Data from 20 cities around the world, collected for the UN-Habitat report Solid Waste Management in the World’s Cities, reveals how the organic fraction of municipal solid waste is managed across a variety of countries. Although it’s not highly documented, organic waste recovery is still practised in low and middle-income cities, explains David Wilson, Anne Scheinberg and Ljiljana Rodic.
Waste and organics generation rates
Data from reference cities shows that although there is wide variation, generally as a nation’s wealth increases, so does its per capita production of waste. Average figures are 225kg per capita per year in low-income, 330kg in middle-income, and 550kg in high-income countries.
This reflects the higher prevalence of packaging and other consumer products that end up in the waste stream as incomes increase.
Interestingly, the per-capita generation of organic waste in kg per year appears to be relatively constant, irrespective of income level. But there is some evidence that the nature of the organic fraction is different: in low- and middle-income countries it is primarily inedible food waste, such as vegetable trimmings; while in higher-income countries there is more food waste that could have been eaten, as well as more garden or yard waste.
Information from the 20 cities suggests that some degree of organic waste recovery is practised in low and middle-income cities. But because this activity is largely informal and domestic, it is neither ‘seen’ nor documented.
Integrated and sustainable benchmarks
The comparative analysis focused on the three physical elements of an integrated and sustainable waste management (ISWM) system: waste collection, disposal and material recovery, as well as on aspects of good waste governance. Table 1 summarises the key indicators for the three physical elements across 20 cities. Data on the coverage of waste collection and street sweeping in each city – i.e. the percentage of population that has access to waste collection services – is a key indicator of public health. Strong evidence links uncollected household wastes and, in particular, the putrescible organic fraction to higher incidence of diarrhoea and acute respiratory infections in children. In our survey, collection rates are high in most of the middle- and high-income cities, with many low-income cities awaiting progress.
A similar trend is also apparent in environmental control over waste disposal – the indicator shows the percentage of total waste from the waste collection system destined for disposal in a ‘controlled’ facility.
|Separate food waste collection in Tomkins County, New York State, USA|
The comparative data on levels of valorisation – including both materials recycling and organics recycling and recovery in the agricultural supply chain – are interesting, although the averages in Table 1 hide considerable variation between the cities.
The high rates in the high-income countries have been (re)built from relatively low levels over the last 10-30 years. This is as a result of the cities investing heavily in both physical infrastructure and communication strategies to increase public participation in separate collection schemes.
|One size does not fit all: a small composting plant in Canete, Peru. [Credit: Oscar Espinoza, IPES]|
These formal-sector recycling systems, run by or on behalf of the city administration, contrast sharply with the almost entirely informal-sector recycling, repair and reuse systems in low-income countries. Here the sole driver is the market value of the recovered materials, which provides a livelihood for millions of the urban poor. Recent work has shown that the informal recycling sector saves many large cities in low-income countries 20% or more of their waste management budget.
Examination of financial sustainability as part of good waste governance in the reference cities reveals that budget per capita per year figures rise sharply with income levels. This varies from just US$1.5 for the low-income cities, to $10 for lower- and $33 for upper-middle-income cities and $75 for high-income cities. In terms of budget as a percentage of GDP per capita per year, the trend is reversed: the average for the low- and middle-income countries is 0.6%, while that for the high income countries is only 0.2%. Strong evidence links uncollected household wastes and, in particular, the putrescible organic fraction to higher incidence of diarrhoea and acute respiratory infections in children.
High organic content wastes
Municipal solid waste outside of high-income countries has a high organic content, which generally means very dense waste, high moisture content – often increased by a high tropical rainfall – and low heating value. This suggests a need for waste management and valorisation approaches that put organic waste at the centre of the logistics and technology choice.
More generally, if the local waste contains 60% – 80% organic fraction, one could reasonably suggest that biowaste focused options should be seen as the ‘baseline’ technology rather than landfilling. Similarly, waste to energy plants would, at a minimum, need major reconsideration to avoid the need for additional fuel to support combustion of wet, organic waste. These conclusions are further reinforced when one considers financial sustainability. Such high technology solutions are not only inappropriate but unaffordable and unsustainable in most lower-income cities.
What does the data for the 20 cities tell us about the current status of management options for the organic fraction? Eight cities have little or no valorisation of organics; eight cities valorise between 1% and 10% of their waste generated, while the remaining four cities valorise 20% – 31% of their waste generated as organics. Interestingly, these are Adelaide and San Francisco at one end of the modernisation spectrum and Bamako in Mali and Moshi in Tanzania at the other end. These relatively low rates suggest that organic valorisation has not yet received the attention it deserves.
The 3Rs and the organic fraction
Reduction, reuse and recycling - the 3Rs - sit at the top of the waste hierarchy. For organics, reduction has been a major focus in some high income countries recently. Examples of direct reuse from the reference cities are in Belo Horizonte, Brazil and in San Francisco, U.S. Here food which is near its expiry date is donated by supermarkets to NGOs which distribute the still usable food to shelters for homeless people.
Organic learning: educating women in home composting in Siddhipur, Nepal
Whereas many – if not most – countries have an industrial value chain that demands recyclable materials such as metals, paper, glass, plastics and textiles, the agricultural value chain works differently. Organic wastes are putrescible, so use has to be organised quickly and reliably. Also, partly because it decomposes quickly and smells, food waste is seen as ‘dirty’ in different ways to, say, bottles or paper. First of all, informal organic valorisation consists almost entirely of direct use as animal feed. If this is done within the home, it is a form of reduction or reuse. If it is done after collection, it is on a level with other material recycling. In the 20 reference cities, animal feeding is important in the process flow diagrams for, inter alia, Moshi in Tanzania, Sousse in Tunisia, Nairobi in Kenya, and Managua in Nicaragua. Another example is Bamako in Mali, which is typical of west African cities.
It reported that 85% of waste is valorised via the traditional practice of terreautage, whereby unprocessed waste is sold to crop farmers (céréaliculteurs), and waste that has already partially decomposed in the collection sites (fumure) is sold to the maraîchers, the vegetable farmers in the floodplain of the Niger River. A similar system worked well in China up to the 1960s.
In contrast, formal recovery of organic waste is very often financed primarily by the avoided cost of disposal. In high-income countries, with a fully modernised waste management system and a high cost for disposal, ‘composting’ comes into play as a processing technique that creates the saleable commodity, compost.
In the beginning, compost is not (yet) seen as a product: a market generally needs to be developed, by building urban-rural linkages and by educating potential users and buyers of compost about its properties, nutrient value, and substitution value in relation to the fertilisers and mulches, which are better known.
This process takes several years, and compost operations generally only become sustainable when compost itself becomes a commodity with a market price. High-income countries have done much work on product specifications, to give the buyer confidence in the quality of the compost product. Composting can be carried out at various scales. Carried out at the level of individual households, home composting can be viewed as a means of waste reduction.
As an example, the initiative by local professionals in Waste Concern, Dhaka, is worth highlighting as good practice. They have developed a model for community composting on a relatively large scale, working with existing informal sector collectors and recyclers. The project has been deliberately designed to be pro-poor: collection is by tricycle carts; the process is not fully mechanised so that it allows opportunity to employ more people from the informal sector; salaries are comparable with government rates and good working conditions include health insurance, daycare and free meals.
The stories from the 20 reference cities – rich and poor and in all parts of the world – show that it is possible to make progress in tackling organic waste management under all kinds of circumstances. There is no ‘one size fits all’. Taking local needs and priorities into account and building on the existing local good practice is more effective than pursuing some global ideal.
The high organic content of municipal solid waste in most of the world (except the high-income countries) points to the potential for biowaste focused management options, such as animal feeding or preparation of compost. Information from the 20 cities suggests that some degree of organic waste recovery is practised in low and middle-income cities. But because this activity is largely informal and domestic, it is neither ‘seen’ nor documented. Planners are thus well advised to investigate how the existing agricultural value chain works before developing a strategy for valorisation of organic waste materials in their city.
Developing and having a good market is key to valorising organic wastes to agriculture. As long as they are familiar with it, farmers are generally willing to pay for good quality animal feedstock or soil conditioner/fertiliser. Collecting source-separated food waste from households, restaurants, markets and shops is the key to a good product.
Prof. David C Wilson is an independent waste and resource management consultant and a Visiting Professor at Imperial College, London.
Anne Scheinberg is at WASTE, Gouda; and Wageningen University and Research Centre; Netherlands
Dr. Ljiljana Rodic is a senior lecturer in Urban Environmental Management at Wageningen University, the Netherlands.
The authors are grateful to UN-Habitat and in particular to Graham Alabaster who conceived and arranged financing for the book on which this article is based. We also acknowledge the contribution of some 35 collaborators, largely drawn from the Collaborative Working Group on Solid Waste Management in Low- and Middle Income Countries - www.cwgnet.net.
Solid waste management in the world’s cities is published by Earthscan, London - ISBN 978-1-84971-170-8. Earthscan is offering a 20% discount to readers who order direct from www.earthscan.com, quoting promotional code ISWA.More Waste Management World Articles
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