Environmental Engineering Reference
In-Depth Information
Corning 400) employing a low-pressure butane gas as fuel. EC was measured from a soil:
water (1:5) suspension using an electrical conductivity meter (model Jenway 4020) after
allowing settling. The determination of pH was done in a 1:5 soil: 0.01CaCl
2
suspension
using a pH meter (model: Corning 220).
Trace nutrients B, Cu and Zn and total trace metals were extracted using the USEPA
3050 method of double acid (nitric-perchloric (HNO
3
/HClO
4
)) digestion following the
recommendations of Henning
et al
. (2000) and Page
et al
. (1982). The method has been
adapted by USEPA as a standard method of extraction and recovers almost 100% of the
total metals in the samples (Henning et al. 2000). Soil samples were weighed, ashed and
taken up in HNO
3
/HClO
4
and made up to a known volume. The trace metals in the
extract were determined with an atomic absorption spectrophotometer (AAS) (model:
VARIAN TECHTRON SPECTRAA 50B [110 SOFTWARE]) employing an air-
acetylene flame.
The determination of pollution loads to the farm was not possible because water
quantities were not measured during the period of study, due to non-functioning
measurement devices, but effluent characteristics were determined. Time-integrated
effluent samples were collected every 20 minutes from 9 a.m. to 12 p.m. from the
location E as shown in Figure 10.3. The parameters tested and testing procedures were
the same as the ones used for groundwater determination (section 5.1).
4.3
Ponds effluent quality
Results with respect to ponds effluents used for irrigation are presented in Table 10.5.
The SAR
2
value, calculated based on the mean concentrations of Na, Ca and Mg, is 4. In
general, this is a low value, which would not require restrictions to use this effluent for
irrigation purposes. However, if it is considered in conjunction with the EC value, it
shows that this effluent would require a moderate restriction for reuse (Table 10.2). With
respect to Na ions, the effluent could be used with no restrictions. The same applies to Zn
and Cu. (Tables 10.3). However, the Cd concentrations exceed twice the maximum
permissible limit with respect to Cd and about 10 times the limit with respect to Cr,
which is a point of serious concern. Another observation is connected to the very high
values of TKN and ammonia, typical for raw sewage, which indicates the very poor
performance of the treatment facilities. These two parameters are usually not restricted by
regulations, because it is expected that they would be transformed and absorbed by the
soil, and special attention is given to nitrates, with respect to their mobility. However,
high loads with respect to ammonia, could lead to leaching of this element to ground
water.
4.4
General parameters and nutrients
The results with respect to general parameters and nutrients characteristic for this specific
site, are presented in Table 10.6. With respect to the pH of the control sites, the results
show natural acidic soils. This agrees well with similar results in respect to sandy soils in
Mhondoro and Chinhamora Communal lands studied by Nyamangara et al. (2000).
Nyamapfene (1991) explains the low pH by leaching of basic cations (Ca
2+
, Mg
2+
, Na
+
