Environmental Engineering Reference
In-Depth Information
dumped into the river. The relatively low pollutant constituents at site 4 could be
associated with the dilution effect of tributaries and partial self purification due to the
high DO values.
3.7
Discussion
During the period of study, the water quality legislation of the country was under
revision. A comparison with the suggested draft river water quality standards shows a
high level of pollution of the stream, which receives the effluents from the treatment
plant. The limiting value for TSS was 25 mg/l and it was exceeded at sites 2, 3 and 4. The
BOD
5
limiting value of 5 mg/l was exceeded at site 3 only. With respect to ammonia, the
stipulated limit was 0.08 mg/l and it was exceeded at sites 3 and 4. The ortho-P values
were exceeded at sites 2 and 3. The nitrate limiting value (50 mg/l) is higher compared to
other regulatory instruments, which recommend a 10-mg/l threshold (WHO 1984,
Viljoen 1992, WWEDR 2000), and was not exceeded at any of the tested locations. With
respect to bacteriological contamination, the TC and FC indicators exceeded the safe
limit at sites 2 and 3. It could be stated that at site 4, where river water could be used
directly for domestic purposes, the water quality was not exceeding the maximum
permissible values with respect to the tested parameters, except for ammonia.
The results of this study show that the major sources associated with the diffuse
pollution of Mbabane River (site 2) are associated with urban runoff from industrial sites,
residential areas (in terms of informal sewage discharges) and solid wastes' depositions
along the riverbed and banks. The comparison of the observed pollutant constituents with
regulatory documents indicates that the extent of the pollution is not alarming and is
pronounced with respect to ortho-P, TC and FC only. A considerable pollution with
respect to the organic and bacteriological constituents and nutrients has been contributed
by the malfunctioning of the treatment plant (site 3).
The enforcement of the new regulatory instruments would require the implementation
of a regular and continuous monitoring program in order to control the river water quality
status and to enforce them. This study could be regarded as a preliminary survey for the
establishment of such a program. In this aspect, the following recommendations could be
made:
• Considering the fact that downstream of the City, the Mbabane River water is used for
domestic purposes without pre-treatment, a stringent monitoring program should be
implemented in order to control the river water quality in terms of seasonal variations
and long-term trends. A careful consideration of different possible pollution sources
from industrial enterprises could help to develop an optimal choice of parameters
(Ongeley 1998). The information collected could serve to justify management
decisions with respect to pollution prevention and provide a warning to downstream
users in cases of high concentrations of selected pollutants.
• Monitoring network - in addition to the locations in this study, sampling sites could be
established along the Pholinjane stream (after the industrial site and the City center)
and on Mbabane River after the confluence of the stream, which collects the discharge
of the treatment plant.
