State of the Bay Report 2010-Final - Anchor Environmental

Anchor Environmental
The concentration of phosphorus in the effluent has only been measured since October
2007 showing a distinct seasonal pattern, with the highest values occurring mostly during the
summer months and lowest values in winter. This is consistent with the higher influx of visitors
during summer. In recent years values have remained below the allowable limit of 10mg/l (Figure
20).
Chlorine gas, generated through a process of electrolysis, is toxic to most organisms and is
used to sterilise the final effluent (i.e. kill bacteria and other pathogens present in the effluent)
before it is released into settling ponds or the environment. Chlorine breaks down naturally through
reaction with organic matter and in the presence of sunlight, but must not exceed a concentration
0.25 mg/l in terms of the general authorisation under which the Langebaan WWTW operates. The
frequency of exeedence for this parameters since 2003 is 47.3% (i.e. nearly 50% of the readings are
above the allowable limit).
4.3.6.2 Water quality parameters associated with the Langebaan WWTW
Water quality parameters associated with effluent from the Langebaan WWTW have only
been measured since June 2009 (Figure 4.20-Figure 4.22). Faecal coliforms counts have exceeded
the allowable limits specified on 4 occasions since 2009, which correspond to 19% of time (Figure
4.21). Total Suspended Solids have only once exceeded the allowable limits, while measurements
for Chemical Oxygen Demand exceeded allowable limits on 29% of the occasions (Figure 4.21).
Flow (m 3 /day)
7000
6000
5000
4000
3000
2000
1000
0
May-09
Aug-09
Dec-09
Figure 4.20. Monthly trends in the volume of effluent discharged from the Langebaan WWTW in the period
June 2009-February 2011, and allowable limits as specified in terms of a General Authorisation
under the National Water Act 1998 (red line).
The levels of Ammonia Nitrogen discharged from the Langebaan WWTW have exceeded the
allowable limit of 3 mg/l since measurements began in June 2009, while the levels of Ortho
Phosphorus fluctuate in a seasonal pattern similar to that seen at the Saldanha WWTW and have in
the last two years remained mostly below the allowable limits (Figure 4.22). The levels of Nitrate
Nitrogen have not exceeded allowable limits since measurements began in 2009, while levels of free
active chlorine have exceeded allowable limits more than half (58%) of the time since monitoring
commenced (Figure 4.21).
State of the Bay 2010: Saldanha Bay and Langebaan Lagoon 74
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