Environmental Letters
ISSN: 0013-9300 (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/lesa17
The Use of Activable Tracers in the Evaluation of the Performance of Wastewater Treatment Plants T. F. Craft & G. G. Eichholz To cite this article: T. F. Craft & G. G. Eichholz (1975) The Use of Activable Tracers in the Evaluation of the Performance of Wastewater Treatment Plants, Environmental Letters, 9:3, 307-325, DOI: 10.1080/00139307509435858 To link to this article: http://dx.doi.org/10.1080/00139307509435858
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Date: 06 October 2015, At: 15:39
Eg~~~~?I!E?ITAG LETTERS, 9 ( 3 ) , 307- 325 (1975)
m~ USE
OF ACTIVABLE TRACERS IN THE EVALUATIOX OF THE PERFORXWCE OF IJASTEL‘ATER TREATMENT PLANTS
Key Words:
Neutron Activation, Stable Tracers, Waste T r e a b e n t
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T. F. C r a f t and G. G. Eichholz
Engineering Experiolent S t a t i o n and School of Nuclear Engineering Georgia I n s t i t u t e of Technology Atlanta, Georgia 30332 ABSTRACT
The use of s t a b l e , a c t i v a b l e t r a c e r s has been studied i n a p p l i c a t i o n s
t o e s t a b l i s h the performance of waste treatment p l a n t s and d e t e c t causes of i r r e g u l a r o r improper functioning of individual p l a n t processes. Various s o l u b l e t r a c e r s were evaluated, among then i n d i m , scandium, and bromine.
The i n e r t t r a c e r s were compared with dye t r a c e r s and were found
t o be superior i n t u r b i d Liquids and t o g i v e more q u a n t i t a t i v e information.
On the o t h e r hand dye t r a c e r s a r e more convenient f o r rapid v i s i b l e i n d i cation of t h e i r a r r i v a l whereas a c t i v a b l e t r a c e r s r e q u i r e c o l l e c t i o n and removal t o a neutron source, such a s a r e a c t o r , f o r i n d i c a t i o n .
Activable
t r a c e r s a r e r e l a t i v e l y simple t o apply and the c o s t per t e s t i s reasonable. INTRODUCTIOX
The growth of urban populations i n recent decades and t h e steady i n c r e a s e in water use f o r i n d u s t r i a l and domestic purposes has posed a heavy burden on e x i s t i n g wastewater treatment f a c i l i t i e s uany of which a r e operating well beyond t h e i r design capacity f o r extended periods.
In
a d d i t i o n , i t i s o f t e n d i f f i c u l t t o determine p r e c i s e l y whether t h e various
30 7 Copyright 0 1975 hy Marcel Dckker, Inc. All Rights Rcrcrred. h’eithcr this work nor m y p3rt m3y be reproduccd Or transmitted in any form or by any means, electronic or niech3nica.l. including photocopying. microfilming, and recording, or by m y inforination storage and retrieval system, without permission in writing from the publisher.
30 8
CRAFT AND EICHHOLZ
component p a r t s of a p l a n t a r e o p e r a t i n g a t o r n e a r o p t h u m d e s i g n condit i o n s and m a l f u n c t i o n s o r l o w - e f f i c i e n c y o p e r a t i o n s may f r e q u e n t l y cont i n u e unchecked o v e r prolonged times.
It i s , t h e r e f o r e , of prime h p o r -
t a n c e t o i n t r o d u c e methods of t e s t i n g and d i a g n o s i s t o such p l a n t s t h a t
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can y i e l d needed d a t a w i t h o u t i n t e r f e r i n g with system o p e r a t i o n s and b y methods t h a t can b e handled r e a d i l y by p r e s e n t p l a n t p e r s o n n e l . Of t h e v a r i o u s t r a c e r n e t h o d s i n u s e , f l u o r e s c e n t dye t r a c e r s have been used widely, p a r t i c u l a r l y i n strean flow and h y d r o l o g i c a l a p p l i c a t i o n s . These methods are s i m p l e and convenient and l e n d themselves t o r a p i d v i s u a l i n d i c a t i o n i n c l e a r flowing streams."*
They a r e less e a s i l y ap-
p l i e d , u n d e r r e c i r c u l a t i o n c o n d i t i o n s and i n t u r b i d w a t e r s , such as t h o s e t h a t may b e encountered i n t r e a t n e n t p l a n t s .
Of t h e a l t e r n a t i v e s ,
r a d i o a c t i v e t r a c e r s have been used e x t e n s i v e l y i n h y d r o l o g i c a l and i r r i g a tion
and f o r i n d u s t r i a l p l a n t
investigation^.^'^
They p r o -
v i d e a r a p i d and convenient means of o b t a i n i n g q u a n t i t a t i v e d a t a on modera t e - s i z e d f l o w systems and trace element movement i n t h e a q u a t i c environment.
They are less a p p r o p r i a t e i n l a r g e - f l o w o r l a r g e - s c a l e o p e r a t i o n s
o r i n p u b l i c waters h e r e t h e l a r g e amount of r a d i o a c t i v i t y needed nay pose h a n d l i n g problems.
Environmental and p o l i t i c a l c o n s i d e r a t i o n s may
make t h e uncontained r e l e a s e of r a d i o n u c l i d e s , even i n s m a l l amounts and
on r a r e o c c a s i o n s , q u e s t i o n a b l e and u n d e s i r a b l e . For t h e s e r e a s o n s , t h e u s e of s t a b l e a c t i v a b l e t r a c e r s h a s been i n vestigated.
In t h i s method a s o l u b l e compound c o n t a i n i n g an element n o t
n o r n a l l y found i n t h e water o r t h e wastes i s added t o t h e s t r e a m i n r e q u i s i t e amounts.
The stream i s then sampled a t i n t e r v a l s a t a l l p o i n t s and
d e p t h s of i n t e r e s t .
The samples are then taken t o a s o u r c e of n e u t r o n s ,
such a s a n u c l e a r r e a c t o r , a c t i v a t e d by n e u t r o n bombardment, and counted
E V s U A ~OF~WASTEVATER ~s TREATMENT in a s u i t a b l e d e t e c t o r system.
is
PLANTS
309
P r e r e q u i s i t e f o r a s u i t a b l e t r a c e r element
of a c t i v a t i o n W g h neutron capture cross s e c t i o n ) , ready a v a i l -
a b i l i t y a t acceptable Cost, and non-toxicity i n water a t the concentrations nployed.
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By choosing an element meeting those requirements, i t i s p o s s i b l e t o develop procedures t h a t lend themselves t o use a t treatment p l a n t s without i n t e r f e r e n c e with normal operations.
Samples can be e a s i l y c o l l e c t e d by
r e l a t i v e l y u n s k i l l e d p l a n t personnel, though the counting and evaluation requires a knowledgeable person and access t o a r e a c t o r ; both of these requirements a r e now r e a d i l y a v a i l a b l e i n many places a l l over t h e world. of course, the time delay i n analyzing samples deprives t h i s t r a c e r method
of the advantage of imnediate evaluation of counting data, such a s i s obt a i n a b l e with gamma-emitting r a d i o t r a c e r s , but t h e o t h e r advantages e a s i l y outweigh t h i s drawback.
In those cases where t r i t i m i s used a s the
r a d i o a c t i v e t r a c e r , even t h i s aspect i s n o t g r e a t l y d i f f e r e n t from t h e use
of a c t i v a b l e t r a c e r s .
Some previous work with a c t i v a b l e t r a c e r s i n e s t u a -
r i n e waters has been described by Kruger*”;
Gatz e t a1.”
have used them
a s atmospheric t r a c e r s . There a r e s e v e r a l parameters i n the-operation of waste treatment p l a n t s t h a t a r e of s i g n i f i c a n c e i n a s s e s s i n g e x i s t i n g p l a n t conditions and operating e f f i c i e n c y .
These include t h e flow r a t e s i n various p a r t s of
the system, residence times, flow paths, and r e c i r c u l a t i o n paths.
A l l of
these parameters may be measured by t r a c e r methods, by dye, r a d i o t r a c e r , o r s t a b l e t r a c e r procedures.
D i f f i c u l t i e s may a r i s e from the presence of
suspended m a t t e r , t h e t u r b i d i t y of the water involved, and, of course, t h e open-air s i t u a t i o n of such p l a n t s .
Both dye and r a d i o a c t i v e t r a c e r s have
CRAFT AND EICHHOLz
310
been used i n t h e present i n v e s t i g a t i o n f o r convenience and t o provide corr e l a t i o n with previous work; however, t h e n a i n purpose of the p r o j e c t was t o i n v e s t i g a t e the u t i l i t y of s t a b l e t r a c e r s and t o develop procedures t o make t h e method acceptable and p r a c t i c a l f o r p l a n t operators.
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EXPERIEIENTAL DETAILS Tracer Selection Post-sampling a c t i v a t i o n a n a l y s i s d i f f e r s from conventional radioa c t i v e t r a c e r work i n s e v e r a l respects.
hbereas i n t h e c a s e of r a d i o a c t i v e
t r a c e r s i n stream s t u d i e s i t i s h e l p f u l t o have comparable i n e r t m a t e r i a l present t o avoid r a d i o c o l l o i d formation and excessive f r a c t i o n a t i o n , the use of s t a b l e t r a c e r s r e q u i r e s the choice of a n a t e r i a l t h a t i s normally c m p l e t e l y absent from t h e water under t e s t .
Since the amount of i n e r t
t r a c e r used i s governed e n t i r e l y by considerations of expected d i l u t i o n , d e t e c t a b i l i t y , and c o s t , i t i s important t o s e l e c t a m a t e r i a l t h a t i s environmentally acceptable and completely non-toxic i n t h e concentrations expected.
Since sewage i s n o t n a t u r a l l y ingested, only e f f l u e n t concentra-
t i o n s need be considered h e r e .
Another important d i f f e r e n c e conpared w i t h
r a d i o t r a c e r s l i e s i n the choice of t h e a c t i v a t e d isotope.
A f t e r sampling,
the t e s t sample i s exposed t o neutross i n a r e a c t o r and the induced a c t i v i t y is d e t e c t e d and counted.
To be r e a d i l y detected t h e t r a c e r must have
a high thermal neutron cross s e c t i o n and a good s p e c i f i c a c t i v i t y a f t e r
activation.
This implies a f a i r l y s h o r t h a l f l i f e , c e r t a i n l y much s h o r t e r
than would be convenient for r a d i o t r a c e r f i e l d tests.
I n a d d i t i o n , the
g a m rays emitted should be r e a d i l y discriminated a g a i n s t those from o t h e r t r a c e elements normally present i n t h e waste waters, notably s o d i m , t h a t w i l l be a c t i v a t e d a t t h e same time.
E V a U ~ OF ~ ~WA OST~EWATER TREATMENT PLANTS
311
h%en p a r t i c u l a t e s a r e t o b e l a b e l e d , f i r m attachment of t h e t r a c e r i s
sought.
I n flow measurements, where t h e t r a c e r i s used i n d i s s o l v e d form,
n i n h m a b s o r p t i o n o r adsorption on any p a r t i c u l a t e s p r e s e n t i s d e s i r e d . Another important f a c t o r i s t h e p o s s i b l e p r i o r presence of t h e same element
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in the system t o be s t u d i e d .
Complete absence would be b e s t , of course,
b u t i t may o f t e n be p o s s i b l e t o s u b t r a c t o u t any e x i s t i n g known background
as long a s i t i s n o t excessive.
Manganese f a l l s i n t h i s category, a s i t
has a p p r o p r i a t e n u c l e a r and o t h e r p r o p e r t i e s , b u t i t i s found almost i n v a r i a b l y i n t h e waters of t h e A t l a n t a a r e a .
Some p o t e n t i a l l y u s e f u l e l e -
ments a r e q u i t e expensive and t h i s may l i m i t t h e i r use.
The following elements were considered a s p o t e n t i a l t r a c e r m a t e r i a l s
on account of t h e i r high neutron c a p t u r e c r o s s s e c t i o n s , u, s u i t a b l e gammaray emission, and probable absence frcm l o c a l waters: scandium:
Sc-45 (u = 13b); Sc-46 (t
84d)
cobalt:
Co-59 (a = 19b); Co-60 ( t
5.3 y r )
indium:
In-115 (ueff = 1.47b);
cerium:
Ce-142 (aeff = O.llb); Ce-143
tantalum:
Ta-181 (a = 21b); Ta-182 (
.4
k
In-ll&(t
4 (t 4
%
53.7 rnin) 33.7 h r )
dl
Chrmium, molybdenm, and bromine were aJso used.
No i n d i c a t i o n of any t o x i c i t y i n d i l u t e s o l u t i o n h a s been found in t h e
l i t e r a t u r e f o r e i t h e r indium o r scandiun, n o r any of t h e o t h e r s above under the conditions prevailing. Tanning T e s t s I n waste treatment p l a n t s i t i s of i n t e r e s t t o determine both t h e normal stream flow p a t t e r n s a s well a s t h e behavior and p o s s i b l e f r a c t i o n a t i o n of any suspended s o l i d s and sedimentary matter.
For t h i s reason
CRAFT AND EICHHOLZ
312
t e s t s were conducted b o t h on s o l u b l e t r a c e r s and on t h e i n c o r p o r a t i o n of
t r a c e r m a t e r i a l i n t o n a t u r a l o r simulated p a r t i c u l a t e s . Laboratory experiments have been performed t o e v a l u a t e t h e e a s e and e f f e c t i v e n e s s of i n c o r p o r a t i n g a t r a c e r element i n t o o r g a n i c ' a n d i n o r g a n i c
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particles.
F o r t r a c e r t e s t s on suspended matter one r e q u i r e s a b a t c h of
p a r t i c l e s of chosen s i z e each c o n t a i n i n g s m e t r a c e r atoms a t t a c h e d so f i m l y t h a t they would n o t b e d i s s o l v e d away o r leached o u t on prolonged exposure t o water.
The d e n s i t y as w e l l as t h e s i z e of t h e l a b e l e d p a r t i -
c l e s should b e t h e same as t h o s e of t h e whole group of p a r t i c l e s whose movement i s t o b e t r a c e d . Vermiculite It had been demonstrated p r e v i o u s l y t h a t t h e high c a t i o n exchange c a p a c i t y of v e r m i c u l i t e can b e u t i l i z e d i n t h e p r e p a r a t i o n of r a d i o a c t i v e Ground v e r m i c u l i t e i s s l u r r i e d w i t h a s o l u t i o n of t h e
tracer particles."
t r a c e r c a t i o n , d r i e d , c a l c i n e d , and reground.
The d e s i r e d s i z e f r a c t i o n s
a r e o b t a i n e d by s i e v i n g .
Scandium and indium on v e r m i c u l i t e have now been
p r e p a r e d by t h i s method.
Other inorganic c a r r i e r s studied included kaolin,
g l a s s f r i t , and b o t t l e g l a s s . Ten grams of v e r m i c u l i t e ground t o p a s s a 100 mesh s c r e e n w e r e s l u r r i e d f o r s e v e r a l h o u r s i n w a t e r c o n t a i n i n g 20 mg of indium s u l f a t e .
After
s t a n d i n g o v e r n i g h t , t h e l i q u i d w a s decanted and t h e s o l i d r e s i d u e transferred t o a quartz dish.
It was d r i e d under a h e a t lamp and then h e a t e d t o 2050°F
i n a muffle furnace.
mill.
A f t e r c o o l i n g , t h e s i n t e r e d mass was ground i n a b a l l
Neutron a c t i v a t i o n a n a l y s i s of water i n which t h e ground s o l i d was
soaked f o r s e v e r a l days showed a n e t count r a t e of z e r o compared t o 44,000 f o r s o l i d i r r a d i a t e d s i m u l t a n e o u s l y , confirming t h e h i g h s t a b i l i t y of t r a c e r attachment.
T h i s p r o c e d u r e h a s a l s o been used with scandium a s t h e
E.~~~ATION
313
OF WASTEWATER TREATMENT PLANTS
l a b e l i n g e l e n e n t and with k a o l i n a s t h e s u b s t r a t e .
sults.
A 1 1 gave s i m i l a r re-
The h i g h r e s i s t a n c e t o l e a c h i n g i s b e l i e v e d due t o d i f f u s i o n of
t r a c e r i n t o t h e p a r t i c l e s and a l s o a s u r f a c e m e l t i n g of t h e p a r t i c l e s , o f f t h e a c t i v e exchange s i t e s .
11 Previous work i n t h i s l a b o r a t o r y
bas shown t h a t i n v e r m i c u l i t e t r e a t e d i n t h i s manner t h e t r a c e r c o n c e n t r a -
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t i o n i s independent of p a r t i c l e s i z e , i n d i c a t i n g t h a t t h e attachment of t r a c e r i o n s i s n o t merely a f u n c t i o n of s u r f a c e a r e a .
GLass T r a c e r elements s t i r r e d i n t o molten g l a s s y i e l d p a r t i c l e s t h a t a r e very r e s i s t a n t t o l e a c h i n g .
The procedure c o n s i s t e d of m e l t i n g about 200
grams of b o t t l e g l a s s o r g l a s s f r i t (Pemco brand) i n a p o t f u r n a c e .
Bottle
g l a s s melted i n t h e range of 1000-2000°F. The t r a c e r element i n d r y form (indium s u l f a t e , molybdenum t r i o x i d e , s c a n d i m o x i d e ) was then s t i r r e d i n t o t h e melted glass.
A f t e r allowing the m e l t t o soak f o r a while, i t was
poured i n t o c o l d water.
The r e s u l t i n g s t r a n d s and p a r t i c l e s of g l a s s were
then ground i n a b a l l m i l l . Organic P a r t i c l e s I n t h e p r e s e n t work, o r g a n i c p a r t i c l e s t h a t have been s u b j e c t e d t o l a b e l i n g procedures i n c l u d e sewage s l u d g e , oatmeal, g r i t s , and wool.
The
g e n e r a l technique was t o s t i r t h e o r g a n i c p a r t i c u l a t e s i n t o a s o l u t i o n cont a i n i n g the d e s i r e d element.
Half of t h e m i x t u r e w a s b o i l e d while s t i r r i n g
and t h e remainder was s t i r r e d c o l d .
Wool w a s n o t t r e a t e d by t h i s technique,
b u t was mordant dyed, u s i n g t h e d e s i r e d c a t i o n as t h e mordant.
Effective-
n e s s of t h e l a b e l i n g procedure was e v a l u a t e d by a c t i v a t i o n a n a l y s i s of the P a r t i c u l a t e m a t t e r , t h e d e c a n t a t e , and s e v e r a l s u c c e s s i v e wash w a t e r s . A f t e r h a l f an h o u r t h e s o l i d s were allowed t o s e t t l e u n t i l a reasonably S m P l e of t h e W a t e r could be o b t a i n e d .
The s o l i d was then washed
with S e v e r a l p o r t i o n s o f w a t e r , each time s e p a r a t i n g t h e s o l i d s by set-
314
CRAFT AND EICHHOLZ Samples of t h e s o l i d , t h e i n i t i a l d e c a n t a t e , and t h e wash w a t e r s
tling.
were then analyzed f o r t r a c e r c o n t e n t . The r e s u l t s were n o t v e r y p r e c i s e due t o t h e v a r i a b l e m o i s t u r e content of t h e s l u d g e , b u t they gave t h e r e l a t i v e d i s t r i b u t i o n . o f t h e t r a c e r be-
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tween t h e s o l u t i o n and t h e s l u d g e in t h e form i t would b e u t i l i z e d .
The
r e s u l t s of s e v e r a l experiments are s m a r i z e d i n Table 1 f o r v a r i o u s na-
terials. ture.
There a p p e a r s t o b e no c l e a r - c u t advantage in b o i l i n g t h e m i x -
Grits seem t o b e a n u n s a t i s f a c t o r y medium f o r t h i s purpose.
EXPERPIENTAL PROCEDURE To compare t h e t r a c e r method w i t h the dye method, tracer s o l u t i o n and
a dye were r e l e a s e d s i m u l t a n e o u s l y f o r most t e s t s .
The appearance of t h e
dye marker a t the p o i n t of i n t e r e s t a l s o s e r v e d t o s t a r t t h e sampling procedure.
Rhodine 6B w a s used a s t h e dye marker i n most c a s e s .
The dye
i t s e l f r a r e l y gave q u a n t i t a t i v e i n f o r m a t i o n in t u r b i d streams o r h i g h l y
TABLE 1 R a t i o of S o l i d s / D e c a n t a t e Indium C o n c e n t r a t i o n s i n Labeling Experiments Substrate
Lhboiled
Boiled
Sewage Sludge
3.8
1.54
Oatmeal
1.64
2.02
Oatmeal
1.45
0.81
Grits
1.90
0.80
Grits
0.32
0.92
G r i t s (cobalt tracer)
0.36
0.69
315
E V ~ ~ J J A T I O NOF WASTEWATER TREATfIENT PLANTS colored wastes but i t s appearance was q u i t e v i s i b l e i f a l a r g e amount
A f l u o r e s c e n t dye, such a s Rhodamine
(400 grams) was added t o t h e stream.
{a,&ich
r e l i e s on a f l u o r m e t e r f o r i t s d e t e c t i o n , has been found unsuit-
able f o r t h i s type of a p p l i c a t i o n .
Tracer measurements on both the l i q u i d ,
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using a s o l u b l e t r a c e r such as sodium bromide, and on suspended material have been conducted.
These tests i n sone cases have indicated t h e e x i s -
tence of appreciable v a r i a t i o n s i n flow paths and residence t i n e s . For conparison, a f e w t e s t s have employed a r a d i o a c t i v e t r a c e r , such a s 15-hour sodim-24, t o p o i n t up t h e advantages and disadvantages of the two procedures. ployed.
A s c i n t i l l a t i o n probe and single-channel s c a l e r were em-
Fig. 1 shows t h e r e s u l t s of one p a r t i c u l a r t e s t which conparedthe
flow p a t t e r n through a sedimentation basin.
The s c i n t i l l a t i o n d e t e c t o r
readings represent on-the-spot measurement of t o t a l r a d i o a c t i v i t y from the Na-24 t r a c e r ; t h e single-channel analyzer readings r e f l e c t subsequent o f f s i t e measurement of samples. tically significant.
The divergences seen a r e probably n o t s t a t i s -
From a p r a c t i c a l p o i n t of view, the most important
drawback of r a d i o t r a c e r s compared with a c t i v a b l e t r a c e r s l i e s i n the license requirements f o r t h e anploynent of t h e r a d i o t r a c e r ; i t i s n o t immedia t e l y evident t o h a t e x t e n t a municipal u t i l i t y could o r would obtain a l i c e n s e t o possess and use a r a d i o a c t i v e t r a c e r m a t e r i a l f o r such a purpose. A l s o , t h e i n j e c t i o n of t h e t r a c e r r e q u i r e s considerable c a r e i n shipping
and handling of the source container. Neutron Activation Analysis Sample a n a l y s i s i n a l l cases was done by conventional procedures i n the Georgia Tech Research Reactor v i a the pneumatic tube f a c i l i t y .
All
sanples t o be analyzed were placed i n polyethylene v i a l s , heat-sealed t o prevent leakage and i r r a d i a t e d i n batches of s i x v i a l s .
The a v a i l a b l e
CRAFT AND EICHHOLZ
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316
2
thermal n e u t r o n f l u x was a b o u t 7 x 1 O I 2 n/cm s e c and t h e i r r a d i a t i o n t i m e
’ ,
was s e l e c t e d t o p r o v i d e a s u i t a b l e count r a t e f o r t h e expected c o n c e n t r a t i o n of t h e p a r t i c u l a r element unde;
consideration.
F o r indium, a n i r r a d i -
a t i o n p e r i o d of one t o f i v e minutes produced s u f f i c i e n t a c t i v i t y f o r counti n g p e r i o d s of 100-200 sec l i v e t i m e .
Samples were counted on a 60 c c
Ge(Li) d e t e c t o r used i n c o n j u n c t i o n w i t h a 1024-channel a n a l y z e r , h i c h was i n t e r f a c e d w i t h a s m a l l computer t o c a l c u l a t e t h e n e t c o u n t s under any given photopeak.
To d e t e r n i n e t h e s u i t a b i l i t y of v a r i o u s m a t e r i a l s , b o t h a s s o l u b l e t r a c e r s and a s adsorbed tracers on p a r t i c u l a t e s , a c t i v a t i o n a n a l y s e s were run on blank water samples and on s p i k e d s o l u t i o n s .
The b l a n k s a a p l e s es-
,
E-~~~t\~ION
OF WASTEWATER TREATPENT PLANTS
317
tablished t h e p r e s e n c e o r absence of background t r a c e c o n c e n t r a t i o n s i n local u ~ t e rsamples f o r t h e element concerned.
The s p i k e d s a n p l e s s e r v e d
determine t h e s e n s i t i v i t y of t h e s e l e c t e d a c t i v a t i o n procedure f o r t h a t t o c a l i b r a t e the g a m a - r a y s p e c t r m e t e r , and t o i n d i c a t e any i n -
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t e r f e r i n g a c t i v i t y peaks from o t h e r t r a c e elements. Sampling Procedure For f i e l d tests a t sewage t r e a t m e n t p l a n t s , l i q u i d samples were c o l l e c t e d f r m t a n k s , channels, and o t h e r l o c a t i o n s by dipping with simple long-handled sample cans, t h a t w e r e capable of s t a n d i n g up s a f e l y .
The
c o l l e c t e d samples are subsequently t r a n s f e r r e d t o one ml p o l y e t h y l e n e v i a l s by a d i s p o s a b l e p i p e t t e a t t a c h e d t o a 1 0 - m l s y r i n g e .
Cross-contamina-
t i o n i s p o t e n t i a l l y a s e r i o u s problem and t h e p l a s t i c v i a l s cannot be reused. During a r u n , t h e sampler was r i n s e d i n t h e l i q u i d t o be sampled a few seconds b e f o r e t h e moment of c o l l e c t i o n .
A f t e r t h e sample was obtained,
t h e p i p e t t e was then r i n s e d with one o r two p o r t i o n s of t h e s a n p l e , and t h e desired sanples pipetted i n t o the v i a l s .
The sample w a s s t i r r e d w i t h t h e
p i p e t t e i f any r a p i d l y - s e t t l i n g s o l i d s were observed.
Duplicate o r t r i p l i -
c a t e samples were c o l l e c t e d , and t h e v i a l s c l o s e d w i t h t h e i r a t t a c h e d l i d s . They were then ready f o r t r a n s p o r t a t i o n t o t h e l a b o r a t o r y f o r a n a l y s i s . Idhen t h e s o l i d s c o n t e n t of a flow was t o b e c o n s i d e r e d s e p a r a t e l y
from t h e l i q u i d , l a r g e r samples were r e q u i r e d .
P i n t milk b o t t l e s were used
and were f i l l e d by dipping where needed. In the l a b o r a t o r y t h e s e samples were f i l t e r e d by s u c t i o n i n a Buchner
funnel.
A f t e r a l l t h e l i q u i d had passed through, t h e f i l t e r paper was
f o l d e d and f o r c e d i n t o an i r r a d i a t i o n v i a l .
P o r t i o n s of the s u p e r n a t a n t
were p i p e t t e d i n t o o t h e r v i a l s f o r s e p a r a t e a n a l y s i s .
CRAFT AND EICHHOLz
318
EXPERDINTAL RESULTS Tracer Selection I t was found t h a t indium i n t h e form of indium s u l f a t e o r n i t r a t e was
t h e most convenient i n e r t t r a c e r .
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each t e s t .
About 25 grams of compound were used in
Indium i s n o n - t o x i c and n o t p r e s e n t i n normal waste streams.
It was a l s o found t h a t indium can b e used t o l a b e l s l u d g e f o r t e s t
work on s e d i m e n t a t i o n b a s i n s .
F o r t h i s purpose, approximately t h r e e g a l -
lons of s l u d g e were c o l l e c t e d from t h e sump a t t h e s e d i m e n t a t i o n b a s i n and p l a c e d i n a f i v e g a l l o n can.
Ten grams of i n d i m (as t h e s u l f a t e ) d i s -
s o l v e d i n a l i t t l e w a t e r were added, and t h e m i x t u r e w a s h e a t e d almost t o b o i l i n g o v e r a p o r t a b l e propane f u r n a c e . t h e h a l f hour heating period.
The m i x t u r e was s t i r r e d d u r i n g
The odors produced by t h i s procedure were
u n d e s i r a b l e and i t was found l a t e r t o b e unnecessary t o b o i l t h e s l u d g e . Flow Measurements Flow measurements have been made i n sewer s y s t a n s t o determine f l o w times and t o d e t e c t any hold-up o r blockage.
T r a c e r measurements on t h e
l i q u i d , u s i n g NaBr a s s o l u b l e t r a c e r , and on suspended m a t e r i a l s were conducted.
These t e s t s demonstrated t h e s u i t a b i l i t y of t h i s approach and i n -
d i c a t e d t h e e x i s t e n c e of a p p r e c i a b l e v a r i a t i o n s i n flow p a t h s and r e s i d e n c e times i n some c a s e s . Movement of A c t i v a t e d S l u d g e A t e s t was conducted t o o b t a i n i n f o r n a t i o n on flow c o n d i t i o n s i n a n
a c t i v a t e d s l u d g e tank.
A t t h e time of t h e s t u d y , t h e flow r a t e through the
tank i n v o l v e d was a b o u t 5 m i l l i o n g a l l o n s / d a y OIGD), which i n c l u d e d 1 EIGD of r e t u r n s l u d g e .
The placement of t h e a i r d i f f u s e r s i n t h i s tank produces
a r o l l i n g motion i n t h e l i q u i d , and a given p a r t i c l e presumably moves i n a
s p i r a l f a s h i o n from t h e i n l e t t o t h e o u t l e t of t h e tank.
The t h e o r e t i c a l
E
~
a
~ OF ~ WASTEWATER ~ ~ O N TREATMENT PLANTS
319
detention time was about 2 1 / 2 hours and t h e suspended s o l i d s i n t h i s sysaveraged about 2300 mg/L. It was thought t h a t the vigorous motion of t h e tank contents would
produce a l a r g e amount of mixing and concomitantly a high d i l u t i o n of t h e added t r a c e r .
Referring t o F i g . 2 , i t w i l l be seen t h a t s m e longitudinal
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nixing occurred so t h a t t h e i n i t i a l concentration of 63 ppb decreased f o r
35 minutes a t which time a very high peak (130 ppb) appeared, representing an unmixed zone. The i n d i m l e v e l decreased gradually t h e r e a f t e r w i t h a small, presumably i n s i g n i f i c a n t , f l u c t u a t i o n near the two hour t i n e .
A t the half way s t a t i o n ,
140
110
100
L
L
5-
ao
c
L I-
2
60
z 0 0
'2
40
I
a0
01 0
10
60
40 TIME
I
I
t
80
100
120
MINUTES
FIG. 2 Activable Tracer Test on Sludge Basin
CRAFT AND EICHHOLZ
320
a s i m i l a r p a t t e r n was noted.
The maximum concentration t h e r e was only 70
ppb and occurred 15 minutes a f t e r the maximum a t t h e q u a r t e r location.
Two v i a l s were f i l l e d from t h e sampler a t each time i n t e r v a l , and agreement between the two p o r t i o n s was l e s s s a t i s f a c t o r y than f o r other experinents.
The lack of consistency may have been due t o v a r i a t i o n s It i s believed t h a t a
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caused by t h e r a p i d l y - s e t t l i n g s o l i d s present.
l a r g e portion of the t r a c e r was absorbed by t h e s o l i d s p r e s e n t , and any d i f f e r e n c e i n t h e amount of s o l i d s t r a n s f e r r e d t o d u p l i c a t e v i a l s would cause l a r g e d i f f e r e n c e s i n the observed r e s u l t s . Trickling F i l t e r Studies One of the l o c a l treatment p l a n t s had been having d i f f i c u l t y f o r some time with t h e i r t r i c k l i n g f i l t e r .
Ponding was evident, b u t more impor-
t a n t l y , t h e BOD reduction across t h i s f i l t e r was e s s e n t i a l l y zero.
Gas
production of both d i g e s t e r s was f a r below normal l e v e l s and a common cause of these d i f f i c u l t i e s was suspected.
This provided an opportunity
f o r comparison of the flow p a t t e r n through a badly clogged f i l t e r with the normal p a t t e r n t o be obtained a t a l a t e r d a t e a f t e r t h e f i l t e r had been r e s t o r e d t o normal operation.
The t r a c e r t e s t s were c a r r i e d out using indium a s t h e a c t i v a b l e mat e r i a l p l u s Rhodine 6B f o r v i s u a l observation.
The t r a c e r s o l u t i o n was
poured i n t o the dosing box of t h e f i l t e r and samples were c o l l e c t e d a t the f i l t e r o u t l e t and a t t h e c e n t e r ( i n l e t ) and r i m ( o u t l e t ) of both secondary clarifiers.
The r e s u l t s of the f i r s t t e s t a r e shown i n Fig. 3 .
The curve
labeled "A" represents the concentration of t r a c e r a t the f i l t e r o u t l e t , which i s about e i g h t f e e t below grade l e v e l .
The flow a t t h i s point was
apparently n o t very well mixed a s the dye t r a c e r was more concentrated a t the c e n t e r of the stream of e f f l u e n t .
More thorough mixing occurs i n the
downstream pipes which d i v i d e and d e l i v e r t h e l i q u i d t o the c e n t e r of the secondary c l a r i f i e r s .
I f the flow were completely mixed, the maximum con-
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EVALUATION OF WASTEWATER TREATMENT PLANTS
L 0
1
IS
10
IO
ao
IS
uinuita
is711
TIACCE
32 1
as
40
iwtciio*
FIG. 3 Tracer Test on Trickling F i l t e r
c e n t r a t i o n would be the same a t t h e f i l t e r o u t l e t and the c l a r i f i e r i n l e t s . Similar t e s t s were conducted a t o t h e r treatment p l a n t s .
A discussion of
the operational aspects of these t e s t s w i l l be found elsewhere.
12,13
Sludge S e t t l i n g T e s t s A t t h e o u t l e t of t h e sedimentation basin of another treatment p l a n t , p a r t i c u l a t e m a t t e r was observed passing over t h e weir and t o the p l a n t outEall.
In order t o study t h i s s i t u a t i o n more f u l l y , sludge was labeled with
a t r a c e r and t h e concentration i n the e f f l u e n t measured a s a function of time. The labeled sludge was poured i n t o the i n l e t on t h e e a s t s i d e of t h e sedinentation basin and t h i s was followed by a gallon of water containing
CRAFT AND EICHHOLZ
322 200 grams of Rhodine 6B.
Color appeared i n t h e e f f l u e n t a t 24 minutes and
Quart samples were obtained a t 3 minute i n t e r v a l s .
sampling was begun.
A t 2 minute i n t e r v a l s d u p l i c a t e 1 ml samples were c o l l e c t e d .
No dye c o l o r
was e v i d e n t anywhere i n t h e b a s i n except a t t h e o u t l e t , and s a p l i n g was continued u n t i l t h e c o l o r of t h e e f f l u e n t had faded t o a low l e v e l .
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A t t h e l a b o r a t o r y , t h e q u a r t samples were f i l t e r e d by s u c t i o n and the
Samples of the f i l t r a t e were a l s o
s o l i d m a t t e r c o l l e c t e d was analyzed.
analyzed and found t o c o n t a i n i n d i m , although a t a much lower concentra-
The r e s u l t s of t h e s e a n a l y s e s a r e shown i n F i g . 4 .
t i o n than t h e s o l i d s .
The c o n c e n t r a t i o n of t r a c e r i n t h e sludge i s seen t o f l u c t u a t e i n a v e r y s i m i l a r f a s h i o n although n o t e x a c t l y i n phase with those of t h e sludge.
‘i
5
5U f, U llr
m
60
-
50
-
40
-
20
-
10
-
SUPERNATANT
0 -
a! I-
! SLUDGE
:
20
30! 10
I
I
I
MINUTES
I
I
AFTER
TRACER
I
INJECTION
FIG. 4
Tracer Measurements on Sedimentation Basin
323
E V a ~ ~ ~OF~ W OASN TEWATER TREATMENT PLANTS
This p a t t e r n of behavior i s i n d i c a t i v e of a p a t t e r n of r e c i r c u l a t i o n , w i t h a period of n i n e minutes.
There was nothing about t h i s basin that ac-
counted d i r e c t l y f o r these r e s u l t s .
The sludge scraping mechanism moves
slowly and continuously and does n o t seem capable of producing t h i s pattern.
It i s p o s s i b l e t h a t t h i s c u r r e n t produced a r o l l i n g motion a s i t
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hpinged upon t h e o u t l e t wall of t h e basin.
P a r t of the flow would e x i t
Over t h e weir and the balance would r o l l back toward t h e basin i n l e t .
Each
time t h i s mass of water r o t a t e d , t h e t r a c e r concentration would be lessened by the amount previously l o s t , and by d i l u t i o n . In an attempt t o c l a r i f y t h i s s i t u a t i o n , the experiment was repeated, the only d i f f e r e n c e s being t h a t indium s o l u t i o n was s t i r r e d i n t o t h e sludge without heating and samples were c o l l e c t e d a t one minute i n t e r v a l s .
The
r e s u l t s of t h i s second run i n d i c a t e d a p a t t e r n t h a t was e n t i r e l y d i f f e r e n t from t h a t of t h e f i r s t t e s t .
The r e c i r c u l a t i o n p a t t e r n was abs'ent and
t r a c e r concentrations rose t o a r a t h e r i l l - d e f i n e d maximum and then gradua l l y decreased. As o t h e r conditions about t h e basin appeared t o be t h e same a s previ-
ously, t h e maximum t r a c e r concentrations of t h e two runs a r e taken a s some indication of t h e efficiency of s o l i d s c o l l e c t i o n .
The second s i t u a t i o n
when the indium maximum was only about 1 2 ppm i s taken t o i n d i c a t e b e t t e r operation of t h e basin than i n t h e f i r s t t e s t where t r a c e r concentration went above 30 ppm. CONCLUSIONS
The r e s u l t s reported h e r e have shown t h a t s t a b l e t r a c e r s followed by neutron a c t i v a t i o n a r e a convenient means of i n v e s t i g a t i n g operational cond i t i o n s i n sewage treatment p l a n t s .
The sampling procedure is simpleenough
t o be han'dled by t y p i c a l p l a n t personnel.
The method r e q u i r e s access t o a
324
CRAFT AND EICHHOLZ
n e u t r o n a c t i v a t i o n f a c i l i t y where a n a l y s e s can be done a t a c c e p t a b l e c o s t and would n o t be done on a r o u t i n e b a s i s unless t h e r e are grounds t o susp e c t s e v e r e malfunction i n t h e p l a n t .
I n d i m and scandium s a l t s have
proved t o b e s a t i s f a c t o r y tracer elements g i v i n g adequate s e n s i t i v i t y so t h a t material c o n s m p t i o n can b e k e p t t o a r e a s o n a b l e l e v e l .
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ACKNOWLEDBIENTS
This work w a s done with t h e s u p p o r t of t h e
D i v i s i o n of I s o t o p e Devel.
opment, U. S. A t o m i c Energy Conrmission under C o n t r a c t No. AT-(40-1)-4156. The a s s i s t a n c e of S. N . Plillspaugh and T. PI. Galbreth i n many of t h e f i e l d experiments and sample a n a l y s e s w a s i n v a l u a b l e .
The c o o p e r a t i o n and a c t i v e
s u p p o r t of the s u p e r i n t e n d e n t and personnel of t h e Water P o l l u t i o n Control D i v i s i o n of the C i t y of A t l a n t a and t h e Clayton County Water A u t h o r i t y a r e
W e a r e i n d e b t e d t o D r . R. S. I n g o l s f o r h i s ad-
g r a t e f u l l y acknowledged.
v i c e and many u s e f u l s u g g e s t i o n s . REFERENCES
1.
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Water Supply 1968
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J . F. Wilson, "Fluorometric Procedures f o r Dye Tracing." Water Res o u r c e s I n v e s t i g . Book 3 , ch_apter A12. U. S. Geol. Survey, Washington! D. C . , 1968
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G. G. Eichholz, 14. B. Pluir, PI. J. Bennett, J. D. Wild, C. Lawton, and S. Plostowy, "Radioactive T r a c e r I n v e s t i g a t i o n s i n a F l o t a t i o n Circuit.' Trans. Can. I n s t . Mining Met. 60, 63-69 (1957)
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R. P. Gardner and R. L. Ely, "Radioisotope Pleasurenent A p p l i c a t i o n s i n Engineering." Reinhold Publ. Corp., New York, 1967
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P. Kruger, " P r i n c i p l e s of A c t i v a t i o n A n a l y s i s . New York, 1971
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'I
Wiley-Interscience,
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EVALUATION OF WASTEWATER TREATMENT PLANTS
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P. Kruger, % c t i v a b l e Rare Earth Elements as Estuar i n e Water Tracers." 5th I n t e r n . Conf. Water P o l l u t i o n Research, pergaaon, Amsterdam, 1971 J. K. Channel1 and
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T. F. C r a f t and G. G. Eichholz, 'Tlechanism of Rapid F i l t r a t i o n i n a
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T. F. C r a f t , G. G. Eichholz, and S. N . Millspaugh, "Evaluation of T r e a b e n t P l a n t s by Tracer Nethods." Rept. Om-4156-2, U. S. Atomic Energy Commission, 1973
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T. F. C r a f t and R. S . Ingols, 'Flow Through Tine i n T r i c k l i n g F i l t e r s . " Water and Sewage Works 120 (l), 78-79 (1973)
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Received Narch Accepted A p r i l
14, 1975 1, 1975
ISSN: 0013-9300 (Print) (Online) Journal homepage: http://www.tandfonline.com/loi/lesa17
The Use of Activable Tracers in the Evaluation of the Performance of Wastewater Treatment Plants T. F. Craft & G. G. Eichholz To cite this article: T. F. Craft & G. G. Eichholz (1975) The Use of Activable Tracers in the Evaluation of the Performance of Wastewater Treatment Plants, Environmental Letters, 9:3, 307-325, DOI: 10.1080/00139307509435858 To link to this article: http://dx.doi.org/10.1080/00139307509435858
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Eg~~~~?I!E?ITAG LETTERS, 9 ( 3 ) , 307- 325 (1975)
m~ USE
OF ACTIVABLE TRACERS IN THE EVALUATIOX OF THE PERFORXWCE OF IJASTEL‘ATER TREATMENT PLANTS
Key Words:
Neutron Activation, Stable Tracers, Waste T r e a b e n t
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T. F. C r a f t and G. G. Eichholz
Engineering Experiolent S t a t i o n and School of Nuclear Engineering Georgia I n s t i t u t e of Technology Atlanta, Georgia 30332 ABSTRACT
The use of s t a b l e , a c t i v a b l e t r a c e r s has been studied i n a p p l i c a t i o n s
t o e s t a b l i s h the performance of waste treatment p l a n t s and d e t e c t causes of i r r e g u l a r o r improper functioning of individual p l a n t processes. Various s o l u b l e t r a c e r s were evaluated, among then i n d i m , scandium, and bromine.
The i n e r t t r a c e r s were compared with dye t r a c e r s and were found
t o be superior i n t u r b i d Liquids and t o g i v e more q u a n t i t a t i v e information.
On the o t h e r hand dye t r a c e r s a r e more convenient f o r rapid v i s i b l e i n d i cation of t h e i r a r r i v a l whereas a c t i v a b l e t r a c e r s r e q u i r e c o l l e c t i o n and removal t o a neutron source, such a s a r e a c t o r , f o r i n d i c a t i o n .
Activable
t r a c e r s a r e r e l a t i v e l y simple t o apply and the c o s t per t e s t i s reasonable. INTRODUCTIOX
The growth of urban populations i n recent decades and t h e steady i n c r e a s e in water use f o r i n d u s t r i a l and domestic purposes has posed a heavy burden on e x i s t i n g wastewater treatment f a c i l i t i e s uany of which a r e operating well beyond t h e i r design capacity f o r extended periods.
In
a d d i t i o n , i t i s o f t e n d i f f i c u l t t o determine p r e c i s e l y whether t h e various
30 7 Copyright 0 1975 hy Marcel Dckker, Inc. All Rights Rcrcrred. h’eithcr this work nor m y p3rt m3y be reproduccd Or transmitted in any form or by any means, electronic or niech3nica.l. including photocopying. microfilming, and recording, or by m y inforination storage and retrieval system, without permission in writing from the publisher.
30 8
CRAFT AND EICHHOLZ
component p a r t s of a p l a n t a r e o p e r a t i n g a t o r n e a r o p t h u m d e s i g n condit i o n s and m a l f u n c t i o n s o r l o w - e f f i c i e n c y o p e r a t i o n s may f r e q u e n t l y cont i n u e unchecked o v e r prolonged times.
It i s , t h e r e f o r e , of prime h p o r -
t a n c e t o i n t r o d u c e methods of t e s t i n g and d i a g n o s i s t o such p l a n t s t h a t
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can y i e l d needed d a t a w i t h o u t i n t e r f e r i n g with system o p e r a t i o n s and b y methods t h a t can b e handled r e a d i l y by p r e s e n t p l a n t p e r s o n n e l . Of t h e v a r i o u s t r a c e r n e t h o d s i n u s e , f l u o r e s c e n t dye t r a c e r s have been used widely, p a r t i c u l a r l y i n strean flow and h y d r o l o g i c a l a p p l i c a t i o n s . These methods are s i m p l e and convenient and l e n d themselves t o r a p i d v i s u a l i n d i c a t i o n i n c l e a r flowing streams."*
They a r e less e a s i l y ap-
p l i e d , u n d e r r e c i r c u l a t i o n c o n d i t i o n s and i n t u r b i d w a t e r s , such as t h o s e t h a t may b e encountered i n t r e a t n e n t p l a n t s .
Of t h e a l t e r n a t i v e s ,
r a d i o a c t i v e t r a c e r s have been used e x t e n s i v e l y i n h y d r o l o g i c a l and i r r i g a tion
and f o r i n d u s t r i a l p l a n t
investigation^.^'^
They p r o -
v i d e a r a p i d and convenient means of o b t a i n i n g q u a n t i t a t i v e d a t a on modera t e - s i z e d f l o w systems and trace element movement i n t h e a q u a t i c environment.
They are less a p p r o p r i a t e i n l a r g e - f l o w o r l a r g e - s c a l e o p e r a t i o n s
o r i n p u b l i c waters h e r e t h e l a r g e amount of r a d i o a c t i v i t y needed nay pose h a n d l i n g problems.
Environmental and p o l i t i c a l c o n s i d e r a t i o n s may
make t h e uncontained r e l e a s e of r a d i o n u c l i d e s , even i n s m a l l amounts and
on r a r e o c c a s i o n s , q u e s t i o n a b l e and u n d e s i r a b l e . For t h e s e r e a s o n s , t h e u s e of s t a b l e a c t i v a b l e t r a c e r s h a s been i n vestigated.
In t h i s method a s o l u b l e compound c o n t a i n i n g an element n o t
n o r n a l l y found i n t h e water o r t h e wastes i s added t o t h e s t r e a m i n r e q u i s i t e amounts.
The stream i s then sampled a t i n t e r v a l s a t a l l p o i n t s and
d e p t h s of i n t e r e s t .
The samples are then taken t o a s o u r c e of n e u t r o n s ,
such a s a n u c l e a r r e a c t o r , a c t i v a t e d by n e u t r o n bombardment, and counted
E V s U A ~OF~WASTEVATER ~s TREATMENT in a s u i t a b l e d e t e c t o r system.
is
PLANTS
309
P r e r e q u i s i t e f o r a s u i t a b l e t r a c e r element
of a c t i v a t i o n W g h neutron capture cross s e c t i o n ) , ready a v a i l -
a b i l i t y a t acceptable Cost, and non-toxicity i n water a t the concentrations nployed.
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By choosing an element meeting those requirements, i t i s p o s s i b l e t o develop procedures t h a t lend themselves t o use a t treatment p l a n t s without i n t e r f e r e n c e with normal operations.
Samples can be e a s i l y c o l l e c t e d by
r e l a t i v e l y u n s k i l l e d p l a n t personnel, though the counting and evaluation requires a knowledgeable person and access t o a r e a c t o r ; both of these requirements a r e now r e a d i l y a v a i l a b l e i n many places a l l over t h e world. of course, the time delay i n analyzing samples deprives t h i s t r a c e r method
of the advantage of imnediate evaluation of counting data, such a s i s obt a i n a b l e with gamma-emitting r a d i o t r a c e r s , but t h e o t h e r advantages e a s i l y outweigh t h i s drawback.
In those cases where t r i t i m i s used a s the
r a d i o a c t i v e t r a c e r , even t h i s aspect i s n o t g r e a t l y d i f f e r e n t from t h e use
of a c t i v a b l e t r a c e r s .
Some previous work with a c t i v a b l e t r a c e r s i n e s t u a -
r i n e waters has been described by Kruger*”;
Gatz e t a1.”
have used them
a s atmospheric t r a c e r s . There a r e s e v e r a l parameters i n the-operation of waste treatment p l a n t s t h a t a r e of s i g n i f i c a n c e i n a s s e s s i n g e x i s t i n g p l a n t conditions and operating e f f i c i e n c y .
These include t h e flow r a t e s i n various p a r t s of
the system, residence times, flow paths, and r e c i r c u l a t i o n paths.
A l l of
these parameters may be measured by t r a c e r methods, by dye, r a d i o t r a c e r , o r s t a b l e t r a c e r procedures.
D i f f i c u l t i e s may a r i s e from the presence of
suspended m a t t e r , t h e t u r b i d i t y of the water involved, and, of course, t h e open-air s i t u a t i o n of such p l a n t s .
Both dye and r a d i o a c t i v e t r a c e r s have
CRAFT AND EICHHOLz
310
been used i n t h e present i n v e s t i g a t i o n f o r convenience and t o provide corr e l a t i o n with previous work; however, t h e n a i n purpose of the p r o j e c t was t o i n v e s t i g a t e the u t i l i t y of s t a b l e t r a c e r s and t o develop procedures t o make t h e method acceptable and p r a c t i c a l f o r p l a n t operators.
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EXPERIEIENTAL DETAILS Tracer Selection Post-sampling a c t i v a t i o n a n a l y s i s d i f f e r s from conventional radioa c t i v e t r a c e r work i n s e v e r a l respects.
hbereas i n t h e c a s e of r a d i o a c t i v e
t r a c e r s i n stream s t u d i e s i t i s h e l p f u l t o have comparable i n e r t m a t e r i a l present t o avoid r a d i o c o l l o i d formation and excessive f r a c t i o n a t i o n , the use of s t a b l e t r a c e r s r e q u i r e s the choice of a n a t e r i a l t h a t i s normally c m p l e t e l y absent from t h e water under t e s t .
Since the amount of i n e r t
t r a c e r used i s governed e n t i r e l y by considerations of expected d i l u t i o n , d e t e c t a b i l i t y , and c o s t , i t i s important t o s e l e c t a m a t e r i a l t h a t i s environmentally acceptable and completely non-toxic i n t h e concentrations expected.
Since sewage i s n o t n a t u r a l l y ingested, only e f f l u e n t concentra-
t i o n s need be considered h e r e .
Another important d i f f e r e n c e conpared w i t h
r a d i o t r a c e r s l i e s i n the choice of t h e a c t i v a t e d isotope.
A f t e r sampling,
the t e s t sample i s exposed t o neutross i n a r e a c t o r and the induced a c t i v i t y is d e t e c t e d and counted.
To be r e a d i l y detected t h e t r a c e r must have
a high thermal neutron cross s e c t i o n and a good s p e c i f i c a c t i v i t y a f t e r
activation.
This implies a f a i r l y s h o r t h a l f l i f e , c e r t a i n l y much s h o r t e r
than would be convenient for r a d i o t r a c e r f i e l d tests.
I n a d d i t i o n , the
g a m rays emitted should be r e a d i l y discriminated a g a i n s t those from o t h e r t r a c e elements normally present i n t h e waste waters, notably s o d i m , t h a t w i l l be a c t i v a t e d a t t h e same time.
E V a U ~ OF ~ ~WA OST~EWATER TREATMENT PLANTS
311
h%en p a r t i c u l a t e s a r e t o b e l a b e l e d , f i r m attachment of t h e t r a c e r i s
sought.
I n flow measurements, where t h e t r a c e r i s used i n d i s s o l v e d form,
n i n h m a b s o r p t i o n o r adsorption on any p a r t i c u l a t e s p r e s e n t i s d e s i r e d . Another important f a c t o r i s t h e p o s s i b l e p r i o r presence of t h e same element
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in the system t o be s t u d i e d .
Complete absence would be b e s t , of course,
b u t i t may o f t e n be p o s s i b l e t o s u b t r a c t o u t any e x i s t i n g known background
as long a s i t i s n o t excessive.
Manganese f a l l s i n t h i s category, a s i t
has a p p r o p r i a t e n u c l e a r and o t h e r p r o p e r t i e s , b u t i t i s found almost i n v a r i a b l y i n t h e waters of t h e A t l a n t a a r e a .
Some p o t e n t i a l l y u s e f u l e l e -
ments a r e q u i t e expensive and t h i s may l i m i t t h e i r use.
The following elements were considered a s p o t e n t i a l t r a c e r m a t e r i a l s
on account of t h e i r high neutron c a p t u r e c r o s s s e c t i o n s , u, s u i t a b l e gammaray emission, and probable absence frcm l o c a l waters: scandium:
Sc-45 (u = 13b); Sc-46 (t
84d)
cobalt:
Co-59 (a = 19b); Co-60 ( t
5.3 y r )
indium:
In-115 (ueff = 1.47b);
cerium:
Ce-142 (aeff = O.llb); Ce-143
tantalum:
Ta-181 (a = 21b); Ta-182 (
.4
k
In-ll&(t
4 (t 4
%
53.7 rnin) 33.7 h r )
dl
Chrmium, molybdenm, and bromine were aJso used.
No i n d i c a t i o n of any t o x i c i t y i n d i l u t e s o l u t i o n h a s been found in t h e
l i t e r a t u r e f o r e i t h e r indium o r scandiun, n o r any of t h e o t h e r s above under the conditions prevailing. Tanning T e s t s I n waste treatment p l a n t s i t i s of i n t e r e s t t o determine both t h e normal stream flow p a t t e r n s a s well a s t h e behavior and p o s s i b l e f r a c t i o n a t i o n of any suspended s o l i d s and sedimentary matter.
For t h i s reason
CRAFT AND EICHHOLZ
312
t e s t s were conducted b o t h on s o l u b l e t r a c e r s and on t h e i n c o r p o r a t i o n of
t r a c e r m a t e r i a l i n t o n a t u r a l o r simulated p a r t i c u l a t e s . Laboratory experiments have been performed t o e v a l u a t e t h e e a s e and e f f e c t i v e n e s s of i n c o r p o r a t i n g a t r a c e r element i n t o o r g a n i c ' a n d i n o r g a n i c
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particles.
F o r t r a c e r t e s t s on suspended matter one r e q u i r e s a b a t c h of
p a r t i c l e s of chosen s i z e each c o n t a i n i n g s m e t r a c e r atoms a t t a c h e d so f i m l y t h a t they would n o t b e d i s s o l v e d away o r leached o u t on prolonged exposure t o water.
The d e n s i t y as w e l l as t h e s i z e of t h e l a b e l e d p a r t i -
c l e s should b e t h e same as t h o s e of t h e whole group of p a r t i c l e s whose movement i s t o b e t r a c e d . Vermiculite It had been demonstrated p r e v i o u s l y t h a t t h e high c a t i o n exchange c a p a c i t y of v e r m i c u l i t e can b e u t i l i z e d i n t h e p r e p a r a t i o n of r a d i o a c t i v e Ground v e r m i c u l i t e i s s l u r r i e d w i t h a s o l u t i o n of t h e
tracer particles."
t r a c e r c a t i o n , d r i e d , c a l c i n e d , and reground.
The d e s i r e d s i z e f r a c t i o n s
a r e o b t a i n e d by s i e v i n g .
Scandium and indium on v e r m i c u l i t e have now been
p r e p a r e d by t h i s method.
Other inorganic c a r r i e r s studied included kaolin,
g l a s s f r i t , and b o t t l e g l a s s . Ten grams of v e r m i c u l i t e ground t o p a s s a 100 mesh s c r e e n w e r e s l u r r i e d f o r s e v e r a l h o u r s i n w a t e r c o n t a i n i n g 20 mg of indium s u l f a t e .
After
s t a n d i n g o v e r n i g h t , t h e l i q u i d w a s decanted and t h e s o l i d r e s i d u e transferred t o a quartz dish.
It was d r i e d under a h e a t lamp and then h e a t e d t o 2050°F
i n a muffle furnace.
mill.
A f t e r c o o l i n g , t h e s i n t e r e d mass was ground i n a b a l l
Neutron a c t i v a t i o n a n a l y s i s of water i n which t h e ground s o l i d was
soaked f o r s e v e r a l days showed a n e t count r a t e of z e r o compared t o 44,000 f o r s o l i d i r r a d i a t e d s i m u l t a n e o u s l y , confirming t h e h i g h s t a b i l i t y of t r a c e r attachment.
T h i s p r o c e d u r e h a s a l s o been used with scandium a s t h e
E.~~~ATION
313
OF WASTEWATER TREATMENT PLANTS
l a b e l i n g e l e n e n t and with k a o l i n a s t h e s u b s t r a t e .
sults.
A 1 1 gave s i m i l a r re-
The h i g h r e s i s t a n c e t o l e a c h i n g i s b e l i e v e d due t o d i f f u s i o n of
t r a c e r i n t o t h e p a r t i c l e s and a l s o a s u r f a c e m e l t i n g of t h e p a r t i c l e s , o f f t h e a c t i v e exchange s i t e s .
11 Previous work i n t h i s l a b o r a t o r y
bas shown t h a t i n v e r m i c u l i t e t r e a t e d i n t h i s manner t h e t r a c e r c o n c e n t r a -
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t i o n i s independent of p a r t i c l e s i z e , i n d i c a t i n g t h a t t h e attachment of t r a c e r i o n s i s n o t merely a f u n c t i o n of s u r f a c e a r e a .
GLass T r a c e r elements s t i r r e d i n t o molten g l a s s y i e l d p a r t i c l e s t h a t a r e very r e s i s t a n t t o l e a c h i n g .
The procedure c o n s i s t e d of m e l t i n g about 200
grams of b o t t l e g l a s s o r g l a s s f r i t (Pemco brand) i n a p o t f u r n a c e .
Bottle
g l a s s melted i n t h e range of 1000-2000°F. The t r a c e r element i n d r y form (indium s u l f a t e , molybdenum t r i o x i d e , s c a n d i m o x i d e ) was then s t i r r e d i n t o t h e melted glass.
A f t e r allowing the m e l t t o soak f o r a while, i t was
poured i n t o c o l d water.
The r e s u l t i n g s t r a n d s and p a r t i c l e s of g l a s s were
then ground i n a b a l l m i l l . Organic P a r t i c l e s I n t h e p r e s e n t work, o r g a n i c p a r t i c l e s t h a t have been s u b j e c t e d t o l a b e l i n g procedures i n c l u d e sewage s l u d g e , oatmeal, g r i t s , and wool.
The
g e n e r a l technique was t o s t i r t h e o r g a n i c p a r t i c u l a t e s i n t o a s o l u t i o n cont a i n i n g the d e s i r e d element.
Half of t h e m i x t u r e w a s b o i l e d while s t i r r i n g
and t h e remainder was s t i r r e d c o l d .
Wool w a s n o t t r e a t e d by t h i s technique,
b u t was mordant dyed, u s i n g t h e d e s i r e d c a t i o n as t h e mordant.
Effective-
n e s s of t h e l a b e l i n g procedure was e v a l u a t e d by a c t i v a t i o n a n a l y s i s of the P a r t i c u l a t e m a t t e r , t h e d e c a n t a t e , and s e v e r a l s u c c e s s i v e wash w a t e r s . A f t e r h a l f an h o u r t h e s o l i d s were allowed t o s e t t l e u n t i l a reasonably S m P l e of t h e W a t e r could be o b t a i n e d .
The s o l i d was then washed
with S e v e r a l p o r t i o n s o f w a t e r , each time s e p a r a t i n g t h e s o l i d s by set-
314
CRAFT AND EICHHOLZ Samples of t h e s o l i d , t h e i n i t i a l d e c a n t a t e , and t h e wash w a t e r s
tling.
were then analyzed f o r t r a c e r c o n t e n t . The r e s u l t s were n o t v e r y p r e c i s e due t o t h e v a r i a b l e m o i s t u r e content of t h e s l u d g e , b u t they gave t h e r e l a t i v e d i s t r i b u t i o n . o f t h e t r a c e r be-
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tween t h e s o l u t i o n and t h e s l u d g e in t h e form i t would b e u t i l i z e d .
The
r e s u l t s of s e v e r a l experiments are s m a r i z e d i n Table 1 f o r v a r i o u s na-
terials. ture.
There a p p e a r s t o b e no c l e a r - c u t advantage in b o i l i n g t h e m i x -
Grits seem t o b e a n u n s a t i s f a c t o r y medium f o r t h i s purpose.
EXPERPIENTAL PROCEDURE To compare t h e t r a c e r method w i t h the dye method, tracer s o l u t i o n and
a dye were r e l e a s e d s i m u l t a n e o u s l y f o r most t e s t s .
The appearance of t h e
dye marker a t the p o i n t of i n t e r e s t a l s o s e r v e d t o s t a r t t h e sampling procedure.
Rhodine 6B w a s used a s t h e dye marker i n most c a s e s .
The dye
i t s e l f r a r e l y gave q u a n t i t a t i v e i n f o r m a t i o n in t u r b i d streams o r h i g h l y
TABLE 1 R a t i o of S o l i d s / D e c a n t a t e Indium C o n c e n t r a t i o n s i n Labeling Experiments Substrate
Lhboiled
Boiled
Sewage Sludge
3.8
1.54
Oatmeal
1.64
2.02
Oatmeal
1.45
0.81
Grits
1.90
0.80
Grits
0.32
0.92
G r i t s (cobalt tracer)
0.36
0.69
315
E V ~ ~ J J A T I O NOF WASTEWATER TREATfIENT PLANTS colored wastes but i t s appearance was q u i t e v i s i b l e i f a l a r g e amount
A f l u o r e s c e n t dye, such a s Rhodamine
(400 grams) was added t o t h e stream.
{a,&ich
r e l i e s on a f l u o r m e t e r f o r i t s d e t e c t i o n , has been found unsuit-
able f o r t h i s type of a p p l i c a t i o n .
Tracer measurements on both the l i q u i d ,
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using a s o l u b l e t r a c e r such as sodium bromide, and on suspended material have been conducted.
These tests i n sone cases have indicated t h e e x i s -
tence of appreciable v a r i a t i o n s i n flow paths and residence t i n e s . For conparison, a f e w t e s t s have employed a r a d i o a c t i v e t r a c e r , such a s 15-hour sodim-24, t o p o i n t up t h e advantages and disadvantages of the two procedures. ployed.
A s c i n t i l l a t i o n probe and single-channel s c a l e r were em-
Fig. 1 shows t h e r e s u l t s of one p a r t i c u l a r t e s t which conparedthe
flow p a t t e r n through a sedimentation basin.
The s c i n t i l l a t i o n d e t e c t o r
readings represent on-the-spot measurement of t o t a l r a d i o a c t i v i t y from the Na-24 t r a c e r ; t h e single-channel analyzer readings r e f l e c t subsequent o f f s i t e measurement of samples. tically significant.
The divergences seen a r e probably n o t s t a t i s -
From a p r a c t i c a l p o i n t of view, the most important
drawback of r a d i o t r a c e r s compared with a c t i v a b l e t r a c e r s l i e s i n the license requirements f o r t h e anploynent of t h e r a d i o t r a c e r ; i t i s n o t immedia t e l y evident t o h a t e x t e n t a municipal u t i l i t y could o r would obtain a l i c e n s e t o possess and use a r a d i o a c t i v e t r a c e r m a t e r i a l f o r such a purpose. A l s o , t h e i n j e c t i o n of t h e t r a c e r r e q u i r e s considerable c a r e i n shipping
and handling of the source container. Neutron Activation Analysis Sample a n a l y s i s i n a l l cases was done by conventional procedures i n the Georgia Tech Research Reactor v i a the pneumatic tube f a c i l i t y .
All
sanples t o be analyzed were placed i n polyethylene v i a l s , heat-sealed t o prevent leakage and i r r a d i a t e d i n batches of s i x v i a l s .
The a v a i l a b l e
CRAFT AND EICHHOLZ
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316
2
thermal n e u t r o n f l u x was a b o u t 7 x 1 O I 2 n/cm s e c and t h e i r r a d i a t i o n t i m e
’ ,
was s e l e c t e d t o p r o v i d e a s u i t a b l e count r a t e f o r t h e expected c o n c e n t r a t i o n of t h e p a r t i c u l a r element unde;
consideration.
F o r indium, a n i r r a d i -
a t i o n p e r i o d of one t o f i v e minutes produced s u f f i c i e n t a c t i v i t y f o r counti n g p e r i o d s of 100-200 sec l i v e t i m e .
Samples were counted on a 60 c c
Ge(Li) d e t e c t o r used i n c o n j u n c t i o n w i t h a 1024-channel a n a l y z e r , h i c h was i n t e r f a c e d w i t h a s m a l l computer t o c a l c u l a t e t h e n e t c o u n t s under any given photopeak.
To d e t e r n i n e t h e s u i t a b i l i t y of v a r i o u s m a t e r i a l s , b o t h a s s o l u b l e t r a c e r s and a s adsorbed tracers on p a r t i c u l a t e s , a c t i v a t i o n a n a l y s e s were run on blank water samples and on s p i k e d s o l u t i o n s .
The b l a n k s a a p l e s es-
,
E-~~~t\~ION
OF WASTEWATER TREATPENT PLANTS
317
tablished t h e p r e s e n c e o r absence of background t r a c e c o n c e n t r a t i o n s i n local u ~ t e rsamples f o r t h e element concerned.
The s p i k e d s a n p l e s s e r v e d
determine t h e s e n s i t i v i t y of t h e s e l e c t e d a c t i v a t i o n procedure f o r t h a t t o c a l i b r a t e the g a m a - r a y s p e c t r m e t e r , and t o i n d i c a t e any i n -
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t e r f e r i n g a c t i v i t y peaks from o t h e r t r a c e elements. Sampling Procedure For f i e l d tests a t sewage t r e a t m e n t p l a n t s , l i q u i d samples were c o l l e c t e d f r m t a n k s , channels, and o t h e r l o c a t i o n s by dipping with simple long-handled sample cans, t h a t w e r e capable of s t a n d i n g up s a f e l y .
The
c o l l e c t e d samples are subsequently t r a n s f e r r e d t o one ml p o l y e t h y l e n e v i a l s by a d i s p o s a b l e p i p e t t e a t t a c h e d t o a 1 0 - m l s y r i n g e .
Cross-contamina-
t i o n i s p o t e n t i a l l y a s e r i o u s problem and t h e p l a s t i c v i a l s cannot be reused. During a r u n , t h e sampler was r i n s e d i n t h e l i q u i d t o be sampled a few seconds b e f o r e t h e moment of c o l l e c t i o n .
A f t e r t h e sample was obtained,
t h e p i p e t t e was then r i n s e d with one o r two p o r t i o n s of t h e s a n p l e , and t h e desired sanples pipetted i n t o the v i a l s .
The sample w a s s t i r r e d w i t h t h e
p i p e t t e i f any r a p i d l y - s e t t l i n g s o l i d s were observed.
Duplicate o r t r i p l i -
c a t e samples were c o l l e c t e d , and t h e v i a l s c l o s e d w i t h t h e i r a t t a c h e d l i d s . They were then ready f o r t r a n s p o r t a t i o n t o t h e l a b o r a t o r y f o r a n a l y s i s . Idhen t h e s o l i d s c o n t e n t of a flow was t o b e c o n s i d e r e d s e p a r a t e l y
from t h e l i q u i d , l a r g e r samples were r e q u i r e d .
P i n t milk b o t t l e s were used
and were f i l l e d by dipping where needed. In the l a b o r a t o r y t h e s e samples were f i l t e r e d by s u c t i o n i n a Buchner
funnel.
A f t e r a l l t h e l i q u i d had passed through, t h e f i l t e r paper was
f o l d e d and f o r c e d i n t o an i r r a d i a t i o n v i a l .
P o r t i o n s of the s u p e r n a t a n t
were p i p e t t e d i n t o o t h e r v i a l s f o r s e p a r a t e a n a l y s i s .
CRAFT AND EICHHOLz
318
EXPERDINTAL RESULTS Tracer Selection I t was found t h a t indium i n t h e form of indium s u l f a t e o r n i t r a t e was
t h e most convenient i n e r t t r a c e r .
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each t e s t .
About 25 grams of compound were used in
Indium i s n o n - t o x i c and n o t p r e s e n t i n normal waste streams.
It was a l s o found t h a t indium can b e used t o l a b e l s l u d g e f o r t e s t
work on s e d i m e n t a t i o n b a s i n s .
F o r t h i s purpose, approximately t h r e e g a l -
lons of s l u d g e were c o l l e c t e d from t h e sump a t t h e s e d i m e n t a t i o n b a s i n and p l a c e d i n a f i v e g a l l o n can.
Ten grams of i n d i m (as t h e s u l f a t e ) d i s -
s o l v e d i n a l i t t l e w a t e r were added, and t h e m i x t u r e w a s h e a t e d almost t o b o i l i n g o v e r a p o r t a b l e propane f u r n a c e . t h e h a l f hour heating period.
The m i x t u r e was s t i r r e d d u r i n g
The odors produced by t h i s procedure were
u n d e s i r a b l e and i t was found l a t e r t o b e unnecessary t o b o i l t h e s l u d g e . Flow Measurements Flow measurements have been made i n sewer s y s t a n s t o determine f l o w times and t o d e t e c t any hold-up o r blockage.
T r a c e r measurements on t h e
l i q u i d , u s i n g NaBr a s s o l u b l e t r a c e r , and on suspended m a t e r i a l s were conducted.
These t e s t s demonstrated t h e s u i t a b i l i t y of t h i s approach and i n -
d i c a t e d t h e e x i s t e n c e of a p p r e c i a b l e v a r i a t i o n s i n flow p a t h s and r e s i d e n c e times i n some c a s e s . Movement of A c t i v a t e d S l u d g e A t e s t was conducted t o o b t a i n i n f o r n a t i o n on flow c o n d i t i o n s i n a n
a c t i v a t e d s l u d g e tank.
A t t h e time of t h e s t u d y , t h e flow r a t e through the
tank i n v o l v e d was a b o u t 5 m i l l i o n g a l l o n s / d a y OIGD), which i n c l u d e d 1 EIGD of r e t u r n s l u d g e .
The placement of t h e a i r d i f f u s e r s i n t h i s tank produces
a r o l l i n g motion i n t h e l i q u i d , and a given p a r t i c l e presumably moves i n a
s p i r a l f a s h i o n from t h e i n l e t t o t h e o u t l e t of t h e tank.
The t h e o r e t i c a l
E
~
a
~ OF ~ WASTEWATER ~ ~ O N TREATMENT PLANTS
319
detention time was about 2 1 / 2 hours and t h e suspended s o l i d s i n t h i s sysaveraged about 2300 mg/L. It was thought t h a t the vigorous motion of t h e tank contents would
produce a l a r g e amount of mixing and concomitantly a high d i l u t i o n of t h e added t r a c e r .
Referring t o F i g . 2 , i t w i l l be seen t h a t s m e longitudinal
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nixing occurred so t h a t t h e i n i t i a l concentration of 63 ppb decreased f o r
35 minutes a t which time a very high peak (130 ppb) appeared, representing an unmixed zone. The i n d i m l e v e l decreased gradually t h e r e a f t e r w i t h a small, presumably i n s i g n i f i c a n t , f l u c t u a t i o n near the two hour t i n e .
A t the half way s t a t i o n ,
140
110
100
L
L
5-
ao
c
L I-
2
60
z 0 0
'2
40
I
a0
01 0
10
60
40 TIME
I
I
t
80
100
120
MINUTES
FIG. 2 Activable Tracer Test on Sludge Basin
CRAFT AND EICHHOLZ
320
a s i m i l a r p a t t e r n was noted.
The maximum concentration t h e r e was only 70
ppb and occurred 15 minutes a f t e r the maximum a t t h e q u a r t e r location.
Two v i a l s were f i l l e d from t h e sampler a t each time i n t e r v a l , and agreement between the two p o r t i o n s was l e s s s a t i s f a c t o r y than f o r other experinents.
The lack of consistency may have been due t o v a r i a t i o n s It i s believed t h a t a
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caused by t h e r a p i d l y - s e t t l i n g s o l i d s present.
l a r g e portion of the t r a c e r was absorbed by t h e s o l i d s p r e s e n t , and any d i f f e r e n c e i n t h e amount of s o l i d s t r a n s f e r r e d t o d u p l i c a t e v i a l s would cause l a r g e d i f f e r e n c e s i n the observed r e s u l t s . Trickling F i l t e r Studies One of the l o c a l treatment p l a n t s had been having d i f f i c u l t y f o r some time with t h e i r t r i c k l i n g f i l t e r .
Ponding was evident, b u t more impor-
t a n t l y , t h e BOD reduction across t h i s f i l t e r was e s s e n t i a l l y zero.
Gas
production of both d i g e s t e r s was f a r below normal l e v e l s and a common cause of these d i f f i c u l t i e s was suspected.
This provided an opportunity
f o r comparison of the flow p a t t e r n through a badly clogged f i l t e r with the normal p a t t e r n t o be obtained a t a l a t e r d a t e a f t e r t h e f i l t e r had been r e s t o r e d t o normal operation.
The t r a c e r t e s t s were c a r r i e d out using indium a s t h e a c t i v a b l e mat e r i a l p l u s Rhodine 6B f o r v i s u a l observation.
The t r a c e r s o l u t i o n was
poured i n t o the dosing box of t h e f i l t e r and samples were c o l l e c t e d a t the f i l t e r o u t l e t and a t t h e c e n t e r ( i n l e t ) and r i m ( o u t l e t ) of both secondary clarifiers.
The r e s u l t s of the f i r s t t e s t a r e shown i n Fig. 3 .
The curve
labeled "A" represents the concentration of t r a c e r a t the f i l t e r o u t l e t , which i s about e i g h t f e e t below grade l e v e l .
The flow a t t h i s point was
apparently n o t very well mixed a s the dye t r a c e r was more concentrated a t the c e n t e r of the stream of e f f l u e n t .
More thorough mixing occurs i n the
downstream pipes which d i v i d e and d e l i v e r t h e l i q u i d t o the c e n t e r of the secondary c l a r i f i e r s .
I f the flow were completely mixed, the maximum con-
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EVALUATION OF WASTEWATER TREATMENT PLANTS
L 0
1
IS
10
IO
ao
IS
uinuita
is711
TIACCE
32 1
as
40
iwtciio*
FIG. 3 Tracer Test on Trickling F i l t e r
c e n t r a t i o n would be the same a t t h e f i l t e r o u t l e t and the c l a r i f i e r i n l e t s . Similar t e s t s were conducted a t o t h e r treatment p l a n t s .
A discussion of
the operational aspects of these t e s t s w i l l be found elsewhere.
12,13
Sludge S e t t l i n g T e s t s A t t h e o u t l e t of t h e sedimentation basin of another treatment p l a n t , p a r t i c u l a t e m a t t e r was observed passing over t h e weir and t o the p l a n t outEall.
In order t o study t h i s s i t u a t i o n more f u l l y , sludge was labeled with
a t r a c e r and t h e concentration i n the e f f l u e n t measured a s a function of time. The labeled sludge was poured i n t o the i n l e t on t h e e a s t s i d e of t h e sedinentation basin and t h i s was followed by a gallon of water containing
CRAFT AND EICHHOLZ
322 200 grams of Rhodine 6B.
Color appeared i n t h e e f f l u e n t a t 24 minutes and
Quart samples were obtained a t 3 minute i n t e r v a l s .
sampling was begun.
A t 2 minute i n t e r v a l s d u p l i c a t e 1 ml samples were c o l l e c t e d .
No dye c o l o r
was e v i d e n t anywhere i n t h e b a s i n except a t t h e o u t l e t , and s a p l i n g was continued u n t i l t h e c o l o r of t h e e f f l u e n t had faded t o a low l e v e l .
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A t t h e l a b o r a t o r y , t h e q u a r t samples were f i l t e r e d by s u c t i o n and the
Samples of the f i l t r a t e were a l s o
s o l i d m a t t e r c o l l e c t e d was analyzed.
analyzed and found t o c o n t a i n i n d i m , although a t a much lower concentra-
The r e s u l t s of t h e s e a n a l y s e s a r e shown i n F i g . 4 .
t i o n than t h e s o l i d s .
The c o n c e n t r a t i o n of t r a c e r i n t h e sludge i s seen t o f l u c t u a t e i n a v e r y s i m i l a r f a s h i o n although n o t e x a c t l y i n phase with those of t h e sludge.
‘i
5
5U f, U llr
m
60
-
50
-
40
-
20
-
10
-
SUPERNATANT
0 -
a! I-
! SLUDGE
:
20
30! 10
I
I
I
MINUTES
I
I
AFTER
TRACER
I
INJECTION
FIG. 4
Tracer Measurements on Sedimentation Basin
323
E V a ~ ~ ~OF~ W OASN TEWATER TREATMENT PLANTS
This p a t t e r n of behavior i s i n d i c a t i v e of a p a t t e r n of r e c i r c u l a t i o n , w i t h a period of n i n e minutes.
There was nothing about t h i s basin that ac-
counted d i r e c t l y f o r these r e s u l t s .
The sludge scraping mechanism moves
slowly and continuously and does n o t seem capable of producing t h i s pattern.
It i s p o s s i b l e t h a t t h i s c u r r e n t produced a r o l l i n g motion a s i t
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hpinged upon t h e o u t l e t wall of t h e basin.
P a r t of the flow would e x i t
Over t h e weir and the balance would r o l l back toward t h e basin i n l e t .
Each
time t h i s mass of water r o t a t e d , t h e t r a c e r concentration would be lessened by the amount previously l o s t , and by d i l u t i o n . In an attempt t o c l a r i f y t h i s s i t u a t i o n , the experiment was repeated, the only d i f f e r e n c e s being t h a t indium s o l u t i o n was s t i r r e d i n t o t h e sludge without heating and samples were c o l l e c t e d a t one minute i n t e r v a l s .
The
r e s u l t s of t h i s second run i n d i c a t e d a p a t t e r n t h a t was e n t i r e l y d i f f e r e n t from t h a t of t h e f i r s t t e s t .
The r e c i r c u l a t i o n p a t t e r n was abs'ent and
t r a c e r concentrations rose t o a r a t h e r i l l - d e f i n e d maximum and then gradua l l y decreased. As o t h e r conditions about t h e basin appeared t o be t h e same a s previ-
ously, t h e maximum t r a c e r concentrations of t h e two runs a r e taken a s some indication of t h e efficiency of s o l i d s c o l l e c t i o n .
The second s i t u a t i o n
when the indium maximum was only about 1 2 ppm i s taken t o i n d i c a t e b e t t e r operation of t h e basin than i n t h e f i r s t t e s t where t r a c e r concentration went above 30 ppm. CONCLUSIONS
The r e s u l t s reported h e r e have shown t h a t s t a b l e t r a c e r s followed by neutron a c t i v a t i o n a r e a convenient means of i n v e s t i g a t i n g operational cond i t i o n s i n sewage treatment p l a n t s .
The sampling procedure is simpleenough
t o be han'dled by t y p i c a l p l a n t personnel.
The method r e q u i r e s access t o a
324
CRAFT AND EICHHOLZ
n e u t r o n a c t i v a t i o n f a c i l i t y where a n a l y s e s can be done a t a c c e p t a b l e c o s t and would n o t be done on a r o u t i n e b a s i s unless t h e r e are grounds t o susp e c t s e v e r e malfunction i n t h e p l a n t .
I n d i m and scandium s a l t s have
proved t o b e s a t i s f a c t o r y tracer elements g i v i n g adequate s e n s i t i v i t y so t h a t material c o n s m p t i o n can b e k e p t t o a r e a s o n a b l e l e v e l .
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ACKNOWLEDBIENTS
This work w a s done with t h e s u p p o r t of t h e
D i v i s i o n of I s o t o p e Devel.
opment, U. S. A t o m i c Energy Conrmission under C o n t r a c t No. AT-(40-1)-4156. The a s s i s t a n c e of S. N . Plillspaugh and T. PI. Galbreth i n many of t h e f i e l d experiments and sample a n a l y s e s w a s i n v a l u a b l e .
The c o o p e r a t i o n and a c t i v e
s u p p o r t of the s u p e r i n t e n d e n t and personnel of t h e Water P o l l u t i o n Control D i v i s i o n of the C i t y of A t l a n t a and t h e Clayton County Water A u t h o r i t y a r e
W e a r e i n d e b t e d t o D r . R. S. I n g o l s f o r h i s ad-
g r a t e f u l l y acknowledged.
v i c e and many u s e f u l s u g g e s t i o n s . REFERENCES
1.
"Selected Techniques i n \dater Resources I n v e s t i g a t i o n s . " Paper 1892. U. S. Geological Survey, Washington, D. C . ,
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J . F. Wilson, "Fluorometric Procedures f o r Dye Tracing." Water Res o u r c e s I n v e s t i g . Book 3 , ch_apter A12. U. S. Geol. Survey, Washington! D. C . , 1968
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G. G. Eichholz, 14. B. Pluir, PI. J. Bennett, J. D. Wild, C. Lawton, and S. Plostowy, "Radioactive T r a c e r I n v e s t i g a t i o n s i n a F l o t a t i o n Circuit.' Trans. Can. I n s t . Mining Met. 60, 63-69 (1957)
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R. P. Gardner and R. L. Ely, "Radioisotope Pleasurenent A p p l i c a t i o n s i n Engineering." Reinhold Publ. Corp., New York, 1967
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P. Kruger, " P r i n c i p l e s of A c t i v a t i o n A n a l y s i s . New York, 1971
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EVALUATION OF WASTEWATER TREATMENT PLANTS
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P. Kruger, % c t i v a b l e Rare Earth Elements as Estuar i n e Water Tracers." 5th I n t e r n . Conf. Water P o l l u t i o n Research, pergaaon, Amsterdam, 1971 J. K. Channel1 and
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T. F. C r a f t and G. G. Eichholz, 'Tlechanism of Rapid F i l t r a t i o n i n a
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T. F. C r a f t , G. G. Eichholz, and S. N . Millspaugh, "Evaluation of T r e a b e n t P l a n t s by Tracer Nethods." Rept. Om-4156-2, U. S. Atomic Energy Commission, 1973
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T. F. C r a f t and R. S . Ingols, 'Flow Through Tine i n T r i c k l i n g F i l t e r s . " Water and Sewage Works 120 (l), 78-79 (1973)
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6,
527-537 (1970)
Received Narch Accepted A p r i l
14, 1975 1, 1975
