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Table 2

Wastewater quality of freefall UVD unit effluent and correlation with log-fecal coliform (FC) (n = 22)

Mean ± SDa (min–max)Spearman's rho correlation with log-FCp-value
Fecal coliform (CFU/100 mL)b 18.1 ± 3.6 (<10–690) – – 
Temperature [°C] 21.1 ± 2.5 (16.7–25.6) 0.11 0.639 
pH 6.7 ± 0.8 (4.8–8.3) −0.08 0.715 
Dissolved oxygen [mg/L] 6.8 ± 2.0 (5.4–8.3) −0.01 0.964 
Conductivity [μS/cm2612 ± 302 (227–1,308) 0.67 <0.001 
Turbidity [NTU]c 20.4 ± 19.6 (0–60.6) 0.49 0.032 
UV transmittance [%] 44.5 ± 17.7 (13.3–74.0) −0.40 0.063 
Flowrate [mL/s] 10.2 ± 9.7 (0.5–37.5) 0.41 0.063 
Residence time in UVD unit [min]d 18 ± 30 (1.3–116)   
OSS age [years] 11.6 ± 5.5 (1–22)   
Months since last inspection 4.1 ± 4.3 (0.5–19)   
Months since last bulb replacement 27.8 ± 17.0 (2.0–67.6)   
Months since last cleaning 4.8 ± 5.6 (0.5–20.8)   
UVD unit makee 
 Salcor 3G 27%   
 The Disinfector 73%   
ATU Makee 
 BioMicrobics 73%   
 Delta Environmental 14%   
 Other 14%   
Mean ± SDa (min–max)Spearman's rho correlation with log-FCp-value
Fecal coliform (CFU/100 mL)b 18.1 ± 3.6 (<10–690) – – 
Temperature [°C] 21.1 ± 2.5 (16.7–25.6) 0.11 0.639 
pH 6.7 ± 0.8 (4.8–8.3) −0.08 0.715 
Dissolved oxygen [mg/L] 6.8 ± 2.0 (5.4–8.3) −0.01 0.964 
Conductivity [μS/cm2612 ± 302 (227–1,308) 0.67 <0.001 
Turbidity [NTU]c 20.4 ± 19.6 (0–60.6) 0.49 0.032 
UV transmittance [%] 44.5 ± 17.7 (13.3–74.0) −0.40 0.063 
Flowrate [mL/s] 10.2 ± 9.7 (0.5–37.5) 0.41 0.063 
Residence time in UVD unit [min]d 18 ± 30 (1.3–116)   
OSS age [years] 11.6 ± 5.5 (1–22)   
Months since last inspection 4.1 ± 4.3 (0.5–19)   
Months since last bulb replacement 27.8 ± 17.0 (2.0–67.6)   
Months since last cleaning 4.8 ± 5.6 (0.5–20.8)   
UVD unit makee 
 Salcor 3G 27%   
 The Disinfector 73%   
ATU Makee 
 BioMicrobics 73%   
 Delta Environmental 14%   
 Other 14%   

aSD: standard deviation.

bReported statistics are GM ± GSD.

cDue to instrument imprecision, turbidity measurements should be considered estimated values (within 10 NTU of the true value). It is unlikely that turbidity values are significantly biased.

dApproximate values calculated from flowrate measurements and unit volume estimates.

eValues are percentages of all observed UVD units represented by the given UVD unit make or ATU make that precedes UVD units in treatment sequence.

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