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


3

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).


4

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)


5

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


6

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


7

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)****


8

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


9

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.


10

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)


11

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


12

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


13

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


14

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


15

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.


17

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"

Wastewater Management with Anaerobic Digestion Accra, Ghana

Engineering