Material balances of organics and nutrients in an oxidation pond

";~,)z'er Re~ Vo[. 18. No. 3, pp. 325-333, 1984 Pnnted m Great Bntain

,'-~3-~x54 8-t 53 i.~- ,.2i.~) P~-r~:~mc,n Press Lid

MATERIAL BALANCES OF ORGANICS AND NUTRIENTS IN AN OXIDATION POND ISAO SOMIYA a n d SH1GEO FUJII Department of Sanitary Engineering, Faculty of Technology, Kyoto Uni'.ersi D. Kyoto City. Japan (Receired June 1983)

A~tract--A series of experiments concerning a tertiary' oxidation pond v, as performed from 10 January to 12 November 1979, using a model oxidation pond of 21 m ~ in capacity. The concentrations of organics and nutrients in influent and pond water were measured so as to consider the conversion of water quality in a tertiary oxidation pond. The sedimentation rates were measured weekb, and the final sediments ~ere analyzed at the end of experiments, so that the material balances in respect to carbon, nitrogen and phosphorus were calculated and the various transition reactions were evaluated quantitatively. The result of the material balances showed that there were three main reactions in pond: the assimilation to algae: the sedimentation of suspended substance; and the decomposition of sediments. The regeneration rates of nutrients from sediments were so active that the removal of nutrients by algal solidification were not effective. Consequently, the overall removal efficiency of nutrients was 45"° in total nitrogen and 4Y',, in total phosphorus by a tertiary' oxidation pond with 16 days detention time. Key words--oxidation pond, material balance, carbon, nitrogen, phosphorus, tertiary treatment, algae. setiiments, assimilation, sedimentation, regeneration

INTRODUCTION The oxidation p o n d has been widely employed in small c o m m u n i t i e s as a primary or secondary treatment device. Recently, some research works ( L e o h r and Stephenson, 1965; Public C o r p o r a t i o n , 1970; Potten, 1972; Fujii et al., 1972; G r a b o w a n d Middendorff, 1973) on oxidation p o n d s were performed in the field o f tertiary t r e a t m e n t process with the intention of wastewater renovation a n d the removal of residual organic pollutants and nutrients. After those research works, it was found t h a t this t r e a t m e n t process has such characteristics as the i m p r o v e m e n t of the epidemiological safety by bacteria die-off, the removal of residual BOD, the buffering action to toxic substances etc. A l t h o u g h the capacity o f nutrients removal by the oxidation p o n d has been often stated, there is very little i n f o r m a t i o n on how effective an oxidation p o n d is on the removal of nutrients. In T a b l e 1, the results on organics a n d nutrients removal efficiencies o b t a i n e d from some experiments on tertiary oxidation p o n d s are summarized. As s h o w n in Table 1, the removal efficiency varies widely at each case and the reason of this variance left obscure. The purpose of this study is to clarify the reason o f variance on removal efficiencies a n d to evaluate the t r a n s f o r m a t i o n fluxes of nutrients a n d c a r b o n a c e o u s materials t h r o u g h the experiment d a t a analysis in an oxidation pond. T h e test pilot plant o f a n oxidation pond was set up in a modified model channel. Since the organic load applied to the test p o n d was very low, the pond was kept to the typical aerobic condition. As fish were not b r o u g h t into the pond, its

purification m e c h a n i s m was expected to bc mainly governed by the solidilication reaction by' algal photosynthesis and chemical reaction. EXPERIMENTAl. PROCEDURE ANt) METiIOt)S

The experiment was performed at Biwako Water Pollution Research Laboratory located beside Lake Biwa (Otsu City). The prepared dimensions of the oxidation pond is 0.75 m in depth, [.00 m in width and 28.00 m in length. Its schematic layout is shown in Fig. I as Pond I-Pond 4. The secondary effluent from the activated sludge process was introduced as the influent, and its flow rate was controlled to be 1.31 m s day -* that corresponded to 16 days detention time. The experiment started on 10 January and finished on 12 November 1979. The influent was, however, accidentally stopped during the period 26 July-I September owing to trouble at the secondary' treatment plant. Water samples were taken at 4 days interval from 5 sampling points as shown in Fig. I (namely S-0, S-l, S-2, S-3, S--4). From April, some glass bottles without caps were set on the bottom bed of each pond to collect the sedimentation materials. The renewal of the bottles was carried out at two series; 8 days and l month interval. Furthermore, all sediments in the pond bottom were collected at the end of the experiment (12 November) and composition and quantity of sediments were analyzed. The methods and measured items of chemical analysis were listed in Table 2. PERFORMANCE OF THE PILOT OXIDATION POND T h e average c o n c e n t r a t i o n s of influent and pond waters over the whole experiment period are shown in T a b l e 3. As s h o w n in T a b l e 4, the inorganic c a r b o n (In-C) c o n c e n t r a t i o n s are determined on the basis of the alkalinity relationship a m o n g bicarbonate, carb o n a t e and hydrogen ion. while the organic c a r b o n (OC) c o n c e n t r a t i o n s are obtained from the linear 325

tsao SoMI'~A and SHIGEO FL:m

7" c -

£

-'5

-

m

:a

+..-

-2-

Z

_*

~

g

~:

~

?. ,.

~

,-7

-5

3=

-g

..

-=

E.g

~"

-':

-=

".5 "=

£

5

zj - a ,"C~

~"-

-

.~]

relationship between OC and chemical oxygen demand by Potassium Dichromate Reflux Method (CODcr). as sho,~n in Table 5 Chlorophyll-a (Chl-a}. that shows the amount of algae, increases with the detention time Accordin_ to the algal growth, pH values in ponds exceed 9. and D O concentrations reacn the supersaturatton condition that is more than [0rag Oz I- . The increase o f p H value in the pond would have a great influence on the behavior of carbon, nitrogen and phosphorus. Generally speaking, the fraction of molecular CO~,,, m total inorganic carbon concentration decreases considerably with the mcrease of pH value, so that the algal growth rate would be inhibited by the lack of inorganic carbon (King, 1970). Moreoser. the stripping of molecular NH3~q to atmosphere will easil~ occur. Meanwhile, the coagulation reaction between ortho-phosphate ion (PO]--P} and Ca:" ion bemns to take place in the range of pH values more man 9. Actually, the Ca 2~ concentration decreased slightly from 28,1 mg I -~ in influent to 25.1 mgl ~ in eFtuent. The behavior of organic substance can be investigated from the variance of the associated carbon concentrations in ponds, because carbon is the mare component of orgamcs, of which the content ~ relatively constant ranging l'rom 40 to 5Y' l-:rom Table 3. tt will be easily conceived that the main carbon component in inffuent is the morgamc carbon (In-C), while the organic carbon (OC) increases from 28'! o in the influent to 62'~,, in the effluent. This would mean that the rate of algal photosynthesis exceeded that o f bacterial decomposition m pond. The increase of O C did not occur only in the particle fraction (POC), but also in the soluble fraction (SOC}. The ln-C concentration varies seasonally according to algal activtty as shown in Fig. 2. Especially, the algal activity was high from March to June. The main n,trogen component in the influenl is nitrate ( N O { - N ) that occupies 72~?.o of influent nitrogen. but the high concentration of ammonia ( N H / - N ) is occasionally introduced into the ponds in March and October. as shown in Fig. 3. However.

S-O

S-I

Pond I - lpond't

S-2

Pond 2

S-3

S-4

IPond p' 3 PP o n d 4 l io

P,÷ llt F,f Ill I_

( Unit ; m )

7.00

~4

DeTention

= 28,()0 t~me

Volume

Surface Flow

4,0 ,5.25

area

--I clay

x 4

m 3 x 4

7 O 0 rn z x "~ 1.3

m3doy- '

Fig. I. Layout of the test pond.

Mate~ai

b a l a n c e s o f o r g a n i , . ~ a n d nut,'-ientx in a n o x m a ~ : o n p o n d

327

Tabie 2. Me:hods o f vamous ~ests of series Te~t

Interwai (~in>.~)

Date

Water analysis

i979 i !0 - [ i ~2

4 days ('5!

Sctding material anaiysi~

4 I - !1 i2

8 da'~s (26) 1 month

Sediment analysis

! I 12

Method~,

( 1)

\ l c a . a r e d indexe~,

Sample from each sampling tap

pH. DO. C a : ' , Chl-a. K.ie-N'. 1"-P', P()i P. N O - N. N O ,

Alkaliniiy CODvr* N H , - N. SS -N. Temp

Set the N:,ttle on the bottom of pond. and collect them after certain interval

i B~th ,amples) C'hl-a, ['-P, ( ' O D o r ([ month sample) Kje-N, In-P, SS

C(,tlect ),he sediments at the end of experiment, and analyze its mass and composition

SS. Chl-a. C O D e r , VSS ln-P. Kje-N

*Fihcred and unlihered samples v,ere analyzed.

Table 3. Mean qualities, o f intluent and pond ',),aters Unit

lnfluent

Pond 1

Pond 2

Pond 3

Pond 4

pl[ D() Chl-a C'a-' -

mgl ~ ug I ~ mgl ~

7.43 4.4 0 28.1

8,99 11 7 78 26.2

9.43 14.3 It)() 25.7

q~7 155 118 254

9.88 [66 136 25.4

T-C In-C SOC 1'()17

m g C l -~ m g C I -~ mg C 1 ~ mgC! ~

22.5 16.5 4.6 16

23.6 13.0 64 42

23.6 11.6 70 5.0

247 ]07 76 64

254 98 8.2 7.5

T-N NtL' N NO, N NO~ N S-N POrg-N

mgNI ~ mgNI ~ mg N I i m g N I -~ mgNl ) mg N I - )

10.69 1.70 0.27 7.66 10.41 o.28

T-P P()I S-P P-P

mgPl ~ mg p l t mg P I "' mg P I -~

P

0.751 0.461 0,538 0.203

8.16 0.82 1140 5-22 729 0.87

7.08 0.57 041 4.15 6.00 I ()~

6~0 it3'4 0.44 338 5.01 [3x

5.uo o 26 0.45 2.~3 4.40 1.50

0.554 0.301 0.377 0 I,~5

0482 0.219 0.292 0,198

0.462 0.186 0.253 0.208

0.430 0.154 11.223 0.213

Table 4. Calculation methods of carbon concentrations Condition Inorganic L-arbon

P>O (pH > 8.3) P-0 (pH < 8.3)

Equation (mg C I - ~ )

Ref.

0.2475, (M-P-6)

APHA

0 2403-(M-6 ')

Organic carbon

Terminology M - - A l k a l i n i t y (rag CaCO~ I -~ ) P--Alkalinity (rag CaCO~ I -~ ) d . 6 ' - - r e v i s e d ten'ns on other ions, nearly equal zero % C f ) ~ mole fraction

{19751

Park ( 19691

CODer

:~,---HCO~- mole fraction ( ; O D c r C O D e r (mgO_,l ~)

3

T a b l e 5. C O D c r , C ratio in organic materials

Material Plant G l o y n a ' s l't)rmula (algae) Osv, ald's formula (algae) Marine phytoptank ton A.Igae Euglena .grac¢lis Chtorella p.t'renoidaxa

Helmer's formula (bacteria) Eckenfelder's formula (bacteria Primary treatment wastewater . . ~ o n d a r y treatment wastewater Primary [reatmem v,aqewater Raw wastewater

Formula

C(% g SS -) )

COFxr :C

C~ ~ H~,)()4^ N j~ P C~ ~ H , ~ j O ~ N , ~ P C, I't, I O2 ~N C,:~ H : , ~O~ ,) N ~,~P C~ - H,, ~O z j N

40.3 5..4 57.4 35.8 53.0 44.8 49. I 53.0 531 ---

3.0 3.11 2.7 2, 7 ..9 3.0 .~.o " "~ 2.9 2,7 2.9-3.1 2.8-32 3.1 3._-3. J,

-C,,J-I)..O~, N~-P C,H,O:N --

--

Reference

O d u m ( 19741 Somiya (197X) Os'.,,ald ( 1963} H o g e t s u ( 19741 G o l m a n et aL (1972) Tsuda ( 1964} T s u d a 1t9641 G o d a 119761 G o d a ( 19761 A k l v a m a [1973) Ak y a m a (t9731 M a r u o ([9731 G o d a et al. (1974l

:2:}

ISAO ~r'JMIt'A a n d S~lo~o FUJll

50

--

(

!nfluenr )

H

T-C

30

<.j 20

~o -

0

5 40 5

Pond 41 ~ % ~

30 20

.,lll!~~L;,.~'i,

0 I ,,

3/

-'.-"<-'~~?'<'¢D3j= -'~ .,",",. 5 "'

7" /

~ ! t

I1

Fig, ,~, "~ V a r i a t i o n o f c a r b o n c o n c e n t r a t i o n .

the nitrification reaction and algal assimilation reaction of N H Z - N are active enough to maintain such low N H ; - N concentration as less than 2mg 1' t in the pond effluent. The average of total nitrogen concentration decreases from 10.69 m g N l -~ in the influent to 5 . 9 0 m g N I -* in effluent and the average removal efficiency ts 45~. The concentration of total phosphorus (T-P), soluble phosphorus (S-P) and soluble ortho-phosphorus (PO~,--P) decrease with the increase of detention time. The most remarkable reduction is observed on PO] -P and its removal efficiency is 67~/o. The particle phosphorus (P-P) does not increase in the ponds, and its concentration is relatively constant to the level of about 0.2 mg P 1-~. In seasonal variation, it may be the most characteristic that T-P concentration in influent exceeds 2 mg P 1- in June and October. but such peaks are not detected in the effluent (Fig. 4). MATERIAL BALANCE

Material balance model The behavior of carbon and nutrients in ponds is governed by various reactions including the exchange reactions between pond waters and sediments. In order to obtain the detail knowledge on nutrient and carbon behavior in the oxidation pond, the material balances of them have to be considered. Since each

element changes variously and intensi~et? in its existing chemical forms, it is almost imposslble to complete the material balance sheet based on!} on the experimental data obtained by field works. Hence the following assumptions and models are introduced. The period considered in the material balances Js the whole experimental time from t0 Januar~ ,:o <2 November. because the measurement of sediments mass and its composition has been performed o,'1t', once at the end of the experiment. Flow pattern. The hydraulic balance in an oxidation pond is normally governed by the influent ~ind effluent flow rate. and the rainfall and evapor~ltlon intensity. The rainfall effect on the water balance is evaluated quantitatively with the data measured at the test field site. The evaporation effect on the v, ater balance is. however, neglected, becau.~ it is esumatcd not to be noticeable in comparison with the influent flow rate. Actually, the evaporauon rate ts roughly estimated to be about 67~, of influent flow rate. since the annual average evaporation rate is reported as about 1000mmyr -~ bv Japan Meteorological Observatory. It will be suitable to apply a complete mix)ng model to the flow pattern of each pond. because of its shallow depth and its long detention time. The exchange flow of pond water between each compartment will be caused by man) factors, such as the diffusion, the temporary back mixing by wind and so on. Hence. the flow pattern in ponds is approximately expressed by the model shown in Fig. 5. The material balance on the preservative material iT-P) is roughly analyzed and the exchange ratio (a -0.69) is determined with the minimization of the sum of the deviations of the total storage value in ponds from the value calculated with the above flo~ model on T-P. Main reactions in pond water. The carbonaceous and nitrogeneous substances in pond water are classified into three fractions: soluble inorganic ion, suspended organics and soluble organics. The transformation from inorganic ion to suspended organics, that means the net production on biotic community in pond water, is taken into account in the material balance model. On the phosphorus materials, the}'

(Influenr)

g ,~

H

T-P

'r

.... [

( Pond 4 )

~

I ( Pond 4 )

5

~

0

L

I!1

31l

~,II

FII

91f

lllI

Fig. 3. Variation of nitrogen concentration.

0 ~ I/I

3/I

511

7/I

9/I

ii i i

Fig. 4. Variation of phosphorus concentraiiun.

Material baiance_'sof organics and nutrients in an oxldation pond R Q~

,I o_+e+ool

R

R

R

e~+Z.~+aQ I .q_+3R+oQ I ~,~+4R

!"4

O~ ; u n d o m e n t o i flow (i 3i m 3 d a y - )

Qo; influent flow i ! [0-7131

; ! 31 m 3

7/3!-9/I

;0

doy "~

rn 3 d a y -

9/I-II/12 ;1.31 m3cloy IR ; Ramfol! ( m 3 day -~ pond -~)

a ; Exchonge flow ratio Fig. 5. Flow pattern of the test pond. are classified into the different three fractions: soluble material, inorganic and organic suspended materials. Figure 6 shows the relationship between Org-P and carbon concentration in sedimentation materials. The concentration of Org-P is proportional to that of carbon, and its ratio (P C) is almost constant to 0.021 (that corresponds to 0.007 on P/CODer ratio). Hence, the concentration of Org-P can be approximately calculated from this ratio and CODer value. On the transformation of phosphorus substance, the following two reactions are considered. One is the chemical coagulation reaction on inorganic phosphorus. Another is the assimilation of soluble phosphorus to suspended organics. Furthermore, the following reactions have to be cunsidered: the regeneration from sediments, the assimilation of algae attached on the pond wall and the exchange between pond water and atmosphere. The last process involves the stripping of nitrogen gas which would be formed by the denitrification reaction in sediments, the ammonia-stripping caused by the increase of pH value in pond water and the absorption of carbon dioxide. Calculation ~)/eachfi,tx. An example of calculation methods on carbon balance is shown in Table 6, where Mougeotia (Chlorophyceae) is a filamentous alga that began to grow on the bottom bed of Pond I at the beginning of September. The growth activity of this alga is so high that its effect on material balances has to be taken into consideration. Its total weight and chemical composition were analyzed at the end of the experiment. The ct, lculation on nitrogen and phosphorus balance is performed by the same method as that of carbon. The flux of ammonia-stripping, that is the characteristic reaction of nitrogen, is calculated by the equation reported by Folkman and Wachs (1979).

Carbon balance The carbon balance of each pond is shown in Fig. 7 where the arrow line shows the flow of material and the width of each flux shows its magnitude, and the size of rectangle shape of each component shows its existing quantity averaged over the experimental period based on the assumption that each pond water is completely mixed_ From Fig. 7, it is obvious that the main reactions of carbon balance in oxidation pond are assimilation of In-C, sedimentation of

particle organics and regeneration from sediments. The assimilation rate, which corresponds to the netproduction rate in oxidation pond, ranges from t . 0 6 g C m - Z d a v -~ in Pond 2 to 2 . 6 1 g C m - : d a y in Pond 4. Since the primary net-production rate of eutrophic lake in summer season is about 0 . 1 4 - I . 4 g C m - ' d a y -~ (Hogetsu, 1974), it will be recognized that the activity of algal growth in the oxidation pond is very high. The ratio of assimilation rate vs the average POC mass in pond water is 0.36, 0.29, 0.35 a n d 0 . 4 7 g C g P O C - ~ d a y [ for Pond l to Pond 4, respectively. This value means the growth rate of algae in the pond. tn order to consider the effect of detention time on carbon balance, the cumulative rates on the main reactions in the pond against the detention time are shown in Fig. 8. The cumulative rates of assimilation, sedimentation and regeneration increase progressively with the increase of detention time, while that of sediments increases linearly. This result means that the rates of biotic reactions, such as algal photosynthesis in water and bacterial decomposition in sediments increase with the detention time.

Nitrogen balance The nitrogen balance of each pond is shown in Fig. 9. The main reactions on nitrogen transformation are the assimilation, sedimentation, regeneration and denitrification. The rates of these reactions are relatively low in comparison with the influent nitrogen loading rate. For example, the assimilation flux from In-N to POrg-N in Pond [ is only 9% ( = 1631819) of the influent total nitrogen flux. A great part of the

~L v

I0

[L I

--

o

/

0

02

O~

0.6

Carbon (kg C) Fig. 6. Relationship between carbon and Org-P (sedimentation material).

ISAO SOMIYA a n d

SHIGEt) F t JH

I+aNc 6 CMcula~.ion r~_It:thodtit" each flu'~ i¢:.lrbon~ %+"

"+ 7:w

--k

:C~C

~+et Cu+f!o~ 'ood

C~ Z

,:, I o, - - - : , + c s,, ~->']

-

,,"

"-~SOC

St.

7

/

s++'"

~=3, SOC

~-"

l;'~.~e-"a-?~

k

o

i =(1

.-t FI t'"[('. 2u

, IQ

-Ii

lIR

~-~+ QIC,. . - C

/dr Net o u t t l o ~ load [from p o n d It) P o n d + e II

O =~l..t l~

j'{C..,~o.l

.+~

++°

Eql.iarton 2 C ill Zda~ - • . . . . . . . . . . . . . . . . . . . . . 7" Net tallow load t f r o m P o n d + [ lo Pond z l [

Start

~-

I 3t

/¢~

+uQt('..--(.'..,_~ljdt ~t = I 31 I n c r e m e n t o f storage in p o n d water d u r i n g the e x p e r i m e n t St,=llA./-/IC s -C ~i ~/=l 31 A~sinlilation u ( S - = ~ l t l ' ) ~ - C h ll" .;essile algae -\~,,imtlation m" 5. - I I t 1) / , t M o t, lo[lk~UOl&l 5d = , I I

.~dm~ent.~ Regeneration f ) ¢ c o m p o s i t i o n o f POC" Ash,i n i t i a t i o n in water Ab'~orption o ( CO._ gas

S:=(] R +- Sd R, - 0 R, = O. R+ = t)

"

,,t

Surthce area

I1" 1

A r e a o f ;'+all l i b m : i V o l u m e <5.25 ul+l

(,)

F u n d a m e n t a l flov, ~t 31 m ' d a ~

Q,i R a

[nfluent flo,~ I m ~ d a . ', } Rainfall (m ~ d a y - ' p o n d ' ) Exchange f l o ~ ratio (a -' 11.6t~ a~ , = 1-3. a n d u,=O at ~ = 0 . 4 ) C o n c e n t r a t i o n o f ~ a t e r qualic; (mgl+Ij S e d i m e n t a t i o n rate tg d a y - p o n d C h l - a denstt? o f sessile algae ~gf_'hl-a m - )

t Sm Ch

/

S c d h l l c n t a t t o n o( P O C

Terminology F x p e r l m e n t tlme (3LI6 da!.~i

t ~ i Sm tit

- m-)

• 1o

t /'I-B'Se - S, ~ St - I, 4+St. ~ R, + Sd - I. - R , + S~ 1- S z + St -1

Influeni

~

-R

t

Sc

Dry wetght o f s e d i m e n t s Ig SS p o n d

Mo :~ 1t B

Dr), ~eIght o f Mougeotta ~g SS p o n d C C h l - a ratio in M,,ugeotia C
'~

£fftuent

~

{£) 5 4 0 / / ~ )

!

Iron?"

l/E; ,i:< l?'::,2;ii, Sed+me~ls

(~) ; A s s , m i l o t i o n tB) ; 5 e d l m e n t o t i o n tC) ; Deeom~osifion

(0} , R e q e n e r a h o n (£) ', A b s o r p i , o n of POC

Fig. 7. Carbon balance.

Unit ; mg C m ' Z d a y

( ) ~ Mean

existing moss

m g C m -2

Matenai h a L m c ~ of organics_ and nutrients h~ ~m exidation ~-..~"~'i

of September. it ~cupied relati,.ei,, higher percentage of total nitrogen removal in Pond 1. Since it,; gro'~th period is about 7,) days. its ac~uai assimilation rate of nitrogen is roughly calculated to be about 2 0 0 m g N m - : d a > . This rate is higher than any oti~er rate of nitrogen removal reaction. So. it '.'.ill be easily considered that the nitrogen removal in Pond I depended chiefly on this alga at the period.

A

50 (&

{ • Toto!

oss,milatio~

40 [-~ Asslm, lot,on in

water/ //~//

© Sedimentation

~g

3o - e

~" /,

Regeneration o Sediments /

8 g

~

/

2

/5/./

~g

Phosphorus balance The phosphorus balance of each pond is sho~n in Fig. 11. In the phosphorus balance, the main transformation processes are the assimilation, sedimentation and regeneration. It ~vil[ be easily recognized that each reaction of phosphorus has a great eft:cot on the material balance than that of nitrogen. For example, the sum oF the assimilation flux on the POrg-P in each pond is 1.4 times of iniluent flux of S-P, while that of nitrogen is only a half. The

>= 0

4

E

Detention

8

{2

time

(

",,,..,

!6

day

)

Fig. 8. C a r b o n reaction and d e t e n ' i o n time.

influent nitrogen looks like passing through the oxidation pond v.ith no effect on such reactions. Consequently, the nitrogen storage rate in sediments is not high. and occupies only about 6"o ( = [ 2 3 + 3 l +32+23],1819) of the total nitrogen loading rate. The denitrilication reaction seems to take place in all ponds, and the total denitrification rate corresponds to 23'!,, of the total nitrogen load. while am,nonia-stripping rate is relatively low. In order to investigate the effect of detention time on the removal efficiency, the cumulative removal rates on nitrogen reaction along the detention time are shown in Fig. 10. From Fig. 10, it will be concluded that the cumulative removal rate of each reaction is proportional to the detention time. Concerning the nitrogen removal, the denitrilication reaction is predominant, and its effect occupies 66?;) Although .'l,hm.~,,eotia began to grow at the beginning

z

•

Total

•

Denltr.ftcation

removal /

~

o Sediments o

o

~, A m m o n i a - / "

~,

~/

~rripmno

~

E

4

8

Detenhon

~2 l~me

~6

(day)

Fig. 10. Nitrogen removal and detention time.

Effluenl

HE)IF89

, ;,

yv~ - i\i

, "II ~-4~'~

CA)IL''~°

~ _ ~ (ol-

., ..~-, jLg,

lq

I

C0} II

/ '~.--.%" ", (E}II65 (F)

{I"<, ,,,,o, t I IL.J-L-a-"~CAJ'J. ' ' '

H ,a~

I .~'" ,I

L._._/( o~g-. e3 h

I(F)

l

~., ,~ ~

E,,~ f

[

/lll

(C)~

/

/i Fl~.[..

,-w.

'EL_. Hs,. ,I ~ IJt,o~

H ,54 l,s4 o

O~o-N 3,

h

I (

O,o-N

.

H "~ ,,,

~z

Sediments (2~) , AsstmdOhOn

(D) ~ ~egenerot,on

Un,t ; mg N m"2 tidy -t

(B) ;

(E) , Oenirrification

(

Seal,menTor,on

!CI ; Oecomposi'lon

of POrg-N (F) ;Amrnomo-srripoing

Fig, 9. Nitrogen balance.

} ;

Mean

ex,s!mg mass

mg N m - z

I | 8

,:7.

I

~

S-,

=

Ze3)

!L...~

! il'~,"! il

"[

;

~ i

" "-Vl(2 1

~-P 9

i .J I .5 ."

! i

I

!i

V 5-P

"" ~'-,-,d

~

90

¢ ~"~]

i ~

~

----

S-P

.2

(167)L~,

,t..7.~ !

~.,

!,

i

!

i

Sediments (Ai ; Ass~miiutlon

{O) ; R e g e n e r a t i o n

Unit , mg P m "2 d¢l~ "~

(B);

Sed*menlatlon

(E);

( I

(C);

Chemical

Unknown

, Mean

COaqUlaflon

ex=shng

mass

mg P m -2

Fig. It. Phosphorus balance. difference of nitrogen and phosphorus utilization seems to be caused b> the dill'erence of N/P contents ratios on influent and algae. The assimilation and sedimentation rates are very high in phosphorus balance, but the removal efficienc? of total phosphorus is not so high, owing to the high decomposition and regeneration rate in sediments. The ratio of the regeneration rate against the sedimentation rates ranges from 71°.,, in Pond I to 89% in Pond 4. Since this ratio is effected strongly by such factors as temperature, detention time and runmng period of oxidation pond. it varies intensively in some cases. governing the removal efficiency. This tendency is also recognized on nitrogen. On the other hand. the chemical coagulation rate is much lower than the assimilation rate, and its reaction does not seem to be important on the phosphorus balance, apparently. The inorganic phosphorus fraction in sediments ranges from 36 to 55%. The relationship between the cumulative phosphorus removal rate and the detention time is shown in Fig. 12. The cumulative removal rate of phosphorus is not proportional to the detention time, but the rate on each pond decreases slightly with the prolonged detention time. This tendency can be also observed in the case of each phosphorus fraction, but not m the case of each nitrogen transition reaction. This means that the removal efficiency of phosphorus in oxidation pond does not increase proportionally with the increase of detention time.

The apparent removal efficiency of numcnts was 45% in total nitrogen, and 43% n total phosphorus. Although the behaviors of these nutr}ents in an oxidation pond are governed by various transformation processes, the solidification of the soluble inorganic nutrients is predominantly observed. Based on this experimental data. the material balances concerning carbon, nitrogen and phosphorus in an oxidation pond are obtained under some assumptions. The result of material balance analysis shows clearly that the main reactions on the transformation processes of carbon and nutrients are the assimilation, sedimentation and regeneration. The assimilation rate ranges from 1.06 to 2.61 g C m - : d a y ~. The rates of these reactions increase with detention time. In the nitrogen balance. the denitrification is very important and its effect occupies 66% of the nitrogen removal. In the phosphorus balance, the chemical coagulation is a characteristic reaction of phosphorus. This reacuon ~s not

1o n

300

E

-e

o

Total

removal

Org-P in

./.,4

/e

sedimen~ _e

In-P

in

sediments

/

/ I00

CONCLUSION

A series of the oxidation pond experiments was performed from l0 January to 12 November 1979. The behavior of nutrients and carbon in an oxidation pond and the nutrient removal characteristics are analyzed.

E

0

4

Detention

8

J2

time

(day)

~6

Fig. 12. Phosphorus removal and detention time.

Matena! balances of organics and nutrients in an oxidat,,on pond intensive so far as the p h o s p h o r u s reaction rate, but the inorganic p h o s p h o r u s in sediments formed by this reaction is relatively i m p o r t a n t in the p h o s p h o r u s removal owing to its low resolvability. T h e effects o f detention time on nitrogen and p h o s p h o r u s removals are slightly different from each other. The removal flux of total nitrogen is linearly p r o p o r a t i o n a l to the detention time, while that o f total p h o s p h o r u s does not increase with detention time. .4ckm,wlcd~,ement--We would like to thank Mr. Masazumi Kawamura, Mr Hiroshi Kubo, Mr Kaoru Takeda and Mr Yukimi Yoshinaga for their helps in the experiments and data analyqs,

REFERENCES Akivama T. (1973) Indexes of water pollution and their application. Wut. PuriJ[ Liquid Waste Treat. 14, 361-368 (in Japanese). APHA (t975) Standard Method~ /or the F~vamination of Water attd Wasteu'ater. 14th Edition. American Public Health Association. Washington, DC. Foikman Y. and Wachs A. M. (1972) Nitrogen removal through ammonia release from holding ponds. 6th International Congress o[" Water Pollution Control, pp. 503-515, Fujii H., Omiya K. and Sugimoto K. (1972) The tertiary treatment experiment on lagoon. J. Jap. Sewage Wks ,4ss. 9, 11-22 (in Japanese). Goda T. (1976) Water Quality Control--Application. Maruzen (7o. (in Japanese). Goda T., Somiya I. and Kawamura K. (1974) An energy estimation of municipal sewage and organic indexes. J. Jap. Sewage ~[2s Ass. 11, 21-31 (in Japanese). Goldman J. C. et ul. (1972) The effect of carbon on algal growth--its relationship to eutrophication. Water Res. 6, 637 -679.

333

Grabow W. O. K. and M i d d e n d o ~ I. G. (1973i Survival in maturation ponds of c o l i f o ~ bacteria vdth transferable drug resistance_ Water Res. 7, i589-1597. Hemens J. and Mason M. H. !1968) Sewage nutrient removal by shallow algal stream. Water Res. 2, 277-287, Hogetsu K. (1974) The Ecosystem in Water Bo&'. Kyoritsu Co. (in Japanese). King D. L. (1970) The role of carbon in eutrophication. J, Wat. Pottut. Control Fed. 42, 203%2051. Maruo H. (1973) On the measurement of TOC. lnd. Pollut. Control 8, 146-150 (in Japanese). Leohr R. C. and Stephenson R. L. (1965~ An oxidation pond as a tertiary treatment de;ice. J. sanit. Engng Dic. Am. Soc. cir. Engrs SA3, 31----M~L Odum E. P. (1974) Fandamentat o_t"ecob)gy, 3rd Edition. W. B. Saunders. Philadelphia. Oswald W. J, (1963) Fundamentai factors in stabilization pond design. [n Advance in Biological Wa-~te Treatment (Edited by Eckenfelder W. W. and McCake B, J.), pp. 357-393. Pergamon Press, Oxford. Park P. K. (1969) Oceanic CO: system--an evaluation of ten methods of investigation. Limno!. Oceanogr. 14, 179-186. Potten A. K. (1972) Maturation ponds--experiences in their operation in the United Kingdom as tertian' treatment process for a high quality sewage effluent. Water Res. 6, 781-795. Public Corporation of District in Japan (1970) Sante project--reuse of wastewater (in Japanese). Somiya I. (1978) Oxidation pond treatment, tn New Biological Wastewater Treatment Technique. pp. 211-223. Center of Scientific Technology (in Japanese). Somiya I. and Sakai I. (1974) The oxidation pond experiment with the intention of qualitative improvement of secondary treatment wastewater, l lth Congress of Japan Sewage Works Association, pp. 299-301 (in Japanese), Somiya I. and Sakai A. (1977) Performance of oxidation pond as a tertiary treatment technique--I, variation of water qualities in a pilot oxidation pond. J. Jap. Sewage Wks Ass. 14, 47-58 (in Japanese).