Evaluation of operational challenges and technological performance of wastewater treatment plants in Addis Ababa

Abstract

Rapid urban expansion has led to increased wastewater generation and mounting pressure on existing wastewater treatment plants This study presents a comprehensive evaluation of selected wastewater treatment plants (WWTPs) in Addis Ababa, with a particular focus on operational efficiency, technological deployment, and institutional and financial challenges. A mixed-method approach was adopted, integrating quantitative data from plant operations with qualitative insights derived from stakeholder interviews and on-site observations. The assessment covered key treatment technologies including the Activated Sludge Process (ASP), Upflow Anaerobic Sludge Blanket Reactor (UASBR), and Membrane Bioreactor (MBR), whose performances were evaluated against national effluent discharge standards. MBR systems were found to be predominantly utilized in decentralized treatment facilities, representing 81.8% of such installations, whereas UASBR technology was mainly employed at the central municipal plant. A significant positive correlation was identified between plant treatment capacity and workforce size, with higher-capacity facilities necessitating more personnel. Operationally, 89.1% of the surveyed WWTPs had functional treatment stages, while 10.9% were non-operational. Key operational challenges included equipment malfunctions, poor sludge management, odor emissions, influent flow rate fluctuations (reported in 86.4% of facilities), and limited hydraulic or treatment capacity (64.5%). Financial constraints, reported by 70% of respondents, and low levels of community awareness (20.9%) further impeded effective WWTP operation. These findings underscore the critical need for strategic investment, institutional capacity building, stakeholder engagement, and policy reform to enhance the sustainability, resilience, and long-term performance of wastewater treatment infrastructure not only in Addis Ababa but also in other urban centers facing similar developmental and environmental challenges.

Introduction

The contamination of water bodies is predominantly attributed to the inadequate development of appropriate wastewater treatment facilities, especially in rapidly urbanizing regions^1–3. There is increasing interest in evaluating the environmental impacts of wastewater treatment plants (WWTPs) and enhancing their operational efficiency, as effective wastewater treatment is critical for promoting environmental sustainability and protecting public health^4,5. Thus, wastewater-related issues are increasingly recognized as significant environmental threats with serious implications for human health and ecosystem integrity^6,7. Since the early twentieth century, the development and evaluation of wastewater treatment technologies (WWTTs) have been driven by efforts to mitigate environmental contamination, with growing interest further stimulated by the implementation of national and international regulations aimed at minimizing the environmental impacts of wastewater^2,8. To meet increasingly stringent discharge regulations and enhance water reclamation efficiency, wastewater treatment plants (WWTPs) are adopting advanced technologies; however, energy efficiency has traditionally been underemphasized in their design, a trend now shifting in response to the European Union’s 2030–2050 Climate and Energy Framework⁹.

In Africa, rapid urbanization and financial constraints hinder access to universal sanitation and effective wastewater treatment^10,11, as existing infrastructure is often inadequate, underdeveloped, and poorly maintained, limiting its capacity to meet increasing demand¹². Research into the operational challenges, financial constraints, and institutional barriers facing existing wastewater treatment facilities is critical for informing policy and guiding future capital investments, particularly as evidence indicates that centralized treatment systems in developing countries are often costly and energy-intensive¹³. The Ethiopian Water Resources Management Proclamation (No. 197/2000) aims to protect natural water resources from pollution^14,15, overexploitation, and degradation, serving as a critical legal framework for the sustainable management and socio-economic optimization of the country’s water assets an imperative particularly evident in urban centers like Addis Ababa, where rapid population growth and industrial expansion have intensified concerns over inadequate wastewater treatment¹⁶. Thus, the lack of comprehensive data on municipal wastewater treatment facilities in Addis Ababa hindered the assessment of technical, operational, and financial viability, highlighting the urgent need for research to identify performance barriers and inform the development of context-specific, sustainable sanitation solutions tailored to city’s unique challenges and opportunities^17,18. This study assessed the technical efficiency, operational challenges, and financial sustainability of municipal wastewater treatment plants in Addis Ababa to evaluate their overall viability, offering analysis of key performance indicators to support informed decision-making, investment prioritization, and the advancement of sustainable practices by stakeholders.

Methodology

Description of the study

The study area is delineated by initially situating Addis Ababa within the national context of Ethiopia, followed by a detailed focus on its constituent sub-cities. This hierarchical approach establishes a comprehensive spatial framework that integrates both macro-level regional dynamics and micro-level urban characteristics. Utilizing a dual-map approach, the study spatially identified and localized multiple wastewater treatment plants (WWTPs), including condominium-based and sub-city-specific facilities, to assess their distribution, accessibility, and potential service coverage. Each treatment plant was systematically categorized and labeled by location or facility type, facilitating comprehensive data collection for technical, operational, and financial evaluations. The inclusion of a distance scale enabled precise geospatial analysis of spatial relationships among WWTPs and administrative boundaries, which are essential for correlating plant performance with demographic and urban development factors. This approach implies the use of Geographic Information Systems (GIS) for detailed mapping and spatial analysis, combined with field surveys or official data sources to ensure accurate facility identification. Figure 1 illustrates the spatial distribution of municipal wastewater treatment plants (WWTPs) across the sub-cities of Addis Ababa, the capital of Ethiopia. The left panel displays a political map of Ethiopia, highlighting the location of Addis Ababa within the national context. The right panel presents a detailed map of Addis Ababa, subdivided into its respective sub-cities, and marks the locations of major WWTPs operating within the metropolitan area. The map includes both centralized and decentralized facilities, including conventional plants such as Akaki Kaliti WWTP and decentralized condominium-based systems such as Cheffe Condominium WWTP and Kilinto Condominium WWTP. This spatial visualization supports the contextual understanding of site-specific technological performance and operational challenges discussed in the study. The figure serves to complement, not duplicate, the data presented in tables, which provide technical and performance-specific details for each plant.

Fig. 1.

Spatial distribution of wastewater treatment plant (WWTP) sites across Addis Ababa City Administration.

Research design

The study employed a structured and sequential research design, beginning with the identification of the research problem and the formulation of clear objectives, thereby establishing a solid foundation for systematic inquiry. Data collection was strategically divided into primary and secondary sources, reflecting a comprehensive mixed-methods approach that supports triangulation. The methodological framework, as shown in Fig. 2, adopted in this study for evaluating the operational challenges and technological performance of wastewater treatment plants (WWTPs) in Addis Ababa followed a structured and systematic approach. The process began with the identification of the core research problem and the formulation of specific objectives. Data collection was conducted through both primary and secondary sources to ensure comprehensive coverage. Primary data were obtained using structured questionnaires distributed to plant operators and technical personnel, aimed at assessing the current operational status and functional performance of the WWTPs. In addition, stakeholder interviews were conducted with professionals, municipal authorities, and other relevant actors to capture expert insights on institutional and operational barriers. The responses from the primary data collection were then analyzed quantitatively using Statistical Package for the Social Sciences (SPSS) to derive meaningful patterns and relationships. Complementing this, secondary data were collected from both published and unpublished literature, including peer-reviewed journal articles, academic theses, technical reports, books, and government or institutional websites. These secondary sources provided contextual background and supported the triangulation of primary findings. The combined analysis of both data streams informed the synthesis presented in the Results and Discussion section and led to evidence-based conclusions regarding the performance gaps and improvement opportunities within the city’s wastewater treatment infrastructure.

Fig. 2.

Methodological framework for evaluating operational challenges and technological performance of wastewater treatment plants in Addis Ababa.

Sampling techniques and sample size determination

Both probability and non-probability sampling techniques were employed in this study to ensure the reliability and representativeness of the results. A total of 110 employees from the Addis Ababa municipal wastewater treatment plant were selected using probability sampling methods, including simple random sampling, direct observation, and focus group discussions. In parallel, purposive (non-probability) sampling was utilized to gather general information from 11 municipal and condominium wastewater treatment sites, as detailed in Table 1. To determine the appropriate sample size, key demographic variables such as age, gender, region, and field of specialization were considered. For large populations (N > 10,000), the sample size was calculated using Cochran’s formula (1963), which provides a statistically valid method for estimating sample sizes for proportions:

where, Z is the standard variable error and its value that corresponds to 93% confidence interval and equals to 1.81. e is the allowable error equal to about 7% of the mean (0.07) or the desired level of precision, p is the estimated proportion of an attribute that is present in the population, and q is1-p (0.5, 0.5). In this case, the maximum sample size is estimated as follows:

Table 1.

Summary of wastewater treatment plants in addis ababa: type, technology, capacity, and Workforce.

WWTP	Type of WWTP	Technology	m3/day	No of employers
Akaki Kality municipal WWTP	Municipal	UASBR	100,000	100
Kality Chefe Condominium	Condominium	UASBR	25,000	51
Kilinto Condominium	Condominium	MBR	4000	31
Bole Arabsa 1 A Condominium	Condominium	MBR	2600	16
Bole Arabsa 2 A Condominium	Condominium	MBR	3600	26
Bole Arabsa 2B Condominium	Condominium	MBR	4300	36
Bole Bulbula Condominium	Condominium	MBR	3000	21
Haile garment Oromia Condominium	Condominium	MBR	1200	9
Mekanisa Kotari condominium	Condominium	MBR	1700	10
Kara Kore Condominium	Condominium	MBR	1700	10
Degnet Condominium	Condominium	MBR	1700	10
Total				320

The representative sample size was estimated using the following formula corrected for finite population.

Therefore n = 110.

Data collection

The study employed a combination of primary and secondary data collection methods. Primary data were obtained through structured interviews and questionnaires administered at various wastewater treatment facilities, while secondary data were sourced from both published and unpublished materials, including reports, academic theses, and relevant literature. A mixed-methods approach was adopted for data analysis, integrating both quantitative and qualitative techniques to ensure comprehensive and robust interpretation of the findings. All data collection procedures were conducted in strict accordance with relevant institutional guidelines and national regulations. The study protocol was reviewed and approved by the Kotebe University of Education Research Ethics Review committee, in accordance with the Ethiopia National Research Ethics Review Guideline (Fifth Edition).

Data analysis

A quantitative data analysis approach was employed to evaluate the collected data. Several analytical tools were used to facilitate data processing and interpretation, including SPSS for statistical analysis, Google Earth Pro and ArcGIS version 10.8 for geospatial analysis, and Microsoft Excel and Microsoft Office 2010 for data organization, visualization, and documentation.

Result and discussion

The results in Table 1 provides a comparative analysis of 11 wastewater treatment plants (WWTPs) located in Addis Ababa, comprising one municipal-scale facility and ten condominium-based systems. Key parameters assessed include the type of WWTP, treatment technologies employed, daily treatment capacity, and workforce size. Among these facilities, only one (9.1%) is a municipal WWTP which is Akaki Kality Municipal WWTP, while the remaining ten (90.9%) are condominium-based, underscoring a growing emphasis on decentralized wastewater treatment solutions in residential settings¹⁹. Two primary treatment technologies are utilized across the facilities: Up flow Anaerobic Sludge Blanket Reactor (UASBR) and Membrane Bioreactor (MBR). UASBR is implemented in two plants (18.2%), namely Akaki Kality Municipal WWTP, which has the largest treatment capacity at 100,000 m³/day, and Kality Chefe Condominium, with a capacity of 25,000 m³/day. In contrast, MBR systems are deployed in nine plants (81.8%), indicating a preference for advanced, compact, and efficient technologies suited for small-scale decentralized applications. The combined daily treatment capacity of all plants is approximately 148,100 m³/day. The dominance of MBR technology in condominium systems reflects a strategic transition toward space-efficient and high-efficiency wastewater treatment solutions in urban housing developments²⁰. Despite their relatively small scale, condominium WWTPs play a vital role in enhancing local sanitation and supporting decentralized infrastructure.

The frequency distribution of observations from 11 wastewater treatment plants (WWTPs) offers valuable insights into the operational prominence and relative importance of each facility (Table 2). A total of 110 recorded responses were analyzed, reflecting patterns of usage, public reporting frequency, and perceived relevance within the context of the city’s wastewater management system. The Akaki Kality Municipal WWTP emerges as the most prominent facility, accounting for 34 of the total observations, equivalent to 30.9%. This high frequency underscores its central role in the city’s sanitation infrastructure, likely attributed to its substantial treatment capacity and wide municipal service coverage²⁰. Its dominant early contribution to the cumulative percentage (30.9%) further highlights its operational significance and public visibility. Among the condominium-based WWTPs, several facilities exhibit relatively high observation frequencies. Kality Chefe (Genet) recorded 18 observations (16.4%), followed by Kilinto with 11 (10.0%) and Bole Arabsa 2B with 12 (10.9%). These figures suggest that these facilities serve larger residential populations, maintain reliable operations, or attract greater stakeholder attention. Moderately represented facilities include Bole Arabsa 2 A (8.2%), Bole Bulbula (6.4%), and Bole Arabsa 1 A (4.5%). While these plants contribute to decentralized treatment efforts, their lower frequency indicates comparatively limited recognition or possibly smaller operational scales. Conversely, the least cited facilities Kara Kore and Degnet (each 3.6%), and Haile Garment Oromia and Mekanisa Kotari (each 2.7%) may reflect minimal service reach, reduced functionality, or other barriers to effective utilization. The cumulative distribution reveals that by the time the sixth-ranked WWTP (Bole Arabsa 2B) is included, over 80% of total observations are accounted for. This pattern reflects a concentration of wastewater treatment activity among a limited number of key facilities, while the remaining plants occupy marginal positions in terms of operational relevance²¹. Thus, the distribution demonstrates a highly skewed pattern, where a small number of WWTPs particularly the municipal plant and a few prominent condominiums dominate the wastewater management landscape. This imbalance may stem from disparities in infrastructure investment, population served, or performance efficiency. These findings emphasize the strategic importance of high-frequency WWTPs in informing policy decisions, resource allocation, and future planning for equitable and sustainable urban wastewater treatment in Addis Ababa.

Table 2.

Distribution of wastewater treatment plants in Addis Ababa by type and relative frequency.

WWTP	Frequency	Percent	Valid percent	Cumulative percent
Akaki kality municipal WWTP	34	30.9	30.9	30.9
Kality Chefe (Genet) condominium WWTP	18	16.4	16.4	47.3
Kilinto condominium WWTP	11	10.0	10.0	57.3
Bole arabsa 1 A condominium WWTP	5	4.5	4.5	61.8
Bole arabsa 2 A condominium wwtp	9	8.2	8.2	70.0
Bole arabsa 2B condominium WWTP	12	10.9	10.9	80.9
Bole bulbula condominium WWTP	7	6.4	6.4	87.3
Kara kore condominium wwtp	4	3.6	3.6	90.9
Degnet condominium wwtp	4	3.6	3.6	94.5
Haile garment Oromia condominium wwtp	3	2.7	2.7	97.3
Mekanisa kotari condominium wwtp	3	2.7	2.7	100.0
Total	110	100.0	100.0

Figure 3 illustrates a comparative analysis of the number of employees relative to the treatment capacity, measured in cubic meters per day (m²/day), across various wastewater treatment plants (WWTPs) in the city. The x-axis represents the treatment capacity of each plant, ranging from 1200 m²/day to 100,000 m²/day, while the y-axis denotes the corresponding number of employees assigned to each facility. The chart reveals a clear positive correlation between treatment capacity and staffing levels. Larger-capacity plants tend to employ more personnel. Notably, the Akaki Kality Municipal WWTP, which has the highest treatment capacity of 100,000 m²/day, also has the highest number of employees, approximately 35. This trend suggests that higher-capacity facilities demand more human resources due to greater operational complexity, maintenance requirements, and the need for continuous monitoring. WWTPs with medium capacities, ranging from 25,000 m²/day to 3000 m²/day, show a progressive decrease in staffing levels, from around 16 to 8 employees. These facilities likely represent large condominium or institutional systems, which require a moderate workforce to manage processes such as biological treatment, membrane bioreactors (MBR), or anaerobic technologies like UASBR. At the lower end of the spectrum, plants with capacities at or below 2,600 m³/d, such as those treating 1700 or 1200 m²/day, employ significantly fewer staff, with the lowest observed staffing at around four employees²⁰. These small-scale, decentralized systems may serve individual condominium complexes and are likely to incorporate simpler technologies or higher levels of automation, thereby reducing the need for manual operation. While the overall trend aligns staffing levels with treatment capacity, some deviations suggest that other factors influence workforce requirements²¹. For example, a 1700 m²/day plant employs more staff than a 2600 m²/day facility, implying that technology type, level of automation, system design, or regulatory and operational considerations also play important roles. This analysis underscores the importance of aligning staffing strategies with plant capacity, technological complexity, and operational objectives. The significant staffing levels at high-capacity facilities reflect their critical role in managing urban wastewater, whereas the efficient operation of low-capacity systems emphasizes the value of compact, resource-efficient designs in decentralized sanitation solutions. Such insights are essential for effective infrastructure planning, resource allocation, and policy formulation aimed at enhancing the sustainability and performance of urban wastewater treatment in Addis Ababa¹⁹.

Fig. 3.

Capacity of wastewater treatment plants in Addis Ababa and corresponding workforce.

As shown in Table 3, the Current Status of Capacity of WWTPs in Addis Ababa presents a frequency distribution of wastewater treatment plants categorized by their treatment capacity in cubic meters per day (m²/day). A total of 110 observations were analyzed, offering critical insights into the distribution, operational scale, and functionality of the city’s wastewater infrastructure. The largest share of observations 30.9% falls within the high-capacity range of 70,000 to 80,000 m²/day, representing 34 plants. This category likely includes major municipal facilities such as the Akaki Kality WWTP, which serve extensive urban populations and form the backbone of centralized wastewater management²². Their high frequency underscores the significance of large-scale facilities in handling the bulk of the city’s wastewater load. Plants with medium capacities, ranging between 2000 and 3000 m²/day, account for 18 observations (16.4%). These systems typically serve residential clusters, institutional zones, or condominium complexes, reflecting the role of semi-centralized infrastructure in supporting decentralized urban developments. Their moderate representation highlights a balanced integration of distributed wastewater management solutions. A notable portion of WWTPs 27 plants (24.5%) fall within the 1000 to 2000 m²/day category, indicating a strong presence of low-capacity, decentralized treatment systems. These are often used in individual condominiums or small communities and represent a growing trend in urban sanitation strategies that emphasize decentralized service delivery. Additionally, 19 plants (17.3%) operate within the 100 to 1000 m²/day capacity range. These very low-capacity facilities may include compact treatment units such as membrane bioreactors (MBRs), which are well-suited for limited space and low-flow applications²³. Although less prominent in size, these systems are essential for extending wastewater services to areas not connected to centralized systems. A significant concern arises from the identification of 12 plants (10.9%) that are classified as non-functional. This indicates operational challenges such as poor maintenance, inadequate funding, technological failure, or design flaws. The existence of a substantial proportion of non-operational infrastructure undermines the efficiency and resilience of the city’s wastewater management framework and signals a need for rehabilitation and improved oversight. Cumulatively, 89.1% of the WWTPs are within operational ranges, while the remaining 10.9% are inactive. This pattern highlights that although most plants are functional, the reliability and sustainability of the overall system remain critical issues. This data reflect a heterogeneous and stratified distribution of WWTP capacities in Addis Ababa, representing a hybrid model of centralized and decentralized treatment approaches. While large municipal facilities dominate the upper capacity range, the increasing number of small and very small systems reflects adaptation to localized urban growth¹¹. However, the presence of non-functional plants underscores the importance of policy interventions, technical support, and investment in infrastructure maintenance to ensure effective and sustainable wastewater management in the city.

Table 3.

Assessment of the current capacity status of WWTPs in addis Ababa City administration.

m3/day	Frequency	Percent	Valid percent	Cumulative percent
80,000−70,000	34	30.9	30.9	30.9
3000−2000	18	16.4	16.4	47.3
2000−1000	27	24.5	24.5	71.8
1000−100	19	17.3	17.3	89.1
Not functional	12	10.9	10.9	100.0
Total	110	100.0	100.0

The data in Table 4 provides an overview of the operational status of pretreatment and primary treatment processes across 110 wastewater treatment plants (WWTPs) in Addis Ababa. These initial stages are crucial for the effective removal of suspended solids, oils, fats, and other coarse contaminants, which, if not properly treated, can impair the efficiency of downstream secondary or tertiary processes. Among the total responses, 97 (88.2%) reported having functional pretreatment and primary treatment systems. When considering only valid responses, this accounts for 89.0%, indicating that a significant majority of WWTPs have implemented and are operating these essential processes in line with conventional wastewater treatment protocols¹⁴. This reflects a generally high level of infrastructure development and technical capacity at the initial stage of treatment across the city. However, 12 (10.9%) respondents were identified as non-functional in this regard, representing 11.0% of valid cases. This is a concerning indication of system failures at a fundamental level of wastewater treatment. Non-functionality at the pretreatment or primary stage can lead to overloading of biological treatment systems, increased operational costs, reduced treatment efficiency, and potential discharge of inadequately treated effluent into the environment. These failures may stem from issues related to poor maintenance, design inefficiencies, insufficient funding, or lack of skilled personnel. In addition, 1 response (0.9%) was missing, while this is statistically minimal, it highlights the importance of ensuring complete and accurate data collection in future assessments for robust analysis. The dominance of functional systems is a positive outcome; however, the presence of more than 10% non-functional units necessitates targeted interventions. Thus, the analysis highlights the critical need for regular maintenance, technical audits, and performance monitoring of pretreatment and primary treatment facilities²⁴. While the current infrastructure shows promising levels of functionality, addressing the minority of underperforming systems through rehabilitation, capacity-building, and investment is essential to safeguard public health and improve the overall sustainability and resilience of wastewater treatment services in Addis Ababa.

Table 4.

Evaluation of the status of pretreatment and primary treatment processes in WWTPs.

The pretreatment and primary treatment processes utilized
		Frequency	Percent	Valid percent	Cumulative percent
Valid	All	97	88.2	89.0	89.0
	Not function	12	10.9	11.0	100.0
	Total	109	99.1	100.0
Missing	No answer	1	0.9
Total		110	100.0

The dataset, Table 5, provides an overview of the operational status of secondary treatment processes across 110 wastewater treatment plants (WWTPs) in Addis Ababa. Secondary treatment is a vital stage in wastewater management, typically involving biological processes aimed at breaking down dissolved and suspended organic matter. This step is essential for meeting effluent quality standards and for protecting both environmental and public health.

Table 5.

Evaluation of the operational status of secondary treatment processes in WWTPs.

Secondary process	Frequency	Percent	Valid percent	Cumulative percent
Yes	98	89.1	89.1	89.1
Not functional	12	10.9	10.9	100.0
Total	110	100.0	100.0

Out of the total WWTPs assessed, 98 plants (89.1%) were found to have functional secondary treatment systems. This high percentage suggests that the majority of facilities are not only equipped with but also actively operating this core component of wastewater treatment. The widespread functionality of these systems reflects a robust infrastructure and indicates considerable technical capacity to handle biological treatment processes citywide²⁵. In contrast, 12 plants (10.9%) were reported as having non-functional secondary treatment systems, representing a significant operational gap. Failures at this stage can result in the discharge of poorly treated wastewater with elevated levels of biochemical oxygen demand (BOD), nutrients, and pathogenic organisms, posing serious environmental and health risks. The existence of these underperforming systems points to potential deficiencies in operation, maintenance, technical design, or financial resources, all of which necessitate targeted corrective measures. The cumulative data confirm that all facilities are accounted for, with responses divided between either functional or non-functional categories. This binary operational distribution underscores a clear divide in performance, where the majority of systems function as intended while a notable minority faces critical challenges. This data highlight a strong level of implementation of secondary treatment systems in Addis Ababa’s WWTPs, which is a positive indicator of treatment capacity and infrastructure maturity. However, the presence of 10.9% non-functional units exposes a significant weakness in the treatment chain. Addressing this issue requires urgent technical assessments, followed by targeted rehabilitation, enhanced maintenance protocols, and capacity-building efforts to ensure all plants meet regulatory discharge standards and contribute to sustainable urban wastewater management²⁰.

The results provide valuable insights into the range of factors affecting the functionality of 110 wastewater treatment plants (WWTPs) in Addis Ababa (Table 6). Understanding these factors is essential for developing targeted and effective interventions to enhance the performance, resilience, and sustainability of the city’s wastewater management systems. Among the valid responses, the most frequently cited issue was “All”, reported by 48 respondents (43.6%). This category indicates that a significant proportion of WWTPs are affected by a combination of technical, financial, institutional, and social challenges, rather than a single isolated problem. Such a finding emphasizes the complexity of wastewater treatment management and the need for integrated solutions that simultaneously address multiple dimensions including infrastructure upgrades, financial planning, institutional capacity, and public engagement¹⁹. The second most commonly reported factor was “Community awareness”, cited by 23 respondents (20.9%). This underscores the critical role of public understanding and involvement in the proper functioning of wastewater systems. Limited community awareness can contribute to poor wastewater practices, misuse of facilities, and lack of support for maintenance efforts, thereby exacerbating operational challenges. This finding highlights the necessity of sustained public education and stakeholder participation in promoting effective sanitation practices. Other influential factors identified include population growth (6.4%), which places increasing demand on aging infrastructure as urban areas expand, and industrial pollution (4.5%), which may involve the discharge of untreated or inadequately treated effluent from industrial sources, potentially overwhelming WWTP capacity or disrupting biological processes²⁶. Lack of proper maintenance, reported by 3.6%, reflects recurring issues related to operational oversight and the availability of technical support and spare parts. Additionally, inadequate or outdated technology was reported by 2.7% of respondents, suggesting that some facilities may be operating below optimal standards due to obsolete equipment. Insufficient funding and resources, though mentioned by only 0.9%, is a foundational constraint that may underlie many of the other issues observed, from technological deficiencies to maintenance failures. An unspecified category (coded as “9”) accounted for 7 responses (6.4%), the meaning of which is not clearly defined in the dataset and may require further clarification. Lastly, 12 responses (10.9%) were categorized as “Not functional,” indicating complete inoperability or a breakdown of WWTP systems. From a cumulative perspective, 89.1% of all influencing factors are explained by the identified categories, with the remaining 10.9% corresponding to non-functional or undefined conditions. This suggests a concentration of concern around a few dominant and interconnected challenges, particularly those related to multi-dimensional system failures and low levels of public awareness²⁷. Therefore, the functionality of WWTPs in Addis Ababa is shaped by a mix of technical, financial, environmental, and social factors. While some challenges are directly tied to infrastructure and maintenance, others stem from broader systemic issues, such as insufficient funding and lack of community engagement. To address these challenges effectively, a comprehensive and multi-sectoral strategy is required one that incorporates technological modernization, capacity building, policy reforms, sustainable financing mechanisms, and enhanced public participation. Such an approach is vital for ensuring the long-term sustainability and environmental integrity of the city’s wastewater treatment systems¹.

Table 6.

Assessment of factors influencing wastewater treatment plant functionality in addis Ababa City administration.

Factors affecting the functionality of wastewater treatment plant
		Frequency	Percent	Valid percent	Cumulative percent
Valid	Lack of proper maintenance	4	3.6	3.6	3.6
	Insufficient funding and resources	1	0.9	0.9	4.5
	Inadequate technology or outdated equipment	3	2.7	2.7	7.3
	Population growth	7	6.4	6.4	13.6
	Industrial pollution	5	4.5	4.5	18.2
	Community awareness	23	20.9	20.9	39.1
	9	7	6.4	6.4	45.5
	All	48	43.6	43.6	89.1
	Not functional	12	10.9	10.9	100.0
	Total	110	100.0	100.0

As presented in Table 7, a detailed overview of the day-to-day operational challenges reported across 110 wastewater treatment plants (WWTPs) in Addis Ababa. It reveals both isolated and interconnected issues that undermine the operational efficiency, reliability, and long-term sustainability of these facilities. The most frequently reported response was the “All” category, cited by 72 plants (65.5%), indicating that a majority of WWTPs are simultaneously experiencing multiple operational issues. These include equipment malfunctions, sludge management difficulties, odor problems, energy inefficiencies, and aging infrastructure. This high proportion reflects the complex and systemic nature of operational challenges within the wastewater sector, underscoring the need for comprehensive and integrated management strategies rather than isolated interventions²¹. Among the individual challenges, odor problems were the most commonly cited, with 8 facilities (7.3%) identifying it as a significant concern. This issue may stem from inadequate ventilation, incomplete biological treatment, or improper sludge handling. Odor emissions not only affect the local environment but also pose public nuisance and social acceptability issues, particularly in urban or residential areas²⁸. Sludge management was reported by 6 plants (5.5%), emphasizing ongoing difficulties in the treatment, storage, and disposal of sludge a by-product of the treatment process that, if not properly managed, can lead to secondary pollution and operational bottlenecks. Inadequate spare part availability was also cited by 5 facilities (4.5%), highlighting logistical and supply chain weaknesses that can delay repairs and compromise operational continuity. Other operational constraints include high energy consumption, reported by 3 plants (2.7%), which reflects the energy-intensive nature of processes like aeration and membrane filtration. In the context of unstable or limited power supply, energy costs can pose a substantial barrier to efficient operation. Additionally, equipment malfunctions and aging infrastructure were each cited by 2 plants (1.8%), pointing to insufficient investment in modernization and the need for preventive maintenance. Importantly, 12 WWTPs (10.9%) were reported as non-functional, indicating total system failure. This suggests that unresolved or cumulative operational challenges can lead to full-scale breakdowns, thereby posing serious environmental and public health risks due to the release of untreated or partially treated wastewater. The cumulative frequency distribution shows that 89.1% of the reported issues fall within the listed operational challenges, while the remaining 10.9% pertain to non-functional plants. This reflects a broad and overlapping pattern of challenges that affect WWTP functionality, reinforcing the necessity for multi-dimensional solutions²¹. This analysis reveals that WWTP operations in Addis Ababa face widespread, multifaceted challenges. The dominance of reports encompassing all categories of problems suggests the need for system-wide reforms, including infrastructure upgrades, regular preventive maintenance, improved spare part supply chains, enhanced sludge handling protocols, better odor management strategies, and investments in energy-efficient technologies. Failure to address these issues collectively could result in worsening system reliability, environmental degradation, and diminished public trust. Conversely, adopting a coordinated and well-funded approach could significantly improve the operational resilience and performance of wastewater treatment systems in the city^1,29.

Table 7.

Frequency and distribution of operational challenges in wastewater treatment plants.

	Challenges faced in the day-to-day operation of the treatment plant
Challenges day to day	Frequency	Percent	Valid percent	Cumulative percent
Equipment malfunctions	2	1.8	1.8	1.8
Sludge management	6	5.5	5.5	7.3
Energy consumption	3	2.7	2.7	10.0
Odor challenge	8	7.3	7.3	17.3
Aging infrastructure	2	1.8	1.8	19.1
Spare part	5	4.5	4.5	23.6
All	72	65.5	65.5	89.1
Not functional	12	10.9	10.9	100.0
Total	110	100.0	100.0

The dataset in Table 8, examines the prevalence of wastewater flow rate fluctuations affecting wastewater treatment plants (WWTPs). Of the 110 WWTPs surveyed, 107 provided valid responses, while 3 did not respond. Among the valid responses, the vast majority 95 plants, representing 86.4% of the total sample and 88.8% of valid responses reported experiencing operational impacts due to flow rate variability. This indicates that nearly nine out of ten WWTPs face challenges linked to fluctuating inflow, which can adversely affect treatment efficiency, system stability, and overall plant performance. In contrast, 12 plants (10.9% of the total and 11.2% of valid responses) were reported as non-functional, potentially reflecting permanent shutdowns or operational failures, possibly exacerbated by the stress of variable flow conditions. The remaining 2.7% of the sample did not provide an answer, a proportion insufficient to influence the overall analysis. These findings underscore that fluctuations in wastewater flow rates constitute a significant operational challenge for WWTPs, emphasizing the need for process designs and management strategies capable of accommodating variable inflows to maintain consistent and reliable treatment performance³⁰.

Table 8.

The prevalence of wastewater flow rate fluctuations affecting wastewater treatment plants (WWTPs).

Wastewater treatment plant affected by fluctuations of wastewater flow rates
		Frequency	Percent	Valid percent	Cumulative percent
Valid	Yes	95	86.4	88.8	88.8
	Not functional	12	10.9	11.2	100.0
	Total	107	97.3	100.0
Missing	No answer	3	2.7
Total		110	100.0

The data depicted in Table 9, summarizes responses from 110 wastewater treatment plants (WWTPs) regarding concerns about their capacity and efficiency to meet current or anticipated treatment demands. Of the total surveyed plants, 106 (96.4%) provided valid responses, while 4 (3.6%) did not respond. Among the valid responses, 71 WWTPs (64.5% of the total and 67.0% of valid responses) expressed concern about their ability to accommodate present or future wastewater treatment loads. This indicates that more than two-thirds of the plants are facing operational uncertainty, likely due to increasing pressure from population growth, urban expansion, industrial activities, and variable flow conditions influenced by climate change. In contrast, 23 WWTPs (20.9% of the total and 21.7% of valid responses) reported no such concerns, suggesting that these facilities may currently have sufficient capacity, operational reliability, or have benefited from recent system enhancements. Additionally, 12 WWTPs (10.9% of the total and 11.3% of valid responses) were reported as non-functional, potentially reflecting significant technical or financial constraints, and possibly representing facilities that have already succumbed to challenges posed by inadequate capacity or deteriorated infrastructure. While the proportion of missing data is minimal (3.6%) and does not substantially influence the interpretation, the overall findings underscore systemic vulnerabilities in the sector. The prevalence of concern among WWTPs signals an urgent need for targeted interventions, including capacity upgrades, process optimization, and adoption of resilient technologies, in order to ensure sustainable wastewater management and long-term service reliability²⁹.

Table 9.

The distribution of responses concerning the capacity and efficiency of wastewater treatment processes to Meet current and future demands.

Concerns about the capacity and efficiency of wastewater treatment processes to meet current or future demand
		Frequency	Percent	Valid percent	Cumulative percent
Valid	Yes	71	64.5	67.0	67.0
	No	23	20.9	21.7	88.7
	Not functional	12	10.9	11.3	100.0
	Total	106	96.4	100.0
Missing	No answer	4	3.6
Total		110	100.0

As summarized in Table 10, the responses of 110 participants indicate their assessment of the overall operational status of wastewater treatment plants (WWTPs) they have visited, encompassing 11 identified facilities in Addis Ababa. In this study, the functionality of the wastewater treatment plants (WWTPs) was primarily assessed through qualitative methods such as operator interviews, operational observations, and review of process parameters. Unfortunately, effluent quality was not directly measured or analyzed due to the lack of available laboratory data during the study period. Among the respondents, 55 individuals (50.0%) rated the overall functionality of the plants as “Very good,” indicating that half of the participants perceived the facilities to be highly effective and efficient in their operations. Additionally, 41 respondents (37.3%) rated the plants as “Good,” suggesting a strong level of satisfaction, albeit with recognition of potential areas for improvement. A small fraction, 2 respondents (1.8%), assessed the functionality as “Average,” reflecting a perception of moderate or satisfactory performance. Meanwhile, 12 respondents (10.9%) indicated that the plants were “Not functional.” Although the reason for this response is not explicitly clear, it may imply either a lack of operational activity during their visit or insufficient information to make an informed judgment. Overall, the findings reveal a predominantly positive perception of WWTP functionality, with 87.3% of respondents rating the plants as either “Very good” or “Good,” while a minority expressed concerns about limited performance or non-functionality^29,31.

Table 10.

Evaluation of the operational functionality of wastewater treatment plants in Addis Ababa.

Functional level	Frequency
Very good	55
Good	41
Average	2
Not functional	12
Total	110

As illustrated in Table 11, wastewater treatment plants (WWTPs) employ four principal strategies to ensure compliance with environmental regulations and standards: regulatory knowledge and awareness, systematic monitoring and reporting, emergency preparedness and response, and addressing issues related to non-functionality. Among these, monitoring and reporting emerged as the most common mechanism, reported by 41 WWTPs (37.3%), suggesting that a significant proportion of facilities prioritize systematic data collection and performance reporting as essential tools for regulatory adherence³². Regulatory knowledge and awareness was identified in 34 WWTPs (30.9%), highlighting the role of institutional understanding of environmental policies, legal frameworks, and operational responsibilities in achieving and sustaining compliance. This emphasizes the importance of ongoing staff training and capacity-building initiatives. Emergency preparedness and response was cited by 23 WWTPs (20.9%), indicating that a smaller segment of facilities has established protocols for handling environmental emergencies such as accidental discharges or system malfunctions. The relatively low percentage in this category may point to insufficient preparedness for acute environmental risks, which could compromise both compliance and public safety. Notably, 12 WWTPs (10.9%) were classified as non-functional with regard to regulatory compliance, potentially reflecting systemic failures, lack of engagement with environmental standards, or absence of formalized procedures. This group represents a critical vulnerability within the wastewater sector. Overall, the findings suggest that while many WWTPs actively pursue compliance particularly through monitoring and reporting a considerable portion remains underprepared or operationally deficient. Strengthening compliance across the sector will require targeted interventions including enhanced regulatory literacy, institutionalization of emergency response frameworks, and rehabilitation of non-functional facilities through improved governance, training, and infrastructure investment³³.

Table 11.

Compliance of wastewater treatment plants with environmental regulations and standards.

Environmental regulation and standard	Ensure compliance with environmental regulations and standards
	Frequency	Percent	Valid percent	Cumulative percent
Regulatory knowledge and awareness	34	30.9	30.9	30.9
Monitoring and reporting	41	37.3	37.3	68.2
Emergency preparedness and response	23	20.9	20.9	89.1
Not functional	12	10.9	10.9	100.0
Total	110	100.0	100.0

As presented in Table 12, data collected from 110 participants elucidate the financial constraints impacting the maintenance and operational efficiency of wastewater treatment plants (WWTPs). A majority of respondents 77 individuals (70.0%) reported that budgetary limitations significantly impacted the upkeep and functionality of their respective facilities. This indicates that financial constraints are a major barrier to effective maintenance and operational performance across a substantial portion of WWTPs. In contrast, 20 respondents (17.4%) stated that their budgetary conditions did not hinder the operation or maintenance of their plants, suggesting a minority of facilities operates with sufficient financial support. Additionally, 13 participants (10.9%) indicated that the question regarding financial limitations was not applicable to their situation; however, the specific reasons for this designation remain unclear. A further 3 respondents (2.7%) did not provide any response on this issue. These findings highlight the pervasive influence of financial constraints on wastewater infrastructure performance. As noted by^1,33, wastewater treatment services are primarily funded through water tariffs paid by citizens, and enhancing the financial sustainability and operational efficiency of WWTPs is crucial for maximizing both environmental and public health outcomes.

Table 12.

Financial constraints affecting the maintenance and operation of wastewater treatment plants.

Budgetary constraints impacting operation and maintenance	Frequency
Yes	77
No	20
Not functional	13
Total	110

Focal group discussion (FGD)

During discussions with key informants, several critical insights emerged regarding the wastewater treatment facilities managed by the Addis Ababa Water and Sewerage Authority (AAWSA). One of the primary concerns highlighted was the range of challenges impeding the effective treatment of wastewater. Participants emphasized that a comprehensive understanding of these operational barriers is essential for optimizing plant performance and achieving treatment efficiency. The discussions also recognized the central role of wastewater treatment plants in safeguarding water quality and public health³⁴. Environmental impacts associated with wastewater treatment were another key theme, with participants noting that these impacts depend on various factors, including plant design, operational procedures, and compliance with regulatory standards. The importance of enhancing technological efficiency through coordinated efforts with AAWSA and other stakeholders was widely acknowledged. Community engagement was also seen as vital for identifying performance gaps and collaboratively developing solutions. Informants underscored the value of incorporating feedback from plant managers and stakeholders to better address operational needs and strategic priorities. The discourse further stressed the public health and environmental implications of wastewater treatment, calling for a strong alignment between facility design and community needs. Integrating stakeholder feedback was deemed essential for identifying deficiencies and implementing targeted improvements. Key factors identified as limiting technological efficiency in Addis Ababa’s WWTPs included the lack of spare parts, inadequate infrastructure, weak regulatory enforcement, and limited financial resources for ongoing maintenance and system expansion³¹. To address these challenges and enhance the performance of WWTPs, participants proposed clearly defining the roles of various actors. The government, they suggested, should establish and enforce strict regulatory standards; the private sector should collaborate with public institutions through public-private partnerships to invest in infrastructure; and local communities should promote awareness about the importance of proper wastewater disposal and its impact on public health and the environment. Additionally, the discussions highlighted the need for increased investment in maintenance and infrastructure development, stronger regulatory enforcement, and the exploration of innovative technologies to overcome current limitations³⁴. Overall, the findings point to the necessity of conducting a feasibility assessment of the current status of wastewater treatment facilities. Such an assessment is essential for improving operational efficiency, protecting public health, and mitigating environmental impacts, in alignment with the broader objectives of the study.

Conclusion

In conclusion, the insights gained from this study are relevant beyond the local context, offering practical lessons for cities worldwide that are experiencing rapid urbanization and struggling with the sustainable operation of decentralized and centralized wastewater treatment systems. The study evaluated the performance of selected wastewater treatment plants (WWTPs) across Addis Ababa city, with particular emphasis on technological efficiency, operational functionality, and institutional and financial barriers. The assessment focused on three primary technologies: Activated Sludge Process (ASP), Upflow Anaerobic Sludge Blanket Reactor (UASBR), and Membrane Bioreactor (MBR). Results indicate that MBR systems are predominantly utilized in decentralized facilities, representing 81.8% of such plants, while UASBR technology is mainly employed at the central municipal treatment plant. A strong positive correlation was observed between plant capacity and workforce size, suggesting that higher-capacity systems require proportionally greater human resources. Although 89.1% of the WWTPs had functional treatment stages, 10.9% were entirely non-operational. Key operational challenges included equipment malfunction, poor sludge management, odor emissions, influent flow rate fluctuations (reported in 86.4% of cases), and limited hydraulic capacity (64.5%). Financial constraints, cited by 70% of respondents, along with low public awareness (20.9%), further limited system functionality. These findings underscore the critical need for strategic investment, institutional capacity building, stakeholder engagement, and policy reform to enhance the sustainability, resilience, and long-term performance of Addis Ababa’s wastewater treatment infrastructure. This study recommends that future studies should incorporate comprehensive effluent quality analysis including key parameters such as biochemical oxygen demand (BOD), chemical oxygen demand (COD), total suspended solids (TSS), and nutrient concentrations to more accurately evaluate the treatment performance and environmental impact of wastewater treatment plants.

Author contributions

D.B.A.: Conceptualization, Writing-review and editing data, curation. Y.A.: Methodology, investigation, writing original draft.

Funding

The authors declare that no external funding was received for the conduct of this study.

Data availability

The data availability statement of this manuscript, indicating that data can be requested from the corresponding author.

Declarations

Competing interests

The authors declare no competing interests.

Ethics approval

The study received ethical approval from the Kotebe University of Education Research Ethics Review committee, in accordance with the Ethiopia National Research Ethics Review Guideline (Fifth Edition).

Declaration of consent

Written informed consent was obtained from all participants who took part in the study, after explaining the purpose and significance of the research. Data collection proceeded only after obtaining fully informed verbal consent from the participants, and confidentiality measures were implemented to protect their privacy by excluding their names and personal identification information.