The term ‘waste’ refers to solid or liquid matter which has no longer any economic value. With industrialization and urbanization, ensuing growth in urban solid and liquid wastes is a relatively recent development in India. During mid-seventies, urban per capita solid waste generation was 250–350 gm/day1, whereas it has increased to 320–530 gm/day in late eighties; total sewage generated in India was about 30 billion liters/day in 1997 and recent figures indicated additional 50-70 % increase2. The quantity of waste generated per capita is estimated to increase at a rate of 1-1.5% annually in India3,4. Such enormous increase in waste (solid) should impose the cumulative requirement of land to around 1400 km2 by 2047 in India5. Large quantity of waste in solid and liquid form is generated by food processing industries, agro-based industries, sugar mills, breweries, distilleries, tanneries4 and pulp/paper6 industry as summarized in table-1. Organic fraction of such solid waste has a large energy potential (20-25 MJ/m3)7.  It is estimated that i. the industrial waste generated coming from agro-waste, food processing industries, dairies, distilleries, pressmud, tanneries, pulp/paper etc., provides scope to set up 12 million plants for generating 17,000 MW bioenergy and ii. under the Ganga Action Plan, 46,000 m3 biogas can be produced daily from the sewage treatment plants in 21 Indian mega-cities by treating about 339 million liters/day municipal wastewater, equivalent to 99,450 kWh/day electrical energy4. From these estimates, it appears well settled that waste management challenges can only be met through marshalling the talents of competent environmental engineers and biological scientists through the design and application of cost-effective solutions3. The word ‘waste’ and the act of ‘wasting’ are human inventions for short-term convenience. Otherwise, waste doesn’t exist in nature. In terms of collection and disposal, they are liquid and solid wastes. While waste is classified differently in different contexts3,7, in the context of theme of this review, the following classification appears appropriate.