wastewater pollution attenuation in a tropical urban wetland ......masaka wwtp serves only 8% of the...
TRANSCRIPT
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By:
Najib B. Lukoyaa (PhD Candidate)
BOKU, VIENNA AUSTRIA
Wastewater pollution attenuation in a tropical urban
wetland system: Nakayiba, Masaka, Uganda
Introduction
Materials and Methods
Results and Discussion
Conclusion and Recommendations
Presentation Outline
Wetland ecosystems have demonstrated a key role in treatment and/or polishing of
wastewater from Urban systems of East Africa (Co´zar et al. 2007; Kansiime et al. 2007a; Kansiime et al. 2007b; Kivaisi 2001; Kyambadde et al. 2004...etc)
Natural wetlands are under threat in the region due to; High Population, Urbanisation,
Agriculture, Industrialisation The impact of wetland degradation on the water quality regulation function has been
reflected and demonstrated by Lake Victoria Key drivers regarding wetlands degradation and water quality deterioration in the Lake Victoria basin
(East Africa)
Increasing Population
Rapid Urbanisation
Industrial development
Increase in wastewater quantity (discharged with inadequate or no treatment)
Introduction
Introduction-Cont’d
Population density (persons/sq km) – Impacts on lake buffer zone and water quality
Source; LVBC, 2010
Introduction-Cont’d
Wastewater treatment systems: Inadequate in terms of network coverage and treatment
efficiency
Municipal wastewater
Storm water from catchment
Industrial wastewater
Inadequate conventional WWTP
Surface water pollution-
Eutrophication
Risks and vulnerability to
communities-public health
Study Objectives and Rationale
Wetland pollution buffers in the Lave Victoria basin like Nakayiba (Masaka, Uganda) are
key landscape ecosystem features Most importantly, they offer municipal wastewater treatment systems, a low cost but
valuable polishing role coupled with a public health risk reduction due to potential surface and ground water pollution
The main objectives of this study were to;
Characterise the Masaka conventional Wastewater Treatment Plant (WTP) effluent quality
Assess the potential pollution attenuation through Nakayiba Wetland.
Broad Hypothesis: Degradation of the Masaka WTP infrastructure over the years has resulted into a decline
in treatment efficiency hence poor effluent quality. Nakayiba Wetland provides an effective natural pollution buffer Policy implication: Integration of wetland systems in planning urban landscapes to enhance effective
wastewater treatment and water quality regulation
Methods – Study Area: Masaka WWTP and Nakayiba
Wetland
Methods – Study Area: Masaka WWTP and Nakayiba Wetland
Methods – WWTP Effluent Characterization
Many Parameters used to characterise Wastewater – Few prioritised in East Africa due to
analytical limitations
Masaka WWTP effluent monitoring data was obtained from the National Water and
Sewerage Corporation (NWSC) (2008-2012).
Routine WWTP performance monitoring parameters:
pH, Electical Conductivity (EC), BOD, COD, Total suspended solids (TSS), and
Ammonium Nitrogen (NH4-N). Faecal coliform (many gaps)
Parallel analysis carried out during research period (2012-2013) To verify methods and
potential error limits
Rainfall data from local meteorological station (Kitovu-Masaka) obtained to characterise
seasonal variations and potential dilution effects
Methods – Downstream wastewater quality changes
Sampling points:
WWTP Effluent ; Upstream;
Effluent-Wetland confluence;
Three points down stream (WET
1, WET 2, DWN-outlet)
Parameters: Temp, pH, EC, BOD,
COD, TSS, feacal coliform, NH4-
N, TN, TP, PO4-P
Methods:
Temp, pH, EC (Probes on-site)
BOD, COD, TSS, NH4-N, TN,
PO4-TP,TP, feacal coliform
(standard methods-APHA, 1995
as adopted at NWSC laboratories)
Results – Effluent Characterization
Masaka WTP effluent did not meet the National Environment Discharge (Wastewater)
standards almost during the entire five years of the analysis period – for all key parameters
Mean effluent concentrations (Mean ± SE mg/l)
BOD5 (333.7 ± 32.0) standard 50mg/l
COD (666.9 ± 42.1) standard 100mg/l
TSS (346.6 ± 25.3) standard 100mg/l
NH4-N (55.73 ± 3.72) standard 10mg/l
Month
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
CO
D m
g/l
0
200
400
600
800
1000
1200
1400
16002008
2009
2010
2011
2012.
Standard 100mg/l
Month
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
BO
D5 m
g/l
0
200
400
600
800
1000
2008
2009
2010
2011
2012.
Discharge Standard 50mg/l
Results: Effluent Characterization- compliance with discharge standards
Month
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
N-N
H4
mg/l
0
20
40
60
80
100
120
1402008
2009
2010
2011
2012.
Standard 10mg/l
Results: Effluent Characterization-seasonal effects
Month
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
N-N
H4 m
g/l
20
30
40
50
60
70
80
90
100
Rain
fall
mm
0
20
40
60
80
100
120
140
160
180
N-NH4
Rainfall
Month
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Ele
ctr
ical C
ond
uctivity u
s/c
m
1400
1600
1800
2000
2200
2400
2600
2800
Rain
fall
mm
0
20
40
60
80
100
120
140
160
180
Electrical Conductivity
Rainfall
Month
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Co
nce
ntr
atio
n m
g/l
0
200
400
600
800
1000
1200
Ra
infa
ll m
m
0
20
40
60
80
100
120
140
160
180BOD
COD
Rainfall
TSS, BOD and COD – no clear
pattern (not significant).
Other factors influence –
external inputs from the town
unpredictable
Results: Pollution attenuation through the wetland
Despite the dilapidation in wastewater treatment performance,
Nakayiba wetland showed effective downstream pollution
attenuation through reduction of;
Organic matter,
Suspended solids,
faecal coliform
Nutrients (TN and TP)
Results: Pollution attenuation through the wetland-overall removal efficiency
Sampling site Cond. µs/cm pH BOD mg/l COD mg/l TSS mg/l TP mg/l O-PO4 mg/l NH4-N mg/l TN mg/l FC (log10)
Upstream 98.3±24.2 6.9±0.2 12.4±1.8 37.9±2.8 37.6±4.1 1.95±1.13 0.48±0.33 0.66±0.15 3.20±1.11 1.91E+03±7.79E+02
Effluent 1415.7±130.2 7.4±0.1 256.1±27.0 622.0±51.0 426.1±58.5 37.10±15.07 17.78±1.58 65.43±6.85 78.55±7.64 2.18E+09±8.88E+08
Wet 1 863.6±169.2 7.3±0.1 63.1±9.1 213.2±35.8 127.8±24.2 15.82±5.24 7.30±1.43 28.77±5.24 42.71±6.76 3.52E+06±1.44E+06
Wet 2 911.2±93.2 7.4±0.1 64.5±10.1 220.7±20.4 83.3±13.0 17.21±4.74 8.44±2.13 26.47±4.64 32.78±4.89 1.36E+03±5.57E+02
Downstream 300.2±43.5 7.0±0.1 35.2±2.4 109.5±21.0 76.4±7.4 5.81±2.53 2.27±0.63 4.51±1.55 16.24±2.20 1.43E+02±5.82E+01
Removal
Efficiency
(%) N/A N/A 86.3 82.4 82.1 84.3 87.2 93.1 79.3 99.9
Results: Pollution attenuation
through the wetland-overall removal
efficiency
Sampling site
Upstream Effluent input Wet_1 Wet_2 Downstream
Concentr
ation m
g/l
0
200
400
600
800
BOD
COD
TSS
Sampling site
Upstream Effluent input Wet_1 Wet_2 Downstream
Co
nce
ntr
atio
n m
g/l
0
20
40
60
80
100
TN
NH4-N
Sampling site
Upstream Effluent input Wet_1 Wet_2 Downstream
Co
nce
ntr
atio
n m
g/l
0
10
20
30
40
50
60
TP
PO4-P
Conclusion and recommendations
Masaka WWTP serves only 8% of the municipality and its effluent does not
meet discharge standards
Nakayiba wetland effectively buffers the Masaka WTP performance
This is essential in enhancing downstream pollution control as well as
safeguarding potential public health constraints.
It is therefore recommended that;
Masaka WWTP requires rehabilitation and expansion of the town sewage
network
Masaka Urban landscape plan needs to critically consider Nakayiba as a key
ecosystem for Municipal sanitation and wastewater management
Acknowledgement s to ADC , NWSC and Assoc. Prof.
Thomas Hein (WCL/BOKU)
Thank you for your attention