Foreword

The world is rapidly moving toward urbanization, and the amount of municipal solid waste (MSW), one of the most important by-products of an urban lifestyle, is growing even faster. Urbanization or "urban transition" is a process of shift in population densities from a rural/agriculture-based economy to a denser population with an industrial and service-based economy. Urbanization has generally been a positive force for economic growth, poverty reduction, and human development. With higher percentages of young urban dwellers, economic activity increases significantly in urban areas, which contributes to GDP growth of urban population in a country. Increase in population in urban areas and GDP growth results in increase in consumption ultimately leading to an increase in waste generation. Therefore, based on the latest data available, global waste generation in 2016 was estimated to have reached 2.01 billion tons (4.4 trillion lb) (World Bank Report 2018a). By 2030, the world is expected to generate 2.59 billion tons (5.71 trillion lb) of waste annually, and by 2050, waste generation across the world is expected to reach 3.40 billion tons (7.5 trillion lb).

However, sustainable waste management is a major issue for both developed and developing countries. Traditionally, as solid waste management practices and collection improve, waste will begin to be placed in open dumps or landfills, which still poses human health/safety threats via disease vectors, water pollution, and explosive conditions. Even though, source reduction or recycling is preferred choice of waste management, over 70% solid waste is open dumped or landfilled globally. Locally and globally, existing solid waste management/mismanagement presents challenges and opportunities.

In developing countries some current waste crises are presented as follows:

1. 1/3 to 2/3 of the solid waste is currently dumped indiscriminately in streets and drains, where it can breed insects and rodents that transmit communicable diseases such as dysentery, typhoid fever, cholera, yellow fever, and plague (Zhu et al. 2007).
2. Waste is traditionally burned in the streets and fields in and around city centers, producing dioxin emissions and damaging the air quality through soot emissions and the climate through carbon dioxide emissions. Poorly managed waste has an enormous impact on health, the local and global environment, and the economy, and improperly managed waste usually results in down-stream costs that are higher than the cost of managing the waste properly in the first place.
3. In developing countries, the rate of waste collection is between 20% and 60%. Uncollected waste dumped in open places, on roads and streets, in water bodies, and in most public areas is getting into city's drainage system. Presence of highly nondegradable plastic bottles and plastic bags are clogging the city's drainage system and causing flash flooding.
4. Inappropriate operational practices are causing serious health hazards for waste pickers at working face of a dumpsite. In some cases, failure of an open dumpsite is costing hundreds of people's lives living next to an open dumpsite (as in Koshe Dumpsite in Ethiopia).
5. Recent China Ban on importing recycled products from global market has caused serious effect on recyclables plastics and other waste components. Many cities are discarding their recycling programs and sending them to landfill as they did not have a local market for reusing the recyclables. Years of hard work to build recycling system and market needs revival with incentives from city officials or regulators. The problems created by China Ban can be a great opportunity for local young entrepreneurs to create new products and market using recyclables.

Regions of Africa, Latin America, South Asia, East Asia, the Pacific Islands, and the Caribbean are urgently in need of help in mitigating problems associated with increasing population growth, urban consumption, and waste production. If safe waste management practices are not incorporated into their development plans, the proliferation of poor health and sanitation conditions will persist. The real challenges of successful solid waste management are essentially those listed below.

• Lack of public awareness of waste management and its impact on health and well-being, the environment, and the local and global economies.
• Insufficient collection and management systems in developing countries that cause major health, sanitation, and environmental issues.
• Improperly managed open dumpsites and their serious consequence of environment and public health.
• Lack of space for new landfills every 20/25 years as urbanization and migration of population to urban areas causes serious strain on urban waste management system.
• Inadequate sustainable waste management technology and implementation of the technology in developing countries.
• Lack of training on waste management technology and lack of management assistance for local authorities and waste management personnel in developing countries.
• The marginal or nonexistent guidelines or ROADMAP for developing waste management protocols or regulatory frameworks at both the local and national levels in many of the poorest countries in the world.

In Developed Countries: (i) Landfills typically occupy an area from several to hundreds of acres, and the current lack of available space for new landfills is a real problem for future waste management. Due to rapid growth and urbanization of cities beyond their current limits, many previously closed landfills which were outside the city limit during their closure, are now within the city limits. Opening a new landfill within the city limits often causes violent protests similar to those which occurred when demonstrations and protests against the opening of a new dump (landfill) on the slopes of Mount Vesuvius in October 2010 led to a riot and violent clash between the local residents and police. (ii) Waste minimization and the reuse of existing landfills is key for sustainable urban development, but even the most preferred choices of waste management, recycling, and reuse have inherent problems. For instance, Sweden is a recycling-happy land. The incineration of solid waste provides power to 250?000 of their homes and heats 810?000 homes. Recycling is so effective in Sweden that only four percent of all waste generated in the country is landfilled. However, the Swedes ran out of garbage needed for the incinerators and have had to import it from Norway (Hickman 2018).

In the last 40-50 years, developed countries have moved from open dumps to sanitary or engineered landfills, while the developing world is still practicing open dump methods. Very recently, the developing countries in South Asia, Latin America, Africa, and Eastern Europe have begun transitioning from open dumps to sanitary landfilling systems. However, based on the increasing rate of urbanization and the rate of increase in waste generation, the current ways of managing waste through landfilling or sanitary landfill systems may not be sustainable. Because of urbanization, it is almost impossible to find land on which to build new sanitary landfills every 20-25 years, so that is not a sustainable solution. The problems associated with the waste generation and management by current systems are summarized below.

• Populations in urban mega cities are increasing at an alarming rate, and the amount of waste that is being generated is also increasing.
• The available land for building residential houses to accommodate the influx of people from rural areas to urban areas is shrinking every day. Consequently, the cost of land for building a landfill within the city or in nearby cities is extremely high.
• The level of resistance to building new waste management facilities (landfills) within communities is very high, which causes major distress within the cities' political system. Therefore, the policy makers or city officials are reluctant to approve the construction of new landfills within the city limits.
• Waste-to-energy (WTE) or incineration can provide a lucrative solution to waste management as WTE plants can address the issue of land/space in both developed and developing countries. It is an appropriate technology for waste management in developed countries such as Europe, the USA, Japan, and South Korea, where the waste is relatively dry and the substantial presence of plastics, paper, and wood make it a good source of combustible materials. The waste in developing countries has a higher percent of food waste (more than 70%) and high moisture content than that of the waste in European countries. Therefore, generating power through WTE or incineration, using this low calorific (organic waste) and highly wet waste may not be applicable or cost-effective for developing countries, if without detailed studies and analysis.

The hierarchy of waste management may not be the same for all countries or all kinds of solid waste generated. In other words, ONE SOLUTION DOES NOT FIT ALL. The handling of solid waste requires solutions that are flexible, but robust enough for urban sustainability.

A clear understanding of waste generation, collection, and management practices, as well as a roadmap for sustainable waste management in developing countries is vital for environmental sustainability, good health, the safety of waste pickers and people living in communities near dumpsites, and above all, for creating healthy urban cities...