Anaerobic Digestion, Waste-to-Energy and the Hierarchy of Sustainable Waste Management

Contents:

1. The Hierarchy: Follow this link

2. Energy Recovery

2.1 Anaerobic Digestion

2.2 Refuse Derived Fuel (RDF)

2.3 Waste-to-Energy (WTE)

Spittelau Waste-to-Energy Plant, Source: josylein

1. Hierarchy of Sustainable Waste Management, Please follow this link

2. Energy Recovery

Energy requirements of a community can be satiated to some extent by energy recovery from wastes as a better alternative to landfilling. Energy recovery is a method of recovering the chemical energy in MSW. Chemical energy stored in wastes is a fraction of input energy expended in making those materials. Due to the difference in resources (materials/energy) that can be recovered, energy recovery falls below material recovery on the hierarchy of waste management.

2.1 Energy and Material Recovery: Anaerobic Digestion (AD)

Other names: Anaerobic Composting, Biogas, Biomethanation

The USEPA defines Anaerobic Digestion (AD) as a process where microorganisms break down organic materials, such as food scraps, manure and sewage sludge, in the absence of oxygen.  In the context of SWM, anaerobic digestion (also called Anaerobic Composting or Biomethanation) is a method to treat source separated organic waste to recover energy in the form of biogas, and compost in the form of a liquid residual. Biogas consists of methane and carbon dioxide and can be used as fuel or, by using a generator it can be converted to electricity on-site. The liquid slurry can be used as organic fertilizer. The ability to recover energy and compost from organics puts AD above aerobic composting on the hierarchy of waste management.

Recycling, Composting, and the Hierarchy of Sustainable Waste Management

Contents
1 The Hierarchy
2. Material Recovery: Recycling
3. Material Recovery: Aerobic Composting


1. The Hierarchy
The Hierarchy of Sustainable Waste Management (Figure 10) developed by the Earth Engineering Center at Columbia University is widely used as a reference to sustainable solid waste management and disposal. This report is presented in reference to this hierarchy. For the specific purpose of this study, “Unsanitary Landfilling and Open Burning” has been added to the original hierarchy of waste management which ends with sanitary landfills (SLFs). Unsanitary landfilling and open burning will represent the indiscriminate dumping and burning of MSW and represents the general situation of SWM in India and other developing countries.

Figure 10, The Hierarchy of Sustainable Waste Management for India and Other Developing Nations

The hierarchy of waste management recognizes that reducing the use of materials and reusing them to be the most environmental friendly. Source reduction begins with reducing the amount of waste generated and reusing materials to prevent them from entering the waste stream (15). Thus, waste is not generated until the end of “reuse” phase.

Recognition and Integration of the Informal Sector in India

Contents
1. Organizing the Informal Sector
2. Public Policy
3. Integrating the Informal Sector into Formal SWM Systems

4. Change in Perception

1. Organizing the Informal Sector

The informal recycling sector in India is in fact well-structured and has a huge presence, especially in mega cities. This sector is responsible for the recycling of around 70% of plastic waste (37) and up to 56% of all recyclable waste generated in India. On the basis of all information collected during this visit, the author estimates that the informal sector recycles about 10 million tons of recyclable waste per year.

A women waste-picker employed at a composting facility to separate recyclables from the MSW

The high percentage of recycling the informal sector is able to achieve is the cumulative effort of large numbers of WPs on the streets, at the bins and dumpsites. For example, the informal sector in Delhi employs about 150,000 people who are 0.9 % of the population of Delhi (16.75 million) (3) (33) (39).