Wastewater treatment

Everyone knows die Fracht from the docks and the airport: it is cargo, and der Frachter is the ship that carries it. In a treatment works the same word does quite different work. Die Fracht is the load, the mass of a substance that arrives in a given time, usually counted in kilograms a day, and it is set against die Konzentration, which only says how much is in each litre. The distinction is the whole point. After heavy rain the concentration of nitrogen falls because the sewage is diluted, while die Stickstofffracht barely changes: the town has not eaten less. A plant is designed for its loads, and so the phrase die Fracht hat sich verdoppelt in an operating report is a warning about the biology, not news about deliveries. The plural is die Frachten in both senses.