African Journals Online
WaterSA

Volume 28, Issue 1, 2002
ABSTRACTS

A preliminary analysis of water chemistry of the Mkuze Wetland System, KwaZulu-Natal: a mass balance approach

Barnes, K.; Ellery, W.; Kindness, A.

Abstract: The Mkuze Wetland System in northern KwaZulu-Natal constitutes an important source of freshwater to Lake St Lucia. The St Lucia System, including both the Mkuze Wetland System and Lake St Lucia, is recognised as a Wetland of International Importance under the Ramsar Convention. The long-term survival of Lake St Lucia depends on an adequate supply of freshwater. Consequently, the role of the Mkuze Wetland System in water quality enhancement is essential. In order to investigate the water chemistry of this system, water samples were collected throughout the study area from surface water, groundwater, pan and reed swamp sites, as well as a rainwater sample. These were analysed for chloride, sodium, potassium, calcium, magnesium, iron and silicon. Four main water bodies were identified using the multivariate techniques, classification and ordination. Of these four groups, two represented the major water sources to the system, these being the Mkuze River and floodplain and the Mbazwane System. The third represented outflow into Lake St Lucia, while the fourth represented scattered ground and surface water samples some distance away from the main watercourses. The solute concentrations of the two water sources were compared using a mass-balance approach. Chloride was identified as a conserved solute and the increasing chloride concentration from the less concentrated inflows (especially the Mbazwane System) to the concentrated outflow into Lake St Lucia, is considered to reflect evapotranspiration. By considering chloride to be conserved, the degree of evaporative enrichment was estimated in the Mkuze Wetland System and used to determine the percentage of solutes retained in the swamp. The wetland was found to be an important sink for calcium (~50% retention), potassium (~70% retention) and silicon (~80% retention), with magnesium and sodium being retained to a lesser extent. The TDS value supports these findings as it is lower than expected in the outflow by a similar percentage to the magnesium and sodium retention. The removal of solutes by the Mkuze Wetland System, not only has far-reaching implications for Lake St Lucia in maintaining a freshwater supply, but could also have significant impacts on the ecology and geomorphology of the Mkuze System itself. The fate of solutes and the processes of solute retention are subjects of ongoing research.

Efficiency of the SASS4 rapid bioassessment protocol in determining river health: a case study on the Mhlathuze River, KwaZulu-Natal, South Africa

Vos, P.; Wepener, V.; Cyrus, D.P.

Abstract: The purpose of the study was to verify the ability of the South African Scoring System version 4 (SASS4), to assess the health of aquatic ecosystems. The macroinvertebrate community attributes of the Mhlathuze River (KwaZulu-Natal, South Africa) were studied by applying the SASS4 rapid bioassessment method. In testing the effect of spatial and temporal variability in community structure on SASS4 scores it was found that there was a stronger spatial than a temporal effect. It was determined that of the indices used in association with SASS4, the biotic indices (average score per taxon, total score and number of taxa) reflected changes in community structure, but the abiotic habitat quality index did not. It was found that qualitative family-level data provided an adequate classification of sites for use in routine biomonitoring. Ambiguous results were obtained with respect to the importance of measuring abundance during routine biomonitoring. No definite conclusion with respect to the ability of the SASS4 to reflect physical-chemical water quality changes could be drawn from the results obtained in this study. SASS4 was able to reflect the effect of the tidal push from the Mhlathuze Estuary, but this marine influence probably masked less pronounced effects exerted by the remainder of the physical-chemical variables that were investigated.

Valuing water gains in the Eastern Cape's Working for Water Programme

Hosking, S.G.; Du Preez, M.

Abstract: Water is one of the most important measured benefits of the Working for Water Programme (WWP). This programme entails the removal of high water-consuming alien vegetation and the restoration of low water-consuming indigenous vegetation. For this reason it is crucial that the pricing of this water be an accurate reflection of its relative scarcity. This paper sheds more light on this aspect. A procedure for pricing water is described and applied in six WWP projects in the Eastern Cape province: Tsitsikamma, Kouga, Port Elizabeth Driftsands, Albany, Balfour and Pott River. It is shown that the procedure yields very different prices at the different sites, and higher prices for projects that increase river flows feeding metropolitan demand.

Biolog for the determination of diversity in microbial communities

Van Heerden, J.; Korf, C.; Ehlers, M.M.; Cloete, T.E.

Abstract: Diversity and dynamics of microbial communities have been analysed by culture-dependent methods, which exclude the majority of fastidious microbes due to the selective nature of the media. Molecular methods have been used to determine diversity of microbial communities, but indicate the genetic complexity within a community. An alternative approach is to examine components of functional biodiversity (i.e. substrate utilisation), for which there exists a reasonable chance of detecting patterns, which could be related to the functional diversity of the species present in the community. In this study, different carbon source profiles were generated by inoculating Biolog GN and GP microtitre plates, with different dilutions of microbial communities. The high number of substrates utilised at the lower dilutions (10^-1 and 10^-2) indicated a high functional diversity in the communities tested. This, however, did not necessarily reflect the evenness of the functionality. Functional evenness of each species was reflected upon further dilution. Our results indicated differences in the functional diversity of the microbial communities amongst some of the natural environments studied. The results indicated that evenness and dominance can be demonstrated by mixtures of cultures as well as in natural environments.

The separation and simultaneous determination of V(IV) and V(V) species complexed with EDTA by IC-ICP-OES

Coetzee, P.P.; Fischer, J.L.; Hu, Mingsong

Abstract: A method for the separation of V(IV) and V(V) in the form of the EDTA complexes using anion chromatography with a Dionex AG5 anion exchange guard column, and the simultaneous determination of V(IV) and V(V) by inductively coupled plasma optical emission spectrometery is described. The interference from other elements is negligible. The detection limits of V(IV) and V(V) were 0.02 mg/l and 0.05 mg/l, respectively, using a glass nebuliser and 2 ?g/l for both species by using an ultrasonic nebuliser. The linear range was two orders of magnitude. The method was applied to the analysis of spiked water and industrial samples containing V in different oxidation states.

The influence of chloride and sulphate ions on the slaking rate of lime derived from different limestone deposits in South Africa

Gheevarhese, O.; Strydom, C.A.; Potgieter, J.H.; Potgieter, S.S.

Abstract: This paper describes an investigation into the influence of chloride and sulphate ions on the slaking of lime prepared from limestones of different geological origin in South Africa. It was endeavoured to assess the effects of the presence of chloride and sulphate ions on the hydration rate of lime, compared to its slaking in pure water. It was found that the rate of hydration is slightly retarded in the presence of a high concentration of chloride ions, while sulphate ions retard the slaking of lime significantly. This investigation indicated that impurities present in the original limestone, as well as those commonly found in water used for slaking purposes, may exert an influence on the hydration behaviour of lime.

Development of a method to enhance granulation in a laboratory batch system            49

Britz, T.J.; Van Schalkwyk, C.; Roos, P.

Abstract: The success and efficiency of the UASB process are dependent on the formation of active granular biomass and since this is a slow process, one of the main problems in the application of the technology remains the long start-up periods. Batch cultures with lactate, glucose or sucrose as substrate, were seeded with anaerobic sludge and incubated in shake waterbaths over a period of 14 d. For all substrates, a drop in pH within the first 2 d was experienced. In the glucose and sucrose units the pH dropped to 6.0 and to below 5.5, respectively within the first 24 h. Thereafter, a continual drop was experienced, eventually resulting in system acidification. With the lactate units, the pH dropped to 6.5 by Day 2, with a subsequent climb until the pH stabilised at around 6.7 to 6.9. The volatile fatty acid (VFA) profiles of all the units showed an increase of acetic and propionic acids, with the latter at the highest concentration during the first 5 d, corresponding to the decrease in pH. An increase in granulation was observed for the glucose (354%) and lactate (559%) units, but no granulation increase was found for the sucrose units. The increase in granule formation indicated that granulation may be enhanced in batch systems over a shorter period and that the granulation process is facilitated by a rapid drop in pH at the start, resulting from the major increase in propionic and acetic acids, followed by a subsequent increase and stabilisation in pH, and an increase followed by a steady decrease in propionic and acetic acid concentrations until the formation stabilised.

Analysis of key variables controlling phosphorus removal in high rate oxidation ponds provided with clarifiers

García, Joan; Hernández-Mariné, Mariona; Mujeriego, Rafael

Abstract: This study evaluates the influence of hydraulic retention time (HRT), solar radiation, and water temperature on phosphorus removal from two experimental high rate oxidation ponds (HROP) with clarifiers. Both HROPs were operated for a period of one year with different HRTs (3 to 10 d), but under the same environmental conditions. Phosphorus species, phytoplankton biomass, solar cumulative radiation, water temperature and pH were measured once a week. Average total phosphorus removal (TP) was higher in the HROP operated with a higher HRT (43%) than in that using a lower HRT (32%). TP removal was due to dissolved reactive phosphorus (DRP) removal in the mixed liquor of the HROPs and transformation of DRP into particulate phosphorus (PP), with subsequent sedimentation of PP in the clarifiers. The influence of HRT on TP removal was due mainly to its control over DRP removal, which was observed to be more important in autumn and winter. The lowering of solar radiation and temperature in autumn and winter and their influence on DRP removal can barely be compensated by HRT to obtain a significant TP removal. This work indicates that DRP transformation into PP depends mainly on environmental factors through their mediated influence on pH and chemical precipitation.

Start-up of a UASB effluent treatment plant on distillery wastewater

Wolmarans, Bileen; De Villiers, Gideon H.

Abstract: Distillery effluent is a contaminated stream with COD values of up to 30 000 mg/l and low pH values of between 3 and 4. The anaerobic biological treatment of distillery effluents is widely applied as an effective step in removing more than 90% of the COD in the effluent stream. This paper reports on the seasonal operation of a UASB treatment plant treating a distillery wastewater stream with particular focus on seasonal start-up conditions after the first process commissioning. The start-up period was typically one week before process stability could be achieved. It is recommended that the loading rate to the plant be controlled between 4 and 8 kg COD/m³·d until the process is stable and COD removal efficiencies remain, on average, higher than 90%. After the start-up period the loading rate applied (4 to 18 kg COD/m³d) did not significantly affect the COD removal efficiency of the plant. High removal efficiencies of higher than 90% were achieved and stop-start operation of the UASB process posed no problem for treatment.

Cationic polymers in water treatment: Part 1: Treatability of water with cationic polymers

Polasek, P.; Mutl, S.

Abstract: This paper investigates the best attainable treatability to which a water polluted with a technologically significant concentration of organic matter is treatable by different cation-active polyelectrolytes and their blends with mineral coagulants in comparison to that attainable by traditional hydrolysing coagulants. The negative influence of these reagents used as primary coagulants on the treated water quality is demonstrated in the case of Saulspoort Waterworks.

Cationic polymers in water treatment: Part 2: Filterability of CPE-formed suspension

Polasek, P.; Mutl, S.

Abstract: Part 2 of the paper compares filterability of CPE-formed and mineral coagulant-formed suspensions.

Fermentation of a low VFA wastewater in an activated primary tank

Barajas, Maria Guadalupe; Escalas, Antoni; Mujeriego, Rafael

Abstract: A low volatile fatty acid wastewater from a Barcelona residential area was prefermented in a laboratory-scale primary clarifier operated as a prefermenter -an activated primary tank. Total suspended solids (TSS), oxidation-reduction potential (ORP) and temperature were measured in the prefermenter. Influent and effluent were characterised through chemical oxygen demand (COD), soluble COD, volatile fatty acids (VFA), VFA potential, soluble PO₄-P, NH₄-N, pH and alkalinity. Solids retention times (SRT) of 5 d and 10 d were tested. Best results were obtained for the 5 d SRT with the prefermenter covered for better temperature and ORP control. For these conditions, COD solubilisation was measured as 22 mg COD/l, 66 mg COD/g influent particulate COD, or 91 mg COD/g influent VSS. VFA-formation was measured as 34 mg VFA-COD/l, 142 mg VFA-COD/g influent VSS, or 77 mg VFA-COD/g influent COD. These values indicate remarkable solubilisation and fermentation in the prefermenter. The VFA/PO₄-P ratio was improved from 0.9 to 5.5 mg VFA-COD/mg PO₄-P, but did not approach the recommended value for biological P removal (20 mg/mg). VFA production could not reach the influent VFA-potential either (110 mg VFA-COD/l) and VFA-potential was lower in effluent than in influent. With a 5 d SRT and the prefermenter uncovered, a small VFA formation and no solubilisation were observed. This was interpreted as the VFA being formed from the influent soluble COD. With a 10 d SRT, a very low ORP was measured. Neither solubilisation nor VFA production were detected in the prefermenter. Concurrent acidogenic fermentation and methanogenesis are compatible with these results. P and N solubilisation was low or moderate in the prefermenter over all periods, and increased with increasing SRT and TSS, and decreasing ORP, and pH and alkalinity were quite stable, due to the high influent alkalinity and the moderate VFA formation and N solubilisation.

Characterisation and concentration profile of aluminium during drinking-water treatment

Srinivasan, P.T.; Viraraghavan, T.

Abstract: An aluminium(Al) characterisation study was conducted at a surface water treatment plant (Buffalo Pound Water Treatment Plant (BPWTP) in Moose Jaw, Saskatchewan, Canada) to understand better the effect of alum coagulant on various Al fractions. The raw water source for BPWTP is Buffalo Pound Lake water. The Al sources at BPWTP are: • present naturally Al in the raw water and • Al derived due to use of alum as a coagulant. Seasonal evaluations of Al at BPWTP showed that raw lake water total concentrations were highly variable. Suspended (filterable) Al was the predominant species of raw water total Al. Organic-bound or organo-Al complex Al appeared to be the predominant species of dissolved Al in both raw and treated water during the September to November 1997 Al characterisation study. However, during October to December 1998, inorganic Al dominated dissolved Al content. Characterisation of Al at BPWTP showed that the use of (liquid) Al sulphate (alum) did not increase the concentration of total Al levels. This was because: • alum coagulation was practised at pH 7, at which the Al is least soluble • clarifier and filtration units effectively removed particulate Al and • granular activated carbon (GAC) was capable of removing part of the organic dissolved Al. The study showed that BPWTP would be able to comply with the requirement of Health Canada Guideline value (for conventional treatment plants) for Al of less than 100 ?g/ l as total Al. Turbidity and dissolved organic carbon of the raw water influenced the applied alum dose at BPWTP.

Influence of diethyldithiocarbamate on cadmium and copper toxicity to freshwater macrophyte Spirodela polyrhiza: short communication

Saadi, A.; Guerbet, M.; Garnier, J.

Abstract: Toxic effects of two heavy metals, cadmium (Cd) and copper (Cu), and a fungicide, diethyldithiocarbamate, have been evaluated, alone and in association, on Spirodela polyrhiza duckweed cultivated in a synthetic mineral medium and in a distilled water medium. The composition of the culture medium influenced the toxicity of the three compounds and the effects of their associations were clearly shown in the distilled water medium. Copper has an antagonistic effect on Cd and reduced its absorption by duckweed. On the other hand, Cd in the culture medium increased Cu absorption. The most significant effect was observed with diethyldithiocarbamate simultaneously associated with Cu and Cd. The diethyldithiocarbamate association largely inhibited the absorption of Cd and Cu by duckweed and so appeared to have a complexant effect that reduced the toxicity of these two metals.

Modelling of a recycling sludge bed reactor using AQUASIM: reprint

Ristow, N.E.; Whittington-Jones, K.; Corbett, C.; Rose, P.; Hansford, G.S.

Abstract: The recycling sludge bed reactor (RSBR) allows for increased solids retention time, resulting in greater substrate conversion for all particulate degradation and biological reactions. The purpose of the RSBR 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 RSBR. The hydrodynamic processes taking place in the RSBR 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 RSBR, 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.