Wastewater Management with Anaerobic Digestion Accra, Ghana

HafenCity Universität Hamburg
M. Sc. Resource Efficiency in Architecture and Planning (REAP)
Technologies for Sustainable Water Resource Management
Winter Semester 2015/16
Final Report
Wastewater Management with Anaerobic Digestion
Accra, Ghana
Submitted to: Professor Dr.-Ing. Wolfgang Dickhaut
On: Thursday, March 31st
, 2016
Contributing Authors
Asiedu-Danquah, Kwadwo : 6028962
Troutman, Heather : 6028601
Abstract
This analysis identified Old Fadama, an informal settlement of 80,000 inhabitants in Accra, Ghana,
that currently lacks adequate access to sanitation facilities, clean water, electricity, and is burdened by
severe environmental degradation as a possible site to implement a system of small-scale anaerobic
digesters throughout the community as a means to treat 122,139 L of wastewater per day producing
20,727 to 29,406 m3
biogas per day, which is sufficient to run a cooking stove for 3.24 to 4.59 hours
per house per day (assuming 5 inhabitants per house). Additionally, this system can provide sufficient
fertilizer and soil amendment for utilization in urban and peri-urban agriculture, which provides
livelihood for 18 percent of Accra’s total population and produces 90 percent of all perishable
produce consumed in the city.
This analysis discusses potential incentives and threats to implement such a system under two
scenarios. Under Scenario One, 100 fixed dome anaerobic digesters (AD), each 50 m3
, would be
constructed. Under Scenario Two, 1,173 fixed dome ADs, each of 3.125 m3
, would be constructed.

Technologies for Sustainable Water Management
Wastewater Treatment with Anaerobic Digestion - Accra, Ghana
2
Table of Contents
1. Introduction……………………………………………………….………………………………03
2. Anaerobic Digestion……………………………………………..………………………………..04
2.1. Fundamentals…………………………………………………………………………………..04
2.2. Technology Overview..………………………………………………………………………..05
2.3.Hydraulic Retention Time..……..….…………………………………………………………..08
3. Accra, Ghana……………………………………………………..………………………………..09
3.1. Case Study – Old Fadama……………………………………………………………………...11
3.1.1. Location and Population………………………………………………………………...11
3.1.2. Existing Sanitation System……………………………………………………………...12
3.1.3. Water Consumption……………………………………………………………..............12
3.1.4. Wastewater Characteristics……………………………………………………………...14
3.1.5. Local Stakeholders and Workforce Capacity…………………………………………...15
3.2. Justification for AD in Old Fadama…………………………………………………………...15
3.3. Proposed System……………………….……………………………………………………...17
3.4. Potential Problems……………..……………………………………………………………...20
4. Conclusion…………………………………..……...……………………………………………...21
Figures and Tables
Figure 2.1.1: Biogas digester types appropriate for developing countries………………………..…..04
Figure 2.2.1: Fixed dome digester schematic…………………………………………………………05
Figure 2.2.2: Floating drum digester schematic……………………………………………………….06
Figure 2.2.3: Tubular digester schematic……………………………………………………………...06
Table 2.2.1: Comparison between Fixed Dome, Floating Drum and Tubular Digesters……………..07
Table 2.3.1: Hydraulic retention times for various temperature windows……………………………08
Figure 3.1.1: Sanitation service delivery mode in Accra, Ghana……………………………………..10
Figure 3.1.2: Overview of the current (2007) wastewater management situation in Accra, Ghana…..10
Figure 3.1.3: Map of Study Area (Old Fadama)………………………………………………………11
Figure 3.1.4: Sanitation system for the design of the Anaerobic Digester……………………………12
Table 3.1.3: Overview of access to and expenditure on clean water in Accra………………………..13
Table 3.1.4: Seasonal wastewater characteristics in Accra, Ghana…………………………………...14
Table 3.1.5: Stakeholders involved in Faecal Sludge and Wastewater Management in Accra……….15
Table 3.3.1: Wastewater characteristic in Old Fadama, Accra, Ghana (80,000 inhabitants)…………17

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1. INTRODUCTION
Wastewater treatment continues to be an issue of nuisance and threat to public health in many parts of
the world. Accra, Ghana is no exception; wastewater is disposed of in nearby water bodies, often
without any form of treatment. In order to protect the environment as well as the health of humans, it
is important to take the issue of sanitation seriously.
According to the United Nations (2016), globally some “2.4 billion people lack access to basic
sanitation services, such as toilets or latrines, and more than 80 per cent of wastewater resulting from
human activities is discharged into rivers or sea without any pollution removal.” The 6th
goal of the
Sustainable Development Millennium Goals aims at improving access to water and sanitation by
2030.
Old Fadama, an informal neighbourhood in Accra, is considered to be one of the areas discharging
large volume of untreated wastewater directly in waterbodies and across the landscape via direct
disposal (i.e. dumping of pan/bucket latrines and/or open defecation) or indirectly through illegal
dumping of septage sludge. Old Fadama has been selected as a case study to identify the potential of
small-scale and decentralized anaerobic digestion technologies to sustainably (emphasizing people,
profit, planet) treat and utilize wastewater. To evaluate the effectiveness of the technology and
guarantee a well functioning system, the conditions within the study area needed to be critically
studied in order to make it possible to determine the characteristics of the wastewater and decide on
the most appropriate use of the technology. The issues investigated within the area focused are the
demographics of the population (social class, which probably has an impact on diet affecting faecal
characteristics), the type of sanitation systems used (i.e. flush, pit latrines, etc), temperature of the
area, water consumption of the community, among others. Based on this information, a system of
small-scale anaerobic digesters was dimensioned as a feasible wastewater treatment for the area.
“Anaerobic digestion of organic waste provides many benefits. This includes the generation of
renewable energy, a reduction of greenhouse gases, a reduced dependency on fossil fuels, job
creation, and closing of the nutrient cycle. It transforms organic waste material into valuable resources
while at the same time reducing solid waste volumes and thus waste disposal costs. Biogas as a
renewable energy source not only improves the energy balance of a country but also contributes to the
preservation of the natural resources by reducing deforestation, and to environmental protection by
reducing pollution from waste and use of fossil fuels” (Al Seadi et al., 2008).

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2. Anaerobic Digestion
Definition
“Anaerobic digestion (AD) is a microbiological process whereby organic matter is decomposed in the
absence of oxygen. This process is common to many natural environments such as swamps or
stomachs of ruminants. Using an engineered approach and controlled design, the AD process is
applied to process organic biodegradable matter in airproof reactor tanks, commonly named digesters,
to produce biogas. Various groups of microorganisms are involved in the anaerobic degradation
process, which generates two main products: energy rich biogas and a nutritious digestate” (Vögeli et
al, 2014).
2.1. Fundamentals
There are a number of anaerobic digesters that have been developed in different parts of the
world, and the decision as to which one to choose depends on different factors such as
demographics of the population, the user interface of existing sanitation systems, temperature of the
area, and water consumption of the community, as indicated in Table 2.2.1. Their designs are in
some cases simple and in other cases complex. Anaerobic digesters can be categorized based
on their operating parameters and features of their design (Vögeli et al, 2014). These features
include:
 the total solids content of the substrate that is inputted into the system (wet/dry),
 the feeding mode (continuous/batch),
 the operating temperature (mesophilic/thermophilic),
 number of stages the system goes through (two or multi-stages).
Figure 2.1.1: Biogas digester types appropriate for developing countries. Source: (Vögeli Y., et al, 2014)

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This paper considers the designs of some selected AD technologies that are applicable in
developing countries: fixed-dome, floating drum and tubular digesters. These technologies
are all wet digestion systems, operating under a continuous mode and under mesophilic
conditions (Vögeli et al, 2014).
2.2. Technology Overview
The basic design of the system is very simple. Its components include:
 an inlet for the substrate (organic wastes),
 the digester, and
 outlets for the digestate and biogas.
Fixed Dome
A fixed-dome digester, as its name suggest,
is a domed shaped system that consists of
an inlet for waste, a gas collector that stores
the produced gas, a gas pipe, an outlet and
an overflow tank that acts as a
compensation tank. The gas produced is
stored in the upper part of the digester. With
time, the gas stored in the digester
increases and this exerts pressure on the
slurry thereby causing the digestate to flow
out into the compensation tank; but,
whenever the gas pipe is opened, pressure is released and the slurry flows back into the system. Most
of these systems are constructed underground in order to protect it from low temperatures (Vögeli et
al, 2014).
The digester needs to be air tight and as a result, experts are needed during the construction phase of
the system. The system normally has a life span of between 15 to 20 years, since it has no moving
parts.
Figure 2.2.1: Fixed dome digester schematic.
Source: Vögeli et al, 2014

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Floating Drum
The floating drum digester is a system cylindrical in
nature with a drum floating above the digester. The
system is normally constructed below the ground while
the drum floats above it. The construction of the entire
digester can be of bricks, concrete and metals, or with
fiberglass reinforced plastics. The drum acts as a gas
holder and moves upwards or downwards, depending
on the amount of the gas in the system. Other
components of the floating drum include an inlet for the
feedstock, an outlet, an overflow tank and a gas pipe. In
humid areas, the gas holder can last between 3 to 5
years, as against in dry areas where it can last much
longer, between 8-12 years. In terms of sizes, the
floating drum digester ranges between about 1 to 50 m3
(Vögeli et al, 2014).
Tubular digester
Tubular digesters are the simplest and
least expensive systems to construct
(Spuhler, n.d). These digesters are
longitudinal in nature and have a
plastic balloon which serves both as a
digester and a gas holder. The digester
has an inlet, an outlet and a gas pipe,
which are all attached to the system.
The slurry remains at the lower part of the system whereas the gas produced is stored at the upper part
of the plastic balloon.
The system has no stirring device but gas can be increased by exerting heavy objects on the system. It
is normally constructed underground and has a life span of about 2-5 years (Vögeli et al, 2014). Since
the system is made from plastic bags, it is prone to damage; hence, extra care needs to be taken in
order to protect it for instance, when exerting weight on it to increase gas pressure. Also, the system
should not be exposed to direct sunlight.
Figure 2.2.2: Floating drum digester
schematic. Source: Vögeli et al, 2014
Figure 2.2.3: Tubular digester schematic. Source: Vögeli et al, 2014

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Comparison between the systems
Table 2.2.1: Comparison between Fixed Dome, Floating Drum and Tubular Digesters
Factors Fixed Dome Floating Drum Tubular
Gas storage Internal Gas storage up
to 20m3*
Internal Gas storage drum
size*
Stored in External
plastic bags*
Input
materials
Animal and Human
Excreta
Mainly designed for digesting
animal and human faeces***
Domestic Waste and
animal excreta
Skills of
contractor
Masonry and
Plumbing* (high)-
Biogas technicians
needed
Masonry, Plumbing and
welding (high)*
Plumbing*
Availability
of materials
Masonry structures,
structures of cement***
Masonry structures.
****Steel and plastics***
Mainly plastic
materials (rubber bag
or reinforced
plastics)***
Durability /
Life span
Up to 20 years*(long) Up to 20 years***. Drum is
the problem* (short)
Between 2 and 5
years.***depending on
the lining*
Sizing 6 to 124 m³ digester vol
normally*Could also to
up to 200m3***
Up to 20 m³* the size could
also be up to 100m3***
Combination possible*
Climate Preferred for warm
climates***
Preferred for warm
climates***
Preferred for warm
climates but needs to
be prevented against
direct sunlight***
Maintenance Cost is low** High because the metal parts
have to be prevented from
corrosion** Regular
maintenance needed****
Likelihood of
mechanical damage
and usually not locally
available***
Required
work place
Requires more
excavation**
Relatively less excavation is
needed**
Requires less
excavation****
Installation
cost
Less expensive** Relatively more expensive**
because of the materials
Low cost***
Sources: (Energypedia, 2016)*, (Saleh, n.d)**, (Kossmann, et al., n.d)*** & (Vögeli, Lohri, Gallardo,
Diener, & Zurbrügg, 2014)****

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2.3.Hydraulic retention time
The hydraulic retention time (HRT) is the length of time the wastewater must remain in the digester
for effective treatment (i.e. thorough pathogen destruction). The HRT is dependent on the ambient
temperatures, the variation in temperature between night and day, and between seasons, and the
concentration of pathogens in the utilized wastes. In hot and temperate climates, the HRT in the
reactor needs to be at least 15 days and 25 days, respectively (Spuhler, n.d). A HRT of 60 days is
important for inputs high in pathogens.
Efficiency of pathogen destruction is classified in three temperature windows: thermophilic (53-55
°C), mesophilic (35-37 °C), psychrophilic (8-25 °C), see Table 2.3.1. If a temperature above 50 °C
(i.e. thermophilic) can be maintained evenly throughout the digester, a HDT of 2-5 days is sufficient
for complete pathogen destruction, requiring no additional post-treatment (e.g. composting) of the
effluent. For sustained internal temperatures below 50 °C but above 35 °C (i.e. mesophilic), a HDT of
1-2 months is required, depending on the concentration of pathogens present in the inputted
wastewater (i.e. higher pathogen concentration require longer retention times). If temperature drop
below 25 °C (i.e. psychrophilic), the system should be heated by an external source. Best practices
prescribe regular record keeping of internal temperatures to ensure after-use safety of the digestate,
especially for use in agriculture. Temperatures can be taken manually and kept as a written record, or
more sophisticated systems can install automated and computerized recording devices (Tilley, 2008).
Table 2.3.1: Hydraulic retention times for various temperature windows

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3. Accra, Ghana
Ghana is being faced with a lot of political issues that have hindered the government in tackling the
problems of sanitation. Insufficient attention and government effort and resources have been allocated
to waste management (both wastewater and solid wastes); and, on the other hand, the city is growing
and industrializing at a very fast pace. The government’s unwillingness to pay attention to sanitation
together with the rapid growth and industrialization of the city together has resulted in extreme
amounts of waste generation, which are in most cases not treated. This has over the years caused a lot
of environmental problems hence, reducing the quality of life of the inhabitants (Awuah & Abrokwa,
2008).
Accra has a current population of about 3 million and according to Lydecker & Drechsel (2010), the
city’s inhabitants produce about 80 million liters of wastewater daily. However, an evaluation of the
condition of wastewater and fecal sludge conducted by the International Water Management Institute
(2009) indicated that out of 37 wastewater treatment plants that have been constructed in Accra, only
10 percent of them were operational, see Figure 3.1.1. Wastewater treatment in Accra is mainly
decentralized and serves small communities and institutions. Obuobie et al. (2006) state that even if
all the treatment plants in Accra were operating at full capacity, only 17 percent of the daily generated
wastewater could be treated. Currently, more than 90 percent of the generated wastewater ends up in
water bodies untreated (IWMI, 2009). This highlights how severe the problem related to wastewater
treatment and management in Accra is.
Just a few number of houses in Accra (about 30 percent) have flush toilets and even among this
number, about just 20 percent have water flowing. Most of the population depends on public toilets at
a ratio of about 1toilet to about 10 inhabitants (Thompson, 2013). Emptying of the pit latrines and
septic tank in Accra are carried out through the use of the vacuum tankers when the tanks are filled to
capacity; however, the monitoring during the emptying process is not done well enough (Boot &
Scott, 2008). Instead of these feces being treated, they are most often disposed directly into the river
bodies or surrounding areas because of the poor and non functional wastewater treatment plants
available (Kathijotes, 2012). The amount of faecal sludge discharged at Korle Gono average’s
700m³/day, from an average of 100 vacuum tankers daily (Boot & Scott, 2008). Boot and Scott (2008)
again added that in 2006 about 200,000m3
of faecal sludge was discharged at Korle Gonno untreated.

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Figure 3.1.1: Overview of the current (2007) wastewater management situation in Accra, Ghana. Source:
(Adank et al, 2011)
Figure 3.1.2: Sanitation service delivery mode in Accra, Ghana. Source: (Adank et al, 2011; adapted from
GSS, 2008)

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This problem is exacerbated by the fact that these water bodies serve as the major source of drinking
water to most parts of the city as well as a source of water for irrigation of the existing agricultural
lands. A number of deaths have been recorded as a result of poor environmental conditions in Accra
(Thompson, 2013) (Obuobie et al., 2006).
These problems call for urgent proper and more sustainable wastewater management facilities. It is
based on these pre-mentioned problems in the city of Accra why this paper seeks to address and
tackle some small scale wastewater treatment systems that could serve a basis and foundation for
other projects in the future.
3.1. Case Study – Old Fadam
3.1.1. Location and population of the study area
Old Fadama is situated in Ashiedu Keteke sub-metropolis in Accra and it is the capital’s largest
informal settlement with a population of about 80,000 inhabitants on land reclaimed from the Korle
Lagoon (Udofia, Yawson, Aduful, & Bwambale, 2014), see Figure 3.1.1. It is a low income
neighborhood with a population density of about 2,424.18 persons per hectare (Braimah & Lawson,
2014). The area creates numerous sanitation problems because of the poor sanitary conditions and the
frequent wastewater disposal that affects the existing water bodies. The situation is made worse
because of the number of industries that are concentrated in this area, all disposing of almost their
entire wastewater into the water bodies.
Figure 3.1.3: Map of Study Area (Old Fadama). Source: Monney et al, 2013

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3.1.2. Existing sanitation system
Figure 3.1.4: Sanitation system for the design of the Anaerobic Digester. Adopted from (Tilley et.al.,
2008)
**How the existing system functions is what is heighted in red in Figure 3.1.2.
The inhabitants in this area depend mainly on public shared toiles, which is normally called the
Kumasi Ventilated Improved Pit (KVIP). Sadly, about 80,000 residents depend on as low as 39 toilet
facilities (Monney, Odai, Buamah, Awuah, & Nyenje, 2013). There is insufficient information to
determine the number of self-made toilet systems, such as simple pit latrines, or the frequency of use
of pan/bucket latrines, which can be assumed to be dumped untreated directly into the environment,
and open defecation.
According to Adank et al (2011) (a SWITCH project), it is estimated that between 1.1 and 4.3 percent
of the total Accra population (i.e. 33,000 to 129,000 inhabitants) practice open defecation, and an
additional 3.2 percent (i.e. 96,000 inhabitants) use pan/bucket latrines, see Figure 3.1.2 and 3.1.4
Considering the there are 80,000 inhabitants of Old Fadama sharing access to only 39 public toilets, it
is plausible that many of the residents of Old Fadama are using pan/bucket latrines, practicing open
defecation, or have constructed private or shared simple pit latrines in backyards.
3.1.3. Water consumption
The community relies on water that is supplied by vendors to the inhabitants at a cost, see Table 3.1.3.
The main source of this water is from the Ghana Water Company Limited. Water is an issue in this
community and the flow is not always constant. According to Monney, Odai, Buamah, Awuah, and
Nyenje (2013), “the average per capita water consumption for the community is 50L/cap/day.” It was

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again added that the price of water in this area affects the per capita water usage, which increases the
pollutants in the waste water.
Lack of access to running water is not only an infringement of environmental sustainability. High-
and medium-income residents serviced by direct household connections to city water services pay
0.66 GH¢ per m3
while low-income residents (including all of the inhabitants of Old Fadama) pay
between 5 and 12 GH¢ per m3
, see Table 3.1.3 (Adank et al, 2011). Similarly, residents with
connection to the centralized wastewater infrastructure pay 4.6 to 6 GH¢ per months while residents
using public toilets pay 7.5 to 22.5 GH¢ per person per month. The average cost to use a public toilet
is 0.05 to 0.15 GH¢ per visit (AMA, 2009). This is a direct infringement of environmental justice. The
Accra Learning Alliance, formed in consortium with the SWITCH Ghana project, aims to address this
injustice, discussed in more detail, below.
Table 3.1.3: Overview of access to and expenditure on clean water in Accra. Source: Adank et al, 2011

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3.1.4. Wastewater characteristics
Research conducted by Monney, Odai, Buamah, Awuah, and Nyenje (2013) indicated that the PH of
wastewater from the area was comparatively low because of the existence of detergents and soapy
water. These values differed between the dry and the wet season; during the dry season, the pH was
about 7.58 ± 0.22 while in the wet season, it was 7.87 ± 0.37. In their research, they also measure the
average temperature of the wastewater. The values recorded were 30.08 ± 0.88°C and 28.93 ± 0.7°C
for the dry and wet seasons, respectively.
During the research, the organic content of the recorded were <0.01mg/L in the dry season and 0.21 ±
0.15mg/L during the wet season. “The mean total dissolved solids (TDS) of the wastewater for both
the dry and wet seasons were 1,640 ± 260mg/L and 1,233.84 ± 444.7mg/L, respectively, mostly
exceeding the EPA effluent guideline value of 1,500mg/L in the dry season” (Monney, Odai,
Buamah, Awuah, & Nyenje, 2013). The total suspended solids (TSS) recorded in the wastewater for
the area indicated that the value during the dry season was about 575.58 ± 88.12mg/L, which was
comparatively about 11 times more than the 50mg/L provided by the EPA effluent guideline.
“Biological oxygen demand (BOD) levels in the wastewater were 545.63 ± 99.88mg/L and 645.94 ±
331.43mg/L during the dry and wet seasons respectively being consistently higher than the EPA
effluent guideline value of 50mg/L. Chemical Oxygen demand (COD) also showed the same trend
with levels as high as 1,415.12 ± 722.83mg/L in the wet season and 1,100.45 ± 167.16mg/L in the dry
season compared to an EPA effluent guideline value of 250mg/L” (Monney, Odai, Buamah, Awuah,
& Nyenje, 2013).
Table 3.1.4: Seasonal wastewater characteristics in Accra, Ghana
Parameter Units Accra (dry season) Accra (wet season) EPA Guidelines
pH pH 7.58 ± 0.22 7.87 ± 0.37 6-9
Temperature ° C 30.08 ± 0.88 28.93 ± 0.70 --
Organic Content mg/L <0.01 ± 0.00 0.21 ± 0.15 --
TDS mg/L 1,640 ± 260 1,233.84 ± 444.7 1,500
TSS mg/L 575.58 ± 88.12 ? 50
BOD mg/L 545.63 ± 99.88 645.94 ± 331.43 50
COD mg/L 1,415.12 ± 722.83 1,100.45 ± 167.16 250

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3.1.5. Local Stakeholders and Workforce Capacity
Table 3.1.5: Stakeholders involved in Faecal Sludge and Wastewater Management in Accra
Stakeholder Responsibilities Source
AMA(Waste management
Department (WMD), Liquid
waste management group)
- Managing the disposal/treatment
facilities
-Monitoring and regulation of operations
-Enforcing by-laws
(Boot & Scott,
2008)
Environmental Protection
Agency
-Regulation of services
-Monitoring the WMD and the private
sector
(Boot & Scott,
2008)
Private Vacuum tanker
contractors
-Assisting in setting tariffs for emptying
services
-Monitoring tankers entering and leaving
the faecal sludge disposal point
-Communicating with the WMD
(Boot & Scott,
2008)
Ministry of Local Government
and Rural Development
-Responsible for environmental sanitation
-Mobilizing and negotiation for funding
for projects
(Darteh, Adank, &
Manu, 2008)
Ministry Water Resources,
Works and Housing
-Supply of drinking water (Darteh, Adank, &
Manu, 2008)
3.2. Justification for AD in Old Fadama
Accra Learning Alliance 2030 Vision
There are several reasons that it is believed that AD is a highly suitable option for wastewater
treatment in Old Fadama. While the Accra Metropolitan Assemble has been active in assessing the
current sources of inadequacy in the existing sanitation network (or lack there of) within the city of
Accra and have published progressive strategic plans to ameliorate human and environmental health
risks related to poor sanitation over the coming two decades, Old Fadama is not in that vision. As an
informal settlement, it is unlikely that the city will bring costly infrastructure to this area without
formally developing the land, which would result in mass displacement of the current inhabitants. For
example, the Accra Learning Alliance, formed in consortium with the SWITCH Ghana program,
created a Strategic Vision for Sanitation: Accra 2030, which aims at providing “at least 80 percent of
Accra’s citizens … access to an acceptable level of sanitation facilities” (Adank, 2011). Regrettably,

16
it is imaginable that Old Fadama is within the neglected 20 percent. AD offers ancillary and
potentially economically profitable by-products that can help recover the costs the community will
need to invest to construct and operate the system.
Direct access to polluted river ways and Korle lagoon
As previously discussed, Old Fadama is situated on recovered land of the Korle Lagoon, which is the
dumpsite of 85 percent of the city’s daily wastewater generation, all untreated. This area is grossly
polluted, resulting in above average incidences of sanitation related illnesses (Monney, Odai,
Buamah, Awuah, and Nyenje, 2013). Provided treatment to the wastewater generated by this district,
representing less than 3 percent of the total city population, will not result in a rehabilitated
environment, but it should, none-the-less, be considered a top priority.
No access to electricity
Not only do the inhabitants of Old Fadama lack access to sanitation services, they also lack access to
electricity. As such, the majority of households cook over open, indoor fires and use candles for
lighting (Abraham, 2007). The health hazards associated with degraded indoor air quality are well
established (WHO, 2006). AD is one of very few low-tech, decentralized and low-cost systems for
wastewater treatment that also produce biogas readably usable in inexpensive lanterns and stoves. It is
imaginable that the inhabitants of Old Fadama will find greater value and livelihood improvement
from the prevalence of a renewable and affordable energy source than a waste treatment service.
Urban Farmers’ livelihoods
Plant-available nutrients and digestate rich in organic matter that is fantastic as a soil amendment is
another by-product of the AD treatment process. 18 percent of the population of Accra participate in
urban and peri-urban farming as a primary means of livelihood; the vast majority of these farmers live
in informal areas (Abraham, 2007). Urban farming is a (comparatively) lucrative livelihood because
there is a high demand for perishable fruits and vegetables in the city; 90 percent of which is grown in
urban and peri-urban small plots (Abraham, 2007). It is assumed that 100 percent of the produce
grown in the urban environment is irrigated with untreated wastewater, resulting in frequent food-
borne illness (Odowa, 2006). Wastewater is used for two reasons, first because of lack of available
clean water and also because, as a sub-Saharan city, Accra soil has poor agricultural characteristics.
Nutrient-rich digestate resulting from the AD process is a viable and safe option to fertilize crops and
treat soil for enhanced productivity (WHO, 2006; IWMI, 2006; FAO, 1998; USEPA,1995). There
often exist regulatory barriers to the reuse of digestate in agriculture. Local AD advocates are
encouraged to use the referenced resources for the safe use of this valuable material, training of local
farmers and for effective persuasion of policy makers.

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3.3. Proposed System
Background conditions
The case study location, Old Fadama, is home to approximately 80,000 inhabitants, 100 percent are
serviced by 39 public toilets, roughly 2,000 people per toilet (Monney, Odai, Buamah, Awuah, &
Nyenje, 2013)! These toilets are basic pit latrines, no added water, assumed to be emptied by a
vacuum truck once every two years (Adank et al, 2011).
Daily per capita wastewater generation
Measurements collected by Rose et al (2015) suggest that the average low-income resident in Accra
produces 1.4 L/cap/day urine and 0.127 L/cap/day feces (or, 128 g/cap/day wet weight). Considering
that the public toilets are not watered (i.e. no-flush), this calculation assumes that 1.527 L/cap/day of
waste water are generated from a population of 80,000, totaling 122,139 L/day wastewater.
Hydraulic Retention Time (HRT)
Tropical climates with average ambient temperatures of 25-30°C have a recommended HRT of 30
days (Vögeli, 2014). To meet this recommended HRT, 3,664 m3
of reactor volume is needed (i.e.
122,139 L/day * 30 days * 1,000 L / m3
).
Feedstock characteristics
Feces Urine Total
L/cap/day 0.127 1.4 1.527
Total Solids (TS)
kg/cap/day
0.029 0.059 0.088
Volatile Solids (VS) %
of TS
89 16 - 32 -
VS kg/cap/day 0.02581 0.00944 – 0.0188 0.03525 – 0.04461
VS kg/day (80,000
inhabitants)
2,065 755 – 1,510 2,520 – 3,575
VS kg/m3
inflow 201.64 6.74 – 13.49 20.63 – 29.27
Table 3.3.1: Wastewater characteristic in Old Fadama, Accra, Ghana (80,000 inhabitants). Source:
Authors

18
Organic Loading Rate (OLR)
OLR = Q * (S/V)
Where:
Q = substrate flow rate (m3
/day)
S = substrate concentration in the inflow (VS kg/m3
)
V = volume of the reactor (m3
)
OLR = 122.139 (m3
/day) * [ (20.63-29.27 (VS kg/m3
)) / (3,664 m3
) ]
= 0.63 – 0.894 kg VS per m3
reactor volume per day
It should be noted that systems with a OLR under 2 kg VS/m3
reactor volume and day is ideal for a
non-stirred system (Vögeli, 2014). Mixed organic food wastes have an average TS content of 20%
and a VS content of TS of 80%. Assuming that moisture content is not absorbed during storage of the
urine (especially in the pit latrine of the public toilet), this system could be optimized by adding
mixed organic food wastes.
Sizing the AD system
A fixed-dome system is easiest to construct and operate, as there are no moving parts. As this system
is to be built within the informal community, it is assumed that there will be no community
member(s) with existing knowledge of this system, or with high levels of engineering or mechanical
skills. Considering this, we opt for a fixed-dome system. The standard design according to Vögeli et
al (2014) is 75 % of the total reactor volume is used for active slurry, and 25 % for biogas. The
proposed system requires 3,664 m3
volume for active sludge (75 %), which requires an additional
1,221 m3
volume for biogas (25 %) for a total of 4,885 m3
total reactor volume (100 %).
As previously mentioned, both of the high-capacity, high-technology waste treatment plants under
management of the Accra Municipality have been non-operational for nearly the full lifespan of
technology due to lack of skilled workforce. For example, the 32 million USD, World Bank,
International Monetary Fund, and African Development Bank funded Up-flow Anaerobic Sludge
Blanket (UASB) sewage treatment plant at James Town, Accra became non-operational within the
first year that the municipality took over operations in 2002 (the Dutch engineer firm, Lettinga
Associates Foundation, that designed the plant successfully operated it for the first 2 years), and still
remains non-operational today (Adank, 2011).
To avoid such a terrible waste of investment, this project recommends installing multiple small-scale
AD reactors, which have very simple maintenance, throughout Old Fadama. Average small-scale,

19
fixed-dome AD systems range from 50 m3
to 200 m3
. Accordingly, 98 (50 m3
) to 25 (200 m3
) AD
reactors will need to be constructed within Old Fadama to treat 100% of the wastewater produced by
80,000 inhabitants.
However, a more in depth, site specific analysis (i.e. pilot study) should be conducted before full-
scale implementation for several reasons. As previously discussed, it is assumed that many of the
80,000 inhabitants use pan or bucket latrines, which they likely dump themselves into the open
environment, and/or practice open defecation due to the insufficient number of public toilets in the
area. Additionally, it is expected that make-shift simple latrines have also been dug where space is
available. These facilities are likely inaccessible, and it is foreseeable that the owners/inhabitants will
be reluctant or unable to pay for a pit emptying service. All of these factors will reduce the expected
wastewater loads, and it is not possible to quantify these reductions. The most secure method to
quantify projected loads would be to build one to five pilot Ads in various sections of Old Fadama
and record the volumes of wastewater received over time.
Assuming 100 50m3
ADs were planned to service 80,000 inhabitants, and an average household of 5
persons, then each AD should accommodate approximately 160 households. The pilot should be
controlled in a way to have a secure sense of the number of inhabitants each AD is servicing so that
up-scaling for all of Old Fadama is not over capacity, resulting in wasted financial and material
resources, or under capacity, resulting in continued environmental and human health degradation.
This project would be enhanced by the additional of a parallel strategy to introduce more sanitary
toilets into the area to secure input volumes.
Biogas and Methane Yield
Wastewater has an average biological methane potential (BMP) of 0.1645 m3
CH4 / kg VS (Nielfa et
al, 2015). Assuming the produced biogas is 60 percent CH4 (Tilley et al, 2008) then the biogas yield
per kg VS (i.e. B) will be 0.2742 m3
biogas / kg VS.
Qbiogas is the daily biogas production. This system will produce 20,727 to 29,406 m3
biogas / day
[(0.63 – 0.894 VS kg/m3
/day) * (0.2742 biogas m3
/kg VS) * (3,664 m3
)].
Qbiogas = OLR * B * V
OLR = organic loading rate (VS kg/m3
)
B = biogas yield per kg VS
V = volume of the reactor (m3
)

20
The efficiency of an AD system is measured by the gas production rate (GPR) or Qbiogas per reactor
volume. This system has a GPR of 5.66 to 8.03 m3
biogas per m3
reactor volume per day.
Biogas utilization (and value)
An average biogas stove consumes approximately 0.4 biogas m3
/hr (Kossman et al, n.d.). This
example will produce enough biogas to power a cooking stove for 51,818 to 73,515 hours. Assuming
there are, on average, five inhabitants per house and 80,000 inhabitants, then we expect approximately
16,000 homes in Old Fadama. This system will produce enough biogas for each home to use a biogas
powered cooking stove for 3.24 to 4.59 hours per day.
3.4. Potential Problems
Flooding
Old Fadama is located in a flood prone area (UniversityCollegeLondon, 2013) between the Odaw and
Agbogbloshie drains (Figure 1) making it vulnerable to floods in the rainy season (Monney, Buamah,
Odai, Awuah, & Nyenje, 2013). Flooding around the toilet areas hinder toilet operators from
emptying pits (Osumanu, Abdul-Rahim, Songsore, Braimah, & Mulenga, 2010). Flooding could also
affect the internal reactor temperature if the reactors are built below ground or placed within a
depression.
Local Incapacity to Maintain System
A number of infrastructural projects implemented in Accra have failed; one of which was the
Jamestown UASB wastewater treatment plant. According to Awauh & Abrokwa (2008), one major
reason that led to the failure of this project was the lack of education and technical training. Old
Fadama is a settlement predominately made up of traders and head porters with either little or no
education. This is potentially the largest threat to this project as it relies on nearly 100 small-scale AD
units across all of Old Fadama.
This threat can be managed by participatory planning and construction with the entire community that
is enhanced with thorough and practical training. It is possible that the locals will manage their own
community system with higher efficiency than the municipality has shown if they are given rights to
the biogas and digestate, both of which have great potential to substantially improve their livelihoods.
Improper Handling of Collected Wastewater, Effluent, or Digestate
According to (Boot & Scott, 2008), pit latrines are emptied by private operators and number of these
operators indulge in “unsanitary practices”. A major problem during collection process reported by
some private vacuum tankers is that the pit latrines are difficult to empty because the excreta normally

21
needs to be liquefied and stirred as water is added prior to its discharge from the vacuum tanker
(Boot & Scott, 2008). In addition, it was reported that the private tanker-operator contractors are not
monitored effectively and regularly in their operations by the Waste Management Department. If AD
systems are overloaded, there is a great risk that the pre-maturely ejected digestate will contain high
concentrations of pathogens. If the AD system is under-loaded, there is a threat that needed microbes
in the digester will die off, which would require about a month for the microbial community to revive
itself before the system produced gas again (Kossman et al, N.D.).
Obstruction of Biogas Containers – Fire Hazzard
Old Fadama is made up of wooden structures. In addition to its unplanned nature, the area is dense
making it susceptible to fire outbreaks (Kumah, 2012). In 2009 and 2012, the settlement recorded fire
outbreaks which rendered a lot of people homeless (Paller, 2015). In such a situation, it is important to
ensure a complete air tight system to avoid fire outbreaks.
Disease Outbreak – Contaminated Wastewater
The area has a low average per capita water consumption (ranging between 21 –82L/cap/day) which
affects the amount of water usage and also increases the level of pollutant in the wastewater. As a
result of the high pollutant content of the wastewater, intensive treatment is needed. If this treatment
is not done properly, the organisms found in the wastewater, it can lead to disease outbreaks like
typhoid fever, dysentery, diarrhea and cholera (Monney, Odai, Buamah, Awuah, & Nyenje, 2013).
4. Conclusion
This analysis identified Old Fadama, an informal settlement of 80,000 inhabitants in Accra, Ghana,
that currently lacks adequate access to sanitation facilities, clean water, electricity, and is burdened by
severe environmental degradation as a possible site to implement 100 fixed dome anaerobic digesters
(AD), each 50 m3
, as a means to treat 122,139 L of wastewater per day producing 20,727 to 29,406
m3
biogas / day, which is sufficient to run a cooking stove for 3.24 to 4.59 hours per house per day
(assuming 5 inhabitants per house).
Old Fadama is not serviced by electricity, and many inhabitants cook indoors over open fires. This
analysis proposes to connect the AD systems to community kitchens so that the biogas is transported
no more than a few meters, minimizing possible risks associated with gas leaks and possible
obstruction of underground gas pipes, and provides inhabitants a safer means of cooking, improving
indoor air quality and minimizing associated health risks. If each AD is connected to a community
kitchen, then 1,600 families (i.e. 8,000 inhabitants) would share a single kitchen. One could imagine
this resulting in many problems. Assuming that 50 families per community kitchen would be
functional, then 1,173 AD units of 3.125 m3
reactor volume would be needed.

22
Due to the limited education and training of the inhabitants, severe poverty and high crime rates,
building essential infrastructure (sanitation) at such a frequent and decentralized scale may cause
micro problems throughout Old Fadama if individual units experience complications, such as
destruction, over/under loading, mismanagement of biogas or digestate, or fire.
Risk mitigation of foreseen problems is possible through participatory planning, construction,
maintenance and training. The project should begin as a pilot of a few AD units throughout Old
Fadama for site-specific data collection, which will very likely affect the results of this analysis. Over
time, additional units should be gradually incorporated while training the community member on how
to construct and operate the systems. Accra has a long history of mismanaging technology. The
authors believe that this can be avoided if the community receives additional benefits from the system
beyond wastewater treatment, such as biogas for cooking and lighting and fertilizer and soil
amendment for agricultural production. These value-added system outputs should incentivize the
community members to ensure the productivity and functionality of the system.
REFERENCES
Abraham, Ernest Mensah; Rooijen, Daan van; Cofie, Olufunke; Raschid-Sally, Liqa (2007) “Planning
urban water – dependent livelihood opportunities for the poor in Accra, Ghana” International
Water Management Institute (IWMI) SWITCH Ghana
Adank, M.; Darteh, B.; Moriaty, P.; Osei Tutu, H.; Assan, D.; Rooijen, D. van (2011) Towards
integrated urban water management in the Greater Accra Metropolitan Area: Current status
and strategic directions for the future. SWITCH/RCN Ghana
African Development Fund (2005) “Accra Sewerage Improvement Project (ASIP)” Appraisal Report
Awuah, E., Abrokwa, K.A. (2008) “Performance evaluation of the UASB sewage
treatment plant at James Town (Mudor), Accra” 33rd
WEDC International Conference,
Accra, Ghana: Access to Sanitation and Safe Water – Global Partnerships and Local Actions
Boot, N., & Scott, R. (2008). "Access to Sanitation and safe water, Global partnership and local
actions:Faecal sludge management in Accra, Ghana: strengtehening links in the chain." 33rd
WEDC Internation Conference, Accra, Ghana,2008:
Braimah, F., & Lawson, E. (2014). Does it matter where I live? Comparing the Impact of Housing
Quality on Child Development in Slum and Non-Slum Areas in Ghana. International Journal
of Child, Youth and Family Studies , 5 (3), 375-393.
Darteh, B., Adank, M., & Manu, K. (2008, March 31). Integrated Urban Water Managment in Accra:
Institutional Arrangements and Maps. Retrieved March 15, 2016, from Switch Urban Water:
http://www.switchurbanwater.eu/outputs/pdfs/W6-
1_CACC_RPT_D6.1.2b_Institutional_Mapping_-_Accra.pdf

23
Energypedia. (2016, January 7). Fixed-dome Biogas Plants. Retrieved March 17, 2016, from
Energypedia information Summary:Wiki: https://energypedia.info/wiki/Fixed-
dome_Biogas_Plants
EPA - United States Environmental Protection Agency (1995) “Process Design Manual: Land
Application of Sewage Sludge and Domestic Septage” National Risk Management Research
Laboratory (EPA/625/R-95/001)
FAO - Food and Agriculture Organization of the United Nations (1996) “Biogas Technology: A
training manual for extension” Support for Development of National Biogas Programme
(FAO/TCP/NEP/4451-T)
GTZ - Deutsche Gesellschaft f r Technische usammenarbeit (GTZ), GmbH. (2015) “AT
Information: Biogas” Information and Advisory Service on Appropriate Technology (ISAT).
Kossmann, W., Pönitz, U., Habermehl, S., Hoerz, T., Krämer, P., Klingle, B., . . . Euler, H. (n.d).
IWMI - International Water Management Institute (2006) "Recycling Realities: Managing health risks
to make wastewater an asset" Water Policy Breif. Issue 17
Kossmann, Werner; Pönitz, Uta; et al. (n.d.) Biogas Digest: Application and Product Development.
Retrieved March 16, 2016, from Information and Advisory Service on Appropraite
Technology:http://www.sswm.info/sites/default/files/reference_attachments/ISAT%20GTZ
%201999%20Biogas%20digest%20Volume%20II%20Biogas%20Application%20and%20Produ
ct%20Development.pdf
Kossmann, Werner; Pönitz, Uta; et al. (n.d.) “Biogas Digest: Biogas Basics” Information and
Advisory Service on Appropriate Technology (ISAT). Deutsche Gesellschaft f r Technische
Zusammenarbeit (GTZ), GmbH. vol. 1.
Kumah, P. (2012, May 22). Fire Outbreak in Old Fadama. Retrieved March 29, 2016, from Word
Press: https://philipkumah.wordpress.com/2012/05/22/fire-outbreak-in-old-fadama/
L thi, Christoph et al, 2011. Community-Led Urban Environmental Sanitation Planning (CLUES).
Swiss Federal Institute of Aquatic Science and Technology (Eawag), D bendorf, Switzerland.
Miezah, Kodwo; Obiri-Danso, Kwasi; Kádár, Zsófia; Fei-Baffoe, Bernard; Mensah, Moses (2015)
"Municipal solid waste characterization and quantification as a measure towards effective
waste management in Ghana" Waste Management, 46, 12-27.
Monney, Odai, S. N., Buamah, R., Awuah, E., & Nyenje, P. M. (2013). Environmental impacts of
wastewater from urban slums: case study - Old Fadama, Accra. International Journal of
Development and Sustainability, 2(2), 711-728.
Monney, I., Buamah, R., Odai, S., Awuah, E., & Nyenje, P. (2013). Evaluating Access to Potable
Water and Basic Sanitation in Ghana's Largest Urban Slum Community: Old Fadama, Accra.
Journal of Environment and Earth Science , 72-79.
Nielfa, A.; Cano, R.; Fdz-Polanco, M. (2015) "Theoretical methane production generated by the co
digestion of organic fraction municipal solid waste and biological sludge" Biotechnology
Reports. Vol. 5, 14-21

24
Osumanu, K., Abdul-Rahim, L., Songsore, J., Braimah, F., & Mulenga, M. (2010, October). Urban
water and sanitation in Ghana: How local action is making a difference. Retrieved March 29,
2016, from International Institute for Environment and development:
http://pubs.iied.org/pdfs/10586IIED.pdf
Paller, J. (2015, April). Politics of Daily Life: Process, Networks, Spontaneity. Retrieved March 29,
2016, from Political Concepts:Committee on Concepts and Methods Working Paper Series:
http://www.concepts-methods.org/Files/WorkingPaper/PC%2065%20Paller.pdf
Reymond, Philippe; Cofie, Olfunke; Kone, Doulaye (2009a) "Participatory Design and Construction
of On-Farm Wastewater Treatment Ponds for Reuse in Urban Agriculture: Dzorwulu / Roman
Ridge, Accra, Ghana" SWITCH, (in partnership with: International Water Management
Institute (IWMI), Eawag, Sandec)
Reymond, Philippe; Cofie, Olfunke; Raschid, Liqa; Kone, Doulaye (2009b) "Design Considerations
and Constraints in Applying On-Farm Wastewater Treatment for Urban Agriculture"
SWITCH Ghana
Rose, C.; Parker, A.; Jefferson, B.; Cartmell, E. (2015) "The Characterization of Feces and Urine: A
Review of the Literature to Inform Advanced Treatment Technology" Critical Reviews in
Environmental Science and Technolog, 45:17, 1827-1879
Saleh, A. (n.d). Comparison among Different Models of BIOGAS Plants. Retrieved March 17, 2016,
from Biomass Conversion Research Centre: Comparison of biogas Plants:
https://www.academia.edu/1824916/Comparison_among_different_models_of_biogas_pla
nt
Sievers, Jan Christian; Oldenburg, Martin; Albold, Andrea; Londong, Jörg (2014) “Characterisation
of Greywater - Estimation of Design Values” KREIS Project. German Federal Ministry of
Education and Research (BMBF)
Spuhler, D. (n.d). Anaerobic Digestion (Small Scale). Retrieved March 16, 2016, from Sustainable
Sanitation Water Managment:
http://www.iwawaterwiki.org/xwiki/bin/view/Articles/2%29+ACCRA+%28Ghana%29+3
Tilley, Elizabeth et al, (2008) “Compendium of Sanitation Systems and Technologies” Swiss Federal
Institute of Aquatic Science and Technology (Eawag). D bendorf, Switzerland.
Udofia, E. A., Yawson, A. E., Aduful, K. A., & Bwambale, F. M. (2014). Residential characteristics as
correlates of occupants’ health in the greater Accra region, Ghana. BMC Public Health, 1-13.
United Nations. (n.d). 17 Goals to Transform our World:Goal 6-Ensure access to water and
Sanitation for all. Retrieved March 29, 2016, from Sustainable Development Goals:
http://www.un.org/sustainabledevelopment/water-and-sanitation/
University College London. (2013). Environmentally Just Urbanisation through Urban
Agriculture:Accra Ghana Reports 2012. Retrieved March 28, 2016, from Department
Planning Unit: University College London: https://issuu.com/dpu-ucl/docs/urbanagriculture-
accra2012

25
Veenhuizen, René van; Cofie, Olufunke; Martin, Adrienne; Jianming, Cai; Merzthal, Gunther;
Verhagen, Joep (2007) "Multiple sources of water for multifunctional urban agriculture"
SWITCH Ghana
Verhagen, Joep; Darteh, Bertha; Osei-Tutu, Henrietta; Adank, Marieke; Sharp, Philip (2015) "A
Learning Platform to address Urban Water Management in the City of Accra. An Assessment
of the SWITCH project in Accra 2010" SWITCH Ghana
Vögeli, Y., Lohri, C. R., Gallardo, A., Diener, S., & Zurbrügg, C. (2014). Anaerobic Digestion of Biowaste
in Developing Countries:Practical Information and Case Studies. Dübendorf, Switzerland:
Swiss Federal Institute of Aquatic Science and Technology (Eawag).
WHO - World Health Organization (2006) Guidelines for the Safe Use of Wastewater, Excreta and
Greywater: Volume 2 - Wastewater use in agriculture. 3rd
ed.
Wim J. van Nes & Tinashe D. Nhete (2007) “Biogas for a better life: An African initiative”
Renewable Energy World Magazine 10(4) <http:
//www.renewableenergyworld.com/articles/print/volume-10/issue-4/bioenergy/biogas-for-a-
better-life-an-african-initiative-51480.html>
World Bank (2004) "Implementation Completion Report (IDA-28360 PPFI-P8830 PPFI-P8831) On
A Credit In the Amount SDR 47.8 Million to the Government of Ghana for an Urban
Environmental Sanitation Project"

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