Environmental Engineering Reference
In-Depth Information
4.2
Methodology
The location of the sampling points is shown in Figure 8.3. SW1 is located on Marimba
River upstream the farmland and serves as a control point; SW2 is located on Marimba
River at a distance of about 6 km downstream of point SW1 but before the effluent
discharge of the treatment works; SW3 is located on Little Marimba River, downstream
the study area. It is a small stream, but it was not possible to estimate its flow rate due to
time and personnel limitations.
Considering the possible pathways of pollution transport, the worst impact on river
water quality could be expected during the beginning of the rainy season, because of the
relatively low flows, and because of expected higher pollution concentrations in the
runoff and seepage, due to the flushing effect of the first storms. During a typical wet
season, the Marimba River flows increase tenfold (see Fig. 8.6a), leading to a
considerable potential for dilution effect. In addition, pollution concentrations of water
flows from the pasture are expected to decrease, which contributes to the effect of
dilution of pollution concentrations in the river. For this reason, it was decided to study
seasonal variations at three distinct periods - dry season (October), beginning of the wet
season (November) and wet season (February). Sampling was done twice for each
season. Rainfall data during the period of study to support the choice of seasonal
variation is shown in Fig 8.6b. For each sampling occasion duplicate samples were
analyzed.
On each visit, the following parameters were examined in the field: pH, temperature,
EC, turbidity and nitrate (determined as nitrate plus nitrite). Throughout the text, the term
“nitrate” is used for this parameter and results are expressed in mg N/l. TP, TKN, BOD
5
,
TS with mineral (TSm) and volatile (TSv) fractions, Pb, Zn, Cd, Cr (determined as Cr
+6
)
and Ni were analyzed in laboratory conditions. The field measurements were executed on
site by an ELE-Paqualab modular field system, incorporating a photometer, a portable
conductivity/temperature meter and a pH meter. Turbidity was measured on site by a
portable HACH turbidimeter. Samples for laboratory analyses were collected as the
composite of four grab samples, 500 ml each at 30 minutes intervals, then the field tests
were done on the composite sample. During collection and transport samples were kept in
cooling containers filled with ice. Immediately after the composite sample was taken it
was distributed in different polyethylene containers and preservations for TKN (addition
of H
2
SO
4
), TP (addition of HgCl
2
) and metals (addition of HNO
3
) were executed
according to Standard methods 1989. Samples were transported for analysis within 4
hours after sampling. The laboratory analysis were executed as described in chapter 4,
except for metals, which were determined as total concentrations and analyzed, using a
SHIMADZU - AA6401F Atomic Absorption Spectropho-tometer calibrated by standard
solutions after a nitric acid-sulfuric acid digestion.
Data with respect to the effluent and sludge mixture-quality and quantity
characteristics were provided by the municipality.
Statistical calculations (mean, standard deviation and one-tiled Student's t-test at 95%
of confidence) were performed using the Microsoft EXCEL statistical package.
Throughout the text “significant differ-ence” means that
p
< 0.05, when comparing the
mean values of the data sets.
