Recycling Technologies and Engineering Challenges

  • Donald V. Roberts


For an engineer, a sustainable system is one that is either in equilibrium, operating at a steady state, or one that changes slowly at a rate considered to be acceptable. This concept of sustainability is best illustrated by natural ecosystems. They function as semi-closed ‘loops’ that change slowly. For example, the hydrological cycle involves continuous evaporation from the oceans and other surface bodies of water up into the atmosphere. The vapour then moves over land where precipitation occurs as rain or snow. The water then returns back to the ocean through surface streams or groundwater, and the process is repeated over and over. The food cycle involving plants and animals represents another illustration. Plants grow and thrive in the presence of sunlight, moisture and nutrients. They are then consumed by herbivores and insects, which in turn are eaten by various classes of carnivores. The resulting waste products replenish the nutrients, which allows the process to be repeated again and again.


Drip Irrigation System Sustainable System Environmental Restoration Recycle Technology Continuous Evaporation 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Swedish International Development Cooperation Agency, Sida 1997

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  • Donald V. Roberts

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