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Subject
- Sewage disposal1,718
- Refuse and refuse disposal241
- Pollution214
- Water205
- Hazardous wastes204
- Sewage200
- Sewerage189
- Purification155
- Sewage disposal plants108
- Finance106
- Law and legislation106
- Water quality management103
- Water-supply95
- Sewage sludge79
- Environmental aspects76
- Environmental sciences74
- Costs57
- Factory and trade waste48
- Environmental management46
- Sanitation41