Impact of different types of organic micropollutants present on sources of drinking water on the quality of drinking water

The Science of the Total Environment, 47 (1985) 27-44 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

IMPACT OF OIFFERENT OF DRINKING WATER

H.

SONTHEIMER,

TYPES OF ORGANIC MICROPOLLUTANTS ON THE QUALITY OF ORINKING WATER

H.-J.

BRAUCH

and

W.

27

PRESENT

ON SOURCES

KUHN

INTRODUCTION Following rine

of

can

the lead

organic

the

some

is

This chlorination

water

drinking substances

may

the

and

ago,

that

disinfection

THM-substances

(Rook,

water

drinking

fact,

that

has received

some

found

compounds

with 1974),

chlo-

the

subject

of

public

of the micropollutants in the raw water used

for

a lot

formed

preparation

may

be

Water and Health,1980,1982) from Rook and others (Rook 1974) about the have been made on micropollutants in treated not been removed by the usual treatment pro-

first

carcinogenic

many

water,

studies

which

have

some

etc.

publications

THM-formation

drinking

in

to the other

owing

years

of

formation

micropollutants

interest. during

Since

observation

to

have

impact

on

human

health,

as

these

(Orinking

cesses.

order

In nection How

to give

with do

seen

in

such

an overview pollutants

having

are identifiable

a concentration

in the

observed in the following question: answer to this can

impacts

con-

be

water constituents pg/l

range

1

There

we have to consider all those organics as microwhich can be found in the pg/l range or in still lower conwhile the overall organics concentration in most of our drinmicropollutants will be in the mg/l range. This means that the one side through their low concentration. But on the on

is

no

centrations, king waters are defined other side,

the

pollutants,

can

decide

if

out

knowing

the

the

word

vidually gin,

different consider A first

the

should

we define organic micropollutants? the following table. Micropollutants

Fig.

on

one

word

that

itself

a substance exact

single will

has

to defined

be

means,they to

discussed

must be

counted

formula

chemical

micropollutant as

which

doubt

those

substances

substances. in

and

the

be as

pollutants.

we can

be

here some of following chapter. But

or

a pollutant

structure, which

And

usually analysed the

as

nobody

not

with-

restrict indi-

problems

be-

MICROPOLLUTANTS

AND

ANALYSES

very often say, that only dern analytical methods like GC-MS, HPLC etc. are responsible for licity about the micropollutant problems. Nobody really understands, it means, to have p.ex. 100 rig/l of an individual substance in a ter, but one hundred looks like a large number and therefore 100 to be much more than 0.0001 mg/l although both values means the other side we have to consider the following thesis: Water

works

directors

All

substances

are

But

analysed

individually.

present

a very

small

Therefore

may

be

most

doubt,

all defined have concentrations

their

percentage the

mo-

all

pubwhat

given

wa-

rig/l

seem

same.

On the

sources of

regarding

micropollutants

only

in

the

can

unknown

conbe

micropol-

important.

2

There

drinking are in

can

the

concentration. be

water

centration.

lutants

engineers

organic

dissolved

drinking

Fig.

and

be

water sources ug/l range But are

referred

lowing

no

to

as

of

examples

The

next

river ces along

Rhine

The

data

should

we

this

tablegives for river. given

and

to

group

this

table

and

could

How pollutants

can

we

conclude

are of real

years

can

only

analyse

for

that

been

from these importance

of

data,

that respect

these

in they

their

substances

individually?

can The

fol-

understanding.

micropollutants in the on three different pla-

analysed

most

means

regarding

a better

data for parameters

sum

have

1 mg/l,

that

help

analytical

some

in those

we

might

below

occuring

substances

micropollutants

say,

which problem

some

in

called

organic

in

with

the

nonpolar

1975

and

show

that

chlorine compounds as single substances. But these defined substances are only about 10 % of the overall chlorinated organics and only about 1 % of the total organics measured as OOC. While the surrogate parameters are increasing from Base1 to Ouisburg along the Rhine river, we very often find a decrease resulting from removal processes for some of the individual substances, especially for the volatile organics.

we

determine

be

allowed

pollutants,

and the

that

organic

the well to drinking

only

defined water

microquality?

sort of data have to be used to determine for example, treatment We have got another important problem resulting from the efficiencies. large fluctuation in the river flow water. The following table gives some information about this question.

What

29

compound

Easel

K6lll

Chloroform

1.1

0.0

1.1

Carbon

9.3

1.4

3.3

Chloroethanes

2.5

0.2

0.6

Trichloroethylene

0.9

0.0

0.6

Tetrachloroethylene

0.3

0.0

1.5

Chlorobutadienes

4.4

0.4

0.3

Chlorobenzenes

0.9

0.6

5.3

0.5

1.3

Tetrochloride

Chlorotoluenes Benzene

0.2

0.3

0.8

T0lUlYl.Z

0.8

0.7

1.9

Oimethylbenzenes

0.2

0.7

1.4

Trimsthylbenzenes

0.1

0.4

1 .o

0.1

0.5

Tetramethylbenzenes ooclblol

55

78

IO0

D@&“,.I.~

10

5

15

DOC (w/O

2.3

ccncantrction

Fig.3

)uisburq

Organic (1975)

4.6

5.0

in kg/I

compounds

Wcsaerchemic

in the

Rhine

Korlsuhe

river

1965/3604

Chlorobonzono

0.06

1.2-Dlchtorobanzono 1.X-Dlchlorobanrana l.4-Dt~hlombanzsna

0.32 0.05

-r 3.26

0.4i

2.03 2.27 1.92

1.D 0.15 OSf

2.46

O.lf

2.50

0.27

2.26 2.19 LOS

1.6 0.91 0.44

4.45 3.24

2.2

Dlchlomphanola Dlchlomlaopmpytsthar

3.34

.U

DlchlomiaobuM~thor Diothytphthaloi Dibutyiphtholotea

2.77 1.66

1.2 1.9

0.19 0.04

Trichlombenrena~ Tatrcchlorobenzaner Chlomtoluonor Nltrobdnzena Nitrototusnos

I i:“,,

(3)

0.42 0.25

(3)

Nlt~CX)dlofl~~ Mathoxynltrcbenzsnas

0.07 0.09

Chloronttmbsnzenor Dimothytanlllno~

0.32

1.1

Ethyttoluidino NHmphoncls

Fig.4

concentmtlon

in kg/I

Geometric

mean

from near

composite Ollsseldorf

Wcaasrchemie

Kcrtwuha

values samples - 1984)

of

orgcnic over

micropollutants

2 weeks

(Rhine

river

1965/3606

30 These posite

observe

data

don't

from

result

samples

over

fairly

big

2 weeks.

samples

taken

for

Nevertheless

fluctuations.

This

can

be

from

immediately

but

these

samples

seen

mixed

from the or divides

results

comwe

for

the geometric standard deviation.If one multiplies the geometric mean values with the standard deviation you can calculate the limits where 66 % of all data lie within. The c value can be seen as a 95% maximum concentration. Only 5 % of all data are. higher than this value. Although none of the mean values are higher than 1 pg/l, the table shows that the maximum concentrations for some individual compounds will be higher than this general goal. It should be mentioned here, that these fluctuations are fairly typical

for

next

all

diagram

micropollutants

river

in

waters.

This

can

be

seen

from

the

too.

1.2-dichlorobsnzcne

.

Fig.5

concentration

of

water in dependonce Wasserchemie Karlsruhc

1.2-dichlorobenzene of water flow

Here the concentrations of of the river water flow. One are so large here, that there ween the two parameters. The benzene

and

changes

etc.The

samples.

here

we

also

fluctuations

don't

in Rhine river (Dusseldorf-1984) 1985/3815

are given as a functior concentration fluctuations seems to be no worthwhile correlation betsame has been found true for 1,4-dichlorosee any tendency regarding seasonal will even be greater, if we take separate 1,2-dichlorobenzene

can

see

that

the

31

I I

1.4-dichlorobanzcns

1984

Fiy.6

concentration of 1.4-dichlorobenzene woter vs. time (neor Dosseldorf) Wasserchemie

The den means the

data

given

changes

in

that

the

here

sampling

for the evalutation water treatment

out

from

of

of health

two-weekly

cannot is

those

river

1985/3814

quality method

drawn

conclusion

Rhine .

Karlsruhe

result

water

the

in

very data.

seen

important Usually

we

especially

impacts,

Therefore all sudfrom these data. This for the results and for

samples.

been

need in

the

those

mean cases

values

where

to a high removal efficiency. On the other concentrations for treatment considerations, as we can have a much higher breakthrough for peak concentrations when using certain treatment steps like powdered activated carbon with a It is for this reason that peak pollution may determine constant dose. the medium concentrations in the treated water. Here it has been proven worthwhile to calculate the maximum values as the mean values for one day at normal water flow conditions. This proposal has first been made in the IWAR-memorandum (IAWR-memorandum 1973) and methods have been proposed to calculate these maximum concentrations for river waters (Tagungsbericht 1979). side

we

All

need

the

following

the

doesn't

lead

maximum

considerations

discussed

till

now

may

be

summarized

conclusion:

Analytical

control

of single organic

micropol-

be insufficient to maintain a safe drinking water quality. Additional summary and group parameter measurements will always be required. lutants

Fig.

7

may

with

the

32 If

we

want

ring

or

about

get

enough

a river water parameters like

in

summary TOX

to

TOS

etc.

on

water

the

used DOC

for drinking or COO on

other

side.

all

organic

water one

purposes

side

Without

micropollutants

these

we

group

and

data

we

OCCU-

always

need

parameters cannot

like

be

sure

quality.

data

allow

tants

we

have

to

sible

to

determine

These

the

of

information

furthermore

expect all

in single

a water

decisions source,

substances

on the types as

it

which

of micropollu-

usually

will

occur

can

be

impos-

as micropollu-

tants. for river waters like the Rhine river water, where we are not able to analyse more than about 10 % of all micropollutants. In order to underline this general observation and to present some more information about it, some results of gel chromatography studies are given with the next figures. This

is

true

especially

oLOO0

Molekiilmassen

Fig.8

Wasssrchemie

1500

- Verteilung

Karlsruhe

800

LOO

Rhein

160

bei

c

M

Easel 1965 I 3801

The measurements presented in the figure have been made by Fuchs in our institute using TSK gels and DOC measurement for the effluent control after the TSK-gel-column. The procedure developed by Fuchs allows a fairly good separation, where not only the molecular weight is of importance but adsorbability to some extend too. For this the molecular weight data 8 cannot be used as correct figures in all cases but estimate of the type of organics and their molecular weight distribution. One can see that we have roughly two fractions if we make measurements with the Rhine river water above Base1 with about 50 - 60 of humics or better fulvic substances. But there occur some lower molecular weight substances too, but here a part of this peak may result from better adsorbable substances.

given they

within

give

figure

a rough

%

33 If we do the measurement with the Rhine river in Karlsruhe one can from the following figure 9, that here we find many more peaks. This crease in the number of peaks continues as we go north to Wiesbaden then to the lower parts of the Rhine river at Dikseldorf and Orsay.

Molek6lmassenverteilung

Fig.9

SC& Fig.10

Molektilmossen-Verteilung Worserchamic

Korlsruhe

Rhein

1097

5L6

Rhein

bei Karlsruhe.

35

15‘

bei

Dijsseldorf

c"

-Flehe 1985 I x.03

see inand

34

we have

Here the

lower

water

samples

that

many

more

molecular analysed

here

in

these

waters

as the

waters

still

contain

usually

substances,

It

didn't

of

found

different

fractions.

most

the

of

groups

weight

should

contain

analysed

be

volatile

organic

especially

mentioned organics.

has

been

the

This

micropollutants

enrichment

in

that

means,

couldn't

be

partially

done

by

micropollutants

as

it

stripping. These be

from

seen

a larger be

the

column

prepared.

for

next so

In

samples

for

DOC-,

TOX-

addition

10 different

Here

example.

that

different

many

fractions.

the

gel

and

has

are

been

done

measurements

TOS-values

results

The

separation

group-parameter

have

given

in

in

could

been

the

can

measured

following

table.

” YL I

Fig.1

II “1 I”

Y “I Iv II lvnlr*

EEi

Molmossentrennung der trinkwosserrelevonten Stoffe der BASF Ludwigshofen: Verteilung von DOC.AOX.AOS ouf die Froktionen I bis IX [VL =Vorlouf , ADS = odsorbierter

Anteil) vm.,.rewme IoIIwda The ted

cular lar

in

data

given

the

following

weight

organics All

nits These the

removal and

i.e.

of only

substances

water

Beginning

treatment

those

are

in

has

slowly

pass

all plant

the

remain

been

different

the

right

% of

the

hand

side

hand

side

are

adsorbed

and

the

usually

and

will

applied

onto

the

waste

orgaremained.

barriers in

the

ma-

water. water

adsorbed

treatment

high molecu-

column the

substances

occur

orien-

low

the in

easily

relevant”

therefore

are

treated the

are

the

organics

a biologically

water

groups

left

total

biodegraded

“drinking

the

the

which

given

water the

on

on

and

values

Is*, Len> of

composition

way.

This

after

the

substances,while

weight

terial.

for

drinking

in

water.

molecl

35

So

it

or

not.

is

One

important

can

stances

has

organic and

achieve

diagram,

these

that

largest fraction found for the organic

been

the

this

not

the

chlorine

to

or

from

see

comprise

bution

whether

compounds

adsorbable

belong

separation

a full

to

substances.

The

substances

are

micropollutants

the medium molecular weight subof the OOC. A very similar distrisulfur compounds. In contrast the the low molecular weight fraction figure also indicate that we don't

into individual different groups

substances

using

this

method.

are micropollutants. They are however man made pollutants and they can be dangerous for human health. We have to recognize, that organic micropollutants in river waters can never be completely defined. We have in most cases many other pollutants in micro-amounts, which have to be removed during drinking water treatment. It is for this reason that group parameter measurements like TOX and TOS are very important for water quality control. This very often is totally different, when we have organic micropollutants in ground water sources. Here we usually have only to consider a few substances, present in the water. An example for this can be seen out of the following figure. So we

can'tsay,

that

the

parameter

60 0.9 188 184

Trichloroethylene Tetrachloroethylene cis-1,2-Dichloroethylene E

single

as

compound

chlorine

180 13 193

POX

AOX TOX concentration Piy.12

Single

in pg/l

and

polluted Wosscrchemie

If we compare the

POX

values,,

rine

compoundsin

this

case

we

can

this can

control

parameters

of 1985/3819

Karlsruhe

here the we

surrogate

groundwater

sum of all

conclude water.We treatment

that know

micropollutants will be

there all

with no

micropollutants

efficiency

with

in

either

TOX or also organic chlothis water.In group parameter

the

other

36 measurements ground

waters

a solid

individual

with

waste all

right

different area.

many

deposition

the

ORGANIC

If present have

MICROPOLLUTANTS

analyses.

to

cussed stay

speaking

AN0

But

pollutants

e.g.

river We have to recognize Here

as

DRINKING

with

each special WATER

this

may

not

with waters waters, we this

and

be

true

coming cannot choose

for from deter

the

case.

TREATMENT

of different organic micropollutants final drinking water quality, we also know something about the efficiency of different treatment proin removing the organic micropollutants. This problem will be diswithin many different papers given at this conference, so that I with some more general remarks and some examples. Generally the following has to be considered in this respect:

we

cesses

have

in

to

consider

raw water

of

different on

their

water

the

sources

Removal

Fig.

compound

micropollutants. analytical control methods for

mine

can

or

organic

treatment chemical constituents

impact

on

the

micropollutants processes

structure

but

through depends

not

on

other

all

only

as well.

13

Micropollutants don't determine the overall effect of a water treatment process used in drinking water plants. For this reason, we first have to know more about the water in general than about the chemical structure of the micropollutants, if we want to predict the removal efficiency for each pollutant end a given treatment process. In order to get a better understanding of this, a few examples of micropollutant reduction in practical plants will be presented-especially in activated carbon treatment plants at the Rhine river. The first example gives data for trichloroethylene in the Rhine river as well as in the river bank filtrate and after different treatment steps. The results are given as mean concentrations over one week and show primarily that there is no biodegradation during river bank filtration with a retention time of about 6 weeks. In this special case there has been observed a sudden increase of the concentration in the river in January, and one can see that there is some increase about 2 months later in the bank filtrate too. The fluctuations in the bank filtrate are lower, but

we find concentration

about

the

same

equalization

mean

concentration depends

on

as observed in adsorption processes

the

river. within

The the

37

trichloroethylsna

after

bank

filtration after

concentration

F.Lg.14

treatment Wasserchemie

ground.

This

don't

have

is many

one

also

can

trichloroethylene for

the

Oct.

different 82

with

sudden

effect

is

adsorbed

a small

-

April

83

1965/3616

of the reasons,

see

after

period

Korlsruhe

problems

ver. The equalization ces as they are better ver banks. One

of steps

ozone

why

water

even

more

onto

the

decrease

works

using

concentrations

through

pronounced

organic

for material

ozonisation

filtration

bank

changes

within

aromatic within

and

this

ri-

the substanthe

is

ridue

degradation. The reduction is not very impressive however compared with the result from the carbon filter, where practically all trichloroethylene can be removed, since regeneration always occurs before breakthrough of the discussed micropollutants. We have to acknowledge further, that the concentrations found in the Rhine river are usually very low if we take composite samples as it has been done in

to

some

this

stripping

and

some

chemical

case.

regarding the concentrations of these sorts of micropolare very different if we consinder some ground waters. An example for this will be given with the next figure. Here we have nearly about 200 pg/l, but we have three different volatile chlorinated hydrocarbons. And one can observe a vary different adsorption behavior for these three substances. We have to consider further that besides the micropollutants, we also have about 1 - 2 ppm of other organics (humics) competing with the micropollutants. It is for this reason, that we have a lot of difficulties if we want to predict the breakthrough behavior in such a case. The reason for this lies in the fact, that these substances show a non ideal behavior regarding adsorption competition. This effect can be seen from the following figure. The

lutants

situation

38

0

100

Bed

Fig.

15

200

Deplh .cm

Concentration Profiles of Volatile Contaminants in a GAC -Adsorber wo.*cIchIIc Korlaruhr

Organic 1985I30‘3

Trichlorethen 1o.c

2

\

m

.f B g .-E

q =

1 .c

c”

27.4 (

e

h

l e/m’

$6 )

$ $

10

, 100

Filtenulouf-Konzentrotion

in

.l

Fiy.16

Maximum

for

filter

trichlorethylene

loading

vs

A H 71 0 F 100 OAS 12 0 c 25 D TL 8101 0 EK 12 0 ROW 0.8 11 IO mg/m’

influent

concentratior

39

The

data

treatment

summarized plants

within

and

they

this

give

figure

the

maximal

are

taken

loading

from many different found in equilibrium

for seven different carbons. These equilibrium influent concentration of the substance only and are independent of all other micropollutants and the total organics concentration as well as from the type of activated carbon used. This is a very astonishing result and can be explained only with different assumptions on the type of pores available for the different substances within this water. These data prove the non ideal adsorption behavior of the three

with

the

loadings

water

inflowing depend

on

the

chlorinated hydrocarbons and we have to take this a nearly complete removal of these micropollutants,

into account, especially

if we want of trichloro-

ethane.

Regarding

we have to consider that it only gives the maximum loading which can be reached in practical plants. But usually this loading cannot be reached as we have an earlier breakthrough. But here technical solutions can really help and are therefore very important for micropollutant removal also. One example for this can be seen in the next figure. the

figure,

Entering

GAC

Sludge b

k7fluent

GAC

P Withdrawal

Backwash1 Air

I-bEffluent It Backwash Water

Flg.17

GAC-Filter Section Wasserchemie

with Changing Karlsruhe

Cross 1985 I 3593

40 of a GAC-filter, as it is used in Mannheim filter has two different cross-sections and these have a difference in the area for the water flow of about 25 %. This allows a separate backwashing of the upper part of the filter and the carbon therein has a higher loading at total filter breakthrough than the lower part. So this upper part can be fluidized and be pumped to reactivation or an intermediate tank. After this one can fluidize the lower part and pump this carbon which is not fully loaded in a separate tank. Then new or reactivated carbon is placed in the lower part of the filter and on top of this the carbon previously coming from the lower part can be put on top. Thus only one filter is necessary to reach the same effect as when having two separate filters in series. This type of filter operation doesn't only reduce the carbon costs by about 25 %,but it also gives more safety for the removal of organic micropollutants and this may be still more important. The reason for the greater safety lies in the fact, that we have half of the filter volume always as new end unloaded carbon and for this competition is not so important in the first part of the filter run. This example shows that processes considerations play an important role, if we look on the importance of micropollutants on drinking water quality. In order to present some data on the behavior of micropollutants when using different treatment steps in series, the next two figures present data from two different water works at the Rhine river, which show practical results typical for these plants. The data are given as geometric This

is

a schematic

(Kretschmar,

mean

1985)

over

values

drawing

and

this

a period

of

include, besides the filtered raw water data as well as the after the activated carbon filters but

about

3 months

river water quality, the bank results after ozonisation and before the final desinfection which, in 0.1 - 0.15 mg/l chlorine dioxide. Regarding the effect of bank filtration before, that there is some biodegradation

and The

one

of

is

can

done

see,as

with

has

substances

some

a large

has

cases,

and

have

zene

most

chlorotoluenes as well as for real impact on the concentrations influence if we forget about the small

chlorobenzenes doesn't

and

like

naphthalene.

been

shown

benzenes, Ozonjsation

but GAC, as concentrations

expected,

of ben-

toluene.

last

example

the

single

substance

Here the

the effect more polar

are

biodegradable.

gives data,

very the

similar values

data

but

for TOC is fairly

contains

in

addition

to

well as for TOX and TOS. high showing that some of

as

of ground filtration micropollutants, which can't be analysed Here, the effect of carbon filtration

individually,

is worthwhile

41

Oh, OAC 0.40 0.19 0.23 0.37 0.03 n.n. “.“. 0.13 0.06 0.29 0.01 0.09 0.09 0.39 0.09 0.17 0.05 0.08 concantmtion in ps/l Removal of organic micropollutants an the lower Rhine (1983) Warssrchsmis Korlrrvhs

Fig.18

I

parameter

Rhine water

Chloroform Carbon Tetrochloride Trichloroethylsne Benzene TOlUC,M Xylsnes Dichlorobenzenes Chlorotoluener AOX TOS TOC h/l) W(254) (m-‘)

Fig.19

0.29 0.06 0.30 0.40 0.01 “.“. 0.05 0.05 0.03 0.04 <0.005 0.01
51 93 3.4 a.2

concentration in pg/l Efficiency of drinking

works

on the

Wasserchemie

1 .oo

0.44 0.56 0.60 0.74 0.75 0.81 0.20

lower

Karlsruhe

water

0.32 0.09 0.17 0.32 0.01 “3. 0.04 0.05 0.03 0.04 <0.005 0.01 co.005 0.01 0.01 0.06 o.o* <0.005

in a water

0.21 0.02 0.01 0.01 <0.005 “.“. “.“. 0.05 0.03 0.01 “A co.005 “.“. “A “.“. “A. “.“. “.“. works

lSE5/3607

I

after banl filtration

0.61 0.29 0.60 0.05 0.04 0.07 0.45
treatment

steps

in

a water

Rhine’ 1985/3805

42 for the removal of the organic chlorine concentration, but not as good for the removal of sulfonic acids. We have to ask in this case, if the removal efficiency of GAC, which is very good for the defined compounds can be different for the unknown micropollutants. But, the combined treat ment with the three different processes is highly efficient and, if we would only control UV-absorbance or DOC we would get similar results, compared to controlling all individual micropollutants. SUMMARY

AND CONCLUSIONS

If we consider the water source on drinking

possible

water

impact quality,

of micropollutants we

usually

come

present in the to the following

points:

Possible impact of organic micropollutants - Direct or indirect health effects. - Necessity of additional treatment steps. - Corrosion activation and inhibition. - Impact on water uses. Fig.

20

Besides the always most important health effects, we have to consider corrosion effects and also special water uses. Very often micropollutants lead to the necessity of other treatment steps. But the possible health aspects usually are most important. There is no doubt, that we can't decide without knowing the chemical structure, if an organic micropollutant has some adverse health effects or not. Also when we have this knowledge, we very often don't have the necessary toxicological data. So we have difficulties to fix an acceptable maximum concentration. And if we don't have the necessary toxicological information,we don't need the exact chemical structure either. This is one of our big problems in connection with organic micropollutants. We can overcome this, partially measuring group parameter data like TOX and by trying to reduce this concentration as far as possible. This very often is a more worthwhile control method compared to analysing the individual substances in the rig/l range. The second problem we have to deal with is safety. Here, besides analytical control, which usually is very limited, we can use a combination of different treatment processes.

43 of for of different

Effective only

removal

be achieved

bination logical

and

activated Fig.

chemical

organic most

micropollutants pollutants

treatment

steps

oxidation

as

can

using

a com-

including

bio-

well as granular

carbon.

21

of in

Most

present

the

problems

have

steps.

tants

too. As

these

the

source

in

Especially

a final

biological

conclusion

substances

as

with

organic

micropollutants

one

But,

in water

oxidation

can

say the

micropollutants,

if we are answered

substances.

occur

practice

works without sufficient treatprocesses are of large importance, here especially if they are done through ground filtration. This has been found true for two reasons. First biological oxidation within the ground needs time and second longer retentions times lead to a better equalization and this reduces peak concentrations. Furthermore experience with chemical wastewaters has shown that the more toxic substances are very often slowly biodegradable and are therefore removed during ground filtration. Besides this after biological oxidation the remaining substances are most easily adsorbed and this helps for a better overall treatment efficiency too. In addition to biological oxidation within the ground, activated carbon filters are very important for a safe drinking water. Here, we can now predict the breakthrough behavior of micropollument

water

we

have

solved

following.

which this

can analytical

be

We usually analysed problem,

cell as

only

individual

most

of our

more easily:,if we have to final concentration. We also can study treatment steps to remove the pollutant within the water work or, last but not least, at the place where it comes from. But after this we still stay with the question if there are any unknown micropollutants within our water which we can't determine individually and these unknown substances are in most cases more problematic and possibly more dangerous for human health than all our well known organic pollutants. Here we have to find the right control method and strategy and here we have to spend more work and activity in the future if we want a safe drinking water. questions

remove

the

identified

too.

substances

We can

decidethen

and

to

whet

44 LITERATURE 111

Rook,

J.J.:

of Haloforms Waters. Water Treatment and Formation

IV

Drinking

Water

National

Academy

u.

131

141 1st

Vol.

4

and

during

Exam.

23

of Natural

Chlorination

(1974),

2,

234

Health

Press,

Washington,

D.C.

Vol.

3

(1980)

(1982)

der IAWR (Internationale Arbeitsgemeinschaft der Wasserwerke im Rheineinzugsgebiet) Rheinwasserverschmutzung und Trinkwassergewinnung, Mai Memorandum

Tagungsbericht (Arbeitsgemeinschaft

7. ARW-Arbeitstagung, Easel 1979 Rhein-Wasserwerke

e.V.)

Kretschmar, W.: Chlorinated Hydrocarbons in Drinking Water Water Supply, Vol. 3, Berlin "8"-Pergamon Press Ltd. pp 197 - 202 (1985)

1973