Abstract:For farmers, composting of all and any organic scraps has been a fact of life through the ages. The organic scraps end up on the compost heap whereby they become compost manure, and are hence returned to the earth for the nourishment of crops. Here, the cycle of biogenous waste is closed. In conurbations one get a very different picture – organic kitchen waste has always been, and is even today destined either for the municipal dump, or for the incinerator.
How can this be changed?
During the period between 1952 and 1988, Swiss cities attempted to close the organic waste circle by the introduction of large scale waste composting. Eighteen waste composting sites were operational, mainly in tandem with waste incineration sites. In the year 1974, by way of illustration, twelve of these sites produced 80'000 tons of waste compost.
The reasons for the subsequently diminishing success of the sites are:
– The low quality of the compost meant that it could only be used on a few, less vulnerable sites, such as vineyards. Foreign substances, such as glass and plastics present in the compost, were detrimental to intensive agriculture
– Consumers were not made sufficiently compost aware
– The levels of certain hazardous substances in the compost, especially of heavy metals, were above the permitted thresholds laid down by Swiss regulations
In contrast to this decline in waste composting, the quantity of compost from goods collected separately is on the increase (garden clippings, kitchen scraps, waste from public parks and gardens). Some of the former waste compost sites have been remodelled to process green waste (for instance the plants at Beringen close to Schaffhausen, Bollingen and Küssnacht). Today the composting of organic residential waste is regulated by the Technical Waste Order and the Harmful Materials Order, which define the following quality standards (which also apply to sewage sludge – see chapter 12):
There are three options for composting:
– Composting in private gardens: Many communities and councils offer composting tips via the phone. They also operate a mobile equipment service in autumn and spring to help private composters shred tree and bush clippings
– Residential neighbourhood composting: A city like Zurich has only a small number of private gardens. There have been initiatives to operate compost heaps in designated areas shared by the inhabitants of a district – however, this requires a person or group to take responsibility for maintenance of the heap
– Communal or regional composting: Numerous simple sites, with permanent locations and mobile crushing and conversion apparatuses have been created since 1984. The following quantities of green waste (in metric tons) were centrally composted in Switzerland:
1985: 200'000 1990: 280'000 1995: 400'000
2000: 641'000 2001: 650'000 2003: 740'000 2004: 770'000 2005: 770'000
Of the 650'000 metric tons of “green goods” processed in 2001, 86 mass% – or 550'000 tons – were treated at 107 plants with a yearly capacity of over 1'000 tons. Almost two thirds of the composted biogenic wastes were deposited in open heap composting sites (see section 10.4.1), where only 12 mass% was fermented. 200 smaller plants were essentially rural composting sites (see section 10.4.1), of which approximately 10 mass% of the green goods were processed.
Document Type: Research Article
Publication date: January 1, 2008