African
Journals Online
WaterSA
Volume 27, Issue 4, 2001
ABSTRACTS
Measurement of pH, alkalinity and
acidity in ultra-soft waters
Lahav,
O.; Morgan, B.E.; Loewenthal, R.E.
Abstract:
Conventional characterisation of low alkalinity waters via pH
measurement and titration of total alkalinity to a prescribed
end-point invariably leads to large errors. These errors result from
instability of the pH probe and an unknown titration end-point. In
this paper two indirect methods (termed the "double Gran
function" and the "blend" method) for the
characterisation of such waters are evaluated critically. A blend
composed of the raw water, sodium chloride (to increase conductivity),
and standard bicarbonate (to increase buffering capacity) was titrated
with standard strong acid in two pH regions: 6.3 < pH < 7.0, and
3.5 > pH < 4.0. In both methods, total alkalinity was determined
using the latter set of points, and the first Gran function. In the
double Gran function method the upper set of titration points was used
to determine CO2 acidity using the second Gran Function. In
the "blend" method, equilibrium chemistry data were used to
calculate total acidity for each point based on the known total
alkalinity, pH reading, temperature and ionic strength. The two
methods gave excellent results (in terms of both repetition and
accuracy) as compared to characterisation based on total alkalinity
and inorganic carbon analysis. A detailed procedure for the execution
of the two approaches is given in an appendix.
Treatment of grain distillation
wastewaters in an upflow anaerobic sludge bed (UASB) system
Laubscher,
A.C.J.; Wentzel, M.C.; Le Roux, J.M.W.; Ekama, G.A.
Abstract:
In operation of the full-scale upflow anaerobic sludge bed (UASB)
system at the Stellenbosch Farmers' Winery (SFW) Wellington
distillery, a problem encountered in the treatment of grain
distillation wastewater was the accumulation of a floating scum layer.
On occasion this was so severe that it forced shutdown of the UASB
system to facilitate the physical removal of the scum. A preliminary
investigation indicated that the scum-layer behaviour could be
replicated at laboratory-scale. Thereafter, two laboratory-scale UASB
systems were run in parallel: one (control) receiving wine
distillation wastewater as influent, and the other (experimental)
grain distillation wastewater at both high and low total suspended
solids (TSS) concentrations. Scum-layer accumulation, COD removal and
concentration profiles along the axis of flow through the reactors
were compared. The scum layer developed only with grain distillation
wastewater as influent, and its severity appeared to be linked to the
TSS content of the grain wastewater. Reducing the TSS by drum
filtration, settling or blending with wine wastewater could reduce,
but not eliminate, the scum-layer accumulation. With wine distillation
wastewater as influent, concentration profiles exhibited the typical
three distinct zones of sludge bed behaviour. However, with grain
distillation wastewater as influent, the concentration profiles were
markedly different; the three zones of behaviour did not develop. This
raises the question of the long-term viability of a UASB system
treating grain distillation wastewaters.
Modelling of a falling sludge bed
reactor using AQUASIM
Ristow,
N.E.; Hansford, G.S.
Abstract:
The falling sludge bed reactor (FSBR) allows for increased solids
retention time, resulting in greater substrate conversion for all
particulate degradation and biological reactions. The purpose of the
FSBR is to hydrolyse primary settled sewage (PSS). Soluble products
are then used for the biological treatment of acid mine drainage. A
mathematical model has been developed that describes the anaerobic
digestion of PSS and biological sulphate reduction in the FSBR. The
hydrodynamic processes taking place in the FSBR have been simulated
using a system of mixed reactors connected by water flow and mass flux
streams. Trends obtained from varying the hydraulic retention time,
the sludge recycle ratio, and the feed COD: SO4 2-
ratio allow for identification of the critical biological processes
taking place in the FSBR, as well as the influence of the operating
parameters. Areas where there is a lack of understanding in the
mechanism and kinetics have been identified, and these include the
influence of sulphate reduction on the hydrolysis of particulate
organic matter, as well as the mathematical influence of sulphide
inhibition on the various biological groups. A sensitivity analysis
shows that hydrolysis is the rate-limiting process, while sulphide
inhibition is of importance when sulphate conversion increases.
Investigation of the
immobilisation / mobilisation of nickel, copper, chromium and zinc
following co-disposal of activated sewage sludge with synthetic refuse
Ehlers, George A.C.; Daneel, Richard A.; Senior, Eric
Abstract:
Laboratory microcosms were packed with synthetic refuse and waste
activated sewage sludge in two ratios (4.1:1 and 4.1:2 v/v). The
sludge was spiked (100 mg·l-1 or 200 mg·l-1)
with the salts of each of four heavy metals (Ni2+, Cu2+,
Cr3+ and Zn2+). Subsequently, the metal
concentrations were increased progressively. For all the microcosms,
including an unperturbated control, unbalanced fermentations resulted
as evidenced by low pH values. Thus, heavy metal presence was not the
sole cause. The leached metal concentrations were in a consistent
order with high Zn and Ni concentrations recorded compared with
immobilised Cr and Cu. After 15 weeks of operation, despite extensive
retention, increases in Cr, Ni and Zn were detected in the leachates
following elevated loadings. Due to the high redox potentials (+2 to
+170 mV), precipitation of the metals as insoluble sulphides was not
attainable.
Survey of heavy metals in the
sediments of the Swartkops River Estuary, Port Elizabeth South Africa
Binning, Karen; Baird, Dan
Abstract:
Elevated levels of heavy metals in the sediment can be a good
indication of man-induced pollution. Concentrations of chrome, lead,
zinc, titanium, manganese, strontium, copper and tin were measured in
the sediments taken along a section of the Swartkops River and its
estuary. These results showed that the highest heavy metal
concentrations in both the estuary and river were recorded at points
where runoff from informal settlements and industry entered the
system. Comparison of the results for the estuary with those obtained
in a similar survey made about 20 years ago revealed some remarkable
increases. This raises concern over the long-term health of the
Swartkops River ecosystem.
Situation analysis of water
quality in the Umtata River catchment
Fatoki,
O.S.; Muyima, N.Y.O.; Lujiza, N.
Abstract:
The Umtata River was characterised by using standard physico-chemical
and microbiological methods to assess the present water quality in the
river. The results indicated high turbidity, gross microbiological and
cadmium pollution. Turbidity values ranged from 0.28 NTU to 1 899 NTU
highlighting the known problem of donga erosion in the catchment.
Faecal coliform counts varied between 0 and 21 000 counts/100 ml while
the total coliform counts ranged from 0 to 69 000 counts for all the
sites sampled. The levels of cadmium varied between 0.01 mg/l and 1.0
mg/l. Nutrient levels were also high. Nitrate values ranged from
0.01mg/l to 28.0 mg/l as N while phosphate values varied between 0.02
mg/l and 5.0 mg/l as P. The high coliform counts and the nutrient
values exceeding acceptable limits are indicative of pollution from
domestic wastes from several informal settlements located along the
riverbank. Water uses in the area were determined and were found to be
mainly domestic and recreational. The gross pollution of the river
exposes the local people who depend on it for their primary water
source to serious health risk. Another use included livestock
watering.
Assessment of the impact of
point source pollution from the Keiskammahoek Sewage Treatment Plant
on the Keiskamma River - pH, electrical conductivity, oxygen-
demanding substance (COD) and nutrients
Morrison,
G.; Fatoki, O.S.; Persson, L.; Ekberg, A.
Abstract:
The treatment performance of the Keiskammahoek Sewage Treatment Plant
(KSTP), was assessed in terms of pH, conductivity, and COD and
nutrients removal from the influent. The contributions from this and
other smaller point sources in the town to these parameters in the
receiving Keiskamma River were determined by simultaneously monitoring
the parameters in the river over a period of about 1 month. The COD
and orthophosphate in effluents exceed the SA Effluent Quality
Standards for these parameters in effluents to be discharged into a
river. Also, significant pollution of the receiving Keiskamma River
was indicated for orthophosphate, COD and NH4-N.
Optimal water meter selection
system
Johnson,
E.H.
Abstract:
The comparison of the particular accuracy envelope of a water meter
with a consumer's diurnal demand pattern by means of a common
reference facilitates the optimal selection of water meters. The
accuracy curve and envelope of a new water meter is governed by the
type of water meter and relevant standards. Water demand patterns vary
with time, period, seasons, consumers and combinations of these
factors. The classical accuracy envelope and demand pattern are not
directly comparable, and require a common comparison reference. The
relative frequency of the volume of water passing through a meter at
various flow rates and the weighted accuracies of these measured
volumes play a pivotal role in establishing a common comparison
reference. The time unit selected to calculate the volume of water
passing through the meter is guided by the type of water reticulation
infrastructure within which the meter is installed. However,
experience and literature show that a flow interval of less than 1 min
would result in the application of unrealistic high flow rates. A
simplified example for the determination of the weighted accuracy of a
water meter monitoring a theoretical demand pattern illustrates the
methodology used to establish the common comparison reference.
Economic/financial analysis based on an income statement together with
capital budgeting techniques assist with the determination of the
financial suitability of investing in a new replacement water meter.
This financial analysis includes various potential income and
expenditure components that will result from the installation of a new
water meter. Sensitivity analysis facilitates the decision-making
process. The analysis of flow data by a computer program developed in
context with the described methodology illustrates that the savings
achieved by the improved accuracy of matching the optimally selected
meter and a particular demand profile can finance the costs of such an
investment.
Evaluation of short-term weather
forecasts in South Africa
Banitz, Estelle
Abstract:
In this paper a brief overview will be given for the reasons for doing
evaluations of short-term weather forecasts as well as the methodology
thereof. Short-term weather forecasts are defined as a forecast valid
for the current day as well as the next day. In other words up to 48 h
ahead. Results are given for South African Weather Service
temperature, rainfall and severe weather forecasts as issued by head
office in Pretoria. Temperature forecasts generally tend to be
accurate to within a limit of 2.3°C. A comparison is made between
temperature forecasts for an inland station, a coastal station and a
station influenced by the escarpment. Tendencies of rainfall forecasts
show that rain is forecast more often than it occurs. Comparative
rainfall forecasts for a summer and winter rainfall region are shown.
Severe weather events are sometimes captured well, but severe
thunderstorms are not predicted with great accuracy. Once again the
tendency is to over-forecast. With one of the scientific aims of
forecasting evaluations being to concentrate on areas of
under-performance, these statistics show that a better observation
network would improve conditions for evaluation of forecasts. Further
research should be focused on alternative or better techniques to
forecast precipitation (general and severe)with greater accuracy.
The hydrogeology of the
Uitenhage Artesian Basin with reference to the Table Mountain Group
Aquifer
Maclear,
L.G.A.
Abstract:
The Uitenhage Artesian Basin (UAB) lies in the Eastern Cape and is
South Africa's most important artesian groundwater basin, supplying
approximately 1 400 Ml/yr (44 l/s) of water from springs for domestic
use to Uitenhage, as well as supporting large citrus irrigation
schemes. Groundwater from this basin has been extensively utilised
from the early part of the 20th century, including periods
of over-exploitation resulting in the declaration of a groundwater
control area to limit abstraction to sustainable rates. The aquifer
comprises fractured Table Mountain Group (TMG) sandstones confined in
the eastern part of the basin by overlying Cretaceous siltstones and
mudstones, resulting in artesian conditions. The Coega Fault is a
major structural feature dividing the basin into separate systems,
viz. the southern Swartkops Aquifer and the northern Coega Ridge
Aquifer, that are hydrogeologically independent of each other. The
Elands River syncline divides the Swartkops Aquifer further into the
Kruisrivier and Bethelsdorp Units. Borehole yields commonly range from
5 to 10 l/s and the groundwater quality is excellent with low
salinities. Water hardening, however, is required due to the acidic
and corrosive nature of the groundwater, typical of other Table
Mountain Group aquifers in South Africa. Using 14C data,
the age of the groundwater in the basin ranges from 1 500 to 28 000
years with a calculated flow rate of 0.8 m/a. From the chloride mass
balance method, recharge rates are determined to be 25 to 55% of
annual rainfall. Groundwater temperatures generally show that depths
of groundwater strikes do not necessarily correspond with depth of
origin, indicating a complex groundwater circulation pattern within
the basin. Whilst the UAB has been well studied locally, a basin-scale
hydrogeological characterisation is considered to be necessary,
followed by recommendations and formulation of a management plan to
ensure the continued sustainability of groundwater supply from this
national asset.
A baseline limnological study
of Wagendrift Dam (Thukela basin, KwaZulu-Natal)
Hart,
Rob C.
Abstract:
Basic features of the physical and biological limnology of Wagendrift
Dam, a moderately large impoundment on the Boesmans River, were
studied between July 1989 and May 1990. This man-made lake showed a
typical monomictic pattern of summer stratification (November through
April) and holomictic winter circulation (May to October). Water
quality was chemically good (Department of Water Affairs and Forestry
records), with little evidence of nutrient enrichment. Water clarity
during the study was moderately low (mean SD and K d PAR
values of 0.45 m and 2.55 m-1), with little evidence of
persistent mineral turbidity, suggesting reasonably satisfactory
catchment conditions. In keeping with the low nutrient status, surface
chlorophyll content remained below 5 ?g ·l -1 throughout
the study. In terms of ecological groupings, the phytoplankton was
numerically dominated mostly by 'Competitive' green algae for most of
the year. 'Stress-tolerant' cyanophytes were continuously sparse, but
were marginally more abundant during summer stratification. Diatoms
and other disturbance-tolerant 'ruderal' algae persisted throughout
the year. No spring peak in ruderal algae was evident, but it may have
been masked by high zooplankton grazing pressure. An autumnal peak in
ruderal algae coincided broadly with flood-related inflows and annual
de-stratification. Zooplankton was dominated (numerically and/or
gravimetrically) by typical clear-water taxa. The copepod Tropodiaptomus
spectabilis and cladoceran Daphnia pulex along with various
unidentified cyclopoids and rotifers were seasonally persistent, while
other cladoceran taxa (D. laevis and Diaphanosoma excisum)
showed considerable seasonal periodicity. Zooplankton standing stock
was collectively substantial, annually averaging around 0.65 g·m -2
DM, and approaching 1 g·m -2 DM in spring/early summer,
implying potentially significant natural grazer-control of
phytoplankton, aided perhaps by large numbers of benthic bivalve
molluscs (Unio caffer), observed stranded in littoral margins
following reservoir draw-down.
Extending flood damage
assessment methodology to include sociological and environmental
dimensions
Viljoen,
M.F.; Du Plessis, L.A.; Booysen, H.J.
Abstract:
Optimal and sustainable flood plain management, including flood
control, can only be achieved when the impacts of flood control
measures are considered for both the man-made and natural
environments, and the sociological aspects are fully considered. Until
now, methods/models developed to determine the influences of floods
and flood control measures in South Africa, and elsewhere in the
world, focus on the man-made environment and neglect the natural
environment and social dimensions. Two models, recently completed in
South Africa, namely FLODSIM (flood damage simulation model for
irrigation areas) and TEWA (flood damage simulation model for urban
areas) are cases in point. This paper gives an overview of the
development of flood damage assessment and mitigation methodology in
South Africa. Emphasis is placed on the evolution from the traditional
ex-post approach to the latest ex-ante approach in which the
sociological and natural environmental dimensions are included.
Deliverables from the presentation should be of value to researchers
and managers in the fields of flood management and environmental
impact assessment worldwide.
Evaluation
of detection methods for Legionella species using seeded water
samples
Bartie,
C.; Venter, S.N.; Nel, L.H.
Abstract:
South African laboratories are currently using various methods in a
non-standardised approach to detect Legionella species in
environmental samples. In an attempt to provide guidelines for the
development of a standard method, a number of currently available
detection methods were evaluated, using seeded samples of sterile and
non-sterile tap water, cooling water and make-up water. The samples
were seeded with a type strain of L. pneumophila serogroup 1
(American Type Culture Collection 33152). The effect of sample
concentration by centrifugation and membrane filtration followed by
either vortex or sonication for resuspension of organisms was studied.
Three currently available culture methods were evaluated: the
International standard method (ISO/DIS 11731), the Australian standard
method (AS 3896 - 1991) and a locally-developed adaptation of the most
probable number method (MPN). In addition, the direct
immunofluorescence test and a commercially available latex
agglutination test kit were included in the evaluations. The
usefulness of treatment with acid or heat prior to culture was also
compared. Our results indicated that concentration by membrane
filtration using nitro-cellulose filters with a pore size of 0.45 ?m,
followed by sonication for 10 min, would be the most appropriate
concentration and resuspension method for the samples. In the absence
of sample pretreatment with acid or heat, organism recovery from
sterile seeded samples on BCYE ranged from 85.9 - 98.7%. However, in
the non-sterile samples, these figures dropped to 8.1 - 38.5%. Sample
pretreatment resulted in a further loss of at least 50% of organisms
in all the samples, regardless of the pretreatment method or culture
medium used. In general, the ISO and AS methods were more appropriate
than the MPN method for organism recovery from sterile seeded samples.
However, for the nonsterile samples, the MPN method yielded better
recovery.
Comparative
water use of wattle thickets and indigenous plant communities at
riparian sites in the Western Cape and KwaZulu-Natal
Dye,
P.; Moses, G.; Vilakazi, P.; Ndlela, R.; Royappen, M.
Abstract:
Large-scale funding by both the Government and the private sector
continues in support of the Working-for-Water Programme, which is
active in many regions of the country. One justification for this
programme of alien tree removal is the streamflow enhancement that is
believed to follow the replacement of dense stands of invasive trees
by indigenous, largely herbaceous or shrub dominated plant
communities. Often the densest stands of invader trees occur within
riparian zones, where removal of trees in close proximity to stream
channels is believed to strongly enhance streamflow. Few data are
available, however, to support this assumption. Results from a number
of research catchments have consistently shown that afforestation
significantly decreases streamflow where the pre-afforestation
vegetation was seasonally dormant mountain grassland or fynbos
(Versfeld, 1994). The net difference in evapotranspiration (ET)
between riparian thickets of alien trees and riparian fynbos may be
quite different, due to the yearlong availability of soil water and
enhanced plant growth in riparian zones. The water use of alien
invasive trees in South Africa remains largely unknown, adding further
uncertainty to the effect of alien removal on streamflow. This paper
describes the results of a comparative study of annual ET between
indigenous riparian plant communities and riparian wattle thickets (Acacia
mearnsii() at four sites in the Western Cape and KwaZulu-Natal.
The Bowen ratio energy balance (BREB) technique was used to record a
12-month record of 20 min evaporation rates from a fynbos riparian
plant community in the Jonkershoek valley (Western Cape), and a
grassland riparian community on the property Gilboa in the
KwaZulu-Natal midlands. Closed-canopy, mature stands of
self-established (A. mearnsii( in the Wellington and Groot
Drakenstein areas of the Western Cape were selected to provide
comparative transpiration data. The heat pulse velocity (HPV)
technique was used to record hourly sap-flow rates in six sample trees
representing the range of tree sizes at both wattle sites. Total daily
sap flow in all sample trees experiencing adequate soil water
availability was found to be very closely correlated to tree size and
an index defined as the product of mean daily vapour pressure deficit
(VPD) of the air and the number of daylight hours. These relationships
were used to predict the water use of wattle thickets at Jonkershoek
and Gilboa, using VPD and day-length data recorded at these sites.
Published estimates of canopy rainfall interception were added to the
sap flow (transpiration) component to yield a combined annual ET to
compare to the BREB ET data. Table 1 summarises the annual
evapotranspiration at each site. (table***) We conclude that the
removal of riparian wattle and its replacement by indigenous
herbaceous plants may indeed result in significant reductions in
annual ET, and could very likely lead to streamflow enhancement.
However, this study has clearly shown that annual ET varies
considerably in different riparian plant communities, and that one
must consider the structural and physiological characteristics of both
the pre-clearing and post-clearing vegetation in order to predict the
net change in ET. This conclusion supports an earlier view (Versfeld
et al., 1998) that an improved methodology of general applicability is
required to enhance the accuracy of water use predictions for a wide
range of alien and indigenous plant communities. Such predictions are
important to prioritise clearing operations in areas invaded by alien
trees.
Indicators of sustainable
development for catchment management in South Africa - Review of
indicators from around the world
Walmsley, Jay; Carden, Mark; Revenga, Carmen; Sagona, Frank;
Smith, Malcolm
Abstract:
Indicators are the ideal means by which progress towards sustainable
development can be measured. However, most indicator initiatives
throughout the world have been aimed at state-of-the-environment
reporting, with relatively few aimed at developing sectoral
indicators. This paper provides the results of a review to establish
trends in the development of indicators that assist in integrated
water resource management. Twenty-one organisations from around the
world were approached with regard to whether they had developed
indicators of sustainable development for catchment management. Of
these, only five organisations had developed, or were in the process
of developing, indicator sets that were available for review. These
included the Fraser Basin Council (Canada), the Murray-Darling Basin
Commission (Australia), the Tennessee Valley Authority (USA), the
United States Environmental Protection Agency and the World Resources
Institute. All of these indicator sets were developed using an
issuesbased approach. Each indicator set was unique, reflecting the
policy, both national and organisational, upon which it had been
based. An analysis of these five indicator sets revealed that the most
important themes that required information for water resource
management at a catchment level, were biodiversity and ecosystem
integrity, land-use change, water quality, waste production, water
availability and resource use. Common indicators included
population growth; community involvement; water availability; water
use; water quality trends; soil contamination; non-compliance; species
at risk; key species assessment; change in vegetation; agricultural
impact; access to recreational opportunities, and ecosystem health.
The identification of these themes and common indicators will be
useful for the development of indicators for catchment management in
South Africa. More importantly, policy frameworks and the physical
characteristics of catchment systems in the country need to be taken
into account. Additionally, it is recognised that no effective
indicator set can be developed without the input of stakeholders.
Utilisation of factorial
experiments for the UV/H2O2 process in a batch reactor
Drouiche,
M.; Lounici, H.; Mameri, N.; Piron, D.L.; Kharroune, M.
Abstract:
Factorial experiments provide a comprehensive understanding of the
impact of operational variables on process performance. Utilisation of
the Hadamard matrix taking into account all interaction effects,
appeared to be efficient for giving a mathematical model that
conformed to criteria validity. The predictions given by the factorial
experiments model were confirmed by the experiments. Phenol oxidative
degradation kinetics were not significantly influenced by pH or
hardness of the solution to be treated, as is predicted by factorial
experiments. On the other hand, initial H2O2
concentration, initial phenol concentration and temperature
significantly influenced the efficiency of the process. Optimal values
were determined: a temperature of about 20°C and a CH2O2/Cphenol
ratio of 120 (mg/mg).
The analysis of 74 years of
rainfall recorded by the Irwins on two farms south of Potchefstroom:
technical note
Lynch,
S.D.; Zulu, J.T.; King, K.N.; Knoesen, D.M.
Abstract:
Rainfall records for three rain gauges on the farm Limerick and three
rain gauges on the farm Mealielands were recorded from 1924 until 1999
by Mr DJ Irwin and his son Mr NG Irwin. The observations from these
two nests of rain gauges are used to analyse the trends in rainfall
measurements over time and to analyse the correlation of rainfall
measurements between these rain gauges. The results presented in this
report highlight the fact that the observations of rainfall are
different to one another in many cases, indicating that care should be
taken when selecting a rain gauge to represent the rainfall over a
particular area. Analysis of the annual totals of rainfall has also
found that at least 15 years of observations are required to determine
a representative MAP value. The analysis of the monthly rainfall data
also indicates that the rainy season commences in November and ends
towards the end of April. A study of the extreme daily rainfall events
shows that many of the storms are localised and are confined to an
area around the rain gauges. The length of the droughts on these two
farms are not as long as the national figures which would indicate
that more point rainfall estimates are required to understand fully
the spatial extent of a drought.
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