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.

"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 . ,

Water Supply 1968

2.

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

3.

"Guidebook on Nuclear Techniques i n Hydrology." Techn. Reports S e r i e s No. 91, I n t e r n a t . A t m i c Energy Agency, Vienna, 1968

4.

"Isotope Hydrology 1970." Proc. Vienna Symp. I n t e r n a t . Atmic Energy Agency, Vienna, 1970

5.

"Isotope and Radiation Techniques i n S o i l P h y s i c s and I r r i g a t i o n S t u d i e s . " I n t e r n a t . Atomic Energy Agency, Vienna, 1967

6.

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)

7.

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

8.

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

-

'I

Wiley-Interscience,

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EVALUATION OF WASTEWATER TREATMENT PLANTS

9.

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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

10. D. F. Gatz, A. N. Dingle, and J . W. Winchester, "Detection of Indium a s an Atmospheric Tracer by Neutron Activation." J. Appl. Meteor. t?, 229-235 (1969)

11.

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

12.

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)

Uniform F i l t e r Bed."

Water Resources Research

6,

527-537 (1970)

Received Narch Accepted A p r i l

14, 1975 1, 1975

The use of activable tracers in the evaluation of the performance of wastewater treatment plants.

The use of stable, activable tracers has been studied in applications to establish the performance of waste treatment plants and detect causes of irre...
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