Techniques and timelines

A city or town can be envisioned as a thermodynamic system with a continuous input of materials and energy, generating work and wastes as output. Most material chains in today's globalized cities are open loops, starting as raw materials and ending up as wastes in landfills. They are not sustainable as the materials move in a single direction resulting in significant depletion of natural resources and causing environmental degradation over time. The creation of natural resources involves energy inputs which are embodied in the wastes that are generated at the end of material loops. Thus, closed material cycles where materials and energy are recycled or recovered hold a key to sustainable world.

Composting

Sustainable waste handling practices should give priority to material recovery over energy recovery. Composting thus precedes waste to energy methods on the waste management hierarchy (Fig. 1).

Figure 1: Solid Waste Management Hierarchy

Composting is a comparatively old technique practiced in a decentralized fashion in individual households with backyards and farms. However, rapid urbanization squeezed houses, as a result pushing wastes onto the streets. Thus, the responsibility of waste management was transferred to public representatives, requiring the system to be centralized. Centralized waste handling requires dedicated infrastructure, which developing nations lacked and composting as a waste management practice declined altogether. Despite this, urban compost has been a steady nutrient supplement to surrounding farms all over India, but it took place in a very small scale with no imperative for waste management <1>.