Environmental Engineering Reference
In-Depth Information
tributary, which does not allow considerable dilution of the effluent. The discharge from
the plant could not be considered as a well-defined point source of pollution. The ponds
are full with sediments and vegetation has grown at separated spots. Wastewater is
flowing along naturally formed channels and small ponds, the banks of the ponds are not
well defined, and the inlet and outlet facilities are clogged and do not function properly.
The effluent finds its way to the stream at several, naturally formed locations, but not
only at the discharge outlet. As a result, the treatment effect in the ponds is limited to
partial sedimentation and retention of the course material and a fraction of the suspended
solids. It could be expected that the washout of pollutants constituents during peak flow
rates would be high.
The measured T values are within the range of 18ºC to 20ºC, with no significant
spatial variation. The values of pH (Fig. 11.8a) vary within the normal range and the
variation is not significant with respect to sites 1, 2 and 4, while at site 3, the mean value
is significantly lower compared to the other sampling sites. This could be explained with
the contribution from the ponds effluent, where anaerobic conditions exist, leading to a
decrease in the pH of the effluent, which alters the river water quality with respect to this
parameter. This explanation is supported by the high concentrations of ammonia, BOD
5
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and the low DO values at this point. With respect to EC (Fig.11.8a), a significant increase
was found, when comparing the control point to sites 2 and 4. At site 3, the EC value is
significantly lower compared to all other points, which contradicts the rest of the results.
Additional measurements with respect to this parameter, could clarify this contradiction.
Most probably, it could be explained by a human error during the results' processing
stage, because the chlorides and sulfates variation (Fig. 11.8c) show a completely
different trend. Chlorides' concentrations show a considerable increase at sites 2 and 3,
with a maximum concentration at site 3. Chloride, being a conservative constituent, could
reduce its value from site 3 to site 4 due to dilution only. Sulfates show a similar trend,
however the maximum concentration was found at site 2, which could be associated with
industrial discharges.
The results of the Duncan's test for a statistically significant difference of the mean
values among the different sampling locations are presented in Table 11.3. The test is
performed based on 8 observations for all sampling locations and parameters, at an “□”
value of 0.05. The ranking of the mean values is presented with capital letters from A to
D in decreasing order. Mean values denominated with the same letter are not significantly
different.
TSS and turbidity (Fig. 11.8b) show a good correlation, with a clear indication of
pollution at sites 2 and 3. With respect to turbidity, all measured values were significantly
different, with the highest concentration at site 3. This spatial variation underlines the
same trend shown by the other parameters.
With respect to organic pollution Fig.11.9a the spatial variation is similar with a well-
pronounced influence of the ponds effluent. The spatial variation of DO confirms this
trend, with the lowest concentrations measured at site 3. In general, it was found that the
urban runoff does not influence significantly the river water quality in terms of organic
pollution. As the city is located in a hilly mountainous area, the river flow is relatively
rapid, which allows for good aeration, and this explains the relatively high DO
concentrations, and indicates to a potentially high self-purification capacity.
