TABLE 1.

Water quality measurements for influent tap water and BARs^a

Water quality parameter	Measurements (mean [SD]) for:
	Influent tap	BAR1	BAR2	BAR3
HPC (log10 CFU ml−1)	2.45 (0.25)	3.58 (0.70)	3.71 (0.73)	3.65 (0.79)
pH	8.35 (0.18)	ND	ND	ND
Temp (°C)	19 (3.5)	20.8 (2.3)b
Total alkalinity (mg liter−1)	70 (22)	ND	ND	ND
Hardness (mg liter−1)	154 (17)	ND	ND	ND
Turbidity (NTU)	0.35 (0.95)	ND	ND	ND
Free Cl2 (mg liter−1)	0.96 (0.18)	0.61 (0.24)	0.62 (0.21)	0.54 (0.23)
Total Cl2 (mg liter−1)	1.07 (0.18)	0.71 (0.24)	0.72 (0.22)	0.64 (0.24)
NO3 (mg liter−1)	0.86 (0.23)	ND	ND	ND
PO4 (mg liter−1)	0.15 (0.07)	ND	ND	ND
TOC (mg liter−1)	0.99 (0.77)	1.11 (1.01)	1.02 (0.81)	1.00 (0.62)
Essential elementsc
Ca	30.60 (4.80)
Cu	0.01 (0.01)	ND	ND	ND
Fe	0.02 (0.04)	ND	ND	ND
K	2.40 (0.71)	ND	ND	ND
Mg	9.08 (1.96)	ND	ND	ND
Total N	0.83 (0.13)
Na	26.00 (8.69)	ND	ND	ND
Total P	0.19 (0.08)	ND	ND	ND
Zn	0.02 (0.01)	ND	ND	ND
Beneficial elementsd
Si	2.28 (0.69)	ND	ND	ND
Toxic elementse
Al	0.05 (0.04)	ND	ND	ND

^aAbbreviations: BAR, biofilm annular reactor (three operated in parallel for biofilm development; see Materials and Methods); Cl₂, chlorine; HPC, heterotrophic plate count; ND, not detected; NO₃, nitrate; NTU, nephelometric turbidity units; PO₄, phosphate; SD, standard deviation; TOC, total organic carbon. Other parameters detected, mean mg liter⁻¹ (SD): Ba, 0.04 (0.01); S, 21.18 (4.82); Sr, 0.22 (0.05). Other parameters not detected: Be; NH₃, ammonia as N; Sb; and V.

^bTemperature was measured in BAR3.

^cClassifications are based on the World Health Organization criteria (65).

^dClassifications are based on the World Health Organization criteria (65). Mn and Ni were not detected.

^eClassifications are based on the World Health Organization criteria (65). As, Cd, Li, Pb, and Sn were not detected.