3.1 Introduction
3.3.1 Bacterial indicator profiles
83 3.3 Results
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between 41.56 – 100% with a 100% reduction in faecal coliform load obtained in October 2012 and January 2013 only. However, higher levels of some indicator bacteria were observed at the discharge point at certain months when compared to counts before chlorination, with February 2013 samples exhibiting an increase for all bacterial indicators enumerated namely; total coliforms (21.73%), E. coli (72.14%), faecal coliforms (5.65%), faecal streptococci (100%) and enterococci (108.93%) for the NWWTP (Figure 3.1). A similar trend was observed for the NGTW (total coliforms (39.29%), E. coli (69.55%), faecal coliforms (137.80%), faecal streptococci (228.42%) and enterococci (39.26%)) during May 2012 (Figure 3.3). In addition, April (119.34%), June (48%), December (220%) and February (5.65%) were characterised by an increased faecal coliform load at the discharge point for the NWWTP (Figure 3.1) whilst the evaluation of the results obtained for the NGTW revealed a 137.8% and 16.47% increase in faecal coliform load during May and September 2012 respectively (Figure 3.3). Heterotrophic and total coliform populations (in CFU/ml) in treated effluent samples before chlorination ranged between 0.227 × 103 – 11.84 × 103 (TC) and 160 × 103 - 2026.67 × 103 (HPC) for the NWWTP (Figure 3.5) and 1.55 × 102 – 152.53 × 102 (TC) and 71.13 × 102 – 6026.67 × 102 (HPC) for the NGTW (Figure 3.6) respectively.
Seasonal averages indicate a higher heterotrophic bacterial population within the receiving watershed during winter, upstream (1128.89 × 103 CFU/ml) and downstream (1804.44 × 103 CFU/ml) of the Umgeni river (Figure 3.5) whilst a higher bacterial load was obtained upstream (3.502 × 105 CFU/ml) and downstream (2.74 × 105 CFU/ml) of the Aller River (Figure 3.6) during summer and spring respectively. Extremely low levels of all indicators were detected during March (0 – 0.017 × 102 CFU/ml), April (0 – 0.32 × 102 CFU/ml) and July (0 – 0.033 × 102 CFU/ml) for the Aller River whilst September revealed exceptionally high levels of all indicators (in CFU/ml) upstream and downstream of the Aller River (Figure 3.4) respectively
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(total coliforms (212.2 × 102; 120.5 × 102), E. coli (101 × 102; 31.8 × 102), faecal coliforms (122.7 × 102; 31.8 × 102), faecal streptococci (224 × 102; 6.93 × 102) and enterococci (290.7 × 102; 8.32 × 102). Seasonal averages revealed higher levels (in CFU/ml) of total coliforms (7.61 × 103; 25.85 × 103), E. coli (3.65 × 103; 4.16 × 103) and faecal coliforms (3.42 × 103; 1.73 × 103) in the final effluent and discharge point, respectively during summer for the NWWTP. Similarly, higher levels (in CFU/ml) of E. coli (3.47 × 102; 4.64 × 102) and faecal coliforms (19.27 × 102; 3.97 × 102) were observed during summer in the final effluent and autumn at the discharge point.
The faecal coliform to faecal streptococci ratio (FC/FS) ranged between 0 – 13.79 and 0 - 33 at the discharge point for the NWWTP and NGTW, respectively whilst a ratio of 0 – 51 and 0 – 115.58 was obtained for the receiving Umgeni River and Aller River respectively. Fifty-eight percent (7/12) and 50% (6/12) of before chlorination and discharge point samples had a FC:FS ratio of greater than 4. Similarly for the NGTW, 42% (5/12) and 17% (2/12) of samples exhibited a FC:FS ratio of greater than 4.
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Figure 3.1: Presumptive E. coli (EC), faecal coliform (FC), faecal streptococci (FS) and enterococci (ENT) load in NWWTP effluent samples before chlorination (BC) and at discharge point after chlorination (DP) between March 2012 and February 2013. All bars represent average (n=3) values ± standard deviation.
0 2 4 6 8 10 12
BC DP BC DP BC DP BC DP BC DP BC DP BC DP BC DP BC DP BC DP BC DP BC DP
MAR '12 APR '12 MAY '12 JUN '12 JUL '12 AUG '12 SEPT '12 OCT '12 NOV '12 DEC '12 JAN '13 FEB '13 MICROBIAL COUNTS (CFU/ml x103)
SAMPLING POINTS / SAMPLING TIMES
EC FC FS ENT
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Figure 3.2: Presumptive E. coli (EC), faecal coliform (FC), faecal streptococci (FS) and enterococci (ENT) population detected upstream (US) and downstream (DS) of the Umgeni River between March 2012 and February 2013. All bars represent average (n = 3) values ± standard deviation at a CFU/ml as indicated however E.coli population detected downstream during August 2012 is represented as x104 CFU/ml.
0 1 2 3 4 5 6
US DS US DS US DS US DS US DS US DS US DS US DS US DS US DS US DS US DS
MAR '12 APR '12 MAY '12 JUN '12 JUL '12 AUG '12 SEPT '12 OCT '12 NOV '12 DEC '12 JAN '13 FEB '13 MICROBIAL COUNTS (CFU/ ml x103)
SAMPLING POINTS / SAMPLING TIMES
EC FC FS ENT
E.coli -1x104
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Figure 3.3: Presumptive E. coli (EC), faecal coliforms (FC), faecal streptococci (FS) and enterococci (ENT) load detected in NGTW effluent samples before chlorination (BC) and at the discharge point after chlorination (DP) between March 2012 and February 2013. All bars represent average (n=3) values ± standard deviation at a CFU/ml as indicated.
0 5 10 15 20 25 30 35 40 45
BC DP BC DP BC DP BC DP BC DP BC DP BC DP BC DP BC DP BC DP BC DP BC DP
MAR '12 APR '12 MAY '12 JUN '12 JUL '12 AUG '12 SEPT '12 OCT '12 NOV '12 DEC '12 JAN '13 FEB '13
MICROBIAL COUNTS (CFU/ml x102)
SAMPLING POINTS / SAMPLING TIMES
EC FC FS ENT
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Figure 3.4: Presumptive E. coli (EC), faecal coliform (FC), faecal streptococci (FS) and enterococci (ENT) populations detected upstream (US) and downstream (DS) of the Aller River between March 2012 and February 2013. All bars represent average (n = 3) values ± standard deviation at a CFU/ml as indicated however E.coli population detected downstream during August 2013 as well as all indicators detected during September 2013 are represented as x103 CFU/ml.
0 20 40 60 80 100 120 140 160
US DS US DS US DS US DS US DS US DS US DS US DS US DS US DS US DS US DS
MAR '12 APR '12 MAY '12 JUN '12 JUL '12 AUG '12 SEPT '12 OCT '12 NOV '12 DEC '12 JAN '13 FEB '13 MICROBIAL INDICATORS (CFU/ ml x102; x 103)
SAMPLING POINTS / SAMPLING TIMES
EC FC FS ENT
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Figure 3.5: Total coliform (TC) and total heterotrophic bacterial (THB) population enumerated before chlorination (BC) and after chlorination (AC) at NWWTP as well as upstream (US) and downstream (DS) of the Umgeni River between March 2012 and February 2013. Values represent averages (n
= 3) ± standard deviation at a CFU/ml as indicated, however, the total coliform population detected downstream during August 2012 is represented as x104 CFU/ml.
0 10 20 30 40 50 60 70
0 5 10 15 20 25 30 35 40 45 50
BC DP US DS BC DP US DS BC DP US DS BC DP US DS BC DP US DS BC DP US DS BC DP US DS BC DP US DS BC DP US DS BC DP US DS BC DP US DS BC DP US DS
MAR '12 APR '12 MAY '12 JUN '12 JUL '12 AUG '12 SEPT '12 OCT '12 NOV '12 DEC '12 JAN '13 FEB '13 TOTAL HETEROTROPHIC BACTERIAL 5COUNT -(CFU/ml 10) TOTAL COLIFORM COUNT - (CFU/ml 103)
SAMPLING POINTS / SAMPLING TIMES
TC THB
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Figure 3.6: Total coliform (TC) and total heterotrophic bacterial (THB) population enumerated before chlorination (BC) and after chlorination (AC) at the NGTW as well as upstream (US) and downstream (DS) of the Aller River between March 2012 and February 2013. Values represent averages (n = 3) ± standard deviation at a CFU/ml as indicated, however, the total coliform population detected upstream (US) during August 2012 is represented as x103 CFU/ml.
0 10 20 30 40 50 60 70 80
0 50 100 150 200 250 300 350
BC DP US DS BC DP US DS BC DP US DS BC DP US DS BC DP US DS BC DP US DS BC DP US DS BC DP US DS BC DP US DS BC DP US DS BC DP US DS BC DP US DS
MAR '12 APR '12 MAY '12 JUN '12 JUL '12 AUG '12 SEPT '12 OCT '12 NOV '12 DEC '12 JAN '13 FEB '13
TOTAL HETEROTROPHIC BACTERIAL COUNT -(CFU/ml 104) TOTAL COLIFORM COUNT - (CFU/ml 102)
SAMPLING POINTS / SAMPLING TIME
TC THB
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