Disposable diapers have become a ubiquitous product in modern society, offering convenience and hygiene benefits. They have brought about much-needed convenience to mothers in taking care of their children, especially when they are traveling. White et al. [1] noted that, however, their disposal presents a complex challenge, particularly in developing world cities where waste management infrastructure is often inadequate and levels of technology to aid waste management are generally at their infancy stage. Some recent technologies that can be used for AHPs waste management are documented in Khoo et al. [2] . To support this notion, Mudau et al. [3] posited that, in developing countries, the use of disposable diapers is steadily increasing, posing a significant challenge in the management of the associated waste since these countries lack the expertise and financial resources that can help in the adoption of state-of-the-art technologies to deal with solid waste. Zhang et al. [4] reiterate that, while most Municipal Solid Waste (MSW) and sewage are collected, reused, and recycled in industrialized countries, collection and adequate disposal are not yet a reality for most developing countries, not to mention well-designed municipal treatment facilities. Controlled disposal of diapers and sanitary pads, also known as Absorbent Hygiene Products (AHPs), has over the years proved to be a daunting task for city authorities in Zimbabwe among other developing nations, as these are non-biodegradable, which makes them seen everywhere in public places as shown in Figure 1 .

Zimbabwe is one country where diaper waste has become a menace. There is a relatively poor waste collection and disposal system in the country, and in most cases, waste is dumped in any open space available in Manyame [6] . Diapers are among the bulk of waste found at both legal and illegal dumpsites in low-class residential areas. As their consumption continues to increase in developing world regions due to rapid growth in human population and urbanization, the absence of efficiency in their disposal is likely to worsen the resultant public health and environmental challenges. Studies on diaper usage estimation are found in Nell et al. [7] and Thomas-Possee et al. [8] . The urban population in developing countries is growing at an alarming rate, which is a cause for concern for solid waste management in Voukkali [9] . Materials used to make these indispensable sanitary products are among several factors that make their disposal a difficult task, especially in developing world cities. Generally, a typical disposable diaper consists of wood pulp fluff, sodium polyacrylate (also referred to as SAP or absorbent gel), polyolefin nonwoven fabric, adhesives, polyolefin film, and synthetic rubber elastic strands, as described in Ntekpe et al. [10] . Studies on the AHPs materials are found in Khanyile et al. [11] , Mirabella et al. [12] , Tariq et al. [13] , and Bachra et al. [14] . Among those materials used in making baby diapers, polypropylene plastic from petroleum, as noted in Siregar [15] , has been cited by different authorities as the most difficult to dispose of, given that it is non-biodegradable. Disposal of diapers as well as other sanitary materials, is associated with quite a number of methods, as highlighted in the literature. Some of the methods commonly used in developing world cities to dispose of this kind of waste include uncontrolled incineration, burying in Schenck et al. [5] , illegal open space dumping, throwing in toilets as in Schenck et al. [5] and White et al. [1] , and landfilling, but more sophisticated and technologically based ones like recycling in Khoo et al. [2] and Itsubo et al. [16] , and controlled incineration, are less common. This can be supported by findings from a related study by Mudau et al. [3] , which states that there are various methods used by communities to dispose of waste in the category of Absorbent Hygiene Products (AHP), which include burning as in Schenck et al. [5] , composting in Mutowo & Mzengi [17] , Espinosa-Valdemar et al. [18] [19] , and Colón et al. [20] , recycling in Shah et al. [21] , or reusing and illegal dumping of waste in undesignated areas. There are various methods used by communities to dispose of waste which include burning, burying, composting, recycling or reusing, and illegal dumping in Nyamayedenga & Tsvere [22] of waste in undesignated areas. Improper disposal of diapers together with other sanitary materials has serious environmental and public health issues, including the spread of infectious diseases, contamination of water sources, and air pollution. Studies on the environmental and health impact of AHPs are found in Ntekpe et al. [10] , Makoś-Chełstowska et al. [23] , White et al. [1] , Płotka-Wasylka et al. [24] , Cordella et al. [25] , Reese et al. [26] , Mendoza et al. [27] , and Weisbrod & Van Hoof [28] . Literature has well documented that landfilling, a commonly used waste disposal method in developing world cities, emits the most greenhouse gas (GHG) compared to anaerobic digestion, thus contributing to the greenhouse effect and global warming, as noted in Zhang et al. [4] . Other authorities have established that diapers themselves have some health implications for babies. Thus, according to Jamwal et al. [29] , diapers lead to the risk of diaper dermatitis, also called diaper rash, mostly affecting body parts in contact with it, such as buttocks, lower abdomen, genitalia, and upper thighs. City authorities in developing world cities blame improper disposal of diapers along natural waterways and storm drains as one of the main contributing factors toward poor drainage, which increases the chances of flooding, as these would have blocked the drainage system. Incorrect disposal of litter such as diapers, plastics, and sanitary pads clogs Harare’s drainage system, particularly in the Central Business District (CBD), as noted in Manyame [6] . Furthermore, Hoang and Fogarassy [30] highlighted that inadequate municipal solid waste management (MSWM) has given rise to a range of unexpected consequences, including the contamination of oceans and drains, the occurrence of floods, and the transmission of infections through the breeding of vectors. In this vein, it can be noted that improper dumping of diapers together with other wastes in the same category is a key driver of some of the disaster risks facing the urban poor, mainly including slum dwellers and low-income residents, given their location in disaster-sensitive areas, inclusive of water channels, river banks, among others, as well as their marginalization by policing and service provision. Supporting this notion, Mlilo et al. [31] noted that refuse collection in Bulawayo, in general, and Cowdray Park suburb, in particular, has been unreliable; and these areas could go for months without municipality waste management services. Arriving at an optimal method of disposing of wastes such as diapers by Local Governments (LGs) running developing world cities is associated with complexity. There are several stakeholders who must be involved, and there are socioeconomic and also environmental factors to be taken into account. Put in other terms, the optimal disposal method should embrace all the elements of sustainability, thereby contributing toward achieving sustainable urban development in developing states, given their rapid urbanization. Through this optimal method, authorities must see to it that disaster risk reduction goals are met, considering that improper disposal of wastes is a key driver of some biological and hydrological disaster risks that have proven to be perennial in most third world cities, such as epidemics and flash floods due to blocked drainage systems. To address this issue, a comprehensive and sustainable approach is required to manage diaper waste. This study aims to develop an MCDM framework to identify the optimal diaper disposal method considering multiple criteria, including environmental impact, economic feasibility, social acceptability, and public health implications. Although there is rich literature regarding garbage disposal in developing world cities, there is still a grey area to be filled. Works involving the application of MCDM in informing better decision-making on the best garbage disposal methods are limited. This study is therefore aimed at contributing toward covering this gap while improving waste disposal, especially of non-biodegradable items such as AHPs, together with related policymaking under increasing waste generation associated with rapid urbanization in developing world cities.

In this study, the methodology included gathering data associated with the disposal of diapers and sanitary pads in the developing world city of Bulawayo in Zimbabwe. There was triangulation of data collection tools, including questionnaire surveys for the AHP method, interviews and conversations, and a review of available literature. Site visits to locations including dumpsites and facilities, regulatory agencies such as the Bulawayo City Council (BCC), Environmental Management Agency officials (EMA), non-governmental organizations (NGOs), environmental pressure groups, and academics were made to support and supplement information gathered by the surveys. Interviews and conversations with health practitioners, environmental regulatory agencies, recycling industry experts, and PRO committees were conducted to obtain details of recent progress and development associated with AHPs management. These experts were selected purposively and conveniently. Available literature was also obtained and examined to compare AHPs waste management in Zimbabwean cities with that in other developing world cities and regions.

This section shows results from analyzed expert judgments and household opinions collected through surveys and interviews. The data covered diaper disposal methods, criteria, and sub-criteria used for the Analytical Hierarchical Process. The main goal was to determine the optimal method that can be used for diaper disposal by developing world cities.

Figure 2 shows the relative importance of criteria and sub-criteria used to determine the optimal disposal method local governments can prioritize in the long run. On the first level criteria, Environmental impact had the greatest relative importance (0.446) whilst on the second level criteria, Air-borne diseases had the highest relative importance followed by water pollution with (25.8% and 23.2%) respectively.

Recycling was found to be the best diaper disposal method (28.7%), followed by anaerobic digestion (19.7%). The commonly utilized disposal method, that is, uncontrolled open space dumping, was ranked the least (2.7%), falling in the same category as other highly practiced methods, including latrine disposal (3.8%) and burying (4.6%), among others, as shown in Figure 3 .

This study used an MCDM approach, specifically the Analytic Hierarchy Process, to evaluate and select the most appropriate solid waste in the form of Absorbent Hygienic Products, focusing on disposal strategies for Zimbabwean cities.

Emphasis by experts on health and environmental factors at the expense of economic feasibility in the context of a developing world city, where issues to do with costs form a major barrier, is possibly a consequence of serious risks that are associated with improper disposal of these non-biodegradable wastes, emphasizing the dire need for responsible waste management practices. This underscores the need to minimize pollution, enhance waste management, and promote waste reuse for effective community-based diaper waste collection. Thus, environmental pollution from some current AHPs disposal methods has hazardous short-term and long-term effects on the life and health of citizens; hence, the criterion on health and environmental factors has more importance than the economic criterion. While economic feasibility ranked lower, it remains an important criterion in selecting the most sustainable solid waste disposal method, especially in developing nations with fragile economies.

Comparatively, our findings resonate with those from similar studies in South Africa, Kenya, Nigeria, and Pakistan, as reported by Slekiene et al. [34] , Maluni [35] , Ntekpe et al. [10] , and Mujaba et al. [36] , among others. Recycling was suggested to be the best diaper disposal method in the majority of studies on non-biodegradable waste disposal, such as AHPs, which are the focus of this study. These findings point to Environmental Impact as the most crucial factor in determining the best action for municipal solid waste management in Zimbabwean cities, particularly Bulawayo, and they can inform policy development and help guide future research on sustainable waste management practices in rapidly urbanizing developing world cities across the global village.

The study’s participants, who are experts from different fields related to the subject under investigation, were chosen through purposive sampling, focusing on the city of Bulawayo. Consequently, the insights obtained are closely linked to this city, limiting the generalizability of our conclusions across different regions or other socio-economic contexts. Furthermore, the assessment is based on current conditions and may not account for future changes in waste generation or technological advancements in waste management. This sampling approach, while beneficial for in-depth, context-specific understanding, may not reflect the full spectrum of experiences and behaviours present in varied settings. The study only utilized a single multi-criteria decision-making tool, the Analytical Hierarchical Process, to select the best disposal method for absorbent hygienic products (AHPs) in the developing world city of Bulawayo in Zimbabwe. Although the tool is versatile, the decision-making process could be enhanced by considering a hybrid multi-criteria approach where the technique can be combined with others such as TOPSIS, GIS, among others.

Future research should consider expanding the geographic scope of the study to include a wider range of urban settings, stakeholders, and communities, utilizing random sampling methods where feasible to enhance the representativeness of the findings. Also, the use of hybrid methods such as AHP-DEA applied to solve logistics problems in Sibanda et al. [37] and AHP-TOPSIS-SWARA applied in landfill selection by Mvembe et al. [38] should be considered.

The study aimed to determine the best waste disposal method for diapers among other AHPs for developing world cities, given the high fertility rates and rapid urbanization they are facing. The Analytical Hierarchical Process was used to rank the possible disposal methods (alternatives), among which recycling and anaerobic digestion were found to be the best and second best, respectively. Sensitivity analysis proved recycling to be the most robust disposal method. The study highlighted several implications for different relevant stakeholders.

Not applicable.

Not applicable.

The data supporting this research are contained in this paper.

This research was supported by the Research and Development Board of the National University of Science and Technology (NUST) [Grant Number RDB/74/25].

All authors contributed equally.