PROCEDE DE TRAITEMENT DE FORTES CHARGES D'EAUX USEES RENFERMANT DES CARBOHYDRATES

PROCESS FOR HIGH-LOAD TREATMENT OF CARBOHYDRATE-CONTAINING WASTE WATER

Abrégé anglais

(1)
A process for high-load treatment of
carbohydrate-containing waste water comprises the steps of
separating a yeast appearing in the waste water,
subjecting the separated yeast to large-quantity culture,
and treating the waste water by a high-load operation
using the cultured yeast as a seed fungus under the
conditions of a volume load of 10 to 80 kg-BOD/m3 day and
a yeast load of 1.0 to 5.0 kg-BOD/kg-yeastday, whereby it
is possible to treat the high-concentration waste water
efficiently with a small volume for treatment. The
quantity of air required of a diffuser system blower may
be 0.15 to 0.60 kg-O2/kg-BOD-removed, the value being 1/3
to 2/3 times that in a general activated sludge method. A
pH of not more than 5.0 and a residence time of at least
1.5 hours may be employed. To obviate the conflict
between the yeast and bacteria, it is recommendable to add
C?2 to a reservoir in an amount of 10 to 50 mg/?. If it
is impossible to add C?2 to the reservoir, the C?2 may be
added to a yeast tank in the same amount as above-
mentioned. This process, when carried out under the
conditions mentioned above, promises an increase in the
efficiency of the plant for treatment of the carbohydrate-
containing waste water. Upon the treatment of the waste
water, a surplus of yeast is generated, which contains

(2)
proteins and vitamines in high contents and, therefore, is
capable of being taken by a fodder company as fodder or
fertilizer; thus, the disposal cost associated with the
surplus yeast is saved. On the other hand, an about 20%
portion of the influent BOD, which is left upon the
treatment with yeast, requires an after-treatment, so that
an expense is necessary for disposal of the sludge formed.
The disposal cost required in this case, however, is as
low as about 1/4 times that required in the general
activated sludge method, and the disposal cost for the
after-treated sludge is substantially negligible because
it can be canceled by selling the surplus yeast as fodder
or fertilizer, as mentioned above. Thus, the process for
high-load treatment of carbohydrate-containing waste water
promises a marked reduction in the treatment cost for the
waste water.

Revendications

WHAT IS CLAIMED IS:
1. A process for high-load treatment of
carbohydrate-containing waste water which comprises the
steps of separating a yeast appearing in the waste water,
subjecting the separated yeast to large-quantity culture,
and treating the waste water by a high-load operation
using the cultured yeast as a seed fungus under the
following conditions:
volume load: 10 to 80 kg-BOD/m3day, and
yeast load : 1.0 to 5.0 kg-BOD/kg-yeastday.
- 11 -

Description

20009B~
PROCESS FOR HIGH-LOAD TREATMENT OF CARBOHYDRATE-CONTAINING
WASTE WATER
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to a process for high-
load treatment of carbohydrate-containing waste water by
utilizing a yeast appearing in the waste water, with a
higher efficiency as compared to conventional methods.
(2) Description of the Prior Art
As an example of conventional methods for waste
water treatment, there has been a method of treating an
inflow of sewage with an activated sludge in an aerator.
Since the activated sludge in the aerator is
composed mainly of bacteria, a large amount of sludge is
formed upon the treatment. A surplus of sludge is
incinerated in most cases, through it is sometimes
converted into fertilizer by composting.
The conventional sewage treatment method by the
activated sludge requires a large-scale treatment plant,
with a great site area, as well as a high construction
cost inclusive of that for incineration of sludge.
Besides, the conventional method involves heavy expenses
for electric power supplied to a diffuser, for maintenance
such as disposal associated with sludge incineration, etc.
- 1 -

2000982
SUMMARY OF THE INVENTION
This invention contemplates overcoming the
above-mentioned drawbacks of the prior art.
It is an object of this invention to provide a
process of high-load treatment of carbohydrate-containing
waste water which comprises the steps of propagating a
yeast appearing in the waste water, and treating the waste
water by a high-load operation using the propagated yeast,
which promises an increase in the efficiency of a plant
for treatment of carbohydrate-containing waste water, and
which enables the yeast used for the waste water treatment
to be subsequently utilized as fodder or fertilizer,
thereby achieving a corresponding saving in the cost for
disposal, such as incineration.
The process for high-load treatment of
carbohydrate-containing waste water according to this
invention comprises the steps of separating a yeast
appearing in the waste water, subjecting the separated
yeast to large-quantity culture, and treating the waste
water by a high-load operation using the cultured yeast as
a seed fungus under the following conditions:
volume load : 10 to 80 kg-BOD/m~-day,
yeast load : 1.0 to 5.0 kg-BOD/kg-yeast-day.
Preferably, the following conditions will apply:
pH : up to 5.0, and
C 2 addition: 10 to 50 mg/~.

Z000982
Other objects and advantages of this invention
will become apparent from the following detailed
description of some preferred embodiments of the
invention, referring to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a flow sheet showing a device for
treatment of carbohydrate-containing waste water according
to one embodiment of this invention;
Fig. 2 is a diagram showing the relationship
between BOD (Biochemical Oxygen Demand) volume load and
BOD removal rate, for proving the stability of the process
according to the invention; and
Fig. 3 is a flow sheet showing a device for
treatment of carbohydrate-containing waste water according
to another embodiment of the invention.
PREFERRED EMBODIMENTS OF THE INVENTION
As one preferred embodiment of this invention,
an experimental example of a treatment with yeast of waste
water from a bakery will now be explained below.
Referring to Fig. 1, there is shown a flow sheet
of a device for treatment of carbohydrate-containing waste
water used in the experiment of this invention. In the
-- 3

200098~
figure, a raw water reservoir 2 is fed with the
carbohydrate-containing waste water, whereas a yeast
treatment tank 2 is provided for treating the waste water
fed from the raw water reservoir 1 (serving also for
production of yeast), and a sedimentation basin 3 is
provided for sedimentation of a mixed liquid transferred
from the yeast treatment tank 2. The sedimentation basin
3 is so designed that it is possible to transfer the
supernatant therefrom into a catalytic oxidation tank 4,
lo described later, return the sedimented yeast therefrom
into the yeast treatment tank 2, and to withdraw a surplus
of yeast therefrom. The separation between the yeast and
the supernatant may be carried out by any of gravity
separation in the sedimentation basin 3, centrifugation,
film separation, etc. The catalytic oxidation tank 4, as
an after-treatment device, is provided for treating the
substrates in the waste water which have not been removed
by the treatment in the yeast treatment tank 2. The
after-treatment tank, also, may be based on the activated
sludge method or coagulating sedimentation, as reqruied.
The species of fungi associated with the yeast
treatment belonged mainly to the genus Trichorsporon and
the genus Saccharomyces.
The yeast treatment tank 2 was operated under
the following conditions:
-- 4

2000982
(1) Volume load: 25 kg-BOD/m3-day
(2) Yeast load: 1.25 to 2.5 kg-BOD/kg-yeast-day
(3) Yeast concentration: 10000 to 20000 mg/Q
(4) Quantity of O2 required: 0.20 to 0.6 kg-O2/kg-
BOD-removed
(5) Residence time (HRT): 2.5 hr
(6) DO: 0.1 to 0.5 mg/Q
(7) pH: 3.0 to 4.0
(8) SRT: 10 to 20 days.
When heavy propagation of bacteria occurred in
the yeast tank, sodium hypochlorite was added to the yeast
tank for sterilization. In that case, the CQ2
concentration in the tank was set to 20 to 50 mg/Q. When
the raw water contained a large amount of SS (suspended
solid) components, namely, the bacteria propagated in the
raw water reservoir and solids, H2SO~ was added to the raw
water reservoir shown in Fig. 1 so as to obtain a pH of
about 2.0, and CQ2 was added in the above-mentioned amount
of 20 to 50 mg/~, to achieve solubilization of the SS
components and sterilization, thereby enabling the
reactions in the yeast tank to proceed smoothly.
Upon the treatment of the carbohydrate-
containing waste water with the yeast under the above-
mentioned specified conditions, the properties of the
effluent from the yeast treatment tank 2 (the supernatent

2000982
in the sedimentation basin 3) were measured, the results
being shown in the following table.
Table
CODcr BOD T-N T-P n-HEX pH C/N
mg/Q mg/Q mg/Q mg/Q extracts ratio
Influent
water 3800 2600 75 48 138 4.3 19
Effluent less tha~
water 830 330 15 34 9 5.0
Removal
rate 78% 87% 80% 29% 93Z
Besides, for proving the stability of operation
of the yeast treatment tank 2, the relationship between
BOD volume load and BOD removal rate based on the above
results of waste water treatment is shown in Fig. 2.
Further, when the yeast treatment tank 2 is used
as a pre-treatment device, the characteristics of the
yeast enable a high-load treatment of waste water even if
the waste water contains normal-hexane (n-HEX) extracts,
highly salty substrates, antibiotics, etc., by using a
reduced quantity of air and a small volume for treatment,
similarly to the above. This point distinguishes the
process of this invention from the activated sludge method
employing bacteria.
Namely, the experiment of the invention gave a
BOD removal rate of 87% under a volume load of 25 kg-

Z000982
BOD/m3-day, with a surplus of capability. Moreover, the
quantity of oxygen required is small, and under 25 kg-BOD/m3
was 0.2 kg-O2/kg-BOD-removed. Besides, the ratio of air
quantity to the quantity of BOD removed has a tendency to
decrease with an increase in the load, and the process of
the invention is good in stability.
The above results shows that the yeast treatment
tank 2 is best suited for use as a pre-treatment device
for removing at least 80% of the BOD.
Further, the surplus yeast withdrawn from the
sedimentation basin 3 is capable of being utilized
effectively as fertilizer or fodder, because of its high
protein and vitamine contents, and sludge incineration
cost is saved accordingly.
Based on the experimental results above, in this
invention the operating conditions of the yeast treatment
tank 2 have been specified as follows:
volume load: 10 to 80 kg-BOD/m3-day, and
yeast load : 1.0 to 5.0 kg-BOD/kg-yeast-day.
The reason for the neccesity of the high loads
is that a yeast load below 0.5 kg-BOD/kg-yeast-day causes

200098:~
autolysis, and a low yeast load below 1.0 kg-BOD/kg-
yeast-day causes the yeast to tend to conflict with
bacteria (activated sludge) and, as a result, be defeated
by the bacteria. The range of yeast load in which the
yeast is capable of serving for the intended treatment
without being defeated by the bacteria is 1.0 to 5.0 kg-
BOD/kg-yeast-day; the yeast load, when multiplied by the
yeast concentration, gives a volume load value of 10 to 80
kg-BOD/m3-day. When the yeast load is more than 5.0 kg-
BOD/kg-yeast-day, the quantity of oxygen is the rate-
determining factor, so that it is impossible to achieve a
BOD removal rate of at least 80%. Though it seems that
the volume load may take any value that satisfies the
above-mentioned conditions, a volume load of 80 kg-
BOD/m3-day with a yeast load of 5 kg-BOD/kg-yeast-day
corresponds to a required yeast concentration of 16000
mg/0, and agitation is considered to be the rate-
determining factor at yeast concentrations above the
value.
Fig. 3 illustrates another embodiment of this
invention. A catalytic oxidation tank 4 used in this
embodiment is an after-treatment device for treating the
supernatant sent from the sedimentation basin 3 after the

2000982
yeast treatment. The treated water obtained upon the
treatment in the catalytic oxidation tank is sterilized,
before being discharged. The sterilized water is fed back
into the yeast treatment tank 2.
The feed-back of the sterilized water into the
yeast treatment tank 2 is adopted as a measure to cope
with the penetration, if any, of bacteria into the system,
in consideration of the fact that the yeast is mold and
is, therefore, resistant to C~ 2 ~ The yeast, being mold,
is resistant also to normal-hexane extracts and
antibiotics.
As has been described above, according to this
invention, a yeat appearing in a carbohydrate-containing
waste water is utilized to perform a high-load treatment
of the waste water under specified conditions. This
process makes it possible to perform the high-load
treatment of the waste water efficiently by using an
extremely small volume for treatment and a reduced
quantity of air, even if the waste water contains normal-
hexane extracts, highly salty substrates, antibiotics,
etc.. Thus, the process according to this invention is
highly economical to carry out. In addition, the process
of the invention enables the surplus yeast to be utilized
effectively as fertilizer or fodder. Moreover, by the
process of the invention, the surplus of sludge which is

200098;~
removed from the after-treatment device is capable of
being reduced to a very low value of less than 20% based
on that in the conventional activated sludge method.
-- 10 --

Dessin représentatif