Scielo RSS <![CDATA[Water SA]]> vol. 40 num. 1 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>Modelling the change in the oxidation coefficient during the aerobic degradation of phenol by acclimated activated sludge</b>]]> In this work the aerobic degradation of phenol by acclimated activated sludge was studied. Results demonstrate that while the phenol removal rate by acclimated activated sludge follows the Monod model, the oxygen uptake rate obeys a Haldane-type equation. The phenol oxidation coefficient obtained at different intial phenol concentrations ranged from 1.9 to 2.6 mol O2 · mol-1 phenol. A mathematical model based on a simplified version of the catalytic mechanism of the enzyme phenol 2-monooxygenase was developed to predict transient phenol concentrations and oxygen requirements by phenol-acclimated activated sludge in batch reactors under different initial phenol concentrations. The proposed model not only adequately represents the experimental results of the present paper, but also those reported by other authors. Particular cases of the proposed model are discussed. <![CDATA[<b>Characteristics of a bioflocculant produced by a consortium of <i>Cobetia</i> and <i>Bacillus</i> species and its application in the treatment of wastewaters</b>]]> The characteristics of a bioflocculant produced by a consortium of 2 bacteria belonging to the genera Cobetia and Bacillus was investigated. The extracellular bioflocculant was composed of 66% uronic acid and 31% protein and showed an optimum flocculation (90% flocculating activity) of kaolin suspension at a dosage of 0.8 mg/mℓ, pH of 8, and with Ca2+ as a coagulant aid. The bioflocculant is thermally stable, with a high residual flocculoccating activity of 86.7%, 89.3% and 87% after heating at 50ºC, 80ºC and 100ºC, respectively, for 25 min. FTIR analysis of the bioflulant indicated the presence of hydroxyl, amino, carbonyl and carboxyl functional groups. Scanning electron microscopy (SEM) revealed a crystal-linear sponge-like bioflocculant structure and EDX analysis of purified bioflocculant indicated an elemental composition in mass proportions of C:N:O:S:P of 6.67:6.23:37.55:0.38:4.42 (% w/w). The produced bioflocculant was highly efficient in removing turbidity and reducing chemical oxygen demand (COD) in brewery wastewater, dairy wastewater and river water. The bioflocculant could flocculate kaolin clay more efficiently than traditional flocculants; alum and polyethylenimine. <![CDATA[<b>The impact of smallholder irrigation on household welfare</b>: <b>The case of Tugela Ferry irrigation scheme in KwaZulu-Natal, South Africa</b>]]> The potential of smallholder irrigated agriculture to enhance food security and alleviate rural poverty has led the South African Government to prioritise and invest significantly in irrigation establishment, rehabilitation and revitalisation. The question addressed in this study pertains to the extent to which smallholder irrigation has been able to reduce poverty in the rural communities to justify this investment. Using a sample of 251 farmers, this study found that factors such as land size, perceived soil fertility, household size, and access to support services were significant predictors of irrigation participation. The results from the treatment effect model indicated that access to irrigation plays a positive role in the welfare of rural households, with irrigators spending about ZAR2 000 per adult equivalent on consumption more than the non-irrigators. The study, therefore, concluded that government investments in smallholder irrigation for poverty reduction are justified. The other factors that influenced household consumption were off-farm income, land size, livestock size, education level, family size and access to support services and infrastructure. The study recommends that investments in smallholder irrigation continue for poverty reduction, and that priority should also be on finding other feasible rural micro-projects and development initiatives to complement smallholder irrigation and significantly reduce rural poverty. <![CDATA[<b>Response of phytoplankton assemblages isolated for short periods of time in a hyper-eutrophic reservoir (Lake Chivero, Zimbabwe)</b>]]> The response of phytoplankton assemblages isolated in enclosures for short periods of time was examined in hypereutrophic Lake Chivero (Harare, Zimbabwe), to determine the factors that influenced the structure of the phytoplankton community, after noticing a marked decline in the dominance of Microcystis aeruginosa in recent years. The phytoplankton assemblage in the lake during summer, winter and the end of winter was dominated by Cryptomonas sp. and Cyclotella sp., with an average relative abundance of > 95%, based on phytoplankton biomass estimations. Isolation in summer resulted in the exclusion of Cyclotella sp., a decline of Cryptomonas sp. and an increase in M. aeruginosa and Anabaena sp. In winter, when M. aeruginosa was absent in the inoculum, isolation resulted in an increase in Cryptomonas sp. biomass and a decline of Cyclotella sp. At the end of winter Cryptomonas sp. initially increased but later declined following the increase in chlorophytes. The non-equilibrium state in Lake Chivero caused pioneer species to dominate rather than M. aeruginosa. <![CDATA[<b>Removal of pharmaceuticals in WWTP effluents by ozone and hydrogen peroxide</b>]]> Ozonation to achieve removal of pharmaceuticals from wastewater effluents, with pH values in the upper and lower regions of the typical range for Swedish wastewater, was investigated. The main aim was to study the effects of varying pH values (6.0 and 8.0), and if small additions of H2O2 prior to ozone treatment could improve the removal and lower the reaction time. The effluents studied differed in their chemical characteristics, particularly in terms of alkalinity (65.3-427 mg·ℓ-1 HCO3-), COD (18.2-41.8 mg·ℓ-1), DOC (6.9-12.5 mg·ℓ-1), ammonium content (0.02-3.6 mg·ℓ-1) and specific UV absorbance (1.78-2.76 £-mg-1-m-1). As expected, lower ozone decomposition rates were observed in the effluents at pH 6.0 compared to pH 8.0. When pH 8.0 effluents were ozonated, a higher degree of pharmaceutical removal occurred in the effluent with low specific UV absorbance. For pH 6.0 effluents, the removal of pharmaceuticals was most efficient in the effluent with the lowest organic content. The addition of H2O2 had no significant effect on the quantitative removal of pharmaceuticals but enhanced the ozone decomposition rate. Thus, H2O2 addition increased the reaction rate. In practice, this will mean that the reactor volume needed for the ozonation of wastewater effluents can be reduced. <![CDATA[<b>Fluorescent sensing and determination of mercury (II) ions in water</b>]]> The presence of heavy metals released from industrial activities into water streams is an ever-growing challenge to ensuring a safe and clean aquatic environment. Detection and determination of the levels of these heavy metals in wastewater is an important step before any measures can be taken. In this study we report on a fluorescent sensing probe based on a naphthyl azo dye modified dibenzo-18-crown-6-ether (DB18C6) for the detection and determination of mercury (II) ions in water. The probe showed high sensitivity and selectivity towards the mercury (II) ion among various alkali, alkaline earth, and transition metal ions. The mercury (II) ion quenched the fluorescence of the probe. Stern-Volmer quenching constants (Ksv) were found to be highest for Hg2+ ion at 1.18 x 10(5) M-1 compared to 3.85 x 10(4) M-1 for copper (II) ion. The stoichiometry of the sensor-metal ion interaction was found to be 1:1 for both metal ions using Job plots. The detection limit for Hg2+ was 1.25 x 10-8 M. The dye modified crown ether was then used to detect mercury in a water sample from a coalfired power plant and to determine the amount of mercury in the water sample. <![CDATA[<b>Geographical differences in the relationship between total dissolved solids and electrical conductivity in South African rivers</b>]]> Electrical conductivity (EC) is a useful surrogate for total dissolved solids (TDS). EC is more rapidly and easily measurable with reasonably-priced equipment. However, as an indirect measure EC is subject to uncertainties that are not always apparent to the user. We set out to investigate the relationship between TDS and EC in 144 643 sample results available on the Department of Water Affairs water quality database. TDS is calculated as the sum of the major solutes determined by laboratory analysis and EC is a measurement in a flow cell. The median TDS:EC ratio for 332 high priority sites was 7 mg/ℓ: 1 mS/m. Regional differences ranged from 4.8 to 8.6. Investigation of 38 of these sites using Maucha diagrams suggested that the differences are related to the dominant major ions, with sodium chloride waters having a lower TDS:EC conversion factor than calcium bicarbonate waters. The practical application of these findings is that users of EC meters should not simply apply a blanket conversion factor, but need to select an applicable factor for the river system in which they are measuring. <![CDATA[<b>Measurement of faecal sludge in-situ shear strength and density</b>]]> The provision of affordable urban sanitation presents a unique set of challenges as the lack of space and resources to construct new latrines makes it necessary to empty existing pits, typically done manually with significant health risks. Various mechanised technologies have been developed to facilitate pit emptying, which are currently either tested on faecal sludge or an 'ad-hoc' simulant that (in the opinion of the tester) approximately replicates the behaviour of faecal sludge. This ranges from a watery consistency in some pour-flush latrines to the strong soil found in many alternating pits, making it difficult to evaluate the effect of changes to a design, or to compare the performance of different pit-emptying technologies produced by different organisations in different countries. This study developed the portable penetrometer, a man-portable device to physically characterise pit latrine sludge through in-situ measurement of its shear strength. The machine produces continuous profiles of shear strength with depth and is capable of testing to approximately 2.5 m below the slab. The portable penetrometer was manufactured and tested in the UK, before profiling approximately 30 pits in Kampala, Uganda. The resulting data are compared to the literature on the physical properties of faecal sludge, and are found to significantly extend the measured strength range with a maximum value approximately 5 times higher than previously reported. The effect of physical remoulding is identified through comparison of data from undisturbed and remoulded strength tests and highlights the potential to increase the 'pumpability' of faecal sludge through in-pit fluidisation. The implications for the development of pit-emptying technologies and synthetic sludge simulants are discussed, and potential further work is identified. These include studies on factors affecting pit function and fill-up rates as well as scientific tests on the effect of modifications to latrines. In both cases any change in the physical properties of the faecal sludge can be identified through repeated profiling using the portable penetrometer. It is hoped that the penetrometer can contribute to an improved understanding of the physical properties of faecal sludge and the factors affecting pit function, supporting the development of improved faecal sludge management services.