No.2
24-HOURS VARIATION OF AMOUNT
AND CONTENTS OF WASTEWATER FLOWING TO TREATMENT PLANT IN ZIELONA GORA
Sylwia MYSZOGRAJ University ofZielona G6ra
2007
The article describes daily variations of influents in the aspect of their volume and com- position in the sewage treatment plant of Zielona Gora. With a method of direct measu- rements the flow rate and the concentration of pollutants in the sewage have been mar- ked. Based on the research results the cumulative curves of the flow duration and daily pollutant loads as well as line~ of daily loads variations in raw sewage have been worked.
out.
Keywords: wastewater, contamination loads, variation of contents of wastewater
1. INTRODUCTION
Knowledge of changes in quantity of produced wastewater and contamination loads is necessary in order to design and operate the wastewater treatment plant.
In engineer's practice there are two methods of. solving this problem. At the stage of new systems design a method of unitary coefficients is widely used, whereas at the stage of systems modernization and optimisation a method of direct measurements is commonly applied. Characterising changes in contents and amounts of waste water is a difficult task.
Permanent measurement of flow intensity and concentration of contami- nation entails considerable expenses. Owing to this, engineering solutions and scientific research apply some simplifications in order to determine contamina- tion loads. If samples of wastewater are taken in proportion to the volume of the wastewater, and then decanted to one common sample, then contamination load contained in this sample will be proportional to the load flown in with waste wa- ter. Concentration in a sample obtained in such a way will be similar to the av- erage concentration from a time period and it is called representative concentra-
tion. ·
50 Sylwia MYSZOGRAJ
Tests of non-uniformity of quantity and contents of wastewater should cover a longer period, taking into account not only hourly ,peaks" during 24 hours but also daily ,,peaks" during a year. Flowing through the treatment plant facilities, the wastewaters are averaged both in quantity and contents. Separate containers (settling tanks, active. sediment chambers, etc.) act like buffer conta- iners [1,2].
The paper presents changes in quantity and contents of wastewater flow- ing to the treatment plant in Zielona G6ra during 24 hours. Intensity of flow and contamination concentration were determined using direct measurements. The tests results made it possible to determine curves of accumulated frequencies for flow intensities and contamination loads as well as to draw lines for 24 hour variations in changes of contamination loads included in raw wastewater.
2. SCOPE OF TESTS
The tests covered municipal wastewater flowing to "L'l_cza" treatment plant in / Zielona G6ra. Zielona G6ra is a city of almost 120 thousand inhabitants, occu-
pying the area 58 km2• The wastewater carried to the plant is mostly household wastewater but also wastewater produced by supermarkets and wastewater pro- duced by small plants. ,Ll\.CZA" wastewater treatment plant - central wastewa- ter treatment plant for Zielona G6ra is located about 7 km north of the town and west from L~Z)'ca village. The plant output of Qsrd=51225m3/d was designed in a
syst~m of mechanical-biological wastewater treatment with biological de- phosphatation, de-nitrification and nitrification as well as chemical precipitation of phosphor. Contents of raw wastewater flowing to the plant was analysed in time-proportional samples taken each two hours, during consecutive days from Monday to Friday, during the time between 22.04. to 26.04.2002. The tests were performed using time autosampler, which dosed 200 cm3 of wastewater to sepa- rate containers each two hours (starting from 8:00 a.m.). Simultaneously, the flow intensity of the wastewater flowing into the plant within two hours was· measured.
Scope of analytical control of wastewater contents included; dry residue, suspended matter, dissolved substances, electrolytic conductivity, pH, BODs, COD, total phosphor, total Kjeldahl nitrogen, organic nitrogen, N..:.NH4.
3. RESULTS OF TESTS.
Figure 1 presents changes in wastewater flowing to the plant and in figure 2 shows the summary amount of wastewater brought within 24 hours. The meas- urements were .registered automatically, values were measured in two-hour in-
tervals. The tests carried out show that changes in quantity and contents of wastewater form a series of certain periodicity.
1800
- ---·- -..
Friday Saturday lIl !
1600 I I i j
,,
I...c •I 'I
-. 1200 11
"'a
I1..
'1 !1000 'II !
I! .. . ·- ... ' • i
,,
l i600 - •l
5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 65 69 Time,(2h]
Fig. 1. Changes in amount of wastewater. flpwing in 24 hours
-· -_ ~
In the measurement period analysed, that is from Monday to Saturday, the smallest wastewater flow (below the average flow) was observed in morning hours (6:00 a.m. -8:00a.m.), the biggest at noon (12:00 noon-2:00p.m.) and during late evening (10:00 p.m. -1:00 a.m.). The amount of inflowing wastewa- ter increased within four hours from 10:00 a.m. to 2:00 p.m. from the minimum value (about 65% of the average flow) to the maximum value (about 139% of average flow). The smallest amount of inflowing raw wastewater was observed on Monday (643 m3/h) between 4:00 a.m. and 6:00 a.m., and the biggest on Wednesday (1,568 m3/h) between 10°0 arid 12°0• The difference between these values is 144% in relation to the minimum flow.
0 4 8 1 2 16 20 24 28 32 36 40 44 48 52 56 60 64 68 72 Time,2h
-o-Monday -D-Tuesday -L:r-Wednesday -)::-Thursday - Friday - X-Saturday
Fig. 2. Amount of wastewater flowing to the plant within 24 hours
52 Sylwia MYSZOGRAJ
The analysis of data obtained in figures 1 and 2 enables to state that the course of changes in quantity of wastewater flowing into the plant is character- ised by big repeatability (dry weather). Basing on the measurement obtained it was concluded that day of the week does not influence the amount of inflowing wastewater. The smallest amount of wastewater rim into the plant in 24 hours was observed on Monday- it was 28,574 m3/d, and the maximum inflow of wastewater in the tested period occurred on Friday- 30,326 m3 /d.
160 140 120 100
...
.., E 80
...
60 40
20 0
1 4
Thursady Friday
L= 9 m3/&:=:=.}8~_,2 m3/d
7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 61 Time,[2h]
Fig. 3. 24 hour changes in quantity of the wastewater transported in.
Bigger changes (fig.3) were observed for wastewater transported in sew- age removal trucks. The biggest amount was transported on Monday and Tues- day. The difference between the maximum and the minimum amount of waste- water was about 100 %. The biggest frequency of transported wastewater dis- charge was observed between 12:00 noon and 2:00p.m.
Figure 4 illustrates 24-hour changes of BOD5 and COD in wastewater flowing into the plant are presented. ·
For the five day period under analysis the course of the changes of COD is almost analogical with the value of BOD5• Except for Wednesday, when the additional increase of COD during the night was observed, COD in the whole period varied from 200 g02/m3 to 1160 g02/m3, and BOD5 from 16.4 g0z/m3 to 372 g02/m3•
" .
...
C')E aoo
~
<5, 600
...
400 200
1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58
Tine, [2h] -o-COD ---ts--8005
Fig. 4. Changes in BOD5 and COD in wastewater
Figure 5 presents is the course of changes in concentration of separate forms of nitrogen. N-N~ concentration was relatively stable and was, on the average, 45.35 gN-NRJm3• Whereas changes in organic nitrogen and total Kjel- dahl nitrogen concentration were characterised by 24-hour periodicity;
140 120
100
...
C')E ao
-
zs
6040
Tuesday ~ Wednesday ~ Thursday
---··----.---
Friday :satur.
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59
Czas,[2h]
--o-N-NH4 -o-TKN --ts-N org.
Fig. 5. Changes in concentration ofnitrogen compounds in wastewater
Figure 6 illustrates changes in general phosphor concentration in waste- water. Large 24 hour changes of this parameter were observed. Concentration of phosphor in wastewater changed from 2 gP/m3 to 20-gP/m3• When considering
54 Sylwia MYSZOGRAJ
24 hour periodicity, high concentration was found at noon, whereas the lowest at night. Average phosphor concentration was of 6.39 gP/m3•
25
20
.:;"" 15
a:
E..9 10 5
0
Monday.
I
Tuesday
I
I I I
Wednesday , Thursday
I I
Friday .satur
I
.
I. .
--·--1 I I
+ - - - - J - h -- - -- - - 1 - - - J I - - -- I - ·-·-
1
• I I
-t-+--- - -- -- - - - t - ---
3 5 7
1 I I
9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51 53 55 57 59 Time,(2h]
· Fig. 6. Changes in total phosphate concentration in wastewater
Analysing the course of changes in the value of particular indicators, it was found out that the occurrence of their minimum and the maximum values on successive days of measurements can be characterized by hour periodicity. No influence of days of the week on concentration value was found. On four suc- cessive days, from Tuesday to Friday, these values were comparable.
4. SUMMARY
Basing on five day measurements of flow intensity and contamination concentration in wastewater, lines of 24 hour changes of contamination loads were detennined, being a graphical representation of distribution of load chan- ges of the analysed indicator during 24 hours. The Knowledge of 24 hour lines of BOD5, COD, total Kjeldahl nitrogen load changes, general phosphor is parti- cularly important for operation of the wastewater treatment plant. Figure 7 pre- sents distribution of load changes during 24 hours for BOD5,. COD; total Kjeldahl nitrogen and P gen.·
Analysing the course of
24
hour lines of changes in loads of contamina- tion indicators in raw wastewater their distinct repeatability is observed. The occurring deviations and differences in singular measurement points probably result form analytical errors or random changes of wastewater composition.20 _ _ .. _ _ _ _,,.. .. ___ ~~-... -.... - .. --·-···-··---·~·---·· --·~--··-l
2 0 - - - - -- 18 COD
18 8005 16
16 - 14
14 ~ 12
12 0
~ 10
0 10
8· 8
6· 6
4 4
2 2-
0 0
2 4 6 8 10 12 14 16 18 20 22 24 2 4 6 8 1 0 12 14 16 18 20 22 24 time, h
-o-Tuesday --D-Wednesday -o-Tuesday -o-Wednesday
--l:s-Thursday ~Friday -!::r-Thursday -o-Friday
Fig. 7. Lines of 24 hour changes of loads BOD5, COD, total nitrogen, phosphorus in wastewater
time, h
!
J
56 Sylwia MYSZOGRAJ
Basing on 24 hour lines of changes in contamination loads overload coef- ficient 't was determined as a quotient of maximum load and average 24 hour
~oad. The calculated values are presented in table 1.
Table1. Overload coefficients 'tx
Day 'tsusoension 'tBOD5 'tcoo 'tTKN 'tp
Tuesday 1,66 1,62 2,17 1,59 1,81
Wednesday 3,45 1,67 1,79 1,76 3,77
Thursday 2,50 1,75 1,72 1,43 3,56
Friday 3,27 2,58 1,85 1,64 1,49
For particular contamination indicators values of overload indicators change within the range from 1.49 to 3.56 and correspond with publication data (value 1.5-3) [1,2]. Overload coefficients are used for interpreting results of chemical analysis of raw wastewater while designing devices and modelling processes of biological treatment of wastewater [1,2].
Learning about 24 hour contamination loads enables static elaboration of data by determining accumulated frequency curves for analysed parameter, which are shown in fig. 8.
The analysis of the obtained relations leads to the conclusion that at any time of the day it is possib.le to read with a high accuracy with what percentage of 24 hour load the wastewater treatment _plant is loaded. The value of 85 % of the average 24 hour load of particular types of contamination recommended for the plant design was carried to the plant until 8:00p.m. - 10:00 p.m.
20
18 8005
I .
16 i ;
14
"# 12
10 8 6 4 2
0 : . l .
~ b< <o <0 "'-~ "'-~ "'-~ "-<o "-CO ~~ ~~
1'
time, h
~Tuesday
-o--
Wednesday -lr-Thursday -o-Friday20~~~---
18 16 14
'#. 12 10 8 6 4 2
0+-~~~.-.-.-.-.-.--r.-~
2 4 6 8 10 12 14 16 18 20 22 24
-0-Tuesday --t:r-Thursday
~Wednesday
--o-Friday
time, h
16 ---,
I
I 35 .,---···-·····-···-·· .. ·---···--·--;I
i
jI I
II I
time, h -e-Tuesday -B-- Wednesday
--6-Thursday -e-Friday
30 25 rf. 20 15 10 5
2 . 4 6 8 1 0 12 14 16 18 20 22 24
time, h --o-Tuesday -B--Wednesday • --fs-Thursday -e-Friday
Fig. 8. Sums of loads of BOD5, COD, general nitrogen, phosphor in wastewater The most repetitive and possible to describe with line dependen<:e is the distribution of BOD5, COD and total Kjeldahl nitrogen load. Big differences occur in changes of phosphor loads.
5. CONCLUSIONS
Basing on the tests it has been concluded that:
Changes in amount and contents of raw wastewater flowing to ,Lctcza"
wastewater treatment plant in L~zyca form a time series characterized by periodicity.
Day of the week (in analyzed period- from Monday to Saturday) does not affect considerably the quantity and quality of transported wastewater.
Occurrence of the extreme concentration values of contamination indicators (minimum and maximum) is delayed (on the average - 2 - 3 h) as compared to the extreme concentration of wastewater flowing to the treatment plant in X, as a result of influence of collector system on wastewater composition.
For analysed contamination indicators in raw wastewater: BOD5, COD, total Kjeldahl nitrogen and general phosphor the determined overload coeffi- cients change in the range of values from 1.49 to 3.56 and are comparable with data in publications.
REFERENCES
1. Lomotowski J., Szpindor A., Nowoczesne systemy oczyszczania sciek6w.
(Modern systems ofwastewater treatment). Arkady, Warszawa, 1999.
58 Sylwia MYSZOGRAJ
2. Kayser R., Wymiarowanie oczyszczalni sciek6w - praktyczne wykorzystanie metod komputerowych. (Dimensioning wastewater treatment plants- prac- tical use of computer methods). ATV-DVWK, Gdanska Fundacja Wody, 2001.
3. Dane oczyszczalni ,£4CZA" w L~iycy. (Data of "L'lcza" WWTP in L~zy
ca).
4. Imhoff K., Klaus R. Kanalizacja miast i oczyszczanie sciek6w. (Sewage systems in towns and wastewater treatment) Poradnik, Oficyna Wydawnicza Projprzem-EKO, Bydgoszcz 1996.
5. Malej J., Oc:zyszczanie sciek6w z zastosowaniem cyrkulacyjnych kom6r osa- du czynnego, (Wastewater treatment using circulation chambers of active sludge). 1999.
6. Taylor John R. Wst~ do anali:zy bl~du pomiarowego, (Introduction to measurement error analysis). Wydawnictwo Naukowe PWN, Warszawa
1999.
7. POL- EKO- APARATURA sp. j. Elementarz automatycznego poboru pr6b, (Primer of automatic sampling system). Wydanie V poprawione, 2002r,
8. Polska Norma, PN- ISO 5667- 10, grudzieil1997, Jakosc wody; Pobiera- nie pr6bek; Wytyczne pobierania pr6bek, (Polish Standard PN-IS05667 10.12.1997. Water quality. Sampling, Guidelines for sampling.
ZMIENNOSC DOBOWA ILOSCI I SKLADU SCIEK6W DOPL YW AJA.CYCH DO OCZYSZCZALNI W ZIELONEJ G6RZE
S t res z c z en i e
w
artykule przedstawiono dobowe zmiany ilosci i skladu sciek6w doplywaj8c_cych do oczyszczalni w Zielonej G6rze. Metod3c. bezposrednich pomiar6w wyznaczono natf(zenia przeplywu i st~renia zanieczyszczen w sciekach. Na podstawie wynik6w badan opraco- wano krzywe cz<(Stosci skumulowanych do nat~zefl przeplyw6w i ladunk6w zanieczysz- czefl oraz linie dobowych zmian ladunk6w zanieczyszczen w sciekach surowych.I .
