A practical course on filter assessment for water treatment plant operators
- Van Staden, S.J., Haarhoff, J.
- Authors: Van Staden, S.J. , Haarhoff, J.
- Date: 2011
- Subjects: Water - Purification - Membrane filtration , Water treatment plants , Plant operators, Training of
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/17261 , uj:15863 , Van Staden, S.J. & Haarhoff, J. (2011) A practical course on filter assessment for water treatment plant operators. In: Proceedings of the 2nd Young Water Professionals of Southern Africa Conference, Pretoria, South Africa, 4-5 July 2011, 5 p.
- Description: Abstract Training of treatment plant operators in South Africa faces some special problems. First, the political changes in the past decade led to a complete restructuring of local government. An integral part of the ongoing restructuring process is an aggressive programme for black economic empowerment. This brought many new faces into local government without the practical experience to which the water industry is accustomed, coupled with a massive displacement of technical skills from the sector. From 1989, the number of civil engineering professionals (engineers, technologists, technicians) has dwindled from 22 / 100000 of the population to 3 / 100000 of the population in 2007 (Lawless, 2007). Second, the Water Services Act (1997) of South Africa shifted the burden of water supply squarely on the shoulders of district and local municipalities. The dilution of skills, coupled with increasing responsibility, makes it clear that the water sector in South Africa will have to train itself out of this predicament. As a result, the quality and focus of training programmes, especially at the operator level, is receiving renewed attention. This paper shares the experience of the development and refinement of a training course for filter assessment for operators over the past eight years.
- Full Text:
- Authors: Van Staden, S.J. , Haarhoff, J.
- Date: 2011
- Subjects: Water - Purification - Membrane filtration , Water treatment plants , Plant operators, Training of
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/17261 , uj:15863 , Van Staden, S.J. & Haarhoff, J. (2011) A practical course on filter assessment for water treatment plant operators. In: Proceedings of the 2nd Young Water Professionals of Southern Africa Conference, Pretoria, South Africa, 4-5 July 2011, 5 p.
- Description: Abstract Training of treatment plant operators in South Africa faces some special problems. First, the political changes in the past decade led to a complete restructuring of local government. An integral part of the ongoing restructuring process is an aggressive programme for black economic empowerment. This brought many new faces into local government without the practical experience to which the water industry is accustomed, coupled with a massive displacement of technical skills from the sector. From 1989, the number of civil engineering professionals (engineers, technologists, technicians) has dwindled from 22 / 100000 of the population to 3 / 100000 of the population in 2007 (Lawless, 2007). Second, the Water Services Act (1997) of South Africa shifted the burden of water supply squarely on the shoulders of district and local municipalities. The dilution of skills, coupled with increasing responsibility, makes it clear that the water sector in South Africa will have to train itself out of this predicament. As a result, the quality and focus of training programmes, especially at the operator level, is receiving renewed attention. This paper shares the experience of the development and refinement of a training course for filter assessment for operators over the past eight years.
- Full Text:
Assessments and improvement of filter media cleanliness in rapid gravity sand filters
- Haarhoff, J., Van Staden, S.J., Gendenhuys, J., Sibiya, M., Naicker, P., Adam, N.
- Authors: Haarhoff, J. , Van Staden, S.J. , Gendenhuys, J. , Sibiya, M. , Naicker, P. , Adam, N.
- Date: 2008
- Subjects: Water treatment filters , Rapid sand filtration , Cleanliness
- Language: English
- Type: Report
- Identifier: http://hdl.handle.net/10210/16810 , uj:15809 , Citation: Haarhoff, J. et al. 2008. Assessments and Improvement of Filter Media Cleanliness in Rapid Gravity Sand Filters. Report 1525/1/08 to the Water Research Commission, ISBN 978 1 77005 734 0.
- Description: Introduction: Rapid sand filtration is an essential unit process in the water purification process. It captures and removes coagulated and flocculated material and other suspended matter not removed during the preceding treatment processes. The pores in the filter bed gradually become clogged and the media progressively collects deposit through the continuous use and life of the filter. During normal operations cleaning is initiated by excessive head loss, deterioration in filtrate quality or when the predetermined time for a filter run has elapsed. Air scour, to remove deposit from filter media by vigorous agitation, and wash water, to remove this deposit from the filter bed, are applied. The combined action of air and water should quickly return the media to its original perfectly clean state for the cycle to continue. However, on inspection it is often found that filter sand on purification plants is unacceptably dirty and backwash systems are clearly incapable of cleaning the media to its initial state of cleanliness. It is at times possible to relate the dirty filter media to faulty designs or poor operating procedures, but often the reasons for the media deterioration remain elusive and the media becomes dirtier the longer it is in use. As there was an almost complete lack of published or agreed upon procedures to measure the cleanliness of filter media, rudimentary methods for measuring filter media cleanliness and backwash efficiency were developed. Thereafter filter media from full-scale treatment plants was analyzed with these methods at regular intervals to establish some benchmarks for these determinants. These methods were also applied during the laboratory and pilot plant phases of the project.
- Full Text:
- Authors: Haarhoff, J. , Van Staden, S.J. , Gendenhuys, J. , Sibiya, M. , Naicker, P. , Adam, N.
- Date: 2008
- Subjects: Water treatment filters , Rapid sand filtration , Cleanliness
- Language: English
- Type: Report
- Identifier: http://hdl.handle.net/10210/16810 , uj:15809 , Citation: Haarhoff, J. et al. 2008. Assessments and Improvement of Filter Media Cleanliness in Rapid Gravity Sand Filters. Report 1525/1/08 to the Water Research Commission, ISBN 978 1 77005 734 0.
- Description: Introduction: Rapid sand filtration is an essential unit process in the water purification process. It captures and removes coagulated and flocculated material and other suspended matter not removed during the preceding treatment processes. The pores in the filter bed gradually become clogged and the media progressively collects deposit through the continuous use and life of the filter. During normal operations cleaning is initiated by excessive head loss, deterioration in filtrate quality or when the predetermined time for a filter run has elapsed. Air scour, to remove deposit from filter media by vigorous agitation, and wash water, to remove this deposit from the filter bed, are applied. The combined action of air and water should quickly return the media to its original perfectly clean state for the cycle to continue. However, on inspection it is often found that filter sand on purification plants is unacceptably dirty and backwash systems are clearly incapable of cleaning the media to its initial state of cleanliness. It is at times possible to relate the dirty filter media to faulty designs or poor operating procedures, but often the reasons for the media deterioration remain elusive and the media becomes dirtier the longer it is in use. As there was an almost complete lack of published or agreed upon procedures to measure the cleanliness of filter media, rudimentary methods for measuring filter media cleanliness and backwash efficiency were developed. Thereafter filter media from full-scale treatment plants was analyzed with these methods at regular intervals to establish some benchmarks for these determinants. These methods were also applied during the laboratory and pilot plant phases of the project.
- Full Text:
Comparative study for the removal of natural organic matter from different raw waters by ion exchange
- Lobanga, K.P., Haarhoff, J., Mamba, B.B., Van Staden, S.J.
- Authors: Lobanga, K.P. , Haarhoff, J. , Mamba, B.B. , Van Staden, S.J.
- Date: 2011
- Subjects: Water - Purification - Adsorption , Organic water pollutants , Carbon, Activated , Water - Purification - Organic compounds removal
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/16647 , uj:15793 , Lobanga, K.P. et al.(2011) Comparitive study for the removal of natural organic matter from different raw waters by ion exchange. In: Proceedings of the 4th IWA Specialty Conference on NOM: From Source to Tap and Beyond, held in Costa Mesa, USA. 27-29 July 2011, 9 p.
- Description: Abstract South African water treatment plants mainly utilise surface water sources whose quality is continuously compromised due to indirect reuse and high return flows. In general the methods used by these water treatment plants are based on the removal of turbidity, various chemical contaminants and microorganisms. Recently introduced NOM regulations added the removal of natural organic matter (NOM) as a priority. Basic anion exchange resins are one way of NOM removal, reported on this paper. Due to the variability in the composition of NOM in natural raw water, eight natural raw waters were collected throughout South Africa as representative of the different water types of the country. They were collected three times during a period of eight months. The strong and weak – base anion resins used in the study were chosen for their availability and competitive price at the local market. The removal of the NOM fractions was assessed by measuring ultraviolet absorption at a wavelength of 254 nm (UV254). Freundlich equilibrium isotherms were fitted. It was observed that the Freundlich parameters K and n are related reducing the Freundlich isotherm to a single-parameter model. The two parameters cluster for some waters regardless of season. Two performance indicators, namely 65% initial UV254 removal and absolute level of 6 /m, were adopted. It was found that if the initial UV254 is less than about 15 /m the absolute level of 6 /m is reached first while when the initial UV254 is greater than 20 /m the removal of 65% of UV254 is reached first. It was also observed that the resin usage rate is not only dependent on the initial UV254 value but also on the nature and concentration of the NOM, indicating a need for a better NOM characterization.
- Full Text: false
- Authors: Lobanga, K.P. , Haarhoff, J. , Mamba, B.B. , Van Staden, S.J.
- Date: 2011
- Subjects: Water - Purification - Adsorption , Organic water pollutants , Carbon, Activated , Water - Purification - Organic compounds removal
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/16647 , uj:15793 , Lobanga, K.P. et al.(2011) Comparitive study for the removal of natural organic matter from different raw waters by ion exchange. In: Proceedings of the 4th IWA Specialty Conference on NOM: From Source to Tap and Beyond, held in Costa Mesa, USA. 27-29 July 2011, 9 p.
- Description: Abstract South African water treatment plants mainly utilise surface water sources whose quality is continuously compromised due to indirect reuse and high return flows. In general the methods used by these water treatment plants are based on the removal of turbidity, various chemical contaminants and microorganisms. Recently introduced NOM regulations added the removal of natural organic matter (NOM) as a priority. Basic anion exchange resins are one way of NOM removal, reported on this paper. Due to the variability in the composition of NOM in natural raw water, eight natural raw waters were collected throughout South Africa as representative of the different water types of the country. They were collected three times during a period of eight months. The strong and weak – base anion resins used in the study were chosen for their availability and competitive price at the local market. The removal of the NOM fractions was assessed by measuring ultraviolet absorption at a wavelength of 254 nm (UV254). Freundlich equilibrium isotherms were fitted. It was observed that the Freundlich parameters K and n are related reducing the Freundlich isotherm to a single-parameter model. The two parameters cluster for some waters regardless of season. Two performance indicators, namely 65% initial UV254 removal and absolute level of 6 /m, were adopted. It was found that if the initial UV254 is less than about 15 /m the absolute level of 6 /m is reached first while when the initial UV254 is greater than 20 /m the removal of 65% of UV254 is reached first. It was also observed that the resin usage rate is not only dependent on the initial UV254 value but also on the nature and concentration of the NOM, indicating a need for a better NOM characterization.
- Full Text: false
How can filter cleanliness be determined?
- Haarhoff, J., Van Staden, S.J.
- Authors: Haarhoff, J. , Van Staden, S.J.
- Date: 2011
- Subjects: Specific deposit , Filter media , Filter cleanliness
- Type: Article
- Identifier: uj:5310 , ISSN 1474-7065 , http://hdl.handle.net/10210/6800
- Description: It is general believed that a sand filter starts its life with new, perfectly clean media, which becomes gradually clogged with each filtration cycle, eventually getting to a point where either head loss or filtrate quality starts to deteriorate. At this point the backwash cycle is initiated and, through the combined action of air and water, returns the media to its original perfectly clean state. Reality, however, dictates otherwise. Many treatment plants visited a decade or more after commissioning are found to have unacceptably dirty filter sand and backwash systems incapable of returning the filter media to a desired state of cleanliness. In some cases, these problems are common ones encountered in filtration plants but many reasons for media deterioration remain elusive, falling outside of these common problems.The South African conditions of highly eutrophic surface waters at high temperatures, however, exacerbate the problems with dirty filter media. Such conditions often lead to the formation of biofilm in the filter media, which is shown to inhibit the effective backwashing of sand and carbon filters. A systematic investigation into filter media cleanliness was therefore started in 2002, ending in 2005, at the University of Johannesburg (the then Rand Afrikaans University). This involved media from eight South African Water Treatment Plants, varying between sand and sand-anthracite combinations and raw water types from eutrophic through turbid to low-turbidity waters.Five states of cleanliness and four fractions of specific deposit were identified relating to in situ washing, column washing, cylinder inversion and acid-immersion techniques. These were measured and the results compared to acceptable limits for specific deposit, as determined in previous studies, though expressed in kg/m3. These values were used to determine the state of the filters. In order to gain greater insight into the composition of the specific deposits stripped from the media, a four-point characterisation step was introduced for the resultant suspensions based on acid-solubility and volatility.Results showed that a reasonably effective backwash removed a median specific deposit of 0.89 kg/m3. Further washing in a laboratory column removed a median specific deposit of 1.34 kg/m3. Media subjected to a standardised cylinder inversion procedure removed a median specific deposit of 2.41 kg/m3. Immersion in a strong acid removed a median specific deposit of 35.2 kg/m3.The four-point characterisation step showed that the soluble-volatile fraction was consistently small in relation to the other fractions. The organic fraction was quite high at the RG treatment plant and the soluble-non-volatile fraction was particularly high at the BK treatment plant.
- Full Text:
- Authors: Haarhoff, J. , Van Staden, S.J.
- Date: 2011
- Subjects: Specific deposit , Filter media , Filter cleanliness
- Type: Article
- Identifier: uj:5310 , ISSN 1474-7065 , http://hdl.handle.net/10210/6800
- Description: It is general believed that a sand filter starts its life with new, perfectly clean media, which becomes gradually clogged with each filtration cycle, eventually getting to a point where either head loss or filtrate quality starts to deteriorate. At this point the backwash cycle is initiated and, through the combined action of air and water, returns the media to its original perfectly clean state. Reality, however, dictates otherwise. Many treatment plants visited a decade or more after commissioning are found to have unacceptably dirty filter sand and backwash systems incapable of returning the filter media to a desired state of cleanliness. In some cases, these problems are common ones encountered in filtration plants but many reasons for media deterioration remain elusive, falling outside of these common problems.The South African conditions of highly eutrophic surface waters at high temperatures, however, exacerbate the problems with dirty filter media. Such conditions often lead to the formation of biofilm in the filter media, which is shown to inhibit the effective backwashing of sand and carbon filters. A systematic investigation into filter media cleanliness was therefore started in 2002, ending in 2005, at the University of Johannesburg (the then Rand Afrikaans University). This involved media from eight South African Water Treatment Plants, varying between sand and sand-anthracite combinations and raw water types from eutrophic through turbid to low-turbidity waters.Five states of cleanliness and four fractions of specific deposit were identified relating to in situ washing, column washing, cylinder inversion and acid-immersion techniques. These were measured and the results compared to acceptable limits for specific deposit, as determined in previous studies, though expressed in kg/m3. These values were used to determine the state of the filters. In order to gain greater insight into the composition of the specific deposits stripped from the media, a four-point characterisation step was introduced for the resultant suspensions based on acid-solubility and volatility.Results showed that a reasonably effective backwash removed a median specific deposit of 0.89 kg/m3. Further washing in a laboratory column removed a median specific deposit of 1.34 kg/m3. Media subjected to a standardised cylinder inversion procedure removed a median specific deposit of 2.41 kg/m3. Immersion in a strong acid removed a median specific deposit of 35.2 kg/m3.The four-point characterisation step showed that the soluble-volatile fraction was consistently small in relation to the other fractions. The organic fraction was quite high at the RG treatment plant and the soluble-non-volatile fraction was particularly high at the BK treatment plant.
- Full Text:
How to measure specific deposit washout and backwash efficiency of granular filters
- Van Staden, S.J., Haarhoff, J.
- Authors: Van Staden, S.J. , Haarhoff, J.
- Date: 2011
- Subjects: Water - Purification - Membrane filtration , Water treatment plants , Carbon, Activated
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/16971 , uj:15830 , Van Staden, S.J. & Haarhoff, J. (2011) How to measure the specific deposit washout and backwash efficiency of granular filters. Water Practice and Technology 6 (1) DOI:10.2166/WPT. 2011.014.
- Description: Abstract Practical experience shows that water treatment filters develop problems over time due to the routine running of the filter, including backwashing. There are difficulties in maintaining filters in good condition, given the eutrophic state of many South African raw waters, high water temperatures and the development of difficult-to-remove biofilm as a result. Such difficulties are often related to deposits accumulated on the filter media and it is, therefore, expected that the backwash system should be good enough to ensure that the filter is kept clean in the long run. This paper deals with a fairly simple operational option to significantly improve backwash efficiency at treatment plants where air and water are used consecutively. The paper describes methods used and typical results obtained in the testing of the quantitative benefits of multiple wash cycles. Multiple washing shows great promise for improving backwash efficiency, with an average of an additional 40% to 50% of the solids that would have been washed out with a single wash, removed by a second wash. Furthermore, third and even fourth washes continue to remove additional dirt from the filter. Multiple washing, therefore, may be a useful tool for the effective rehabilitation of a filter, as well as for routine operation procedures.
- Full Text:
- Authors: Van Staden, S.J. , Haarhoff, J.
- Date: 2011
- Subjects: Water - Purification - Membrane filtration , Water treatment plants , Carbon, Activated
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/16971 , uj:15830 , Van Staden, S.J. & Haarhoff, J. (2011) How to measure the specific deposit washout and backwash efficiency of granular filters. Water Practice and Technology 6 (1) DOI:10.2166/WPT. 2011.014.
- Description: Abstract Practical experience shows that water treatment filters develop problems over time due to the routine running of the filter, including backwashing. There are difficulties in maintaining filters in good condition, given the eutrophic state of many South African raw waters, high water temperatures and the development of difficult-to-remove biofilm as a result. Such difficulties are often related to deposits accumulated on the filter media and it is, therefore, expected that the backwash system should be good enough to ensure that the filter is kept clean in the long run. This paper deals with a fairly simple operational option to significantly improve backwash efficiency at treatment plants where air and water are used consecutively. The paper describes methods used and typical results obtained in the testing of the quantitative benefits of multiple wash cycles. Multiple washing shows great promise for improving backwash efficiency, with an average of an additional 40% to 50% of the solids that would have been washed out with a single wash, removed by a second wash. Furthermore, third and even fourth washes continue to remove additional dirt from the filter. Multiple washing, therefore, may be a useful tool for the effective rehabilitation of a filter, as well as for routine operation procedures.
- Full Text:
The use of filter media to determine filter cleanliness
- Van Staden, S.J., Haarhoff, J.
- Authors: Van Staden, S.J. , Haarhoff, J.
- Date: 2011
- Subjects: Water treatment plants - Design and construction - Data processing , Water - Purification - Membrane filtration , Water - Purification
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/16727 , uj:15805 , ISSN: 14747065 , DOI: 10.1016/j.pce.2011.07.067 , Van Staden, S.J., & Haarhoff, J. (2011) The use of filter media to determine filter cleanlines. Journal Physics and Chemistry of the Earth 36 (14-15) 1135-1140. DOI:10.1016/j.pce.2011.07.067
- Description: Abstract It is general believed that a sand filter starts its life with new, perfectly clean media, which becomes gradually clogged with each filtration cycle, eventually getting to a point where either head loss or filtrate quality starts to deteriorate. At this point the backwash cycle is initiated and, through the combined action of air and water, returns the media to its original perfectly clean state. Reality, however, dictates otherwise. Many treatment plants visited a decade or more after commissioning are found to have unacceptably dirty filter sand and backwash systems incapable of returning the filter media to a desired state of cleanliness. In some cases, these problems are common ones encountered in filtration plants but many reasons for media deterioration remain elusive, falling outside of these common problems. The South African conditions of highly eutrophic surface waters at high temperatures, however, exacerbate the problems with dirty filter media. Such conditions often lead to the formation of biofilm in the filter media, which is shown to inhibit the effective backwashing of sand and carbon filters. A systematic investigation into filter media cleanliness was therefore started in 2002, ending in 2005, at the University of Johannesburg (the then Rand Afrikaans University). This involved media from eight South African Water Treatment Plants, varying between sand and sand-anthracite combinations and raw water types from eutrophic through turbid to low-turbidity waters. Five states of cleanliness and four fractions of specific deposit were identified relating to in situ washing, column washing, cylinder inversion and acid-immersion techniques. These were measured and the results compared to acceptable limits for specific deposit, as determined in previous studies, though expressed in kg/m3. These values were used to determine the state of the filters. In order to gain greater insight into the composition of the specific deposits stripped from the media, a four-point characterisation step was introduced for the resultant suspensions based on acid-solubility and volatility. Results showed that a reasonably effective backwash removed a median specific deposit of 0.89 kg/m3. Further washing in a laboratory column removed a median specific deposit of 1.34 kg/m3. Media subjected to a standardised cylinder inversion procedure removed a median specific deposit of 2.41 kg/m3. Immersion in a strong acid removed a median specific deposit of 35.2 kg/m3. The four-point characterisation step showed that the soluble-volatile fraction was consistently small in relation to the other fractions. The organic fraction was quite high at the RG treatment plant and the soluble- non-volatile fraction was particularly high at the BK treatment plant
- Full Text:
- Authors: Van Staden, S.J. , Haarhoff, J.
- Date: 2011
- Subjects: Water treatment plants - Design and construction - Data processing , Water - Purification - Membrane filtration , Water - Purification
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/16727 , uj:15805 , ISSN: 14747065 , DOI: 10.1016/j.pce.2011.07.067 , Van Staden, S.J., & Haarhoff, J. (2011) The use of filter media to determine filter cleanlines. Journal Physics and Chemistry of the Earth 36 (14-15) 1135-1140. DOI:10.1016/j.pce.2011.07.067
- Description: Abstract It is general believed that a sand filter starts its life with new, perfectly clean media, which becomes gradually clogged with each filtration cycle, eventually getting to a point where either head loss or filtrate quality starts to deteriorate. At this point the backwash cycle is initiated and, through the combined action of air and water, returns the media to its original perfectly clean state. Reality, however, dictates otherwise. Many treatment plants visited a decade or more after commissioning are found to have unacceptably dirty filter sand and backwash systems incapable of returning the filter media to a desired state of cleanliness. In some cases, these problems are common ones encountered in filtration plants but many reasons for media deterioration remain elusive, falling outside of these common problems. The South African conditions of highly eutrophic surface waters at high temperatures, however, exacerbate the problems with dirty filter media. Such conditions often lead to the formation of biofilm in the filter media, which is shown to inhibit the effective backwashing of sand and carbon filters. A systematic investigation into filter media cleanliness was therefore started in 2002, ending in 2005, at the University of Johannesburg (the then Rand Afrikaans University). This involved media from eight South African Water Treatment Plants, varying between sand and sand-anthracite combinations and raw water types from eutrophic through turbid to low-turbidity waters. Five states of cleanliness and four fractions of specific deposit were identified relating to in situ washing, column washing, cylinder inversion and acid-immersion techniques. These were measured and the results compared to acceptable limits for specific deposit, as determined in previous studies, though expressed in kg/m3. These values were used to determine the state of the filters. In order to gain greater insight into the composition of the specific deposits stripped from the media, a four-point characterisation step was introduced for the resultant suspensions based on acid-solubility and volatility. Results showed that a reasonably effective backwash removed a median specific deposit of 0.89 kg/m3. Further washing in a laboratory column removed a median specific deposit of 1.34 kg/m3. Media subjected to a standardised cylinder inversion procedure removed a median specific deposit of 2.41 kg/m3. Immersion in a strong acid removed a median specific deposit of 35.2 kg/m3. The four-point characterisation step showed that the soluble-volatile fraction was consistently small in relation to the other fractions. The organic fraction was quite high at the RG treatment plant and the soluble- non-volatile fraction was particularly high at the BK treatment plant
- Full Text:
Treatability of South African surface waters by activated carbon
- Lobanga, K.P, Haarhoff, J., Van Staden, S.J.
- Authors: Lobanga, K.P , Haarhoff, J. , Van Staden, S.J.
- Date: 2013
- Subjects: Activated carbon , Natural organic matter , Surface water , Ultraviolet absorbance
- Type: Article
- Identifier: uj:4834 , ISSN 0378-4738 , http://hdl.handle.net/10210/12480
- Description: Natural organic matter (NOM) in water resources for drinking purposes can be removed by different methods, including activated carbon adsorption. Due to the variability of NOM in natural waters, both in terms of its nature and its concentration, a study was undertaken to investigate NOM removal for a wide range of South African surface waters, sampled at different periods, by the use of granular activated carbon (GAC). NOM removal was assessed by measuring the ultraviolet (UV) absorbance at 3 wavelengths, namely, 254 nm (UV254), 272 nm (UV272) and 300 nm (UV300). A comparison of data between the three wavelengths showed that any of the three wavelengths can be used to assess NOM removal by GAC, which is well described by the Freundlich equilibrium equation. A treatment target of 40% removal of initial UV254 absorbance was considered. It was observed that, although the GAC dosage was generally a function of the initial UV254 absorbance, differences existed between waters. This suggests that GAC usage rate is not only a function of the initial UV absorbance but also of the NOM composition, indicating a need for improved NOM characterisation. Comparison between the UV absorbance and dissolved organic carbon (DOC) data suggested that for some waters UV254 absorbance can be used as a rapid substitute for DOC. Finally, the high GAC dosage rates required for the target criterion revealed that the process is inadequate for use at the initial stage of raw water treatment; GAC adsorption should be used at later stages of drinking water treatment.
- Full Text:
- Authors: Lobanga, K.P , Haarhoff, J. , Van Staden, S.J.
- Date: 2013
- Subjects: Activated carbon , Natural organic matter , Surface water , Ultraviolet absorbance
- Type: Article
- Identifier: uj:4834 , ISSN 0378-4738 , http://hdl.handle.net/10210/12480
- Description: Natural organic matter (NOM) in water resources for drinking purposes can be removed by different methods, including activated carbon adsorption. Due to the variability of NOM in natural waters, both in terms of its nature and its concentration, a study was undertaken to investigate NOM removal for a wide range of South African surface waters, sampled at different periods, by the use of granular activated carbon (GAC). NOM removal was assessed by measuring the ultraviolet (UV) absorbance at 3 wavelengths, namely, 254 nm (UV254), 272 nm (UV272) and 300 nm (UV300). A comparison of data between the three wavelengths showed that any of the three wavelengths can be used to assess NOM removal by GAC, which is well described by the Freundlich equilibrium equation. A treatment target of 40% removal of initial UV254 absorbance was considered. It was observed that, although the GAC dosage was generally a function of the initial UV254 absorbance, differences existed between waters. This suggests that GAC usage rate is not only a function of the initial UV absorbance but also of the NOM composition, indicating a need for improved NOM characterisation. Comparison between the UV absorbance and dissolved organic carbon (DOC) data suggested that for some waters UV254 absorbance can be used as a rapid substitute for DOC. Finally, the high GAC dosage rates required for the target criterion revealed that the process is inadequate for use at the initial stage of raw water treatment; GAC adsorption should be used at later stages of drinking water treatment.
- Full Text:
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