CHAPTER 3 STUDY AREA AND METHODOLOGY
3.1 INTRODUCTION
3.3.2. RESEARCH METHODS EMPLOYED IN THE CURRENT INVESTIGATION
The two most common types of sample collection techniques are grab samples and composite samples. The latter involves collecting individual samples at known time intervals. A grab sample involves taking a sample from the source by submerging sampling bottles into the water, taking the required amount
thereafter immediately sealing the bottle. The following procedures were adopted in this study:
i) THE COLLECTING OF THE WATER SAMPLES
For the present study, the researcher had to ensure some degree of accuracy.
This was maintained by the researcher visiting the area of study, the Umlaas River and obtaining a measurement of the distance of the informal community along the river. This procedure involved the use of a measuring tape which measured a length of 1000 metres. However, due to the area being characterized by violence the researcher had to request the assistance of a community worker to provide assistance during the fieldwork as well as to ensure safety. In avoiding any possible health-related effects on the researcher, protective clothing had to be worn to prevent a contamination from the possible high levels of pollutants in the Umlaas River. The researcher had to also take into consideration a climatic variable as rainfall could dilute the variables present in the water. This was ensured by waiting for a minimum period of at least one month after a rainfall event.
The grab sampling method as well as the systematic sampling procedure was then used. Water samples with an interval of a 100 metres apart were collected upstream and downstream of the informal community. Sterilised glass bottles were used for the collection of Escheria coli (E-coli) samples to prevent any possible contamination. Once the water samples were collected, they were then sealed, placed in a cooler box and then transported to the Ethekwini Wastewater Management Laboratory for analysis. The samples were kept as cool as possible without freezing as freezing would have caused the glass bottles to break. The immediate transportation of the water samples to the Laboratory was to ensure that the shorter the time elapsed between the collection of the samples and its analysis, the more reliable the analytical results would have been.
ii) LABORATORY ANALYSIS
The water samples were then analysed at the Ethekwini Wastewater
Mana!gement Laboratory to determine th!e concientrations of the indicators stated in the objectives of this study.
THE INDICATORS OF THE STUDY IINCLUDE : a) ESCHERIA CQUtE-COLl)
E-coli was chosen as an indicator organism as counts of these organisms give the estimate of recent pollution by wastes from warm blooded animals. The potential for diseaseoould also be quantified.
Plate 3.3 Instrument ColoniccounterlLlsed for E-coli Counts
b) CHEMICAL OXYGEN DEMAND (COD)
When organic compounds are oxidized by microorganisms in the presence of oxygen, the rate at which oxygen is utilized can be used as a measure of the . strength and biodegradability of the organic matter known as the chemical
oxygen demand. Since the reaction is biochemical, it proceeds relatively slowly.
It determines the oxygen absorbed by a sample of water incubated at 20 degrees C for five days.
METHOD: The test portion is digested for 26 minutes in a strongly acidic dichromate solution using silver sulphate as a catalyst and mercuric sulphate as a masking agent. The dichromate is partially reduced the oxidizable material present in the sample. The excess dichromate is titrated with ammonia iron 11 sulphate and the COD value calculated from the amount of dichromate reduced.
Plate 3.4 Instruments : Microwave digestion unit MLS 1200 Mega; Control terminal, Mega 240; Exhaust module Em - 45/A; 10ml micropipettes; bruette and 5 ml automatic dispensing pipette. Used for analyzing COD.
c) TURBIDITY
Turbidity is an expression of the optical property that causes light to be scattered and absorbed rather than transmitted in straight lines through the sample. It can be determined for any water sample that is free of debris and rapidly settling coarse sediments. In river water, turbidity is produced by the presence of suspended solids.
d) CONDUCTIVITY
Conductivity concentration in the Umlaas river is used to estimate the salinity of the river as conductivity gives an indirect measurement of the dissolved solids concentrations.
METHOD
Conductivity - conductivity meter displays the conductivity reading in ms/m over selected ranges.
Turbidity- a comparison of light scattered by the sample under defined conditions with the intensity of light scattered by a standard reference suspension under the same conditions. The higher the intensity of scattered light, the higher the turbidity. Formazin polymer is used as the reference tubidity standard suspension.
Plate 3.5: Instruments : Centre : condudivity meter, used for measuring conductivity.
Right: Hach Model 18900, Turbidimetler, used for measuring turbidity.
e) NITRATE CONCENTRATION
This is used to esfimate eutrophic oonditions in the Umlaas River. Since human excrement is considered to be olile ot non-po'int polluting sources, the nitrate concentration is valuable in the estimation of'Sudh pollution.
METHOD
Nitrate is quantitatively reduced to n~trate by the passage of the sample through a copperized cadmium column. The nitrite (reduced nitrate plus original nitrite) is then determined by diazotizing witlh sUlllfantillamide foHawed by coupling with N-(1- naphthyl) ethylenediamine dihydrochllorided. The resulting water soluble dye has a magenta colour wh'ich is read at 520n. Nitrite alone can be determined by removing the cadmium column.
f) SOLUBLE REACTIVE PHOSPHOROUS
This gives an estimate of the amount of phosphorous immediately available for biological consumption thus indicating the potential growth of algae and aquatic macrophytes. The combined nitrate and phosphorous loadings therefore give an estimation of the nutrient loadings in the Umlaas River. The presence of sewage in the river will also result in phosphorous levels to increase causing a depletion of oxygen.
METHOD
Ammonium molybbdate and potassium antimonyl tartrate react in acid medium with orthophosphate to form phosphomolybdic acid which is reduced to an intensity coloured molybdenum blue by ascorbic acid.
Plate 3.7 Instrument; LCHAT - used for determining nitrate, phosphorous concentration.
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iii) STATISTICAL ANALYSIS
The Student's t-test will be used to determine whether the water samples upstream and down stream of the informal settlement are different. The test is one of the most powerful parametric tests and will establish whether a difference does exist, and how significant it will be at a level of significance of 99%.