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End date: 1999Subject: search.filters.subject.Sewage

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    Identification of polyphosphate accumulating bacteria from pilot- and full scale nutrient removal activated sludges
    (1999) Atkinson, Blaise William; Bux, Faizal
    General removal of phosphorus (P) from wastewater was introduced in Scandanavia in the late 1960's. At that time it was believed that P alone was limiting to algal growth and that the sole removal of P would solve the problem of eutrophication. However, we now know that both P and nitrogen (N) contribute to this deleterious effect and as such, much research has been conducted concerned with both the biological and chemical removal of these nutrients from sewage effluents. Enhanced biological phosphorus removal (EBPR), which is basically the biological accumulation of soluble P (as polyphosphate or poly-P) from the bulk liquid in excess of normal metabolic requirements, still tends to be sensitive to many external parameters and, as such, is subject to fluctuations. This makes it extremely difficult for wastewater treatment installations to achieve and maintain full compliance with strict discharge regulations. A more comprehensive understanding of the microbial community within the mixed liquor of a wastewater treatment system is therefore required which will ultimately assist in improving system design and performance. Chemical and civil engineers, when designing biological wastewater treatment systems, consider only the processes (biological or chemical) taking place within the reactor/s with little or no regard for the individual microbial species or the entire microbial community involved. Process design appears to be tackled empirically from a 'black box' approach; biological reactions or processes occurring within a system such as wastewater treatment are all lumped together and attributed to a single surrogate organism ie., the response of the surrogate to certain stimuli accounts for the total system response. This is similar to an analogy which Professor George Ekama (Dept of Civil Engineering, UCT), a leading scientist in wastewater treatment and process design, refers to where engineers, if, for example, are confronted with modelling the dynamics of carbon dioxide utilisation ofa forest, would recognise the accumulative system response and not give cognisance to each individual tree's contribution. It is true that if one had to consider every microbial species present in a highly organised community such as activated sludge, process models, designed to make quantitative and qualitative predictions as to the expected effluent quality from a particular design, would become increasingly complex and superfluous. It is evident from the countless accomplishments that engineers have succeeded, to a certain degree, in modelling wastewater treatment systems. One only has to consider the tremendous success of biological P (bio-P) removal and nitrification/denitrification processes at full-scale. However, there are limitations to this empirical approach and EBPR processes occasionally deteriorate in phosphate removal efficiency. In order to further optimise biological processes, whether they be organics oxidation, bio-P removal, nitrification or denitrification, biological community analyses will have to play a more significant role in design. The better microbial community structure and function is understood, the better the control and management of the system. With the advent of improved microbial identification and enumeration (to a certain extent) techniques (in situ), it was considered significant to investigate the mechanism ofbio-P removal and to elucidate which bacteria are actively responsible for this process. To this end, experimental work was conducted in two phases: \xAE laboratory, where samples of mixed liquor were obtained from a full-scale wastewater treatment facility exhibiting biological nutrient removal (BNR) characteristics and @ pilot plant, where an enhanced culture ofpolyphosphate accumulating organisms (PAO's) was developed and probed using molecular identification and enumeration techniques (as well as a cultivation-dependent approach). During phase \xAE of experimentat
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    Extraction, characterisation and metal biosorption of extracellular polysaccharides from activated sludge
    (1998) Zondo, Raynold Mduduzi; Swalaha, Feroz Mahomed
    Waste activated sludge is a biological adsorbent whose potential to remove metals from solution and effluent has been demonstrated. Extracellular polysaccharides (EPS) as components of activated sludge are thought to contribute to activated sludge metal biosorption. During the present study characterisation and determination of the metal biosorptive capabilities of domestic and industrial extracellular polysaccharides (EPS) revealed similarities both in terms of chemical composition and metal adsorption potential. Extracellular polysaccharides were extracted from activated sludge, obtained from domestic and industrial sludge treatment plants, using chemical techniques which involved sodium hydroxide extraction and solvent precipitation. A purification technique, which involved precipitation of protein with chloroform and removal of nucleic acids was developed. To assess the efficiency of the purification method, the ratio of extracted polysaccharide to the amount of protein present was determined. This provided an indication of the magnitude of EPS extracted in relation to the degree of cellular disruption. The type of activated sludge being treated was shown to be of particular importance. The quantity of EPS present in the original sample was found to be higher in domestic sludge than in industrial sludge. Purified EPS was fractionated in a column of DEAE-Sepharose CL-6B using stepwise pH gradient elution. Molecular weight distribution was conducted on a column of Sepharose CL-4B. Component monosaccharides were identified by paper chromatography. Monomers identified were glucose, fructose, glucuronic acid and galactosamine. Ion-exchange chromatography results demonstrated the presence of a number of different polysaccharide fractions while gel filtration results indicated a wide molecular weight distribution range of EPS from both domestic and industrial activated sludge. This indicated potential for variety in the EPS content of the activated sludge. Metal adsorption studies were conducted to determine the capabilities of EPS to adsorb metals
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    Evaluation of anaerobic sludges as metal biosorbents and development of a biotechnological process for metal ion removal from selected wastewater
    (1997) Bux, Faizal; Kasan, Hamanth C.
    As a result of rapid expansion of the industrial sector and increasing population, the environment has been under phenomenal stress. The volume of sewage and other effluents has increased tremendously in the last century. Globally, approximately .12 million tonnes of dry sludge biomass is produced and discarded of by landspreading, landfilling, incineration or dumping in lagoons and oceans. The discharge of industrial effluents into receiving waters has been documented to be the cause of severe environmental contamination. Heavy metals have been the cause of particular environmental concern. Their toxic and carcinogenic potentials at low concentrations, as well as the large quantities disposed to the environment, have prioritised them as leading contaminants. Current technologies of remediating heavy metal containing effluents are expensive and, in most cases, ineffective. Locally, most industries are merely diluting their effluents, thus resulting in the loss of valuable water resources. Waste sludges have shown the ability to adsorb heavy metals from their aqueous environment. Therefore, the current study attempted firstly, to compare biosorptive capacities of various waste sludges for a range of heavy metal ions, and secondly, to establish a relationship, if any, between biosorptive capacity and sludge surface charge. Finally, a laboratory scale biosorption process, encompassing desorption and recovery of metal ions from sludge surfaces, would have to be developed. Effluents used included pure, metal solutions of divalent zinc, cadmium, copper, nickel, trivalent and hexavalent chromium. In addition, synthetic effluents comprising a cocktail of the above-mentioned metal ions as well as an industrial effluent from a metal plating company were used. Five waste digested sludges were prepared and challenged against pure metal solutions to determine and compare their respective biosorptive capacities. Mechanisms of biosorption were elucidated using the Langmuir adsorption isotherm model. Sludge surface charge was determined using the millivolt quantification method. Upscaling of bioreactor trials to fully mixed laboratory scale was also investigated. These experiments encompassed the use of three sludges showing the greatest potential for biosorption and desorption using the selected mineral acid, H2S04, In addition, a simultaneous fully mixed biosorption and desorption process was designed and optimised. Subsequent trials involved comparing the latter process with a packed bed configuration whereby biomass was immobilised using poly sulfone resin. The overall comparative adsorptive capacities of the sludges (SI-SS) for metal ions in single solutions was S3 > S2 > S4 > SS > SI. Surface charge determination showed S3 to contain the most electronegative charge, with other sludges following in the same descending order as mentioned above. These findings supported the theory of a direct correlation between sludge surface charge and biosorptive potential. The affinity series of the sludges for metal ions followed the descending order of Cd2+ > Cu2+ > Ni2+ > Zn2+ > Cr6+ > Cr3+. Fully mixed studies, using mixed synthetic effluents, resulted in lower biosorptive capacities being recorded by the three selected sludges ie., S2, S3 and S4, as compared to single solution experiments. Biosorption studies with industrial effluent, containing Zn2+ as the most prevalent metal at 119.4 mg.F'. resulted in S3 biosorbing a maximum of 4.5 mg.g' of the cation. Sulphuric acid (H2S04) at O.2N, hydrochloric acid (HCI) at O.2N and acetic acid (CH3COOH) at O.4N were tested for their desorptive efficiencies. Sulphuric acid proved to be the most effective desorbing agent. Using S3 as biosorbent and O.2N H2S04 as desorbent, the manipulation and operation of a simultaneous process proved to be successful since both biosorption and desorption occurred concurrently, thus reducing time required for successful remediation considerably. Immobilised biomass, in a packed bed configuration, produced acceptable final effluent regarding standards as stipulated by the Durban Municipality for trade effluents. However, biosorption capacity of the sludge was compromised, with subsequent reductions in desorption being recorded, when the process was compared to fully mixed trials. Affinity series determined for the packed bed process wasC~+ >Cd2+>Zn2+>Cu2+>Cr6+ >Ni2+. Waste digested sludge has shown potential as metal biosorbent on an industrial scale. The present findings have succeeded in demonstrating a novel laboratory scale biotechnological process for the remediation of metal laden industrial effluents.