Performance Analysis of a Waste Water Stabilization Pond in Malaysia

8/2/2019 Performance Analysis of a Waste Water Stabilization Pond in Malaysia

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Ujang Z.*, Christensen C.L.**, Milwertz L.,** Thomsen M.H.,** Vollertsen J.** and Hvitved-Jacobsen T. (2002)Performance analysis of wastewater stabilization ponds using respirometry in Malaysia.

IWA Conference on Waste Stabilization Ponds, April 2002, Auckland, New Zealand.

PERFORMANCEANALYSISOFWASTEWATERSTABILIZATIONPONDS

USINGRESPIROMETRYINMALAYSIA

Ujang Z.*, Christensen C.L.**, Milwertz L.,** Thomsen M.H.,** Vollertsen J.** and Hvitved-

Jacobsen T.**

* Institute of Environmental & Water Resource Management, Universiti Teknologi Malaysia, 81310 Skudai,

Johor Bahru, Malaysia. Email: [email protected]

** Department of Environmental Engineering, Aalborg University, Sohngaardsholsvej 57, DK9000,

Aalborg, Denmark. Email: [email protected]

ABSTRACTImproving and upgrading the existing sewerage system was the main agenda in water pollution control in

Malaysia at the moment. The present infrastructures include small and decentralised plants were inadequate

in terms of performance efficiency, as well as service coverage. Improving and upgrading the existing

sewerage system in the Malaysian context, among others, include a possibility of centralization of the

municipal wastewater treatment facilities. The objective of this study was to analyse the performance of a

waste stabilization pond (WSP) system and the possibility to upgrade the WSP for future centralized

wastewater treatment plants. By wastewater characterization and evaluation, primarily using respirometry,

it is found that the performance of the WSP in this study was not even met with the Malaysian effluent

Standard B.

INTRODUCTIONIn the recent years, the Malaysian Government has focused on improving and upgrading the

existing sewerage system and facilities, which is inadequate in terms of treatment efficiency. Inmany cases, the effluent quality has not met the effluent standards required by the authority.Untreated and inadequate treatment of wastewater has been the major factor in causing severe

pollution of rivers and near-shore areas, which consequently increased the health risk for the public

in Malaysia since the rapid industralisation and urbanization programmes in the 1980s.Improvements and upgrading of the existing sewerage system include, among others, re-engineering

in management and financial system, development of new sewer networks and other sewerage

infrastructures, as well as centralization of the small and decentralised municipal wastewater

treatment facilities in major cities. The present Government policy is to change numerable andpoorly equipped sewerage treatment plants to fewer, larger and more efficient centralised

wastewater treatment plants to meet the effluent Standard A (BOD 20 mg/l, COD 50mg/l and SS 50

mg/l).

Due to heavy rainfall, Malaysia has separated municipal sewer system from urban drainage.Municipal wastewater is led through closed municipal sewers underground, whereas rainwater is

disposed of in open drain channels. In Malaysia, no industrial wastewater is allowed to discharge

into public sewerage system. Municipal wastewater is disposed of in both connected andunconnected sewerage systems. Unconnected sewerage means that the wastewater is led either to

private septic tank or discharged directly to the environment. Around 12 out of 23 million people in

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mailto:[email protected]:[email protected]:[email protected]:[email protected]


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Malaysia are severed by public sewerage system in 1999. The present connected sewerage system

consists of approximately more than 10,000 km of sewers and about 7000 connected smallwastewater treatment plants (WWTPs). The small WWTPs consist of communal septic tanks

(55%), Imhoff tanks (13%), WSPs (10%) and mechanical-based plants which are mainly activated

sludge type (22%). Besides the public sewerage service Malaysia also has 1.2 million individual

septic tanks serving more than 6 million people [Hamid and Muda, 1999].

The objective of this study was to analyze an exiting WSP, located in a residential area in TamanSri Pulai, Johor Bahru, Malaysia in order to understand the performance of the treatment processes.

This was conducted by wastewater characterization in various points in the WSP. The primary

parameter to be measured was OUR, in which a detailed information about the organic fractions inthe wastewater will be provided. The organic fractions are relevant because it shows the

biodegradability of organic matter in the wastewater as typically used in activated sludge plants

(Henze et al., 1987). In addition, OUR has never been used to measure the performance of a

municipal WWTP in Malaysia.

MATERIALS AND METHODSThe WSP in Taman Sri Pulai consists of a facultative pond and maturation pond, in which thedegradation of the wastewater is performed by a combination of aerobic, anaerobic and facultative

bacteria. In general, a facultative pond is designed to an overall BOD5 removal efficiency at 80-

95%. At the same time, a high degree of coliform removal is assured even with a 30-day-retentiontime. The maturation pond is designed to provide a secondary effluent polishing. Taman Sri Pulai is

located on the foot of a small hill with the highest point in the northeastern corner and the lowest at

the pumping station south of the ponds. The WSP covers the residential area of approximately 0.7

km2

and PE of 10,327 and receiving municipal wastewater primarily from toilets, bathrooms andkitchens. It has not been possible to collect detailed information about sewer slopes and lengths, but

manually measurements performed at the northeastern sub-catchment area shown a slope of 13 to

14% [Frederiksen and Nielsen, 2001]. The sewer lines in this sub-catchment have a diameter of 32cm, which supposedly is the same for all of the residential area. Most of the sewer pipes in the

catchments area are gravity pipes, which are normally not fully loaded that allow re-aeration of the

wastewater in the gravity pipes causing aerobic conditions. The minimum oxygen concentrationmeasured in gravity pipe in the northeastern sub-catchment was 3.5 mg O2 /L [Frederiksen and

Nielsen, 2001]. This means that the gravity pipes may not contain products from anaerobic processsuch as VFAs, H2S and CH4.

More than 50% of the residential area was connected with the pumping station and the pressurepipe, which makes the pressure pipe important for the whole sewer system. This pumping station

was not leading a continuous stream, but occasionally emptied. Frequently operational problems

with the pumps causes filled pipes in the lower parts of the catchments area. Due to this, largeamount of the total wastewater flow is anaerobic, which causes a production of anaerobic productssuch as H2S. The WSP is located about 50 m from the nearest residential building. Very close to the

ponds are a public school and a new residential area. The effluent from the WSP was discharged to

Skudai River. The water quality of the river was slightly polluted in terms of heavy metals, greaseand oil, nutrients and organic matters.

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Design

The detailed design of the WSP could not be acquired from the contractor. However it is assumedthat the WSP was designed according to the standard practices similar to other facultative and

maturation ponds suggested in Metcalf and Eddy (1991). The WSP is surrounded by tall trees and

thereby partly sheltered from the wind. This is considered to reduce the mixing of the pond

volumes. The WSP is connected in series, where the first pond is a facultative pond and the secondpond is a maturation pond. Figure 1 shows the double pond system. The ponds cover an area of

17,725 m2

and the depths were thoroughly measured in this study to be on average of 1.55 m and1.40m for the facultative pond and maturation pond, respectively. The volume of the facultative

ponds is 16,275m3 and the volume of the maturation pond is 10,115 m3.

1

2

22

2

N

Maturation

Ponds

Facultative

pond

Outlet

Inlet

Figure 1: Outline of the WSP in Taman Sri Pulai.

Note: (1) = Venturi canal. (2 = overflows. (, O, ,) = sampling points

To analyze the performance and the treatment process of the WSP, the wastewater was

characterized by the following parameters: oxygen uptake rate (OUR), temperature, pH, dissolvedoxygen, COD, SS and VSS, TS, VS, ammonium-nitrogen and nitrate-nitrogen, flow, transport time

in sewer.

METHODSSampling For Wastewater Characterization

Samples were taken for wastewater characterization from the sampling points on daily basis for the

period of three months. Table 1 shows the parameters that were measured.

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Table 1: Sampling frequency and points for wastewater characterization of the WSP

Sampling for* Flow Transport Time Depths DO pH Temp

further analysis

Inlet X1 X2+5 X6 X3+6 X3+6

Facultative pond X4 X4 X5 X4+5 X4+5

Facultative pond outlet X2 X2

Maturation pond X4

X4

X7

X7

X7

Outlet X2 X3 X2

Note: * = Wastewater were sampled for analysis of CODtotal, CODdissolved TS, VS SS VSS, NH4+

1. Measured hourly between 7.00, 07.30, 08.30,16.30, 17.30 and 18.305. Measured at 16.20 to the 24.11.00 at 11.206. Measured at 16.20 and at 11.20

7. Measured hourly between 9.00 to 16.00

2. Measured hourly between 07.00 to 19.003. Measured hourly between 7.00 to 19.004. Measured hourly between 8.00 to 16.00

Sampling For OUR Measurement

Samples were collected from three sampling points i.e. inlet, facultative pond outlet and the outletof the maturation pond. OUR samples have been analyzed in the period from 20 September to 5

December 2000. In this study 24 samples have been analyzed for OUR from the inlet, 14 from the

outlet of the facultative pond, 7 from the outlet of the maturation pond, 2 from sludge in the

facultative pond and 1 sludge from the maturation pond.

Table 2: The analysed parameters for the samples collected in the inlet facultative pond outlet and the outlet.

CODtotal CODdissolved TS VS SS VSS NO3- NH4

+

Inlet

Facultative pond outlet -

Outlet -

OUR MeasurementsOUR of the wastewater was determined in two batch reactors of 6.2 liters each. The aeration was

carried out by injection of compressed air into the wastewater, which was kept in suspension bymagnetic stirrers. When the DO in the wastewater below a preset value, aeration of the wastewater

will be started automatically. Once the DO had reached a preset value the aeration stopped. Time,

temperature and DO were automatically logged. After finishing the measurements, the data were

transferred to spreadsheets. OUR was then calculated from the measured time and DO values. OURis the slope of the consumed DO versus time. An OUR modeling programme has been made for

simulating the measured OUR, which enables the determination of the different organic fractions

according to the model proposed by Hvitved-Jacobsen et al. (1998).

Temperature

It is well known that the temperature affects the rates of aerobic microbial process. Hence, therespirometer was set at a constant temperature during the analysis. The temperature was first kept

constant using tap water temperature by circulating tap water in a water bath where both reactorswere placed. The water bath was intended to keep the temperature constant. However, since the

temperature of the wastewaters different by several degrees from the tap water, the temperature in

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the reactors dropped during the first 3 to 5 hours. As a result the aeration was not sufficiently mixed

in the reactors. Instead of keeping the water constant, the temperature was corrected using theArhenius constant and the subsequent measurements were carried out without the water bath.

Reareation

Reaeration occurs by air diffusion through the water surface in the cylinder at the top of thereactors. Reaeration increases the DO concentration in the reactos. This affect the oxygen uptake,

causing the oxygen uptake to be slightly lower than it would have been without reaeration. Thereaeration was presumed to be negligible because the surface of the wastewater was small.

AerationThe wastewater was originally to be aerated by two air pumps introducing air directly into the

reactors through a cylinder. At the beginning it was believed that aeration directly into the reactors

through the cylinder would influence the oxygen sensor. To solve this problem the effectiveness of

the aeration was optimized by adding diffusers at the point where air was led into the reactors.

RESULTSOURTwenty-four measurements were conducted on the wastewater from the inlet. Twenty-one of the

OUR measurements could be simulated to determine the COD fractions. The COD fractions found

by OUR simulation have been tested for normality and found to be the normally distributed. Hence,all the results are assumed to be normal distributed. This complies with Walpole and Myers [1993]

that states that most natural process were normally distributed.

Time (h

5 10 15 20 25

25

15

10

5

0

Ss

Xs,1

Xs,2OUR(mgO2/h)

Figure 2 : Example of a

typical OUR measurements

on inlet wastewater. This is

the OUR measurementfrom 19.10.00 at 9.20 in

reactor 1.

Figure 2 shows a typical OUR curve for the inlet, in the first two hours of the OUR experiment. S sutilized for growth and maintenance of the biomass originated from initially present S s and from

hydrolysis as seen in this wastewater samples. The change from Ss non-limited growth to Ss limited

growth was very clearly demonstrated. The fast decreased in OUR, which was seen when initially

present Ss has been utilized for growth and maintenance of the biomass originated from the fast andslowly hydrolysis products. After 7.5 hours, Ss was utilized for growth and maintenance of the

biomass originated from the slowly hydrolysis products.

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Figure 3 : Example of an OUR

measurement with a characteristic

hump after 10 hours

measurement. This is the OUR

measurements from 21.09.00 at

11.20 reactor 1.

OUR(mg

O2/h)

The COD fractions of SS, Xb and XS1 were simulated and produced 21.76mg COD/l, 80 mg COD/l

and 111 mg COD/l. The values for XS2 and H were then calculated: 263 mg COD /L and 4.9 d-1

respectively. Figures 2 and 3 show that the OUR values are increased after 10 hours. The drastic

increase in OUR value was obvious in Figure 3, caused by the formation of microorganisms that

have been acclimatized to the substrate limited growth conditions and were capable of utilizing asecond substrate that the microorganisms did not be utilise before. It was not possible to simulate

the drastic increase pattern with the tri-substrate model used in this study because more complexparameters have to be integrated.

Figure 4: Example of a 70-hour

OUR measurement. This is the

OUR measurement from 20.10.00

at 9.00 in reactor 1.

Ss

Figure 4 shows the OUR curve for 70 hours. For the first 35-hour of the OUR experiment, S S

utilized for growth and maintenance of the biomass primarily originated from the hydrolysisproducts. The amount of initially present SS was small; hence it was not possible to determine H.

After 25 hours, the production of SS via hydrolysis decrease to insufficient level for sustaining

growth and only the maintenance energy requirement of the biomass are covered. If the

concentration of readily biodegradable substrate produced by hydrolysis was insufficient for

maintaining all the biomass, part of the biomass will be respired endogenously. This was not thecase in Figure 4 where COD fractions of SS, XS2, XS1 were simulated: 10.1 mg COD/l, 59 mg COD

/l and 126 mg COD/l respectively. XS2 was calculated at 137 mg COD/l. The OUR curve in Figure4 was simulated for the first 24 hours, because it was only possible to determine the fractions of SS,

XB, XS1 and XS2 with the applied tri-substrate model. For simulating 70-hour it would be necessary

to extend the OUR model with a fraction more. This fraction, XS2 should be able to characterise theOUR curve from 24 to 70 hours.

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XB can be derived from Figure 4 and was estimated using OUR(t) = qm.XB when the OUR was

more or less unchanged with time, i.e. if no or only little XS1 was present [Vollertsen and Hvitved-Jacobsen, 2001]. After 44 hours, microbial transformation of organic matter XB was reduced to 38

mg COD/l. The COD fractions from the simulation of the 21 measurements of OUR were shown in

Table 3. The average XB was 40 mg COD/l hence the OUR was more or less unchanged with time.

Table 3: The average maximum specific growth rate at 28oC and COD fractions for the 21measurements of OUR in the

inlets with the corresponding standard deviations in the a parentheses.

H[d-1] SS XB Xs,1 Xs,2

& Std. Dev [mg COD/L] [mg COD/L] [mg COD/L] [mg COD/L]& Std. Dev & Std. Dev & Std. Dev & Std. Dev

Inlet Sri Pulai 5.7(2.5) 12.5(8.1) 65(30) 93(32) 309(163)

Characteristic value - 0-50 20-100 50-100 300-450

in wastewater

The COD fractions in Table 3 were in the range or typical values in wastewater. The average SSfraction was in the low range of interval, whereas the average XS1 was at the higher range. The low

SS content could be due to consumption of SS in the sewers. The determination of the average XS2

fraction was uncertain, which was due to the variation in the COD total values. Figure 5 shows theaverage COD fractions variation from 9.00-9.20,11.20-11.30,15.00-16.15 and 17.00-18.35. The

number of OUR measurements for each time intervals was 5, 7, 6 and 3, respectively.

SS Figure 5: The average

concentrations of XS1 at different

time intervals. The periods were

9.00-9.20, 11.20-11.30,15.00-

16.15 and 17.00-18.35.

The COD concentrations were relatively high in the morning, but decreased during the day and in

the afternoon they started to increase again. This was in agreement with the diurnal pattern of

wastewater generation. The concentrations of the COD fractions were expected to follow this

pattern because of deposition of organic matters in the sewer when the flow was low. Then the flowbecame high, the deposited organic matters were resuspended. Another reason was that the

composition of the organic matter varies during the day. XB was high at 17.00 18.35, which may

be due to growth of biomass in the sewers when the deposited SS degraded. XS2 also decreasedduring the day, but in the afternoon it was not increase as expected. This may be due to the

concentrations has not reached the afternoon peak yet. Figure 6 shows the average of COD fractions

as percentages of CODtotal, Ss, XB, XS1 and XS2 account for 3%, 14%, 19% and 64% of CODtotalrespectively.

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Figure 6: Ss, XB, Xs1

and Xs2 as percentage

of CODtotal. All 21

OUR measurements

are included.

SS CODtotal

The results in Figure 6 were compared with values of COD fractions by other researchers, as shownin Table 4.

Table 4. Comparison of wastewater characteristics with other studies.

Studies Country XB Ss Xs,1 Xs,2 X1 S1

% COD

Kappelar and Gujer, 19921

Switzerland 12 9 58 10 1Ekama et al.,1986

1South Africa _* 20 62 13 5

Orhon et al.,1999 1 Turkey _* 9 77 10 4

H-Jacobsen et al., 19983 Denmark 3-16 0-8 8-16 50-75

Talib et al.,2000 3 Malaysia 9 9 12 70

Ujang & Murugesan,20023 Malaysia 3 7 13 77

This Study3

Malaysia 14 3 19 64

Note: * Xb was included in Xs1.Based on Activated Sludge Model 1 (Henze et al., 1987).

2.Based on bi-substrate model proposed by Dold et al. (1980).

3.Based on tri-substrate model proposed by Hvitved-Jacobsen et al.(1998).

The COD fractions are comparable with the values already reported from the inlet wastewater to thewastewater stabilization pond at Taman Sri Pulai (Talib et al, 2000, Ujang & Murugesan, 2002).

Even though this study shows lower values of Ss and XB and higher values of XS1 compared withthe reported values. The COD fractions are in the range of values reported by Hvitved-Jacobsen etal. (1998), although XS1 was a little higher than the Danish values. The results of the COD fractions,

however, are also comparable with those found by Ekama et al. (1986), Kappeler & Gujer (1992)and Orhon et al. (1997). The maximum specific growth rate for this study was in Table 5 listed with

values from other countries. The temperature corrected value for H was 3.6 d-1. Arrhenius constant

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of 1.047 was used because it applied in the range of 15-32 oC and at the same time it was in the

range of other values reported (Zanoni, 1967).

Table 5 Comparison of the average specific growth rate from this study with other values reported. The values are given

at 20oC but the values from this study are given at 28oC.

Country H

[Kappelar and Gujer, 1992]1

Switzerland 1-8

[Bjerre,1996] Germany 6.8 + 1.6

[Henze et al., 1987] Denmark etc. 6.0

This Study Malaysia, Sri Pulai Johor 5.7*

The results from the inlet pint are ilustrated in Table 6.

The relationship between COD and the amount of organic matter was important, as it has almost

constant value of 1.4 mgO2/mg organic matter for wastewater [Henze et al., 1992]. This relationship

can be found in two ways: the ratio of CODtotal /VS and CODParticulate /VSS. On average, these

relationships were 0.5 mg/mg and 2.46 mg/mg, respectively. This inconsistency means that the VSwas too high compared with the COD measurements VSS is too low. This means that major

uncertainties are connected with the measurements of the VS and VSS measurements. This isconfirmed by the fact that the measured VSS is sometimes higher than the measured SS. The trays

used for measuring VS might have affected the measurement, because the preservation acid

damaged them.

Table 6: Average values for the inlet and outlet samples of the WSP.

Parameter Inlet Outlet Standard A Standard B

Temperature[C] 28.1 28.7 40 40pH[-] 6.3 7.28 6.0-9.0 5.5 9.0

CODtotal [ mg O2 /l] 446* 132* 50 100

CODdissolved [ mg O2 /l] 97*

40* - -

SS[g/l] 0.146*

0.04*1 50 100

VSS[g/l] 0.140* - - -

TS[g/l] 2.197 0.754 - -

VS[g/l] 0.834 0.439 - -

Ammonium[mg NH4+

- N/l] 23.1 16.8 - -

Nitrate [mg NO3- -N/l] 1.5 1.2 - -

Ss [mg O2 /l] 12.5 ND

XB [mg O2 /l] 65 2

XS1[mg O2 /l] 93 ND

X S2 [mg O2 /l] 309 ND

H [d-1] 5.7 -

* Dry weather concentration averages; ND = not detectable

Effluent Quality

Eight OUR measurements were conducted on the wastewater from the effluent of the WSP. Figure7 shows the OUR curve of the effluent. The SS utilized for growth and maintenance of the biomass

was products from slow hydrolysis. No initial SS and XS1 were detected. After 11 hours, the

production of SS from XS2 started to decrease to a level insufficient for sustaining growth and only

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maintenance energy requirement of the biomass were covered. After this point the only fractions

present were XB and XS3.

0 5 10 15 20

OUR (mgO2/l.h)

6

4

2

The overview of the effluent quality of this

WSP is presented in Table 6. The effluentwas partly complied with Standard B in the

context of Malaysian wastewater qualitystandard. For CODtotal, 83% of the

measured values were not able to meet the

Standard B. However the SS parameter waswithin the Standard B. Since there was no

nutrient standard required in Malaysia,therefore no effort was made by the

sewerage company on nutrient removal.

Figure 7. Example of an OUR measurement on WSP effluent.

Conclusions

From the performance analysis using respirometry, it can be concluded that organic fractionation

shown that the biodegradation was not able to meet the designed target, particularly for hydrolysis

of slowly biodegradable components in the WSP. This result was not expected since the retentiontime was sufficient. The high concentration of XS components also could be due to maximum

specific growth rate was found not to be temperature dependent, as it was expected. This indicates

that bacteria living under warm temperature conditions have almost similar capabilities in degradingorganic matter as bacteria in temperate climate.

AcknowledgementsThis study was conducted in UTM under the research collaboration between UTM and Aalborg

University, funded by Danish University Consortium on Environment and Development (DUCED).

The fieldwork has been conducted by C. L. Christensen, L. Milwertz and M.H. Thomsen.

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Documents

Performance Analysis of a Waste Water Stabilization Pond in Malaysia