Australia – sensible examples of resource recovery

Thanks to WMAA who draw attention to the Sydney Environmental & Soil Laboratory which reports that it is possible-and even desirable-to make money out of other people‘‘s waste. For purely economic reasons, it‘‘s often cheaper to reuse waste than to buy new materials.



When Sydney Airport‘‘s Third Runway was built, it was landscaped with soil made from sand dredged from Botany Bay and 55 000 tonnes of composted biosolids, equivalent to about 30% of the sewage sludge produced in a year in Sydney. Biosolids are valued for their high organic matter content, which retains soil moisture, and high nutrient content. In fact, demand outstrips supply. Not bad for a waste product that was once flushed out to sea.



In NSW, more than 1.3 million tonnes of organic materials is recycled each year by licensed composting facilities. Over 80% of councils in the Greater Metropolitan Region of Sydney, the Illawarra, the Blue Mountains and the Hunter collect organic wastes-predominantly green waste-and turn it into compost for landscaping projects and even for sale back to the people who threw it away in the first place!



Recycled organic waste has a multitude of beneficial uses:



§ reducing the need for irrigation by retaining moisture and reducing evaporation



§ reducing soil erosion by binding soil aggregates together



§ landscaping



§ returning nutrients removed in crops, thus saving on fertiliser



§ suppressing weeds when it is applied as mulch



§ reducing runoff and thus increasing water infiltration.





The more organic waste that can be kept out of landfill, the less methane will be generated. Methane is produced by the anaerobic decomposition of organic material, such as deep within landfills. It is a potent greenhouse gas, 23 times as powerful as CO2 in trapping heat in the atmosphere. So keeping organic waste out of the ground is critical. But what can we do about the stuff that‘‘s already there, generating methane all the time? In fact, in many places the methane is being tapped and put to good use. For example, methane from landfill at Lucas Heights is used to generate 13 MW of electricity. And because the methane is turned to CO2, the result is 1/23 of the greenhouse effect that the methane would have had.



Inorganic wastes are also potentially useful. For example, excavated soil and rock and demolition rubble can be reused as clean fill or to create artificial soil. Red mud from bauxite processing and the sludge settled out of drinking water by treatment with alum can also be used to create artificial soil.



During the construction of the Olympic site at Homebush Bay, the site was levelled and landscaped with soil created from crushed sandstone, most of which came from excavation for the Eastern Distributor and the Airport railway tunnel: 5500 truckloads of it, all crushed to the desired particle size, was incorporated.



One especially useful inorganic waste is fly ash. This is the mineral residue left over from the combustion of coal in power stations. It consists mainly of silicon dioxide, aluminium oxide and iron oxide, which can be reacted with calcium hydroxide and other alkalis to form calcium silicate hydrates, or cement compounds. Worldwide, more than 65% of fly ash is buried in landfill. And yet it has many uses, including in cement manufacture, as self-levelling fill, for soil stabilisation and for the manufacture of light-weight concrete building blocks.



Many waste products of industry and agriculture can be and should be recycled. Potential areas of growth in waste product reuse include:



§ development of composts from green, food and wood wastes



§ development of soil conditioners and mulches from organic wastes



§ use of industrial waste for soil improvement



§ use of biomass as green fuel for electricity generation<