Hydrological implications of alternative Sanitation solutions in Urban slum areas
P.M. Nyenjea1, J.W. Foppena, S. Uhlenbrooka, R. Kulabakob, A. Muwangab
a
UNESCO-IHE, Institute for Water Education, Delft, The Netherlands
b
Makerere University, Kampala, Uganda
Corresponding author email: p.nyenje@unesco-ihe.org OR nyenje_p@yahoo.com
Abstract
The development and expansion of urban slums is widespread and inevitable with the ever increasing
urbanization in African mega-cities. Poor sanitation and water supply so is one of the major problems
in slum areas. Besides the spreading of diseases, one of the main problems associated with water and
sanitation in slum areas is related pollutant loads and nutrients entering and leaving the slum areas
either as surface water or groundwater. These pollutants affect the environment through the pollution
of groundwater and eutrophication of surface water due to extremely high fluxes discharging those
slum catchments. In relation to this, there still exists a big knowledge gap especially in African cities
regarding the transport of these contaminants in and from the slum catchments. This study thus
focuses on the hydrological aspects of sanitation solutions in slum areas. In this paper, we provide a
review of literature on hydrological, hydro-chemical and hydro-geological processes and quantities
that influence the transport of sanitation-related contaminants in order to identify the impacts on the
environment in both sanitized and unsanitized slum catchments. In this paper, we will also provide
preliminary results from a case study in Bwaise slum, Kampala Uganda in which the water quality and
a snapshot of existing hydrochemical processes in relation to nutrient transport are investigated. This
provides a first step in understanding the transport of nutrients in unsewered slum areas in sub-Saharan
1
Africa.
Key words - Contaminant transport; groundwater; sanitation; slums; sustainability
1. INTRODUCTION
Rapid urban growth, poor urban planning and lack of financial resources have led to widespread and
almost inevitable development of urban slums in African mega-cities (Kulabako et al., 2004; Mireri et
al., 2007; UN-Habitat, 2003). Already the sub-Saharan Africa (SSA) hosts the largest proportion of the
urban population residing in slums estimated at 72% in 2001 (UN-Habitat, 2003). Slums are mainly
characterized by high population density, poor drainage, poor water supply, lack of secure land tenure
and insufficient living space (UN-Habitat, 2003). As a result, municipal authorities usually face
immense challenges in providing basic services to their populations (Lawrence et al., 2000; Mireri et
al., 2007; UN-Habitat, 2003; Zingoni et al., 2005). Sanitation provision in particular, is very poor.
Most often a sewer system is not present and the commonly-used on-site wastewater handling and
reuse practices are frequently unplanned, uncontrolled and inefficient (Foppen and Schijven, 2006;
Lawrence et al., 2000; Wakida and Lerner, 2005). Given the rapidly increasing wastewater generation
in urban settlements, most households poorly dispose of their untreated solid and liquid waste on-site
generating high rates of infiltration to aquifers and pollution loads into streams and fresh water bodies.
This has led to serious health risks characterized by prevalence of diseases in form of epidemics like
cholera and diahorrea especially among children (Nsubuga et al., 2004; Zingoni et al., 2005). Besides
the spreading of diseases, one of the major problems associated with sanitation in slum areas is related
to the transport of contaminants in and out of the slum catchment either as surface water or
groundwater. This water pollutes drinking water, obtained from groundwater aquifers with further
increased incidence of cholera and diarrhea (Howard et al., 2003; Nsubuga et al., 2004), or eutrophies
surface water, due to extremely high nutrient fluxes discharging from those slum catchments
2
(Kulabako et al., 2007). Eutrophication, however, remains a major concern in African cities (Howard
et al., 2003; Kulabako et al., 2008). The input of nutrients (especially nitrogen and phosphorous) to
both surface and groundwater from urban wastewater discharge is increasing rapidly and has led to
serious environmental problems causing eutrophication of near-shore waters and degradation of fresh
water quality (Dillion, 1997; Kemka et al., 2009; Kulabako et al., 2008; Nhapi and Tirivarombo,
2004).
Few studies have been carried out in sub-Saharan Africa to assess nutrient generation and transport
from unsewered urban areas and slums settlements. Likewise few studies (e.g. Kortatsi, 2006;
Kortatsi, 2007; Taylor et al., 2009) have tried to examine the processes influencing the transport of
contaminants and nutrients. Early studies have generally focused on assessing the impacts of sanitation
on groundwater to identify contamination levels in relation to drinking water standards (Byamukama
et al., 2000; Cronin et al., 2007; Dzwairo et al., 2006; Howard et al., 2003; Mwiganga and Kansiime,
2005; Wakida and Lerner, 2005). This paper therefore provides a review of literature on hydrological,
hydro-chemical and hydro-geological processes and quantities that influence the transport of
sanitation-related contaminants and their relation to eutrophication in urban areas in sub-Saharan
Africa. Preliminary results from a case study in Bwaise slum in Kampala, Uganda will also be given.
2. HYDROLOGICAL ASPECTS OF SANITATION
Hydrological implications in urban areas are mainly related to urban landuse changes and sanitation
(Leopold, 1968; Thornton et al., 1991). Changes in landuse mainly affect hydrological responses such
as runoff and recharge. Runoff and recharge are generally modified by the percentage of area made
impervious which affects the rate at which water is transmitted across the land and also results in
lagging of peak flows. Sanitation on the other hand affects the hydrology through deterioration of
water quality as a result of introducing domestic wastewater pollutants (Dillion, 1997). These
pollutants contain dissolved minerals which pollute groundwater and also act as nutrients hence
3
causing eutrophication of streams and lakes. The contamination of groundwater aquifers by domestic
wastewater is an important hydrological aspect of sanitation since groundwater is a major source of
potable water in slum areas and is also an important component of base flow in streams and lakes. The
hydro-geological settings of an area (e.g. alluvial deposits, volcanic systems, consolidated sedimentary
rocks or weathered basement complexes) in a large part determine the how aquifers respond to
groundwater contamination (Morris et al., 2006). Usually, soils present can greatly attenuate these
contaminants. The degree of attenuation depends on the soil/rock types especially in the upper soils
layers where biological activity is greatest (Morris et al., 2006). In assessing the hydrological aspects
of sanitation, it is therefore essential to evaluate soil types, characteristics and hydro-geological
processes in the study area.
Of the most crucial global problems, eutrophication remains one of the most prevalent resulting from
high-nutrients loads mainly phosphorous and nitrogen. In excess, these nutrients cause extensive algae
blooms, depletion of dissolved oxygen, massive fish kills and navigation problems which impacts on
the beneficial uses of water (Verschuren et al., 2002). Urban areas in sub-Saharan Africa are
increasingly experiencing eutrophication of fresh water bodies due to increased discharge of nutrientrich sewage into the environment (Kemka et al., 2006). Slum areas in particular are the largest source
of these nutrients (Dillion, 1997). Knowledge of the source and transport of nutrient pollutants in
urban areas is thus crucial to understanding the drivers for the eutrophication in mega-cities in subSaharan Africa.
3.0 EUTROPHICATION IN SUB-SAHARAN AFRICA
3.1 Evidence of eutrophication in urban areas in SSA
Eutrophication is currently on the rise in SSA. According to a recent issue of The Water Wheel (Water
Research Commission, South Africa; issue September/October 2008), 28% of the lakes/reservoirs in
Africa are impaired by eutrophication. In inland Sub-Saharan Africa, there are many documented
cases of eutrophication of fresh water resources: Lake Victoria, which is shared between Uganda,
4
Tanzania, and Kenya (e.g. Cózar et al., 2007; Hecky and Bugenyi, 1992; Kansiime and Nalubega,
1999; Muggide, 1993; Oguttu et al., 2008; Scheren et al., 2000; Verschuren et al., 2002; Witte et al.,
2008), Lake Chivero in Zimbabwe (Jarvis et al., 1982; Magadza, 2003; Moyo and Worster, 1997;
Munro, 1966; Nhapi, 2008; Nhapi et al., 2004; Nhapi et al., 2006; Robarts and Southall, 1977), Lake
Albert on the boundary between Uganda and Congo (Campbell et al., 2005; Talling and Talling,
1965), various fresh water resources in South-Africa, like the Zeekoevlei (Das et al., 2009; Das et al.,
2008), Rietvlei (Oberholster et al., 2008), and Lake Krugersdrift (Oberholster et al., 2009), rift lakes in
Ethiopia (Beyene et al., 2009; Devi et al., 2008; Talling, 1992; Talling and Talling, 1965; Zinabu et
al., 2002; Zinabu and Taylor, 1989), or inland delta lakes and fresh water resources in western SSA,
like in Cameroon and Nigeria (Arimoro et al., 2007; Kemka et al., 2006). In urban areas in subSaharan Africa, wastewaters from sewage and industries are often discharged untreated in the
environment and are increasingly becoming a major source of nutrients, causing eutrophication of
surface water bodies (e.g. Bere, 2007; Beyene et al., 2009; Dillion, 1997; Kemka et al., 2006;
Kulabako et al., 2007; Mladenov et al., 2005; e.g. Nhapi and Tirivarombo, 2004). Table 1 shows some
documented cases of eutrophication in SSA caused by domestic wastewater from urban areas.
Table 1: Evidence of Eutrophication in urban areas in SSA
Lake
Observations
Lake Victoria, Strong eutrophication effects in the inshores.
East Africa
Yaounde lake,
Cameroon
Lake Chivero
(Zimbabwe
Hennops
River, South
Africa
Borkena River
in Ethiopia
Source
(Hecky
et
al.,
1994); (Muggide,
1993).
Increased nutrient loads at Murchsion base of the Lake (Kansiime et al.,
estimated at 28mg/l HH4-N from 5.6mg.l NH4-N in 1999
2007)
Hypertrophic due to increased inflow of domestic (Kemka et al.,
wastewater from Yaounde city
2006)
Eutrophying influence from Marimba River, which receives (Nhapi
and
treated wastewater from the Crowborough Sewage Tirivarombo, 2004)
Treatment Works in Harare.
Receives treated effluent from the Hartbeesfontein Sewage (Oberholster et al.,
Purification Works, causing eutrophication in the Rietvlei 2008)
nature reserve wetland area.
Hypertrophic due to inflow of wastewater from the towns of (Beyene et al.,
Dessie and Kombolcha
2009)
5
Orogodo River Receives an uncontrolled inflow of nutrient masses from the (Arimoro
in Nigeria
towns of Agbor, Owa-Ofie, Ekuma-Abovo and Oyoko, 2007)
before it ends up in the swamps between Obazagbon-Nugu
and the oil rich town of Oben in Edo State, southern Nigeria
et
al.,
3.2 Nutrient production and disposal in Urban Areas
Several studies currently indicate that nutrient production in urban areas in SSA is more related to
wastewater disposal, especially in densely populated areas (Cronin et al., 2003; Kemka et al., 2006;
Wakida and Lerner, 2005). This immediately poses a number of important questions: How much
wastewater is produced in the larger cities in SSA, which percentage of the wastewater produced is
treated, and what are the predominant treatments and (un)controlled disposal mechanisms? Table 2
gives key figures on the water and sanitation coverage in selected mega-cities in Africa. Although
water supply and sanitation coverage is on average above 70% across sub-Saharan Africa, sewerage
coverage is generally below 30%. It is also clear from Table 2, that the non-sewered part of the total
urban population is more than 70% while 63% of the population (difference between percentage
‘having access to sanitation’ and percentage ‘connected to a sewer’) rely on on-site sanitation systems
either septic tanks or traditional/improved pit latrines. This means that about 63% of the population in
mega-cities in sub-Saharan Africa eventually discharges their wastewater into aquifers underlying
these urban areas.
Based on the data in Table 2, the potential wastewater flows can be obtained by multiplying the
population with the consumption rates factored by the unaccounted for water percentages (Table 3).
With the exception of a few cities in Southern Africa, such as Windhoek, there is a very high
proportion of untreated wastewater across all major cities in Africa compared to the total wastewater
production. On average, over 80% of the wastewater volumes produced in large cities in sub-Saharan
Africa are untreated and are either discharged in the soil via on-site sanitation systems or directly
discharged into rivers and lakes.
6
Table 2: Water and sanitation coverage in selected mega-cities in sub-Saharan Africa in 1999
Water
UnPopulation served
produaccounted % Connections
Pop.
Water Sanitation
ction
for water
City (Country)
(1000s) (%)
(%)
(l/c/d)
(%)
Water Sewer
East Africa:
Addis
Ababa
(Eth)
2,444
98
NMV
40
40
4
NMV
Nairobi (Ken)
2,086
100
99
189
40
78
30
Kigali (Rwa)
445
NMV NMV
118
NMV NMV
Dar-es-salaam
(Tan)
3,000
61
98
150
60
7.3
5
Kampala (Uga)
1,200
72*
78*
110
32*
71*
7*
Southern Africa:
Maputo (Moz)
967
99
96
133
34
22
25
Windhoek (Nam) 271
100
100
214
11
83
83
Harare (Zim)
2,380
NMV NMV
156
30
NMV NMV
Lusaka (Zam)
1,212
81
NMV
225
56
26
NMV
Mbabane (Swa)
94
75
97
100
32
38
47
Luanda (Ang)
4,000
50
62
30
60
18
17
West Africa:
Lome (Tog)
806
67
80
66
28
55
1.02
Cotonou (Ben)
667
81
83
62
41
81
0.2
Dakar (Sen)
1,925
78
78
128
26
63
26
Source:
(JMP, 1999) and (WHO, 2000); NMV = No meaningful value; * 2007 estimates from
Water and Sanitation sector performance report 2007, Uganda.
Table 3: Estimated wastewater volumes in a number of mega-cities in Sub-Saharan Africa
Wastewater production (106 m3/y)
City (Country)
Total
East Africa:
Addis Ababa (Eth)
21.4
Nairobi (Ken)
86.3
Kigali
?
Dar-es-salaam (Tan)
65.7
Kampala (Uga)
32.8
Southern Africa:
Maputo (Moz)
31.0
Windhoek (Nam)
18.8
Harare (Zim)
94.9
Lusaka (Zam)
43.8
Mbabane (Swa)
2.3
Luanda (Ang)
17.5
West Africa:
Lome (Tog)
14.0
Cotonou (Ben)
8.9
Dakar (Sen)
66.6
Source:
JMP, 1999 and WHO, 2000;
Treated
Not treated
?
25.9
?
3.3
2.3
?
60.4
?
62.4
30.5
7.7
15.6
?
?
1.1
3.0
23.2
3.2
?
?
1.2
14.5
0.1
0.0
17.3
13.8
8.9
49.2
7
Dependent on the population size of the city, these untreated wastewater volumes can range from
approximately 20 to 60 million m3/y. When multiplied with the composition of medium strength
wastewater (Table 4), then an approximate annual average of 1 million kg N and 0.1 million kg P is
produced by the mega-cities mentioned in Tables 2 and 3.
Table 4: Characteristics of low, medium, and high strength wastewater
Parameter
BOD (mg/l)
pH
Cl (mgl/)
Ammonia, NH4-N (mg/l)
Nitrate, NO3-N (mg/l)
t- PO4 (mg/l)
Alkalinity (mg/l CaCO3)
Na (mg/l)
Ca and Mg (combined) (mg/l)
Boron (mg/l)
Source:
(Feigin et al., 1991)
Low
100
7
10
10
0
4
50
10
5
< 0.123 - 2.0
Medium
200
7.2
150
25
0.2
10
200
120
10
High
350
8
650
50
1.5
36
400
460
25
In informal settlements, population densities are high, sewerage is lacking, and, if present, sanitation
facilities are almost exclusively on-site (mainly pit latrines, VIP’s, elevated pit latrines, etc) (Kulabako
et al., 2007; Zingoni et al., 2005). The nutrient load produced in these areas is extremely high since the
proportion of urban population living in urban areas is high (Figure 1b). Given the increasing
urbanisation trends in the future (Figure 1a), the number of people living in urban slums in SSA is
expected to rise continuously which will give rise to increased nutrient fluxes from these areas.
8
70
Lusaka (Zambia)
(a)
% of slum
household in
city
(b)
Harare (Zim)
61.67
Urbanisation (%)
60
Windhoek (Nam)
50
50.02
% of total
urban
population
(2007)
Nairobi (Ken)
Kampala (Uga)
40
39.94
30
20
Kigali (Rwa)
32
Johannesberg (SA)
Dar es salaam (Tan)
23.6
Maputo (Moz)
Addis Ababa (Eth)
10
Lilongwe (Mal)
0
1970
1990
2010
2030
2050
0
20
40
60
80
100
Figure 1: Urbanisation trends and slum proportions in Africa: (a) Urbanisation trends % 19702050; (b) Slum proportions (%) in selected cities. Source: (UN-Habitat, 2008)
4. ROLE OF THE URBAN WATER CYCLE IN NUTRIENT TRANSPORT
How important are these loads in the entire water balance of the city and what is the role of the
hydrological processes in the transport of nutrients to surface water bodies? Ideally, a hypothetical
water balance of the upper part of the soil (e.g. 2-4 m below the surface) of an urban area (Fig. 2)
consists of: Precipitation; Evapotranspiration; Imported water; Outflow/inflow to/from groundwater;
Storm water runoff; and Sewer outflow. All these variables indicate flow across the boundary of the
urban catchment (Marsalek et al., 2008). Within the urban catchment the following terms can be
discerned: Impervious surfaces, soil, household and sewerage (wastewater, storm water, or combined).
As an example, the water balance of Kampala city, Uganda (Fig. 2) is given.
9
imported
water
170
evapotranspiration
1151
Precipitation
1450
508
943
Leakage 17
impervious
surface evap. 51
storage
24
outdoor use 5
impervious
surface
148
ET
1100
457
137
indoor use
Pervious surface [soil]
surface
runoff
320
148
wastewater
generated
138
onsite
5
10
public sewer
120
Stormwater sewer
320
Springs
combined sewer
10
10
Groundwater
Total discharge
330
Lake Victoria
Figure 2: Estimated water balance (mm/y) for the upper soil compartment of Kampala city,
Uganda (within the dashed line; data from KDMP, 2004 and Kaggwa, 2009)
The following dominant fluxes of water (or: hydrological pathways) can be identified:

Most of the precipitation (1450 mm/y) is evaporated (1151 mm/y), while the rest (330 mm/y)
flows into Lake Victoria via open and closed drains present in Kampala city.

Around 170 mm of water is imported (from Lake Victoria) and used indoor. Although there
are some leakages (17 mm/y) and outdoor usages (5 mm/y), most of this water (148 mm/y) is
converted into wastewater, and of this wastewater, 138 mm/y is disposed off via on-site
treatment facilities (pit latrines, septic tanks, etc.), while 10 mm/y is transported to Lake
Victoria.

Part of the wastewater disposed of on-site is mixed and diluted with precipitation. Of the total
amount of water reaching the soil (= 1245 mm/y), finally around 120 mm/y recharges
groundwater, of which 10 mm/y reappears as springs. Most of the remainder (= 1100 mm/y)
10
evaporates, while some water (= 24 mm/y) is stored. Of course, the long term storage
component should be zero, indicating a situation of steady state. However, in this case,
Kampala itself is not in a situation of steady state: urbanization is taking place, and, as one of
the consequences, water is stored in the subsurface, and the groundwater table is –on averageon the rise.
Given the scarcity of data, it is difficult to draw up general conclusions on water balances in cities in
sub-Saharan Africa. Nevertheless, based on the example above and available literature, the amount of
wastewater that is disposed via on-site sanitation facilities or via drainage channels without being
treated ranges from 10% to 50%. This is a considerably high percentage, given that precipitation is the
most important, if not the only ‘wastewater diluting agent’ present.
In slum areas in sub-Saharan Africa, most of the wastewater generated is disposed of via onsite
sanitation systems. Of recent, it has become apparent that his way of handling wastewater in
developing countries generates rather high rates of infiltration leading to increase recharge. However,
increased recharge due to urbanization is somewhat contradictory since urbanization involves
construction impervious surfaces such as roofs and paved surfaces which reduce recharge. Impervious
surfaces do indeed reduce recharge from precipitation, and on occasions, cause fast runoff responses
leading to flooding of lower parts of the city. Good examples of the latter are Bwaise III slum area in
Kampala, Uganda (Kulabako et al., 2004, 2007 and 2008), which is frequently flooded by stormwater
from upland catchment areas and other various other slum areas in Nairobi (Kenya), Kampala
(Uganda), Lagos (Nigeria), Accra (Ghana), Free Town (Sierra Leone) and Maputo (Mozambique)
(AAI, 2006). In contrast, Kelbe et al. (1991) reported a reduction in peak discharge in South Africa
from catchments inhabited with informal settlements as compared to similar pristine catchments. It
was not clear from his research the cause of such a hydrological response.
11
5. NUTRIENT TRANSPORT PROCESSES
5.1
Overview of processes for nutrients N and P
The dominant processes related to nitrogen are nitrification and denitrification (Fig. 3). These are
redox reactions which occur depending on the redox state of the environment. The dominant form of
N from wastewater entering the environment (stream, lake, river, soil, and aquifer) is ammonium,
NH4+. Some organic nitrogen will also be introduced which may be rapidly transformed into
ammonium. These N forms are usually represented as Total Kjeldahl N, which is the sum of organic
N, ammonium (NH4+) and ammonia (NH3). Under anaerobic conditions, ammonium (NH4+) and
ammonia (NH3) are stable, and when conditions become aerobic, ammonium is rapidly oxidised into
nitrate (NO3-) via unstable nitrite (NO2-) - this process is called nitrification. Conversely, when a
nitrate-rich environment becomes anaerobic, nitrate is reduced into nitrogen gas (N2), which is stable
and ultimately may escape from the aquifer – a process is called denitrification.
HETEROTROPHIC
CONVERSION
Organic compounds
containing nitrogen
UNDER AEROBIC CONDITIONS
Ammonification
Ammonium
(NH4+)
Assimilation
UNDER
ANAEROBIC
CONDITIONS
Nitrification
Nitrite
(NO2-)
Assimilation of
N into organic
compounds
Nitrogen
fixation
Nitrogen
gas (N2)
Denitrification
Denitrification
Nitrification
Nitrate
(NO3-)
Assimilation of
N into organic
compounds or
denitrification
Nitrous oxide
(N2O)
Figure 3: Nitrogen transformation processes under different redox conditions (after Lawrence et
al., 1997)
Another process associated with N is the sorption of ammonium ions (NH4+) onto sediments through
cation exchange. This results into release of exchangeable ions such as Ca and Mg in water, causing
additional hardness. Several authors have indeed found that aquifers contaminated with wastewater
have hard water characterised by high concentrations of Ca and Mg (Foppen et al., 2008; Lawrence et
al., 2000; Navarro and Carbonell, 2007).
12
Fig. 4 shows the processes related to phosphorous (P). When P from wastewater enters the
environment, it is present as inorganic ortho-phosphate (o-PO43-), organic P, or as particulate P
(Thornton et al., 1999). Of these, ortho-phosphate (o-PO43-) is the important readily available form of
soluble P, which is ‘used’ in the eutrophication process.
Inorganic
orthophosphate +
Organic phosphorus
anaerobic
digestion
Inorganic
orthophosphate
(o-PO43-)
Sorption
Fe and Mn oxyhydroxides
Precipitation /
dissolution
Hydroxy-apatite:
Vivianite:
Variscite
Strengite
(Ca5(PO4)3OH; Ksp = -3.4)
(Fe3(PO4)2·8H2O; Ksp= -36.0)
(AlPO4·2H2O; Ksp= -22.1)
(FePO4; Ksp= -26.4)
Figure 4: The fate of phosphorus in the environment
Phosphates, however, have a strong affinity to sorb onto soil, aquifer and river sediment grains, and
thus they have a reduced mobility when traveling through soils and aquifers. Phosphate is normally
sorbed onto positively charged Fe and Mn oxides (i.e. clay particles) and often tends to accumulate in
the soil (Zanini et al., 1998). Hence eroded sediment can be a significant source of P loading in water
bodies. Besides sorption, phosphates are not very soluble: the solubility products of a number of
important phosphate salts are very low (Fig. 4). As a result, phosphate salts tend to precipitate fairly
quickly. However, depending on the redox condition, P can be remobilised caused by reductive
dissolution of P present in sediments as FePO4 (Datry et al., 2004; Zurawsky et al., 2004). Besides the
reductive dissolution of phosphates, P can also desorb from sediments in lake and river bottoms. This
is an equilibrium process, which is usually governed by a Freundlich isotherm whereby the phosphate
concentration both on the sediment ( Psed ) and in surface water ( P ), plus two constants are important
(Golterman and De Oude, 1991).
13
5.2
Nutrient processes in SSA
In SSA, process-related research on N and P has been mainly focused on the natural retention and
carrying capacity of the environment. Examples include Bere (2007) who studied natural retention
capacity due to swamps in Chinyika River Zimbabwe, Kansiime et al., (2007; 2005) who described
nutrient uptake processes in wetlands in Uganda and Van Dam et al. (2007) who constructed a
dynamic model for nitrogen cycling to understand the processes contributing to nitrogen retention in
the wetland and to evaluate the effects of papyrus harvesting on the nitrogen absorption capacity.
Although more than 60% of wastewater in mega-cities in SSA is disposed via the sub-surface,
research aimed at identifying the fate and transport mechanisms of both N and P in soils and aquifers
is almost completely absent. An exception is Kulabako et al. (2007) who looked at the fate of P in the
Bwaise III slum area in Kampala, and found that P transport mechanisms appeared to be a
combination of adsorption, precipitation, leaching from the soil media and P entrapped in the colloids,
with the latter two, playing a far important role. In general, all samples taken from the shallow
groundwater of the Bwaise III area pointed towards oxic conditions. The presence of nitrate and
therefore the oxic state of groundwater is reported for various locations in the region (Alagbe, 2006;
Arimoro et al., 2007; Barrett et al., 1999; Cronin et al., 2007; Dzwairo et al., 2006; Edet and Okereke,
2005; Efe, 2005; Faillat, 1990; Ikem et al., 2002; Nevondo and Cloete, 1999; Yidana et al., 2008;
Zingoni et al., 2005). There are very few reports testifying of deeply anaerobic conditions of urban
groundwater, whereby sulphides are produced or methane is formed. Exceptions are discussed in
Kortatsi (2007) and Kortatsi et al. (2008), who have reported on the reductive dissolution of iron
oxides and the presence of Fe2+ in the regolith of Ghana at depths varying between 90 and 120 meter.
Dissolved organic carbon (DOC) can be considered a primary driver of chemical processes in aquifers
contaminated with wastewater (Lawrence et al., 2000). Decomposition of DOC by bacterial depletes
oxygen and may lead to nitrate reduction followed by release of Mn and Fe (II), the production of
sulphides and finally methane as suggested in the redox-model formulated by Lawrence et al. (2000).
14
In all reported cases in urban areas in SSA, not even the first zone (nitrate reducing zone) is reported.
It remains unclear why these anaerobic processes have not been identified.
6. CASE STUDY
6.1 Proposed study
In order to make a start with managing the urban population related eutrophication in urban slums,
many actions are required. As a first step, we suggest carrying out an inventory of the water quality in
the study area and it’s urban. This will provide preliminary results in understanding the existing
hydrochemical processes and impacts of sanitation on groundwater and surface water in the study area
and the downstream ecosystem.
6.2 Description of the study area
Bwaise III slum is located in the northern part of Kampala
(b)
(a)
city in Uganda, approximately 4km from the city center (Fig.
5). It is a low-lying area (mostly reclaimed wetland) with a
high water table (<1.5m). The parish has an area of 57ha.
Bwaise III is a typical urban poor settlement in the city,
largely unplanned with lack of basic services, poor road
(c)
access and deplorable housing. Bwaise slum is drained by
Nsooba channel (Fig. 5c) which drains northwards into Lake
Kyoga through Lubigi swamp and Mayanja River.
6.3 Proposed methodology
In order to understand the existing hydrochemical processes and
Figure 5: Location of the study area
impacts of sanitation on groundwater and surface water, sampling will be done in the Bwaise and its
urban catchment including storm water drains, protected springs, boreholes and shallow wells to have
a snapshot of the hydrochemistry and to be able to explain the processes taking place. All sampling
15
stations will be geo-referenced. A minimum set of water quality parameters including pH, EC,
Temperature, DO, NO3, NH4, PO4, SO4 will be tested onsite using a field kit. Pathogenic bacteria
(E.Coli) will also be tested in the Public Health Laboratory, Makerere University. Some samples will
be shipped to UNESCO-IHE Laboratory for a complete hydrochemical analysis of anions and cations.
In order to discern the hydrogeological implication on contaminant transport, we will also review
existing literature and also study soils and aquifer characteristics in the study area.
6.4 Expected results
It is expected that the results enable a detailed understanding of the hydrochemical processes and
evolution of chemical concentrations and of water pollution in the waters and soils of the study area.
The results are also expected to provide a preliminary idea on the contribution of the slum catchment
to the downstream swamp compared to the overall urban catchment.
CONCLUSIONS
A great deal of hydrological problems are currently experienced in mega-cities in sub-Saharan Africa.
Of the most crucial one is the eutrophication of surface water bodies caused by the increased input of
nutrients. Currently, it happens that domestic wastewater generation and improper disposal are
currently the main sources of these nutrients causing deterioration of water quality including the
pollution of groundwater and eutrophication of water resources. Over 80% of the wastewater
generated from urban settlements in sub-Saharan Africa is disposed of untreated or via on-site
sanitation facilities. This corresponds to 20-60million m3/y of this wastewater which is equivalent to 1
million Kg N/y and 0.1 million Kg P/yr. This is rather a very high value considering that wastewater
volumes are generally over 10% of the total precipitation in urban areas in SSA. Available literature
shows that research aimed at identifying the fate and transport mechanisms of N and P in soils in SSA
is almost completely absent. Conversely, the soil aquifer treatment characteristics of the regoliths,
which cover a large part of SSA, are unknown. There are also few reports testifying on deeply
16
anaerobic conditions which are expected in aquifers contaminated with wastewater as demonstrated in
the studies done by Foppen et al. (2008) and Lawrence et al. (2000). The presence of nitrate and
therefore the oxic state of groundwater has, however, been reported for various locations in the region
As a first step with managing the urban population-related eutrophication, we propose to carry out a
water quality inventory in the study area and the urban catchment where it is located to have a
snapshot of the hydrochemistry and possible processes existing in the study area. The results with
provide an initial understanding of the contribution of slum areas to nutrient release in urban slums in
SSA.
Acknowledgments This research was funded by the Netherlands Ministry of Development
Cooperation (DGIS) through the UNESCO-IHE Partnership Research Fund. It was carried out jointly
with UNESCO-IHE, Makerere University, and the Kampala City Council in the framework of the
Research Project ‘Addressing the Sanitation Crisis in Unsewered Slum Areas of African Mega-cities’
(SCUSA). It has not been subjected to peer and/or policy review by DGIS, and, therefore, does not
necessarily reflect the view of DGIS.
REFERENCES
AAI, 2006. Climate change, urban flooding and the rights of the urban poor in Africa - key findings
from
six
African
cities.
Website:
www.actionaid.org.uk/doc_lib/urban_flooding_africa_report.pdf (accessed July 2009)
Alagbe, S.A., 2006. Preliminary evaluation of hydrochemistry of the Kalambaina Formation, Sokoto
Basin, Nigeria. Environmental Geology, 51(1): 39-45.
Arimoro, F.O., Ikomi, R.B. and Iwegbue, C.M.A., 2007. Water quality changes in relation to Diptera
community patterns and diversity measured at an organic effluent impacted stream in the
Niger Delta, Nigeria. Ecological Indicators, 7(3): 541-552.
Barrett, M., Nalubega, M. and Pedley, S., 1999. On-site sanitation and urban aquifer systems in
Uganda. Waterlines, Vol. 17, No. 4: pp. 10-13.
Bere, T., 2007. The assessment of nutrient loading and retention in the upper segment of the Chinyika
River, Harare: Implications for eutrophication control. Water SA, 33(2): 279-284.
Beyene, A., Legesse, W., Triest, L. and Kloos, H., 2009. Urban impact on ecological integrity of
nearby rivers in developing countries: the Borkena River in highland Ethiopia. Environmental
Monitoring and Assessment, 153(1-4): 461-476.
Byamukama, D., Kansiime, F., Mach, R.L. and Farnleitner, A.H., 2000. Determination of Escherichia
coli contamination with chromocult coliform agar showed a high level of discrimination
17
efficiency for differing fecal pollution levels in tropical waters of Kampala, Uganda. Applied
and Environmental Microbiology, 66(2): 864-868.
Campbell, L.M., Wandera, S.B., Thacker, R.J., Dixon, D.G. and Hecky, R.E., 2005. Trophic niche
segregation in the Nilotic ichthyofauna of Lake Albert (Uganda, Africa). Environmental
Biology of Fishes, 74(3-4): 247-260.
Cózar, A., Bergamino, N., Mazzuoli, S., Azza, N., Bracchini, L., Dattilo, A.M. and Loiselle, S.A.,
2007. Relationships between wetland ecotones and inshore water quality in the Ugandan coast
of Lake Victoria. Wetlands Ecology and Management, 15 (6): 499-507.
Cronin, A.A., Hoadley, A.W., Gibson, J., Breslin, N., Komou, F.K., Haldin, L. and Pedley, S., 2007.
Urbanisation effects on groundwater chemical quality: findings focusing on the nitrate
problem from 2 African cities reliant on on-site sanitation. Journal of Water and Health, 5(3):
441-454.
Cronin, A.A., Taylor, R.G., Powell, K.L., Barrett, M.H., Trowsdale, S.A. and Lerner, D.N., 2003.
Temporal variations in the depth-specific hydrochemistry and sewage-related microbiology of
an urban sandstone aquifer, Nottingham, United Kingdom. Hydrogeology Journal, 11(2): 205216.
Das, S.K., Routh, J., Roychoudhury, A.N., Klump, J. and Ranjan, R.K., 2009. Phosphorus dynamics in
shallow eutrophic lakes: an example from Zeekoevlei, South Africa. Hydrobiologia, 619: 5566.
Das, S.K., Routh, J., Roychoudhury, A.N. and Klump, J.V., 2008. Elemental (C, N, H and P) and
stable isotope (delta N-15 and delta C-13) signatures in sediments from Zeekoevlei, South
Africa: a record of human intervention in the lake. Journal of Paleolimnology, 39(3): 349-360.
Datry, I., Malard, F. and Gibert, J., 2004. Dynamics of solutes and dissolved oxygen in shallow urban
groundwater below a stormwater infiltration basin. Science of the Total Environment, 329(13): 215-229.
Devi, R., Tesfahune, E., Legesse, W., Deboch, B. and Beyene, A., 2008. Assessment of siltation and
nutrient enrichment of Gilgel Gibe dam, Southwest Ethiopia. Bioresource Technology, 99(5):
975-979.
Dillion, P., 1997. Groundwater pollution by sanitation on tropical islands, International Hydrological
Programme - IHP-V Project 6-1, UNESCO, Adelaide, Australia.
Dzwairo, B., Hoko, Z., Love, D. and Guzha, E., 2006. Assessment of the impacts of pit latrines on
groundwater quality in rural areas: A case study from Marondera district, Zimbabwe. Physics
and Chemistry of the Earth, 31(15-16): 779-788.
Edet, A. and Okereke, C., 2005. Hydrogeological and hydrochemical character of the regolith aquifer,
northern Obudu Plateau, southern Nigeria. Hydrogeology Journal, 13(2): 391-415.
Efe, S.I., 2005. Quality of water from hand dug wells in Onitsha Metropolitant areas of Nigeria. The
Environmentalist, 25: 5-12.
Faillat, J.P., 1990. Sources of Nitrates in Fissure Groundwater in the Humid Tropical Zone - the
Example of Ivory-Coast. Journal of Hydrology, 113(1-4): 231-264.
Feigin, A., Ravina, I. and Shalhevet, J., 1991. Irrigation with Treated Sewage Effluent: Management
for Environmental Protection. Springer, Berlin, ISBN 3-540-50804-X.
Foppen, J.W.A. and Schijven, J.F., 2006. Evaluation of data from the literature on the transport and
survival of Escherichia coli and thermotolerant coliforms in aquifers under saturated
conditions. Water Research, 40(3): 401-426.
Foppen, J.W.A., van Herwerden, M., Kebtie, M., Noman, A., Schijven, J.F., Stuyfzand, P.J. and
Uhlenbrook, S., 2008. Transport of Escherichia coli and solutes during waste water infiltration
in an urban alluvial aquifer. Journal of Contaminant Hydrology, 95(1-2): 1-16.
Golterman, H.L. and De Oude, N.T., 1991. Eutrophication of lakes, rivers and coastal seas., The
Handbook of Environmental Chemistry 5 (PART A), pp. 79-124.
Hecky, R.E. and Bugenyi, F.W.B., 1992. Hydrology and chemistry of the African Great Lakes and
water issues: problems and solutions. Mitt. Int. Ver. Limnol., 23: 45-54.
18
Hecky, R.E., Bugenyi, F.W.B., Ochumba, P., Talling, J.F., Mugidde, R., Gophen, M. and Kaufman,
L., 1994. Deoxygenation of the deep-water of Lake Victoria, East Africa. Limnology and
Oceanography, 39(6): 1476-1481.
Howard, G., Pedley, S., Barrett, M., Nalubega, M. and Johal, K., 2003. Risk factors contributing to
microbiological contamination of shallow groundwater in Kampala, Uganda. Water Research,
37(14): 3421-3429.
Ikem, A., Osibanjo, O., Sridhar, M.K.C. and Sobande, A., 2002. Evaluation of groundwater quality
characteristics near two waste sites in Ibadan and Lagos, Nigeria. Water, Air, and Soil
Pollution, 140(1-4): 307-333.
Jarvis, M.J.F., Mitchell, D.S. and Thornton, J.A., 1982. Lake Mcllwaine - The Eutrophication and
Recovery of a Tropical Man-Made Lake. Aquatic Macrophytes and Echhormia crassipes. Dr.
W. Junk Publishers, The Hague, the Netherlands, 137-144 pp.
JMP, 1999. Joint Monitoring Programme. Website: www.wssinfo.org (accessed June 2009)
Kansiime, F., Kateyo, E., Oryem-Origa, H. and Mucunguzi, P., 2007. Nutrient status and retention in
pristine and disturbed wetlands in Uganda: Management implications. . Wetlands Ecology and
Management, 15(6): 453-467.
Kansiime, F. and Nalubega, M., 1999. Natural treatment by Uganda's Nakivubo swamp. Water Quality
International (MAR./APR.): 29-31.
Kansiime, F., Oryem-Origa, H. and Rukwago, S., 2005. Comparative assessment of the value of
papyrus and cocoyams for the restoration of the Nakivubo wetland in Kampala, Uganda.
Physics and Chemistry of the Earth, 30(11-16): 698-705.
Kelbe, B.E., Bodenstein, B. and Mulder, G.J., 1991. Investigation of the hydrological response to
informal settlements on small catchments in South Africa. IAHS Publication (International
Association of Hydrological Sciences(203): pp. 219-227.
Kemka, N., Njiné, T., Togouet, S.H.Z., Menbohan, S.F., Nola, M., Monkiedje, A., Niyitegeka, D. and
Compère, P., 2006. Eutrophication of lakes in urbanized areas: The case of Yaounde
Municipal Lake in Cameroon, Central Africa. Lakes and Reservoirs. Research and
Management, 11(1): 47-55.
Kemka, N., Togouet, S.H.Z., Kinfack, R.P.D., Nola, M., Menbohan, S.F. and Njine, T., 2009.
Dynamic of phytoplankton size-class and photosynthetic activity in a tropical hypereutrophic
lake: the Yaounde municipal lake (Cameroon). Hydrobiologia, 625: 91-103.
Kortatsi, B.K., 2006. Hydrochemical characterization of groundwater in the Accra plains of Ghana.
Environmental Geology, 50 (3): 299-311.
Kortatsi, B.K., 2007. Hydrochemical framework of groundwater in the Ankobra Basin, Ghana.
Aquatic Geochemistry, 13(1): 41-74.
Kulabako, N.R., Nalubega, M. and Thunvik, R., 2004. Characterisation of Peri-urban Anthropogenic
Pollution in Kampala, Uganda, Proceedings of the 30th WEDC International conference on
people centred approaches to water and environmental sanitation, 25-29th October. Vientiane:
Lao PDR; 2004. p. 474–82.
Kulabako, N.R., Nalubega, M. and Thunvik, R., 2007. Study of the impact of land use and
hydrogeological settings on the shallow groundwater quality in a peri-urban area of Kampala,
Uganda. Science of the Total Environment, 381(1-3): 180-199.
Kulabako, N.R., Nalubega, M. and Thunvik, R., 2008. Phosphorus transport in shallow groundwater in
peri-urban Kampala, Uganda: results from field and laboratory measurements. Environmental
Geology, 53(7): 1535-1551.
Lawrence, A.R., Gooddy, D.C., Kanatharana, P., Meesilp, W. and Ramnarong, V., 2000. Groundwater
evolution beneath Hat Yai, a rapidly developing city in Thailand. Hydrogeology Journal, 8(5):
564-575.
Magadza, C.H.D., 2003. Lake Chivero: A Management Case Study. Lakes and Reservoirs. Research
and Management, 8(2): 69-81.
19
Marsalek, J., Jimenez-Cisneros, B., Malmqvist, P., Goldenfum, J. and Chocat, B., 2008. Urban water
cycle processes and interactions. , Urban Water Series - UNESCO-IHP Volumes. Taylor and
Francis, Leiden and UNESCO Publishing, Paris.
Mireri, C., Atekyereza, P., Kyessi, A. and Mushi, N., 2007. Environmental risks of urban agriculture
in the Lake Victoria drainage basin: A case of Kisumu municipality, Kenya. Habitat
International, 31(3-4): 375-386.
Mladenov, N., Strzepek, K. and Serumola, O.M., 2005. Water quality assessment and modeling of an
effluent-dominated stream, the Notwane River, Botswana. Environmental Monitoring and
Assessment, 109(1-3): 97-121.
Morris, B.L., Darling, W.G., Cronin, A.A., Rueedi, J., Whitehead, E.J. and Gooddy, D.C., 2006.
Assessing the impact of modern recharge on a sandstone aquifer beneath a suburb of
Doncaster, UK. Hydrogeology Journal, 14(6): 979-997.
Moyo, N.A.G. and Worster, K., 1997. The Effects of Organic Pollution on the Mukuvisi River,
Harare, Zimbabwe. In: N.A.G. Moyo (Editor), Lake Chivero: A Polluted Lake. University of
Zimbabwe Publications, Harare, Zimbabwe, pp. 53-63.
Muggide, R., 1993. The increase in phytoplankton primary productivity and biomass in Lake Victoria
(Uganda). . Verh. Int. Ver. Limnol., 25: 846-849.
Munro, J.L., 1966. A Limnological Survey of Lake McLlwaine, Rhodesia. Hydrobiologia, 28(281308).
Mwiganga, M. and Kansiime, F., 2005. The impact of Mpererwe landfill in Kampala-Uganda, on the
surrounding environment. Physics and Chemistry of the Earth, 30(11-16): 744-750.
Navarro, A. and Carbonell, M., 2007. Evaluation of groundwater contamination beneath an urban
environment: The Besos river basin (Barcelona, Spain). Journal of Environmental
Management, 85(2): 259-269.
Nevondo, T.S. and Cloete, T.E., 1999. Bacterial and chemical quality of water supply in the Dertig
village settlement. Water SA, 25(2): 215-220.
Nhapi, I., 2008. Inventory of water management practices in Harare, Zimbabwe. Water and
Environment Journal, 22(1): 54-63.
Nhapi, I., Siebel, M.A. and Gijzen, H.J., 2004. The impact of urbanisation on the water quality of Lake
Chivero, Zimbabwe. Water and Environment Journal, 18(1): 44-49.
Nhapi, I., Siebel, M.A. and Gijzen, H.J., 2006. A proposal for managing wastewater in Harare,
Zimbabwe. Water and Environment Journal, 20(2): 101-108.
Nhapi, I. and Tirivarombo, S., 2004. Sewage discharges and nutrient levels in Marimba River,
Zimbabwe. Water SA, 30(1): 107-113.
Nsubuga, F.B., Kansiime, F. and Okot-Okumu, J., 2004. Pollution of protected springs in relation to
high and low density settlements in Kampala - Uganda. Physics and Chemistry of the Earth,
29(15-18): 1153-1159.
Oberholster, P.J., Botha, A.M. and Ashton, P.J., 2009. The influence of a toxic cyanobacterial bloom
and water hydrology on algal populations and macroinvertebrate abundance in the upper
littoral zone of Lake Krugersdrift, South Africa. Ecotoxicology, 18(1): 34-46.
Oberholster, P.J., Botha, A.M. and Cloete, T.E., 2008. Biological and chemical evaluation of sewage
water pollution in the Rietvlei nature reserve wetland area, South Africa. Environmental
Pollution, 156(1): 184-192.
Oguttu, H.W., Bugenyi, F.W.B., Leuenberger, H., Wolf, M. and Bachofen, R., 2008. Pollution
menacing lake victoria: Quantification of point sources around Jinja Town, Uganda. Water Sa,
34(1): 89-98.
Robarts, R.D. and Southall, G.C., 1977. Nutrient Limitation of Phytoplankton Growth in Seven
Tropical Man-Made Lakes, with Specific Reference to Lake Mcllwaine, Rhodesia.
Hydrobiologia, 79(1): 1-35.
20
Scheren, P.A.G.M., Zanting, H.A. and Lemmens, A.M.C., 2000. Estimation of water pollution sources
in Lake Victoria, East Africa: Application and elaboration of the rapid assessment
methodology. Journal of Environmental Management, 58(4): 235-248.
Talling, J.F., 1992. Environmental regulation in African shallow lakes and wetlands. Rev. hydrobiol.
trop., 25: 87-144.
Talling, J.F. and Talling, I.B., 1965. The photosynthetic activity of phytoplankton in East African
lakes. Int. Rev. Gesamten Hydrobiol., 50: 1-32.
Taylor, R.G., Tindimugaya, C., Barker, J., Macdonald, D. and Kulabako, R., 2009. Convergent Radial
Tracing of Viral and Solute Transport in Gneiss Saprolite. Ground Water Special issue.
Thornton, J., A., Rast, W. and Holland, M.M., 1999. Assessment and control of nonpoint source
pollution of aquatic ecosystems : a practical approach. Man and the biosphere series v. 23.
UNESCO ; Parthenon Pub. Group, New York, USA, xi, 466 p. pp.
UN-Habitat, 2003. The challenge of slums. In: U.N.H.S.P.-. UN-Habitat (Editor), Slums and housing
in Africa. Earthscan Publication Ltd., London.
UN-Habitat, 2008. The State of African Cities - A framework for addressing urban challenges in
Africa, United Nations Human Settlements Programme (UN-HABITAT), Nairobi, Kenya.
van Dam, A.A., Dardona, A., Kelderman, P. and Kansiime, F., 2007. A simulation model for nitrogen
retention in a papyrus wetland near Lake Victoria, Uganda (East Africa). Wetlands Ecology
and Management, 15: 469-480.
Verschuren, D., Johnson, T.C., Kling, H.J., Edgington, D.N., Leavitt, P.R., Brown, E.T., Talbot, M.R.
and Hecky, R.E., 2002. History and timing of human impact on Lake Victoria, East Africa.
Proceedings of the Royal Society B-Biological Sciences, 269(1488): 289-294.
Wakida, F.T. and Lerner, D.N., 2005. Non-agricultural sources of groundwater nitrate: a review and
case study. Water Research, 39(1): 3-16.
WHO, 2000. Water Supply and Sanitation Sector Report Year 2000 - Africa Regional Assessment.,
World Health Organization.
Witte, F., Welten, M., Heemskerk, M., van der Stap, I., Ham, L., Rutjes, H. and Wanink, J., 2008.
Major morphological changes in a Lake Victoria cichlid fish within two decades. Biological
Journal of the Linnean Society, 94(1): 41-52.
Yidana, S.M., Ophori, D. and Banoeng-Yakubo, B., 2008. Hydrogeological and hydrochemical
characterization of the Voltaian Basin: The Afram Plains area, Ghana. Environmental
Geology, 53(6): 1213-1223.
Zanini, L., Robertson, W.D., Ptacek, C.J., S.L., S. and T, M., 1998. Phosphorus characterization in
sediments impacted by septic effluent at four sites in central Canada. Journal of Contaminant
Hydrology, 33: 405–429.
Zinabu, G.M., Kebede-Westhead, E. and Desta, Z., 2002. Long-term changes in chemical features of
waters of seven Ethiopian rift-valley lakes. Hydrobiologia, 477(1-3): 81-91.
Zinabu, G.M. and Taylor, W.D., 1989. Seasonal and spatial variation in abundance, biomass and
activity of heterotrophic bacterioplankton in relation to some biotic and abiotic variables in an
Ethiopian rift-valley lake (Awassa). Freshwat. Biol., 22: 355-368.
Zingoni, E., Love, D., Magadza, C., Moyce, W. and Musiwa, K., 2005. Effects of a semi-formal urban
settlement on groundwater quality Epworth (Zimbabwe): Case study and groundwater quality
zoning. Physics and Chemistry of the Earth, 30(11-16): 680-688.
Zurawsky, M.A., Robertson, W.D., Ptacek, C.J. and Schiff, S.L., 2004. Geochemical stability of
phosphorus solids below septic system infiltration beds. Journal of Contaminant Hydrology,
73(1-4): 129-143.
21