Note: Descriptions are shown in the official language in which they were submitted.
HOECHST AKTIENGES~LLSCHAFT HOE 88/F 368 DPh.HS/rh
Description
N~thod for ~o~tinuous monitoring of effluent
The invention relate~ to a method for continuou~ monitor-
ing of effluent for watex constituents which interfere
with degradation and inhibi~ bacteria, by measuring the
oxygen depletion o a bacteria sludge suspension with
added effluent.
In view of the generally large numb~r of the effluent
discharge ~ources connected to a treatment plantl and the
a~sociated diversity of the water con~tituent~, effects
cannot be excluded which are caused by inhibitors in the
effluenk. The changing composition and concentration of
the water constituents in the affluent inflow to a
treatment plant can, under some circumstances, al80 lead
to an inhibition of the bacterial activity, caused by
synergistic effects. In order to protect the biologically
operating stage of the treatment plant from ~uch i~ter-
ferences due to effluent, countermea~ures must ~e taken
in good tLme. However, this reguires appropriate monitor-
ing of effluent even up~tream of the trea~ment plant. For
this purpose, so-called toximeters are used which func-
tion intermittently or continuously with sassile or
suspended bacteria.
DE 2,728,071 C2 has disclosed a toximeter method, in
which, for detecting water con~tituents injurious to
bacteria, a mixture of effluent and oxygen-enriched
bacteria sludge i8 continuously pas~ed to an oxygen-
mea~uring ~ec~ion and the oxygen depletion i~ deter~i~ed
~y measuring the oxygen partial pre66ure at the ~kart and
at t~e end of the measuring ~ection.
~he interpretation of the mea~ured osygen consumption
cause~ difficultles. Even i~ parameters such as the p~,
temperature, bacteria mas~ and ef~luent rate are kept
~V~
~ 2 --
constant, the concentration of the water constituents and
henc~ the oxygen depletion vary continually, so that a
decrease in oxygen consumption can be due either ~o
reduced loading or to an inhibiting efflect. In order to
obtain unambiguous information, the inflow of effluent is
in~errupted and nutrient solution, the oxygen demand of
which is known, is fed instead. If reduced oxygen deple-
tion i~ then also foundr ît is certain that the effluent
exerts an inhibiting effect. Especially in the case of
frequently varying effluent loading, this method is
tedious and very laborious. This is ~o be remedied by the
i~ventionO
Accordingly, the invention i8 based on the ob~ect of
providing a method, by mean~ of which the oxygen dep:le-
}5 tion can be assigned unambiguously to an inhibition o
the bacterial activityt independently of the effluent
loading.
Th~ object is achieved by a method of the type de~cribed
at the outset, which comprises passing a part-stream of
the effluent to a measurement, by means of which one of
the total pollution parameters such as COD, TOC or BOD is
determined, mixing a second part-stream of the effluent
with an oxygen-rich bacteria sludge ~uspen~ion, feeding
a constant rate of the mixture to an oxygen-measuring
section, measuring the oxygen depletion ~PO2 and deter-
mining the specific oxygen depletion ~PO2 net from ~he
oxygen depletion and the value of the total pollution
parameter.
The effluent/bacteria sludge suspension rate ratio can be
wîthin the lLmits 1:5 to 1:100. l'he second part-stream of
the effluent should be mixed with the bacteria sludge as
closely a6 po~sible to the entry to the o~ygen-~easuring
~ection. Particularly good result~ are obtained if the
bacteria sludge is used at a constant concentration,
namely at a dry matter content from 1 to 10 g/l, a
t~mperature between 10 and 4S~C, a pH from 5 to 9 and, at
r~ 9
-- 3 --
the 2ntry to the measuring section, an o.~ygen content of
~3 mg/l. In order to ensure adequate mixing of effluent
and bacteria sludge suspension, it is ~ufficient for ~he
mixture to flow through the tesk section at 0.1 to
5 m/minute, 60 that the residence tlTne in the test
~ection then amount~ to 0.2 to 10 minutes/m.
The advantages achieved by the invention are to be seen
especially in the fact that reduced specific oxygen
depletion is substantially independent of the degree of
pollution of the efflu~nt and can thus be assigned
unambiguously to an inhibition of or damage to the
bacteria.
The invention is explained in more detail below by
reference to a flow diagram ~Fi~lre), which is intencled
to repre8ent an illustrative example.
Effluent is contlnuously taken from the incoming s~wer of
the biological treatment plant and passed via li~e 9 to
the apparatus for monitoring the effluent for water
constituenk~ which interfere with degradation an~ inhibit
bacteria. This apparatss contain~, inter alia~ an analy-
tical instrument ~2 for continuou61y me~6uring one of ~he
total pollution parameters Q, such as chemical oxygen
demand (COD), total organic carbon (TOC) or biolvgical
oxygen demand (BOD) ! a measuring section compri~ing
measuring probes 18, 19 and a re~idence time ~ection 20.
The measuring section 1~, 19, 20 is part of a circulation
co~prising a ~tock and preparation tank 1 fsr the bac-
teria sludge, a pum~ 16, a pipe 17, the measuring section
18, 19, 20 and a pipe 21. The ~tock and praparation tank
1 is provided with a final clarification part, which i~
separated from the activatin~ part by a partition 6 and
has an overflow we~r 7~ The analytical instrument 22 and
the mea~uring ~ection 18, 19, 20 are co~nected to a
measuring value-proces~ing and data-output device 23
(8hown in dashed line ) which output~ the measured value~
-- 4 --
28, 29 which have been determined. In the stock and
preparation tank 1, oxygen and/or ai.r is added to the
bacteria ~ludge via line 4 and the gas distributor 5,
chemicals for adjusting the pH to values from 5 to 9 are
added via line 3 andl if nece5sary~ an antioam and
nutrient salt solution are added via line 2. To en~ure
thorough mixing, a partition 8 which has orifices 30 and
31 and around which the suspension circulates in a loop
motion, is located in the tank l. By means of the measur-
ing probes 24, 25, 2S, 27, the pH, the dry matter con-
tent, the oxygen partial pressure and the ~emperature of
the bac~eria sludge are monitored and kept constant
within the abovementioned limits. A part-stream of the
effluent is fed via line 10 and pump 13 to the analytical
instrument 22 for mea~uring the total pollution parameter
Q. The value measured in the analytical in~trument 22 is
processed in the measured value-proce~sing and data-
output device 23 together with the measured values from
the measuring section 18~ 19~ 20.
A second part-stream of the effluent is fed via line 11
and pump 14 to line 17 and, in the latter, mixed with the
bacteria sludge before entry to the measurement section.
The oxygen partial pressure is measured by probe 18 at
the entry and by probe 19 a$ the e~it of the measuring
section. From the oxygen partial pressure~, measured by
the probes 1~, 19, the measured value-processing device
detennines the oxygen consumption ~pO~ in the measurin~
8ection 18~ 19, 20 and, allowing for the base depletion
measllred by the probe 26, the net oxygen consumption ~PO2
net by deduction of the base depletion. This value ~PO2
net is related to the value of the total pollution
parameter Q and thus gives a dimensionless oxygen con-
sumption number
APO2 net
Q
which i~ largely indep~ndent of load fluctuations and
~pecific to the effluent.
2g)~5~
-- 5 --
The effects due to the apparatus and measuring technique
can be compensated on the measured value-processing and
data-output device 23 b~ adjusting the multiplier. 5ince
the effluent-6pecific 0z con~umption nu~ber varies by an
order of magnitude of ~ 20~ depending on the water
constituents, the ~ensi~ivity is approp:riately ~elected
~uch that, for the normal ca~e, the effluent-specific
oxygen consumptlon number is about 70% of the maxLmum
deflec~ion (= 100%) of the indication. The fall of the 2
cons~mption number to 10s~ than half the normal value i6
a sign of a significantly increased inhibition vf degra-
dation by the bacteria and can be utilized for trigyering
alarms at preselected trip points. ~hus, a first trip
point (between 30 and 50~) can first give a provisional
alarm, ~o that there is an opportunity for checking the
apparatus for constancy of the parameters ~uch as pH,
temperature and dry matter content. If the specific
oxygen consumption number falls further, a second trip
point (<30%) triggers the actual alarm, which initiates
the intended preventive measures, for example interrup-
tion o the feed to the treatment plant. If the alimenta-
tion of the bacteria by the effluent fed through line 11
and pump 14 is insufficient, further effl~ent can be fed
~o the bacteria ~ludse suspension via line 12 and pump
15. The displacement water is taken from the stock and
preparation tank 1 via the final clarification part and
weir 7.
