Columbia subject headings:
Harvard subject headings:
Sewage disposal--Germany--Ulm--History--20th century.
Sewage disposal--Germany--Ulm--History--21st century.
Sewage--Purification--Germany--Ulm--History--20th century.
Sewage--Purification--Germany--Ulm--History--21st century.
Princeton subject headings:
Sewage disposal--Germany--Ulm--History.