The aim of a sustainable city is to produce the lowest quantity of pollution possible, to use land efficiently, compost used materials, recycle it or convert waste-to-energy and reduce the city’s overall contribution to reducing its carbon footprint. Alistair Coulstock, ESD Associate, Aurecon believes a systems thinking approach will maximise untapped resources and turn waste streams into energy outputs for communities.
The current way we live in terms of resource use has not changed since the industrial revolution. We take resources from non-rejuvenating sources or renewable sources at a faster rate than they can replenish. These raw materials are processed into the goods and services that we use and consume that often cannot be reused or broken down at the end of its life.
During consumption, the services either produce waste products – such as grid electricity producing CO2 or thrown into landfill.
A systems thinking approach
A systems thinking approach starts to utilise resources that are previously left unconsidered within existing cities. It maximises resources and turns waste streams into inputs for other processes.
There are many brown field sites within existing cities that can be utilised for the new processes required in the systems model. Every city has a significant number of housing suburbs with single residence households with garden plots. The number of people within cities who would like to grow plants is significant, but many don’t. The reasons preventing people from growing fruit and vegetables within their gardens is varied but for many there is a distinct lack of time to either set up a garden in the first place or learn the skills to do so.
A professional gardener is hired to promote and assist local residents to modify a section of garden to agricultural use. This area does not need to be huge, 10-20 m2 could be sufficient. If enough residents are interested in the scheme then a significant amount of land can be found to provide for inner city food production.
The professional gardener can teach residents the skills to grow produce on the land in sustainable ways and provide education to the younger generations in terms of food production and healthy choices. The residents can take some of their produce for themselves and the surplus goes to the local markets for sale. Proceeds from the produce are then passed on to the market seller to pay for their wages and the professional gardener.
In addition to this local scheme, a new waste stream service is set up in addition to the paper tins and plastics service already in place in most city areas. An organic bin collection system is provided that allows people to sort their food scraps from their general refuse. All this waste goes to the local bio digester located in close proximity to the trigeneration plant that provides power, hot and cold water to the local shopping centre.
The bio digester produces methane and fertiliser as products of the digestion process. A clear example of this technology within city boundaries is Earth Power in inner western Sydney.
The methane is utilised in the running of the cogeneration plant, which in turn produces electricity and hot water. The hot water can be used for domestic water uses, heating and also as an input into an absorption chiller. The absorption chiller produces chilled water for cooling processes. As a bi-product of the absorption process low grade heat is produced. This normally cannot be used anywhere and generally uses more energy via rejection through cooling towers. As the trigeneration plant is located in close proximity to the bio digester it can be used to keep the bio digester at a constant temperature of approximately 38°C as required, thus further increasing efficiency of the systems.
The products of the trigeneration systems are utilised locally as electricity is provided to the grid and the heating and cooling is used for local uses within the precincts as required. The other bi product of the bio digester, the fertiliser can be reused on the gardens in the surrounding area and the process continues.
In addition to the organic waste that is now utilised, the sewerage from households can also be used to produce methane and fertiliser.
This addresses one of the major issues with the sanitary system provided in western civilisations. The invention of the sewer was a revolutionary idea in the 1800s and wiped out the fatal disease that went by the name miasma, today known as cholera. However the major down side to this invention is that it has now broken the nutrient cycle. The current estimate is that phosphorus deposits are sufficient for between 50 and 100 years of food production - and given that a significant amount of phosphorus is flushed down the toilet and enters our waterways – it would seem prudent to capture this valuable source of fertiliser and reuse it for food production.
All of these ideas individually are not new, however what is not being carried out to my knowledge is an integrated approach to this valuable resource management that can significantly reduce our impact on the environment.
Aurecon has the skill sets within its offices to deliver such integrated models. Further advanced solutions can be reached via additional inputs such as solar thermal injecting more heat into the absorption chiller process ensuring sufficient energy on hot days to assist the cooling demand in inner city areas.
Such integrated approach reduces our dependence on transporting goods long distances. It reduces our consumption of non-renewable sources such as electricity produced from coal. It also creates an enhanced social structure around the local market experience and promotion of healthy living.