African Journals Online
WaterSA

Volume 28, Issue 2, 2002
ABSTRACTS

Distribution of Shewanella putrefaciens and Desulfovibrio vulgaris in sulphidogenic biofilms of industrial cooling water systems determined by fluorescent in situ hybridisation

McLeod, Elise S.; MacDonald, Raynard; Brozel, Volker S.

Abstract: Limited research has been done on the distribution and role of sulphidogenic facultative anaerobes within biofilms in microbially influenced corrosion (MIC). Sulphate-reducing bacteria (SRB) cause MIC and occur in the anaerobic zone of multispecies biofilms. Laboratory-grown multispecies biofilms irrigated with sulphate or sulphite-containing synthetic cooling water, and biofilms from an open simulated cooling water system, were hybridised with a rhodamine-labeled probe SPN3 (Shewanella putrefaciens) and fluorescein-labeled probe SRB385 (Desulfovibrio vulgaris) and investigated using scanning confocal laser microscopy. The facultative anaerobe S. putrefaciens and the strict anaerobe D. vulgaris synergistically coexisted in multispecies biofilms, but as time progressed, S. putrefaciens flourished, displacing D. vulgaris. The results show that S. putrefaciens is capable of growing in sulphidogenic biofilms in aerated environments such as industrial cooling water systems, colonising sulphidogenic biofilms and out-competing the true sulphate-reducing bacteria.

A review of effective flood forecasting, warning and response system for application in South Africa

Du Plessis, L.A.

Abstract: Cyclone Eline caused severe flood damage in South Africa during February 2000. It has been estimated that the total amount lost was approximately R3 000 million. South African farmers lost more than 50% of their export products. Flood damages and disruptions to humans and animal species were even bigger in Mozambique. The emphasis in South Africa is still on, inter alia, structural mitigation measures. Policy-makers seek foreign support and finances, especially during the reconstruction phase after floods, for reparation purposes only. Little to no attention has been given to scientific hazard and risk assessments to determine a sustainable flood standard for different river reaches, which will contribute to appropriate mitigation and prevention strategies. The aim, after flood disasters, is primarily to ensure that flood losses will be covered and to restore the level of existence of flood victims to where it was before the flood. Furthermore, mainly because of institutional problems currently experienced in South Africa, roles and responsibilities of institutions involved in disaster management are not clearly identified. Last mentioned are the reason for absence in South Africa of a formal flood forecast, warning and response system (FFWRS). In most cases where a flood warning system exists, there is evidence that it is insufficient, mainly because of a lack of knowledge and understanding of a well-functioning, appropriate FFWRS. Sustainable prevention and mitigation strategies should be achieved within a holistic integrated catchment management approach. Such approach is multidisciplinary and is therefore not based on a single engineering solution. The main aim of this paper is to discuss one aspect covered by a holistic integrated catchment management approach, namely a flood forecast, warning and response system, which contributes to the prevention and mitigation of flood losses.

Low-cost domestic water filter: The case for a process-based approach for the development of a rural technology product

Prasad, V.C.S.

Abstract: The paper describes the case of development of a rural technology product in a high-technology IT (information technology) environment. The product is a low- cost water filter for which there is a definite need in rural India. The case brings out how even a simple- looking concept for water filtration has to go through several well-defined steps for successful introduction into the field. These evolutionary steps resulting in a process for product development were found to be not too different from any high-technology product process (including a software product process) leading to the inference that in general the steps for a successful product process are the same whether the end use is for a high -technology application or a low- technology application. The usefulness of carrying out work within a process framework is highlighted. Since the project aims at technology transfer to the rural poor for generating rural livelihoods, appropriate financial models and the general sustainability issues for such an activity are briefly discussed. The usefulness of an IT environment in facilitating the development activity is pointed out. The lessons learnt in this exercise are documented.

Optimisation of soybean peroxidase treatment of 2, 4-dichlorophenol

Kennedy, K.; Alemany, K.; Warith, M.

Abstract: In the presence of hydrogen peroxide (H₂O₂), peroxidase enzymes (PE) catalyse the oxidation of various chlorinated phenols to free radicals, which then combine to form insoluble polymers that precipitate out of solution. This study systematically characterises the treatment of 2, 4-dichlorophenol (2, 4-DCP) using soybean peroxidase (SBP) as an oxidising catalyst. The effects of pH, SBP concentration, polyethylene glycol (PEG) additive and initial chlorophenol concentration on 2, 4-DCP treatments are reported. Optimum pH for removal of 2, 4-DCP without PEG was pH 8.2. The pH operating range of SBP was from 2.5 to 9.4 which is wider than reported for horseradish peroxidase (HRP). A general equation is presented that describes the units of SBP required (without PEG) to treat a given amount of 2, 4-DCP at the optimum pH of 8.2. Addition of PEG increased the effectiveness of SBP by factors of 10 and 50 for PEG-3350 and PEG-8000 respectively. A new pH optimum of 6.2 was also found when SBP was used with PEG. Batch and semi -batch enzyme delivery has also been identified as a crucial parameter for the SBP treatment process. The most effective addition scheme was based on five equal concentrations of SBP and H₂O₂ over 15 min and 30 min intervals respectively compared to a single batch addition. This protocol was the most effective as it took advantage of limiting the amount of SBP and H₂O₂ available at each step. This reduces the possible chance of SBP inactivation by excessive H₂O₂ when using a single batch concentration. Average 2, 4-DCP removals achieved were 83.5%, 75.5% and 71.5% for 100, 200 and 300 mg/l 2, 4-DCP concentrations respectively compared to 62%, 52% and 58% for the single batch addition control.

The effect of media on evaluating the phosphate uptake capacity of activated sludge bacterial isolates

Reddy, T.; Bux, F.

Abstract: Since the identification of Acinetobacter calcoaceticus as the primary agent responsible for biological phosphorus removal, much research has been conducted to either confirm or refute this claim. The majority of these studies was conducted under defined laboratory conditions using various artificial media; as a result, many conflicting reports exist regarding the role of A. calcoaceticus and other activated sludge isolates in their possible roles as true polyphosphate-accumulating bacteria. This study was therefore conducted to determine the effect of media type on biological phosphate removal when performed in the laboratory under defined conditions. Five isolates were obtained from a full-scale biological nutrient removal activated sludge system and a previously identified A. calcoaceticus isolate was inoculated into three different media types. The inoculated media were subjected to anaerobic and aerobic conditions to stimulate the phosphate removal mechanism. The test micro-organisms released phosphate, under anaerobic conditions, in the three test media. Synthetic wastewater was found to promote the release of higher concentrations of phosphate by the micro-organisms than in the other two media. During the aerobic phase, phosphate uptake was highest in synthetic wastewater and settled sewage. Due to inconsistencies obtained in the readily biodegradable chemical oxygen demand, total chemical oxygen demand and soluble oxygen demand tests, it was concluded that the medium formulation may skew qualitative or quantitative data regarding biological phosphate removal. It can be concluded that the media used for P uptake studies are of importance as it was observed that the organisms' removal/uptake capabilities were enhanced or reduced depending on the media used.

Capture zone simulation for boreholes located in fractured dykes using the linesink concept

Xu, Y.; Van Tonder, G.J.

Abstract: Delineation of capture zones for groundwater source protection is normally performed by using numerical codes which are based on the porous medium flow equation. However, boreholes are often sited in or along permeable dykes or single fracture zones through which aquifers are drained. It is very important to take into account dyke-influenced aquifers. This paper makes use of Linesink to simulate permeable dyke or fractured zones and utilises the pathline distribution to delineate the capture zones. Conditions when the influence of a fractured dyke can be considered negligible are also discussed through comparison with stagnation point in a uniform flow field. The approach may be sufficient to illustrate protection zoning requirements when dyke aquifers are considered.

Groundwater-table and recharge changes in the Piedmont region of Taihang Mountain in Gaocheng City and its relation to agricultural water use

Yang, Yonghui; Watanabe, Masataka; Sakura, Yasuo; Changyuan, Tang; Hayashi, Seiji

Abstract: Rapid groundwater drawdown in Gaocheng City, the alluvial plain of the Taihang Mountain in the North China Plain, has become the biggest threat to agricultural sustainability. In order to determine the factors resulting in the groundwater decline and to develop a practical plan for long-term groundwater use, water-table fluctuation data were collected over a period of 25 years. The analysis showed that although the drawdown of the water-table was mainly due to water used for winter wheat production and other crops, another reason for groundwater level decline was the tremendous decline of upstream groundwater recharge. It was estimated that, compared to the 1970s, decrease in upstream groundwater recharge in the 1990s resulted in about 1.2 m/a of groundwater level decline. Thus, decline of upstream groundwater recharge rather than agricultural water use was the main reason for the recent groundwater drawdown. On the other hand, gradually improved agricultural practices have saved a great deal of water since the 1970s. The analysis also revealed that, although the groundwater level declined during the wheat-growing season, corn-growing season and over the whole year strongly correlated with the amount of precipitation in that period, aside from one year of extremely high precipitation, precipitation did not recharge groundwater directly but affected groundwater levels through a decrease in irrigation water use. Finally, in order to maintain the groundwater balance, agricultural practices have to save about 180 mm/a of irrigation water from their present level.

A postal survey of effluent generation and disposal in the Zimbabwean dairy industry

Ikhu-Omoregbe, Daniel I.O.; Masiiwa, Husiel

Abstract: Water is a major utility in the dairy industry, which results in significant effluent volumes being generated, hence the challenge of its disposal cannot be ignored. In Zimbabwe, industry generally is not made to pay the full cost of managing industrial effluents, which inadvertently encourages environmental pollution. This paper presents the results of a postal survey of effluent generation and disposal by the dairy industry. A total of 30 questionnaires were sent out to various milk processors around the country out of which 15 were returned. The useful respondents receive and process 56% of the total milk produced in the country. The data obtained indicated that while some of the plants discharge their effluents into the municipal sewers, others discharge theirs by means of land irrigation. This latter method has the consequence of groundwater pollution. Respondents' knowledge of effluent characteristics was generally low, which is not surprising as there are no stringent penalties for polluting.

Assessment of the conservation priority status of South African estuaries for use in management and water allocation

Turpie, J.K.; Adams, J.B.; Joubert, A .; Harrison, T.D.; Colloty, B.M.; Maree, R.C.; Whitfield, A.K.; Wooldridge, T.H.; Lamberth, S.J.; Taljaard, S.; Van Niekerk, L.

Abstract: The future health and productivity of South Africa's approximately 250 estuaries is dependent on two main factors: management and freshwater inputs. Both management and water allocation decisions involve trade-offs between conservation and various types of utilisation. In order to facilitate decision-making in both of these spheres, it is necessary to understand the relative conservation importance of different estuaries. This study devises a method for prioritising South African estuaries on the basis of conservation importance, and presents the results of a ranking based on the collation of existing data for all South African estuaries. Estuaries are scored in terms of their size, type and biogeographical zone, habitats and biota (plants, invertebrates, fish and birds). Thirtythree estuaries are currently under formal protection, but they are not representative of all estuarine biodiversity. We performed a complementarity analysis, incorporating data on abundance where available, to determine the minimum set of estuaries that includes all known species of plants, invertebrates, fishes and birds. In total, 32 estuaries were identified as 'required protected areas', including 10 which are already protected. An estuary's importance status (including 'required protected area' status) will influence the choice of management class and hence freshwater allocation under the country's new Water Act, and can be used to assist the development of a new management strategy for estuaries, which is currently underway.

Effect of solution physical chemistry on the rheological properties of activated sludge

Sanin, F. Dilek

Abstract: Knowledge on rheological properties of sludge is important for the design of pumping and transport facilities and as a tool in process control during treatment. Concentrated activated sludge is known to behave as a non-Newtonian material. The contribution to non- Newtonian behaviour is believed to originate from the colloidal properties of solids more than from the molecular properties of the suspension. Considering that the colloidal properties of sludge depend on factors like pH, conductivity, solids concentration and flocculation properties, this study examines the effects of these variables on the rheology of activated sludge. Results show that the rheograms obtained fit best to a power law model indicating that the flow of activated sludge can best be expressed by the pseudoplastic flow model. It is also observed that the apparent viscosity increases sharply with the increase of solids concentration. From the pH values studied, the one that causes the lowest viscosity is the pH 5.5. As the pH increases, the viscosity measured increases considerably. This makes sense considering that the isoelectric point of bacteria is at pH 2-4. Conductivity is also found to affect the viscosity greatly; such that as the conductivity increases, the apparent viscosity decreases. Finally, experimental results reveal that the presence of extracellular polymers and the flocculated nature of activated sludge affect its viscosity.

Influence of the COD to sulphate ratio on the anaerobic organic matter degradation kinetics

Vela, Francisco José; Zaiat, Marcelo; Foresti, Eugenio

Abstract: The influence of the COD to sulphate ratio on the substrate consumption kinetic parameters was evaluated using a differential reactor filled with polyurethane foam matrices, taken from a horizontal-flow anaerobic immobilised biomass (HAIB) reactor. Experiments were carried out with synthetic substrate containing glucose, ammonium acetate and methanol, besides sodium bicarbonate. Micronutrients were provided by adding salts and trace metals from a stock solution. The influent chemical oxygen demand (COD) was maintained as constant as possible around 2 000 mg·l^-1 in all the experiments. The reactors were subjected to increasing sulphate concentrations from 100 to 2 800 mg·l^-1. First-order apparent kinetic parameters (K1 ^{a pp} ) decreased from 1.96 x 10^-4 to 1.55 x 10^-4l·mg VSS^-1·h^-1 as the COD to sulphate ratio decreased from 22.6 to 0.8. The progressive but moderate inhibition of the organic matter conversion observed indicates that high sulphate concentrations can be accommodated in HAIB reactors even at very low COD to sulphate ratios.

Application of genetic algorithms - Determination of the optimal pipe diameters

Van Vuuren, S.J.

Abstract: The past decade has marked the development of computational capacity that far exceeds the capacity of the "instructor" to define options to be evaluated when optimisation has to be achieved. In the context of water supply, there are numerous variables that can influence the selection and, hence, the final cost of system implementation, improvement and operation. This article reflects some of the findings of a research project, funded by the Water Research Commission of South Africa to establish the potential use of GAs in the water industry in South Africa. A utility program (GAPOP) was developed to demonstrate the application of GAs in the determination of the optimal pipe diameter.

Faecal indicator organisms in the Renoster Spruit system of the Modder-Riet River catchment and implications for human users of the water

Griesel, M.; Jagals, P.

Abstract: The impact of a variety of urban discharges from Bloemfontein on the numbers of microbiological faecal indicator organisms in the water of the Renoster Spruit subcatchment was investigated using E. coli, C. perfringens and somatic coliphages as microbial indicators. The no-observed-adverse-effect-levels for the occurrence of these organisms in water intended for domestic purposes, for full-body contact recreation as well as irrigation of crops that may be eaten raw, were exceeded. The results indicated that the faecally polluted urban runoff, in combination with inadequately treated wastewater effluents, overcame the assimilation capacity of the Renoster Spruit in the immediate vicinity of the city to such an extent that it posed a possible risk of infection to potential water users for considerable distances downstream from the urban area. The high levels of faecal indicators in the Renoster Spruit diminished to such an extent downstream that the receiving Modder River, directly downstream from the confluence with the Renoster Spruit, posed an infection risk for domestic users only but not for recreational users of the water. Water at this point could also be used to irrigate crops eaten raw.

The effect of irrigation uniformity on irrigation water requirements

Ascough, G.W.; Kiker, G.A.

Abstract: Irrigated agriculture is the largest user of water in South Africa. Due to the limited amount of water resources, the efficient and equitable use of water is of paramount importance. This can only be achieved through effective design, maintenance and management of irrigation systems. The uniformity with which an irrigation system applies water has an affect on the efficiency of the system. The uniformity of an irrigation system needs to be high to ensure that the majority of the crop receives an adequate amount of water. This is needed for fields to produce high yields and to have minimal nutrient loss due to deep percolation. The uniformity of application also plays an important role in determining water allocations and the gross amount of irrigation water to apply. The concept of uniformity and calculation thereof are presented in this paper. Results of research of the application uniformity of different irrigation systems in the sugar industry in five sugar-growing regions in South Africa will be discussed in this paper. From this study the average low-quarter distribution uniformity (DU_lq) of centre pivot, dragline, micro-irrigation, floppy and semi-permanent sprinkler systems was 81.4%, 60.9%, 72.7%, 67.4%, and 56.9% respectively. The percentage of systems that had an excellent field condition DU_lq was 100% for centre pivot, 15.4% for dragline, 30% for micro-irrigation, 0% for floppy, and 14.3% for semi-permanent sprinkler systems. Only three floppy irrigation systems were evaluated during this study, therefore the result for the percentage of systems with an excellent DU_lq may not be representative of these systems in general. Irrigation systems that were well maintained and correctly operated generally had a high and acceptable DU_lq. The average application efficiencies (AE) were 83.6% for centre pivot, 73.5% for dragline, 76.7% for floppy, and 78.9% for semi-permanent sprinkler systems.