Note: Descriptions are shown in the official language in which they were submitted.
~0382 71
This invention relates to a process and an apparatus for
determining acute toxicity of chemical substances in aqueous
liquids, especially in waste water, to microorganisms present
in biological purification plants.
In such plants waste water is purified by contact with
microorganisms, organic material consuming oxygen being
decomposed.
However, the microorganisms can be poisoned, i.e. their
respiration can be inhibited completely or partly, if the waste
~` 10 water influent contains any substance having an acute toxic
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effect on the microorganisms and if this substance is present
~ in a sufficiently high concentration, i.e. in a concentration ~
'`t exceeding the maximum concentration to which the microorganisms - ~ -
can be exposed without being poisoned.
~ Prior known methods to determine the toxicity of chemical
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substances are time-consuming and expensive and can substantial-
ly be divided into four main groups:
1) Introduction of toxic substances in normally operating ;
standard purification plants of the active sludge type, with
a subsequent examination of the deteriorated function. For a
-~ reliable judgement of the toxicity of a chemical substance (one
concentration level) an examination period of about 3 weeks is
~ required.
-~ 2) Respirometric measurements made on active sludge in the
~s~ presence of a substance, which can be easily decomposed biolo-
gically, and in the absence or presence of a toxic chemical sub-
stance in different concentrations. The examination takes about
1 - 2 weeks.
3) Culturing representative microorganisms in purification
plants in the presence of a toxic chemical substance in different
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~` concentrations. This method is also time-consuming.
4) Determination of the dehydrogenase activity in the presence
of a toxic chemical substance in different concentrations. The
dehydrogenase activity of the microorganisms is determined by
means of TTC and is a rather complicated procedure.
However, it is obvious that the presence of any acute toxic
substance is not discovered by such methods until the microo-
rganisms have already been poisoned. Consequently, if such a
substance is present, the purification process must be interrupt-
10 ed and a new culture must be generated. This may cause a shut-
down for several weeks.
. .
Thus, there is a need for a process and an apparatus for
analyzing aqueous liquids, such as waste water, in respect of
the presence of substances being acutely toxic to the microorgan-
isms, before the liquid is introduced into the biological puri-
s fication stage. ~ -
According to this invention there is provided a process ` -~
, for determining acute toxicity in an aqueous liquid, such as
waste water, comprising first preaerating to almost oxygen
20 saturation at least a part of said liquid, then contacting said
s preaerated liquid with a submerse biological bed, and measuring
the oxygen content of the effluent from said bed, the biomass
of the bed being maintained substantially at a constant level.
The process can be carried out continuously or discontinuously.
~ This invention also provides apparatus for determining acute
is toxicity in an aqueous liquid, such as waste water, comprising
a preaerator for preaerating to almost oxygen saturation an in-
fluent of said liquid, a submerse biological bed arranged to ~ -
, receive the preaerated liquid, and a device ~uch as an oxygen
30 electrode~ for continuous ox intermittent measurement of oxygen
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1~38Z71
for measuring the oxygen content of the effluent from said bed,
wherein the biomass of the bed is cultured in at least one set
of two opposed, relatively movable surfaces and wherein channels
are defined between the surfaces to produce contact between said
liquid and the biomass. --
The term "oxygen" as used herein is meant to denote oxygen
in a form which can be readily used by the microorganisms in
their metabolism and is usually synonymous with free oxygen.
The invention is explained in more detail with reference to
the drawings, wherein:-
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Fig. 1 shows apparatus according to an embodiment of the
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inventiOn; -
Fig. 2 shows a cross sectional view of an alternative em-
bodiment of the biological~part of the apparauts;
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Fig. 3 shows the biological part shown in Fig. 2 in greater
detail; and ~-
Fig. 4 shows the oxygen content of the effluent plotted
against the time for poisoning the biomass.
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With reference to Fig. 1 a partial flow of the liquid to
be examined is introduced into a preaerator 1 through an inlet
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2 and is contacted with air, which is supplied through an inlet
3, the preaerator preferably being dimensioned so that the in-
fluent will be almost oxygen saturated. Then the aerated liquid
is passed through a conduit 4 to a biological part 5 consisting
of rotating circular discs 6 on a shaft 14 and of stationary
inserts 7, which are arranged so that the rotating discs 6 lie
between the stationary inserts 7. The discs 6 and the inserts
7 are preferably parallel, but this is not absolutely necessary
and some deviation from a parallel state can be tolerated. By
this design a very good contact between the liquid, e.g. water,
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and the biofilm is obtained. The biofilm is built up both on
the rotating and the stationary parts and its thickness is con-
trolled by abrasion due to the water flow. A particularly good
control and constancy of the thickness of the biofilm is obtain-
ed if the shaft 14 is mounted so that an oscillating motion is
also produced during rotation thereof. Because the distance bet-
ween the rotating and the stationary parts varies part of the
biofilm is abraded by contact. The liquid flows from the biolo-
gical part 5 through a conduit 8 to a measuring part consisting
: 10 of an oxygen electrode 9 and a holder 10 and designed so that
;~ the liquid from the biological part passes the membrane of the ~ -
oxygen electrode at such a high flow rate that the measuring part
does not get clogged, continuous measurement of oxygen being
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made possible. The oxygen content is plotted on a recording
means (not shown).
The liquid flow through the apparatus of the invention is
dimensioned on the basis of the respiration of active sludge.
When adding fresh active sludge an oxygen saturated liquid will
be almost entirely free of oxygen after about 5 minutes. There-
fore the detention time in the biological part has been chosen
I to be S - 6 minutes. With the volume of the biological part
-` shown in Fig. 1 this will provide a liquid flow of about 40
i~ ml/min.
An alternative embodiment of the biological part 5 is shown
~ in Fig. 2. This consists of two opposed discs 12, 13, of which
'~J at least one is rotatable. The discs are provided with flanges
6, 7, the flanges of one disc fitting in the grooves between the
~ flanges of the other disc. In this way a very big contact sur-
'- face is obtained between the liquid entering through the central
30 portion of the disc 13 and the biofilm formed on the flanges 6, ~-
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7 as well as the parts of the discs 12, 13 comprising the sur-
faces between the flanges. The flanges 6, 7 can each have a
rectangular cross section, a cross section of a truncated cone,
or some other suitable cross section. The discs 12, 13 are en-
closed in a container and the liquid is prevented from circulat-
ing through sealings between the walls of the container and the
discs. The liquid is passed to the part for measuring oxygen
through a conduit 8 in the container. The rotating disc may be
centrically or eccentrically mounted on the shaft 14, and the
thickness control of the biofilm is facilitated in the same way
as for the embodiment shown in Fig. 1.
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Fig. 3 shows in detail in cross section how the flanges 6
~ on the disc 12 and the flanges 7 on the disc 13 mutually engage
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~ each other.
,~: When the liquid passes through the biological part the
-~ microoganisms consume oxygen in the metabolism of the decompos-
able material included in the substrate. If a chemical substance
- is present in a toxic concentration in the liquid, the metabolism
of the microorganisms is inhibited and their oxygen consumption
~, 20 stops completely or partly. The measured content of oxygen in-
'.JI creases after abcut 5 minutes which is equal to the detention
time in the biological part, and reaches its maximum concentra-
`, tion after a time depending on the degree of poisoning. Such a
course is represented in Fig. 4. Thus the presence of acute toxic
substance in the waste water can be discovered as early as after
about 5 - 7 minutes and measures can then be taken immediately,
- - e.g. stopping the influent of liguid, or possibly the influent
of a partial flow of liquid, to the biological stage of the puri-
fication plant. The rapid response is an additional advantage
of the process and the apparatus of the invention, since in this
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`~ way it is possible to prevent poisoning of the biological stage
of the purification plant, which would mean a shut-down of
about 2 - 3 weeks. However, a new culture for the biological
part of the apparatus can be regenerated in about 5 - 6 hours.
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