Measurement and expression of granular filter cleanliness
- Haarhoff, Johannes, van Staden, Samantha
- Authors: Haarhoff, Johannes , van Staden, Samantha
- Date: 2013
- Subjects: Water - Purification , Water treatment filters
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/24510 , uj:16224 , Citation: Haarhoff, J. and Van Staden, S.J. 2013. A proposal for the systematic classification of specific deposit on dirty filter media. Water SA, 39(5):701-706.
- Description: Abstract The problem of dirty filter media at water treatment plants, despite having good backwash systems, is a serious challenge that requires constant monitoring and maintenance. To aid the systematic analysis of filter media and the troubleshooting of problem filters, this paper firstly proposes a standard procedure for quantification of the specific deposit on filter media, including tentative guidelines for the interpretation of the results. Secondly, a standard procedure is proposed for the characterisation of the specific deposit, based on its volatility and its acid solubility. These fractions are helpful to trace the origin of excessively dirty filter media. Thirdly, the utility of the proposed procedures is demonstrated by the results of a South African treatment plant survey. This confirms some earlier observations that there often is a real problem with recalcitrant specific deposits that cannot be readily removed by backwashing, a fraction that correlates with the organic fraction in the specific deposit.
- Full Text:
- Authors: Haarhoff, Johannes , van Staden, Samantha
- Date: 2013
- Subjects: Water - Purification , Water treatment filters
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/24510 , uj:16224 , Citation: Haarhoff, J. and Van Staden, S.J. 2013. A proposal for the systematic classification of specific deposit on dirty filter media. Water SA, 39(5):701-706.
- Description: Abstract The problem of dirty filter media at water treatment plants, despite having good backwash systems, is a serious challenge that requires constant monitoring and maintenance. To aid the systematic analysis of filter media and the troubleshooting of problem filters, this paper firstly proposes a standard procedure for quantification of the specific deposit on filter media, including tentative guidelines for the interpretation of the results. Secondly, a standard procedure is proposed for the characterisation of the specific deposit, based on its volatility and its acid solubility. These fractions are helpful to trace the origin of excessively dirty filter media. Thirdly, the utility of the proposed procedures is demonstrated by the results of a South African treatment plant survey. This confirms some earlier observations that there often is a real problem with recalcitrant specific deposits that cannot be readily removed by backwashing, a fraction that correlates with the organic fraction in the specific deposit.
- Full Text:
A Falling-head procedure for the measurement of filter media sphericity
- Haarhoff, Johannes, Vessal, Ali
- Authors: Haarhoff, Johannes , Vessal, Ali
- Date: 2010
- Subjects: Filters and filtration
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/17047 , uj:15836 , ISSN:0378-4738 (Print) , ISSN:1816-7950 (On-line) , Citation: Haarhoff,J. & Vessai, A.2010. A falling-head procedure for the measurement of filter media sphericity. Water SA, 36(1). http://www.wrc.org.za
- Description: Abstract Filter media sphericity is normally determined experimentally in a laboratory filtration column. The pressure drop is measured across a bed of known depth while the filtration rate is kept constant. The sphericity is then calculated from a theoretical headloss relationship using the Ergun equation. This paper proposes a method along similar lines, but suggests a much simpler experimental procedure. Instead of having to maintain a constant flow rate and measuring both the flow rate and the pressure, the column is filled and the water then allowed to drain through the bed. The only measurement to be taken is the time it takes for the water level to drop through a known distance, which is called a falling-head procedure. The full theoretical development of the method is provided, as well as a detailed experimental procedure. The practicality of the method is demonstrated with tests performed on a variety of filter media, and a fully-worked example is presented.
- Full Text: false
- Authors: Haarhoff, Johannes , Vessal, Ali
- Date: 2010
- Subjects: Filters and filtration
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/17047 , uj:15836 , ISSN:0378-4738 (Print) , ISSN:1816-7950 (On-line) , Citation: Haarhoff,J. & Vessai, A.2010. A falling-head procedure for the measurement of filter media sphericity. Water SA, 36(1). http://www.wrc.org.za
- Description: Abstract Filter media sphericity is normally determined experimentally in a laboratory filtration column. The pressure drop is measured across a bed of known depth while the filtration rate is kept constant. The sphericity is then calculated from a theoretical headloss relationship using the Ergun equation. This paper proposes a method along similar lines, but suggests a much simpler experimental procedure. Instead of having to maintain a constant flow rate and measuring both the flow rate and the pressure, the column is filled and the water then allowed to drain through the bed. The only measurement to be taken is the time it takes for the water level to drop through a known distance, which is called a falling-head procedure. The full theoretical development of the method is provided, as well as a detailed experimental procedure. The practicality of the method is demonstrated with tests performed on a variety of filter media, and a fully-worked example is presented.
- Full Text: false
What simple media tests can tell you about filter problems and rehabilitation
- Van Staden, Samantha, Haarhoff, Johannes
- Authors: Van Staden, Samantha , Haarhoff, Johannes
- Date: 2004
- Subjects: Rapid sand filters , Cleanliness , Measurement
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/16658 , uj:15795 , Citation: Van Staden, S.J., & Haarhoff, J. 2004. What simple media tests can tell you about filter problems and rehabilitation. 9th Biennial Conference of the Water Institute of Southern Africa, 2-6 May 2004, Cape Town International Convention Centre, p.1202-1211. ISBN: 1-920-01728-3
- Description: Abstract: Rapid sand filters are expected to continuously produce clean, safe water for many years, during which time some of these filters will inevitably develop some problems. These problems are usually only apparent once the damage is already done, thereby causing expenditure and inconvenience due to rehabilitation. However, if the cleanliness of the media grains is routinely measured, the potential for some of the more serious problems could be detected at an early stage and measures taken to alleviate such problems before serious damage occurs. In 2002 and 2003, the Water Research Group at the Rand Afrikaans University developed a number of tests to quantify filter media cleanliness in a simple yet standard manner. These tests provide information in two important areas. Firstly, they alert the operator when media does not meet an acceptable standard for cleanliness after backwashing. Secondly, they provide pointers to the nature of the residual deposit on the media, suggesting why the media have not been properly cleaned during backwashing. These tests are currently being benchmarked by a series of trials at a number of South African water treatment plants. This paper will provide the details of these tests, together with practical limits for the different parameters. It should make a valuable contribution towards early detection and troubleshooting of filtration problems by operators and managers.
- Full Text:
- Authors: Van Staden, Samantha , Haarhoff, Johannes
- Date: 2004
- Subjects: Rapid sand filters , Cleanliness , Measurement
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/16658 , uj:15795 , Citation: Van Staden, S.J., & Haarhoff, J. 2004. What simple media tests can tell you about filter problems and rehabilitation. 9th Biennial Conference of the Water Institute of Southern Africa, 2-6 May 2004, Cape Town International Convention Centre, p.1202-1211. ISBN: 1-920-01728-3
- Description: Abstract: Rapid sand filters are expected to continuously produce clean, safe water for many years, during which time some of these filters will inevitably develop some problems. These problems are usually only apparent once the damage is already done, thereby causing expenditure and inconvenience due to rehabilitation. However, if the cleanliness of the media grains is routinely measured, the potential for some of the more serious problems could be detected at an early stage and measures taken to alleviate such problems before serious damage occurs. In 2002 and 2003, the Water Research Group at the Rand Afrikaans University developed a number of tests to quantify filter media cleanliness in a simple yet standard manner. These tests provide information in two important areas. Firstly, they alert the operator when media does not meet an acceptable standard for cleanliness after backwashing. Secondly, they provide pointers to the nature of the residual deposit on the media, suggesting why the media have not been properly cleaned during backwashing. These tests are currently being benchmarked by a series of trials at a number of South African water treatment plants. This paper will provide the details of these tests, together with practical limits for the different parameters. It should make a valuable contribution towards early detection and troubleshooting of filtration problems by operators and managers.
- Full Text:
Measuring the cleanliness of filter media
- Haarhoff, Johannes, Van Staden, Samantha
- Authors: Haarhoff, Johannes , Van Staden, Samantha
- Date: 2006
- Subjects: Water treatment filters , Cleanliness , Measurement
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/16675 , uj:15797 , Citation: Haarhoff, J., & Van Staden, S.J. 2006. Measuring the cleanliness of filter media. 9th Biennial Conference of the Water Institute of Southern Africa, 22-24 May 2006, Durban International Conference Centre, 10 p.
- Description: Abstract: Filter media starts its working life as almost pure silica, freshly crushed, sieved, washed and dried. Upon examination a few years later, we find discoloured, often sticky material hardly recognisable as the original. As long as the media retains its granular character and the filter beds stay smooth and level, this is no cause for great concern. However, when the media forms clumps, when cracks become apparent in the bed or the filtrate quality deteriorates for no apparent reason, the media demands closer attention. Such media investigations have been carried out for more than a decade at the Water Research Group of the University of Johannesburg. Drawing on this reservoir of experience and case studies, this paper reviews the different approaches to measuring and expressing the degree of cleanliness of in situ filter media. A conceptual model of the different types of specific deposit on the media is developed first, classifying the specific deposit into those fractions that are washed out by the treatment plant backwash system, the fraction hat can be additionally washed out by a laboratory column, the fraction that needs mechanical agitation to be stripped off the media, and the fraction that can only be chemically stripped. Typical values for the four fractions, as measured during a comprehensive survey of South African water treatment plants, are presented, together with suggested remedial measures for each of the media fractions.
- Full Text:
- Authors: Haarhoff, Johannes , Van Staden, Samantha
- Date: 2006
- Subjects: Water treatment filters , Cleanliness , Measurement
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/16675 , uj:15797 , Citation: Haarhoff, J., & Van Staden, S.J. 2006. Measuring the cleanliness of filter media. 9th Biennial Conference of the Water Institute of Southern Africa, 22-24 May 2006, Durban International Conference Centre, 10 p.
- Description: Abstract: Filter media starts its working life as almost pure silica, freshly crushed, sieved, washed and dried. Upon examination a few years later, we find discoloured, often sticky material hardly recognisable as the original. As long as the media retains its granular character and the filter beds stay smooth and level, this is no cause for great concern. However, when the media forms clumps, when cracks become apparent in the bed or the filtrate quality deteriorates for no apparent reason, the media demands closer attention. Such media investigations have been carried out for more than a decade at the Water Research Group of the University of Johannesburg. Drawing on this reservoir of experience and case studies, this paper reviews the different approaches to measuring and expressing the degree of cleanliness of in situ filter media. A conceptual model of the different types of specific deposit on the media is developed first, classifying the specific deposit into those fractions that are washed out by the treatment plant backwash system, the fraction hat can be additionally washed out by a laboratory column, the fraction that needs mechanical agitation to be stripped off the media, and the fraction that can only be chemically stripped. Typical values for the four fractions, as measured during a comprehensive survey of South African water treatment plants, are presented, together with suggested remedial measures for each of the media fractions.
- Full Text:
An improved filter media test for troubleshooting and rehabilitation of problem filters
- Van Staden, Samantha, Haarhoff, Johannes
- Authors: Van Staden, Samantha , Haarhoff, Johannes
- Date: 2004
- Subjects: Water treatment filters , Floc retention test
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/16754 , uj:15808 , Citation: Van Staden, S.J. & Haarhoff, J. 2004. An Improved Filter Media Test for Troubleshooting and Rehabilitation of Problem Filters. 2004 Water Quality Technology Conference, 14-18 November 2004, San Antonio, Texas, USA, 12p.
- Description: Abstract: A standard “floc retention test” was made available by the American Water Works Association1 to provide a routine measure of filter media cleanliness. This would allow early detection of the potential for serious problems. The test is performed by preparing a 50g media sample and shaking it vigorously in 100ml of water. The resultant suspension is then decanted and, after five repetitions, the turbidity of the combined suspension is measured, doubled and reported as NTU (nephelometric turbidity units)/100g of sand. The turbidity, according to AWWA guidelines, ranges from < 60 (clean filters) to 300 NTU/100g (filters with a possible mudball problem)2. At many South African plants, filters appear to be inadequately cleaned by routine backwash procedures. The hypothesis is that the root of this phenomenon lies in the high degree of biological activity within filter beds. This presumably results in a sticky biofilm on the media grains, which is difficult to remove. The floc retention test proved to be an indispensable tool for a systematic survey of water filtration plants currently being carried out to test this hypothesis. To improve reproducibility and insight into the reasons for media fouling, the floc retention test was refined in a number of ways, which is the main focus of this presentation.
- Full Text:
- Authors: Van Staden, Samantha , Haarhoff, Johannes
- Date: 2004
- Subjects: Water treatment filters , Floc retention test
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/16754 , uj:15808 , Citation: Van Staden, S.J. & Haarhoff, J. 2004. An Improved Filter Media Test for Troubleshooting and Rehabilitation of Problem Filters. 2004 Water Quality Technology Conference, 14-18 November 2004, San Antonio, Texas, USA, 12p.
- Description: Abstract: A standard “floc retention test” was made available by the American Water Works Association1 to provide a routine measure of filter media cleanliness. This would allow early detection of the potential for serious problems. The test is performed by preparing a 50g media sample and shaking it vigorously in 100ml of water. The resultant suspension is then decanted and, after five repetitions, the turbidity of the combined suspension is measured, doubled and reported as NTU (nephelometric turbidity units)/100g of sand. The turbidity, according to AWWA guidelines, ranges from < 60 (clean filters) to 300 NTU/100g (filters with a possible mudball problem)2. At many South African plants, filters appear to be inadequately cleaned by routine backwash procedures. The hypothesis is that the root of this phenomenon lies in the high degree of biological activity within filter beds. This presumably results in a sticky biofilm on the media grains, which is difficult to remove. The floc retention test proved to be an indispensable tool for a systematic survey of water filtration plants currently being carried out to test this hypothesis. To improve reproducibility and insight into the reasons for media fouling, the floc retention test was refined in a number of ways, which is the main focus of this presentation.
- Full Text:
Effective filter backwashing with multiple washes of air and water
- Van Staden, Samantha, Haarhoff, Johannes
- Authors: Van Staden, Samantha , Haarhoff, Johannes
- Date: 2006
- Subjects: Water treatment filters , Backwashing
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/16692 , uj:15800 , Citation: Van Staden, S.J. & Haarhoff, J. 2006. Effective Filter Backwashing with Multiple Washes of Air and Water. 10th Biennial Conference of the Water Institute of Southern Africa, 21-25 May 2006, ICC, Durban, WISA 200, 11 p.
- Description: Abstract: In general, filters develop problems over time due to the routine running of the filter, including backwashing. The difficulties in maintaining filters in good condition, given the eutrophic state of many of our raw waters, the high water temperature and resulting development of difficult-to-remove biofilm, are well known to South African water treatment plant operators. These difficulties are usually related to the deposits accumulated by the filter. The backwashing system, therefore, has to be really good to ensure filter cleanliness 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. If air scour continues for more than about a minute, the media compacts, air channels form and the abrasion amongst media grains largely ceases. By interspersing shorter cycles of air and water, rather than using one single cycle, the media is repeatedly fluidised, giving each new burst of air renewed opportunity to effectively abrade the media grains. This concept is not new – at some South African treatment plants the “double” or even “triple” wash had been used for 15 years with reputed success. However, from 2003 to 2005, the Water Research Group at the University of Johannesburg (UJWRG) has systematically investigated this concept at five water treatment plants and in the laboratory, through the testing of both media and backwash water samples, to determine the quantitative benefits of multiple wash cycles. The paper describes the methods used and the typical results obtained. Multiple washing does indeed show great promise for improving backwash efficiency. On the average, a second wash removes about an additional 40% to 50% of the solids that would have been washed out with a single wash. Furthermore, a third and even fourth wash still continues to remove additional dirt from the filter. Multiple washing, therefore, may be used as a useful tool for effective rehabilitation as well as for routine operation.
- Full Text:
- Authors: Van Staden, Samantha , Haarhoff, Johannes
- Date: 2006
- Subjects: Water treatment filters , Backwashing
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/16692 , uj:15800 , Citation: Van Staden, S.J. & Haarhoff, J. 2006. Effective Filter Backwashing with Multiple Washes of Air and Water. 10th Biennial Conference of the Water Institute of Southern Africa, 21-25 May 2006, ICC, Durban, WISA 200, 11 p.
- Description: Abstract: In general, filters develop problems over time due to the routine running of the filter, including backwashing. The difficulties in maintaining filters in good condition, given the eutrophic state of many of our raw waters, the high water temperature and resulting development of difficult-to-remove biofilm, are well known to South African water treatment plant operators. These difficulties are usually related to the deposits accumulated by the filter. The backwashing system, therefore, has to be really good to ensure filter cleanliness 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. If air scour continues for more than about a minute, the media compacts, air channels form and the abrasion amongst media grains largely ceases. By interspersing shorter cycles of air and water, rather than using one single cycle, the media is repeatedly fluidised, giving each new burst of air renewed opportunity to effectively abrade the media grains. This concept is not new – at some South African treatment plants the “double” or even “triple” wash had been used for 15 years with reputed success. However, from 2003 to 2005, the Water Research Group at the University of Johannesburg (UJWRG) has systematically investigated this concept at five water treatment plants and in the laboratory, through the testing of both media and backwash water samples, to determine the quantitative benefits of multiple wash cycles. The paper describes the methods used and the typical results obtained. Multiple washing does indeed show great promise for improving backwash efficiency. On the average, a second wash removes about an additional 40% to 50% of the solids that would have been washed out with a single wash. Furthermore, a third and even fourth wash still continues to remove additional dirt from the filter. Multiple washing, therefore, may be used as a useful tool for effective rehabilitation as well as for routine operation.
- Full Text:
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