Columbia subject headings:
Recycling (Waste, etc.)--Congresses.
Refuse and refuse disposal--Congresses.
Refuse disposal industry--Congresses.
Urban ecology (Sociology)--Congresses.
Harvard subject headings:
Recycling (Waste, etc.)--Congresses.
Refuse and refuse disposal--Congresses
Refuse disposal industry--Congresses.
Urban ecology (Sociology)--Congresses
Princeton subject headings: