Runoff water from small treatment plants

In Europe, the quality of water discharged from small treatment plants is governed in 91/271/EEC directive.

Class	CSB mg/l	BSB5 mg/l	NH4-N mg/l	Nanorg. mg/l	P mg/l	Faecal coliforme Keime je 1000 ml	AFS mg/l
C	150*/100***	40*/25**	-	-	-	-	75*
N	90*/75***	20*/15**	10**	-	-	-	50*
D	90*/75***	20*/15**	10**	25**	-	-	50*

^* obtained from certified sample, ordinary sample of faecal coliform bacteria

^** ** determined from 24 h mixed sample; NH₄-N and N_anorg.. with temperature of discharged water T ≥ 12°C

Most modern water treatment plants have improved over BOD₅ discharge values of < 25 mg/l.