loading waste water into said biological treatment
system (20).
11.The apparatus (10) as claimed in claim 10, wherein said laser
triangulation device comprises:
- a laser source (16) for projecting a laser light (40) onto said surface
(32), and
- a photodetector (18) for detecting an image of said reflected laser light
(44) reflected from said surface (32).
12.The apparatus (10) as claimed in claim 10 or 11, wherein said thickness
is computed by dividing a difference in length of a reflected offset laser
line (56) and a reflected reference laser line (54) by two.
13.The apparatus (10) as claimed in any of claims 10 to 12, wherein said
laser light (40) is one of a laser spot (41) and a laser line (52).
14.The apparatus (10) as claimed in any of claims 10 to 13, wherein said
surface (32) is a surface of a disk (32) of a rotating biological contactor
(RBC) (22).

15.The apparatus (10) as claimed in claim 14, wherein said disk (24) is
proximal to a side (29) of loading waste water into a trough (28) of said
biological treatment system (20).
16.The apparatus (10) as claimed in any of claims 10 to 15, wherein said
flow rate of said pump (30) is decreased on increase of said thickness of
said microbial biofilm (48).
17.The apparatus (10) as claimed in any of claims 10 to 15, wherein said
flow rate of said pump (30) is increased on decrease of said thickness of
said microbial biofilm (48).

Abstract

Method and Apparatus for controlling loading of waste water
into a biological treatment system
The present invention relates to a method and apparatus for
controlling loading of waste water into a biological
treatment system (20) comprising an attached growth
bioreactor, wherein the method comprises computing a
thickness of a microbial biofilm (48) on a surface (32) of
said attached growth bioreactor by using a laser
triangulation method and controlling loading of waste water
into said biological treatment system (20) based on said
thickness of said microbial biofilm (48).