Urban mining aims to redefine waste as an asset
We need to recognise urban wastes as assets and resources to be reused, recycled and recovered - and this requires some mental digging, argues Chris Coggins
At last the debate is moving forward about recognising and referring to wastes as resources, with much discussion about the circular economy. With over half of the world's population living in urban areas it is becoming important to see these areas as alternative sources of natural resources, and to recognise the importance of urban mining.
Attention in urban mining has increased of late with opportunities offered through declining quality of primary ores, energy-intensive mining and processing methods, transport costs and greater demand through manufacturing, consumption and increased quantities of waste. Since 1967 in the UK, the advent of civic amenity sites - now known as household waste recycling centres - are now well established as urban mines for a range of post-consumer wastes.
With significant quantities of food waste being thrown away by households, and also the commercial and catering sectors, urban biomass has become a more recent resource. Historically food waste might have been home composted or fed to pigs, but it is now collected kerbside by many local authorities and either composted or used as feedstock for anaerobic digestion.
In both cases the organic output may be considered a product and used instead of fertilisers, subject to quality control, and with anaerobic digestion the carbon is converted to methane and available as an energy resource. As such, urban carbon has become increasingly important since the late 1990s, either through source-segregated materials to generate methane through anaerobic digestion or residual wastes combusted in incinerators or used in a variety of advanced thermal treatment technologies such as gasification.
These technologies for residual wastes now have to meet high efficiency requirements and commonly generate electricity plus heating and some also generate cooling - a concept referred to as 'tri-generation'. The future might see further technologies involving bio-refineries and the development of hydrogen fuel cells based on urban carbon wastes.
In terms of carbon, the use of recyclates saves on primary energy, ranging from 95% with aluminium to 24% with cardboard and 5-30% for glass. For all of these urban resources, the principles of extraction from the natural environment are replicated in terms of availability (range of materials targeted for recycling/composting/energy recovery), quality (influenced by source-segregation and MRF technologies) and accessibility (costs of collection and processing versus prices of primary raw materials).
Combinations of these various aspects of urban mining and industrial-scale activities are now found in resource recovery parks, ecoparks, or sustainable growth parks, where different wastes are received and prepared for reuse through re-manufacturing, wastes are recycled into a range of new products and activities are self-contained in terms of on-site energy from waste generation.
We need to recognise urban wastes as assets and resources to be reused, recycled and recovered and not as unloved things to be discarded, thrown away and considered the detritus of urban life; especially if we are to consider sustainability and the future wellbeing of humankind.
Chris Coggins is a resources and wastes management consultant