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space INSIGHT, Spring '96 Edition

A New Method for Processing Street Sweepings
Disposal Costs Can Be Lowered to below Current Landfilling Costs

Urban street sweepings are made up chiefly of reusable materials, including sand and gravel (60%). Depending upon the season, sweepings also contain up to 20% green matter. In contrast, the content of undesirable materials, such as beverage cans and cigarette butts, comprises about 5% of total weight/volume collected in most cities.

Until recently, because of the pollutants (see also accompanying figure) and the lack of suitable treatment facilities, street sweepings were generally discarded. Due to the growing scarcity of landfill capacity and skyrocketing disposal fees, there is, however, increasing interest in the need and efficiency for treatment and utilization of street sweepings. In a city as Osaka in Japan, for example, roadways and pedestrian overpass comprising a total length of 672 km are cleaned by road sweepers, so that street sweepings amount to 7,000 tons per year.

Levels of Pollutants in Street Sweepings

Parameter Unit Mean Value
hydrocarbons mg/kg of dry substances 544.00
cadmium mg/kg of dry substances 0.41
copper mg/kg of dry substances 82.00
chromium mg/kg of dry substances 25.00
lead mg/kg of dry substances 73.00
(source: Brochier Umwelttechnik)

German Brochier Umwelttechnik GmbH has recently released a treatment technology capable of utilizing about 80% of street sweepings. The process consists of a combination of dry- mechanical grading and pneumatic sorting. The process steps - drying, grading, sorting, and off-gas purification - can be arranged in different combinations, thus permitting the process to be flexibly adapted to the shifting composition of input materials.

In the basic format, materials are first screened and the fraction of non-usable residues is separated out. Following this, the remaining fractions are dried. At the same time, dust particles that contain most of the pollutants and adhere to such recyclable materials as sand, gravel, and green matter are removed. The drying process releases no detrimental emissions in the plant's vicinity; this is because it can be optimally regulated using a process-controlled hot-air blower. Following the drying process, the materials are graded and coarser contaminants are removed. The sweepings are separated into recyclable fractions by means of pneumatic sorting. The sorting unit functions in such a way as to separate also the dust particles loosened during the drying process and to carry them away in the current of off-gas. The off-gas resulting from the sorting process is suctioned off and sent to an off-gas purification plant equipped with fabric filters. Depending upon capacity, the plant can be designed to be semi-mobile.

This treatment technique permits various homogeneous fractions to be recovered, including mineral components, organic components, filter dust, and residues. Over the course of a year, up to 65% of the mineral components can be reclaimed and reused, e.g., in street/path construction. On average, twenty percent of the output is compostable green matter; and about 10% is filter dust, the latter of which contains most of the pollutants. The cost of treatment and utilization/disposal is significantly below the current cost of landfilling.

Schematic Diagramme

For those readers interested in learning more about this technology, INSIGHT suggests contacting EBB Information Service, Philosophenweg 2, D-72076 Tübingen, Germany, tel: +(49-7071) 67001, fax: +(49-7071) 68086.




          		
          
          
	        
    
              
	 

	
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