446 Organic Waste Recycling: Technology and Management
large wastewater treatment plants. The total production of sewage sludge per
year in the 15 original European Union countries was estimated to be 10.7
million tons of dry matter in 2005 (www.mapa.es/app); this sludge is disposed
of as follows (Kofoed 1984):
- 29 % is used in agriculture
- 45 % is disposed of on controlled refuse dump
- 7 % is disposed of by incineration
- 19 % is discharged in the sea
Data on sludge production in developing countries are not readily available
because most cities do not have adequate sewerage systems for wastewater
transportation to central treatment plants. However, it can be estimated that each
person generates 25-40 kg dry matter of sludge per year or about 800 kg wet
sludge (95% water content) per year.
Table 9.1 Estimated distribution of municipal sludge in 1980 (U.S. EPA 1983)
Percent of total sludge
Disposal Practice U.S.A. European Community
Beneficial land application 36 32
Landfills 38 48
Incineration 16 13
Surface disposal 10 2
Sea disposal - 5
9.1 OBJECTIVES, BENEFITS AND LIMITATIONS
There are four major categories of sludge land application systems:
- Agricultural utilization: Sludge is used as a source of fertilizer
nutrients and/or as a soil amendment. - Forest utilization: Sludge is used to enhance forest productivity.
- Land reclamation: Sludge is used to reclaim disturbed land, such as
strip mined area for the purpose of re-vegetation, or to reclaim
seashore land. - Land disposal: Sludge is applied to soils, with or without vegetation,
for the primary purpose of sludge disposal. Crop production or
improvement of soil characteristics is of secondary importance.