This article was downloaded by: [York University Libraries] On: 14 November 2014, At: 07:53 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Journal of Environmental Science and Health . Part A: Environmental Science and Engineering and Toxicology: Toxic/ Hazardous Substances and Environmental Engineering Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/lesa19
A continuously regenerated greensand filter for H2S removal from individual water supplies a
D.E. Brune & R.L. Perez
b
a
Associate Professor, Agricultural Engineering Department , Clemson University , Clemson, South Carolina, 29634 b
Research Scientist, Center for Energy and Environment Research , Mayaguez, Puerto Rico , 00708 Published online: 15 Dec 2008.
To cite this article: D.E. Brune & R.L. Perez (1990) A continuously regenerated greensand filter for H2S removal from individual water supplies, Journal of Environmental Science and Health . Part A: Environmental Science and Engineering and Toxicology: Toxic/Hazardous Substances and Environmental Engineering, 25:1, 1-20, DOI: 10.1080/10934529009375536 To link to this article: http://dx.doi.org/10.1080/10934529009375536
Downloaded by [York University Libraries] at 07:53 14 November 2014
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-andconditions
J . ENVIRON. SCI. HEALTH, A 2 5 ( l ) , 1-20 (1990)
Downloaded by [York University Libraries] at 07:53 14 November 2014
A CONTINUOUSLY REGENERATED GREENSAND FILTER FOR H2S REMOVAL FROM INDIVIDUAL WATER SUPPLIES
KEYWORDS:
Hydrogen Sulfide, Greensand, Oxidizing Filter, Water Treatment D. E. Brune1 and R. L. Perez2
1
Associate Professor, Agricultural Engineering Department, Clemson University, Clemson, South Carolina 29634
2
Research Scientist, Center for Energy and Environment Research, Mayaguez, Puerto Rico 00708
ABSTRACT Hydrogen sulfide contamination of individual home water supply is a frequent problem in areas with aquifiers in sedimentary rock. Commercially available systems for removal of H2S are often quite expensive. This paper describes the new design of a low cost oxidizing filter that has been successfully used to remove in excess of 99% of H2S (at concentrations of 1 to 5 mg/1) from the authors home water supply for over four years. The unit used continuously regenerated, 1
Copyright © 1990 by Marcel Dekker, Inc.
2
BRUNE AND PEREZ
parallel flow, greensand filters; the design is such that the system may be constructed from locally available materials with a total cost of 25% of existing commercial units.
Downloaded by [York University Libraries] at 07:53 14 November 2014
INTRODUCTION Nearly 22 million individuals in the United States obtain their drinking water supply from small (500 - 2500 persons), very small (25 500 persons), or individual water systems1. Taste and odor problems, especially problems caused by dissolved gases such as hydrogen sulfide, are frequently associated with small and individual water supply systems2. A number of techniques have been developed for the removal of hydrogen sulfide (H2S) from water. These techniques include removal and/or oxidation by aeration, hydrogen peroxide addition, oxidizing filters or chlorination. Each technique has unique advantages and disadvantages. Aeration systems for the removal of H2S have several disadvantages. First, in order to achieve adequate removal, 2-3 hours of contact time are needed. Secondly, aeration systems require an additional pumping system for repressurization of the water supply. Furthermore, the possibility of contamination of the water supply requires filtration of the air or disinfection of the water following aeration.
REGENERATED GREENSAND FILTER
3
Other systems that have been used for H2S removal involve the controlled addition of oxidizing substances such as chlorine, ozone or hydrogen peroxide into the water system. All of these techniques have
Downloaded by [York University Libraries] at 07:53 14 November 2014
the disadvantage of producing colloidal sulfur as the end product of the oxidation of H2S. At low H2S levels (less than 1 milligram per liter) this may not be a severe problem. Unfortunately, if the feed water contains high levels of H2S (greater than 1 milligram per liter) the resulting free sulfur is a problem, leaving a "greasy" residue on clothing, dishware, skin, etc.
Free sulfur has a taste and odor,
although much less so than the hydrogen sulfide. Furthermore, free sulfur is a difficult material to remove by filtration. It has a tendency to clog the pores of sand filters and is very difficult to remove by normal backwashing procedures. Individually, each of these oxidizing techniques have additional problems. Chlorine residual imparts its characteristic taste and odor and results in a corrosive water. This problem results in the need for additional treatment techniques for chlorine removal. Hydrogen peroxide (H2O2) is difficult to obtain locally in commercial grade (35% concentration). Furthermore, there are no techniques currently available for use by the home owner to detect hydrogen peroxide residual in water. Hence, the possibility of excessive levels of H2O2 in drinking water is likely. Ozone has a major
4
BRUNE AND PEREZ
disadvantage because of the high cost associated with on-site generation. An alternative technique that has been used for many years on an
Downloaded by [York University Libraries] at 07:53 14 November 2014
industrial scale is the removal of H2S by oxidizing greensand filters. Greensand is a naturally occurring zeolite that is prepared in granular form and used as filtration media in water treatment plants. It has a high exchange capacity which is utilized for water softening and removal of iron and manganese. When the greensand is treated with potassium permanganate (KMnO4) a product called manganese greensand is produced, in which the zeolite particles are left coated with manganous oxide3. When saturated with MnO, the greensand is said to be fully regenerated having an exchange capacity of 6.41 Kg/m3 (2800 grains per cubic foot)4. The ion exchange capacity of the manganese greensand is not directly utilized for sulfide removal; rather, the oxidation-reduction reaction of the MnO coating is utilized. This coating serves as a catalyst for the oxidation and removal of hydrogen sulfide or manganese in the influent water.
In general, the phenomena is
visualized as5: Z-MnO2 + H2S - Z-MnA + S° + H2O Where Z = Greensand zeolite.
(1)
REGENERATED GREENSAND FILTER
5
This equation shows how the manganese greensand goes from a regenerated state to an exhausted state, where it can no longer oxidize more H2S. The greensand bed may be regenerated batchwise by
Downloaded by [York University Libraries] at 07:53 14 November 2014
allowing a potassium permanganate solution to stand in the bed or it may be regenerated continuously by passing permanganate solution through the filter by injection into the influent water.
The
regeneration process is visualized as follows: Z-MnA + KMnO4 - Z-MnO2
(3)
After regeneration, the filter media is rinsed with tap water and it is then ready for reuse. Soluble manganese leakage will occur if a filter unit is further regenerated after the fully regenerated state has been reached. The regeneration process uses potassium permanganate to maintain a manganese dioxide coating on the greensand particles. The two methods are called intermittent regeneration and continuous regeneration, depending on the method of applying the potassium permanganate.
In the intermittent process the permanganate is
applied in batch during the backwashing step after the bed has been cleaned and freed of foreign particles.
On the other hand, the
continuous regeneration involves the constant feeding of permanganate to the untreated water ahead of the filter*.
6
BRUNE AND PEREZ
Most commercial systems for removal of HaS at the home level use greensand filters.
In almost all cases these filters are batchwise
regenerated. These systems, although effective in removing H2S from
Downloaded by [York University Libraries] at 07:53 14 November 2014
water supplies, have several disadvantages. The main disadvantage is associated with the fact that oxidation of hydrogen sulfide requires a ratio of 6 g of KMnO4 to 1 g of H2S. If influent H2S levels are high, (in the range of 1-5 mg/1 per liter), the resulting floe concentration may be as high as 30 mg/1 per liter of suspended solids. As a result, the filtration/oxidation demands on a batchwise regenerated column are high. If the filter is regenerated by the home owner, it requires a great deal of time and is wasteful of chemicals. On the other hand, if the units are regenerated by a commercial supplier, the replacement frequency is high, consequently, use of these filters is expensive. The third commercially available alternative is the automatic batchwise regenerating units which are available at prices ranging up to $2,000 per unit, in addition to the monthly cost of chemicals. Therefore, the purpose of this study was to develop a design, and operating procedure for a more cost effective oxidizing filter by applying the common municipal practice of continuously regenerated greensand filters to small or single family water systems.
REGENERATED GREENSAND FILTER.
7
DESIGN METHODS AND MATERIALS Systems Design The overall study consisted of two parts. The first part dealt with
Downloaded by [York University Libraries] at 07:53 14 November 2014
filtration characteristics of greensand and the second part dealt with the actual system design.
Details of the greensand filtration
characteristics are available in Perez7. Design considerations are the primary point of this discussion. The design of the filtration apparatus was based on two considerations; 1) to use materials of construction which were locally available and 2) to address specific problem areas, arising in commercially available filtration units such as malfunctions of automatic valving, and difficulty in properly backwashing the unit. Commercial units will typically be designed to provide one-half square foot (0.05 square meter) of filtration surface area. At typical filtration rates of 5-10 gallons per minute per square foot (203-407 liters per minute per square meter) this gives a household yield of 2.5 to 5 gallons per minute (9.5 to 18.9 liters per minute) which is adequate for most home needs. However, filter backwash rates required to remove the sulfur and MnO2 floe may range as high as 15 gallons per minute per square foot (609 liters per minute per square meter). Therefore, these units are often too large to backwash properly with the water flow rates available from wells serving single family dwellings.
8
BRUNE AND PEREZ
These problems were solved by using manually-operated parallel flow units. This design, illustrated in Figures la and lb, consists of three flow units made from sections of 6-inch (15.2-cm), high pressure
Downloaded by [York University Libraries] at 07:53 14 November 2014
PVC pipe with inlet caps on either end. The overall height of the unit is approximately 4 feet (1.3 meters). The inlet cap is covered with a screen strainer to provide better inlet water distribution and to prevent media loss during backwashing. The outlet cap is fitted with a stainless steel micro screen and a 3/8-inch (9.5-mm) thick stainless steel screen retainer plate. The column is filled with 3 inches (7.6cm) of washed pea gravel covered by 3 feet (0 9-m) of greensahd. Water distribution to the filter is controlled by a manifold consisting of 1/2-inch (1.3-cm) copper tubing and eleven 1/2 inch (1.3-cm) brass gate valves. Each filtration tube has an inlet and outlet valve to allow each unit to be isolated during backwash. In addition, there must be an inlet and outlet shutoff valve as well as backwash discharge valve and filtrate discharge valve. The inlet and outlet lines are connected to the PVC unit by taping and installing a 1/2 inch (1.3-cm) compression fitting in each PVC end cap. The bottom of the filter unit (discharge) is connected to the manifold by means of individual flexible rubber lines. Inlet and outlet lines are equipped with pressure gages for monitoring filter pressure drop.
REGENERATED GREENSAND FILTER
9
System Operation The system is operated as a continuously regenerated greensand bed, with the solution of KMnO4 injected prior to the water
Downloaded by [York University Libraries] at 07:53 14 November 2014
pressurization tank with a chemical feed pump (refer to Figure 2). A number of pumps of various designs are available for this purpose. The pump chosen for this application was a proportioning pump available from Merit Industries, Inc., Cranston, Rhode Island. This pump injects solution at a fixed ratio of 160 to 1 (flow volume to injected volume). This type of pump offers the advantages of not requiring electrical installation yet, providing reliable performance combined with relatively inexpensive cost. When operated in this manner, the primary role of the greensand filter unit is to trap the suspended solids resulting from the reaction of hydrogen sulfide and KMnO4 or to oxidize excess H2S. Excess H2S may be produced as a result of fluctuations in influent hydrogen sulfide levels or fluctuations in either the concentration or injection rate of KMnO
Journal of Environmental Science and Health . Part A: Environmental Science and Engineering and Toxicology: Toxic/ Hazardous Substances and Environmental Engineering Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/lesa19
A continuously regenerated greensand filter for H2S removal from individual water supplies a
D.E. Brune & R.L. Perez
b
a
Associate Professor, Agricultural Engineering Department , Clemson University , Clemson, South Carolina, 29634 b
Research Scientist, Center for Energy and Environment Research , Mayaguez, Puerto Rico , 00708 Published online: 15 Dec 2008.
To cite this article: D.E. Brune & R.L. Perez (1990) A continuously regenerated greensand filter for H2S removal from individual water supplies, Journal of Environmental Science and Health . Part A: Environmental Science and Engineering and Toxicology: Toxic/Hazardous Substances and Environmental Engineering, 25:1, 1-20, DOI: 10.1080/10934529009375536 To link to this article: http://dx.doi.org/10.1080/10934529009375536
Downloaded by [York University Libraries] at 07:53 14 November 2014
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-andconditions
J . ENVIRON. SCI. HEALTH, A 2 5 ( l ) , 1-20 (1990)
Downloaded by [York University Libraries] at 07:53 14 November 2014
A CONTINUOUSLY REGENERATED GREENSAND FILTER FOR H2S REMOVAL FROM INDIVIDUAL WATER SUPPLIES
KEYWORDS:
Hydrogen Sulfide, Greensand, Oxidizing Filter, Water Treatment D. E. Brune1 and R. L. Perez2
1
Associate Professor, Agricultural Engineering Department, Clemson University, Clemson, South Carolina 29634
2
Research Scientist, Center for Energy and Environment Research, Mayaguez, Puerto Rico 00708
ABSTRACT Hydrogen sulfide contamination of individual home water supply is a frequent problem in areas with aquifiers in sedimentary rock. Commercially available systems for removal of H2S are often quite expensive. This paper describes the new design of a low cost oxidizing filter that has been successfully used to remove in excess of 99% of H2S (at concentrations of 1 to 5 mg/1) from the authors home water supply for over four years. The unit used continuously regenerated, 1
Copyright © 1990 by Marcel Dekker, Inc.
2
BRUNE AND PEREZ
parallel flow, greensand filters; the design is such that the system may be constructed from locally available materials with a total cost of 25% of existing commercial units.
Downloaded by [York University Libraries] at 07:53 14 November 2014
INTRODUCTION Nearly 22 million individuals in the United States obtain their drinking water supply from small (500 - 2500 persons), very small (25 500 persons), or individual water systems1. Taste and odor problems, especially problems caused by dissolved gases such as hydrogen sulfide, are frequently associated with small and individual water supply systems2. A number of techniques have been developed for the removal of hydrogen sulfide (H2S) from water. These techniques include removal and/or oxidation by aeration, hydrogen peroxide addition, oxidizing filters or chlorination. Each technique has unique advantages and disadvantages. Aeration systems for the removal of H2S have several disadvantages. First, in order to achieve adequate removal, 2-3 hours of contact time are needed. Secondly, aeration systems require an additional pumping system for repressurization of the water supply. Furthermore, the possibility of contamination of the water supply requires filtration of the air or disinfection of the water following aeration.
REGENERATED GREENSAND FILTER
3
Other systems that have been used for H2S removal involve the controlled addition of oxidizing substances such as chlorine, ozone or hydrogen peroxide into the water system. All of these techniques have
Downloaded by [York University Libraries] at 07:53 14 November 2014
the disadvantage of producing colloidal sulfur as the end product of the oxidation of H2S. At low H2S levels (less than 1 milligram per liter) this may not be a severe problem. Unfortunately, if the feed water contains high levels of H2S (greater than 1 milligram per liter) the resulting free sulfur is a problem, leaving a "greasy" residue on clothing, dishware, skin, etc.
Free sulfur has a taste and odor,
although much less so than the hydrogen sulfide. Furthermore, free sulfur is a difficult material to remove by filtration. It has a tendency to clog the pores of sand filters and is very difficult to remove by normal backwashing procedures. Individually, each of these oxidizing techniques have additional problems. Chlorine residual imparts its characteristic taste and odor and results in a corrosive water. This problem results in the need for additional treatment techniques for chlorine removal. Hydrogen peroxide (H2O2) is difficult to obtain locally in commercial grade (35% concentration). Furthermore, there are no techniques currently available for use by the home owner to detect hydrogen peroxide residual in water. Hence, the possibility of excessive levels of H2O2 in drinking water is likely. Ozone has a major
4
BRUNE AND PEREZ
disadvantage because of the high cost associated with on-site generation. An alternative technique that has been used for many years on an
Downloaded by [York University Libraries] at 07:53 14 November 2014
industrial scale is the removal of H2S by oxidizing greensand filters. Greensand is a naturally occurring zeolite that is prepared in granular form and used as filtration media in water treatment plants. It has a high exchange capacity which is utilized for water softening and removal of iron and manganese. When the greensand is treated with potassium permanganate (KMnO4) a product called manganese greensand is produced, in which the zeolite particles are left coated with manganous oxide3. When saturated with MnO, the greensand is said to be fully regenerated having an exchange capacity of 6.41 Kg/m3 (2800 grains per cubic foot)4. The ion exchange capacity of the manganese greensand is not directly utilized for sulfide removal; rather, the oxidation-reduction reaction of the MnO coating is utilized. This coating serves as a catalyst for the oxidation and removal of hydrogen sulfide or manganese in the influent water.
In general, the phenomena is
visualized as5: Z-MnO2 + H2S - Z-MnA + S° + H2O Where Z = Greensand zeolite.
(1)
REGENERATED GREENSAND FILTER
5
This equation shows how the manganese greensand goes from a regenerated state to an exhausted state, where it can no longer oxidize more H2S. The greensand bed may be regenerated batchwise by
Downloaded by [York University Libraries] at 07:53 14 November 2014
allowing a potassium permanganate solution to stand in the bed or it may be regenerated continuously by passing permanganate solution through the filter by injection into the influent water.
The
regeneration process is visualized as follows: Z-MnA + KMnO4 - Z-MnO2
(3)
After regeneration, the filter media is rinsed with tap water and it is then ready for reuse. Soluble manganese leakage will occur if a filter unit is further regenerated after the fully regenerated state has been reached. The regeneration process uses potassium permanganate to maintain a manganese dioxide coating on the greensand particles. The two methods are called intermittent regeneration and continuous regeneration, depending on the method of applying the potassium permanganate.
In the intermittent process the permanganate is
applied in batch during the backwashing step after the bed has been cleaned and freed of foreign particles.
On the other hand, the
continuous regeneration involves the constant feeding of permanganate to the untreated water ahead of the filter*.
6
BRUNE AND PEREZ
Most commercial systems for removal of HaS at the home level use greensand filters.
In almost all cases these filters are batchwise
regenerated. These systems, although effective in removing H2S from
Downloaded by [York University Libraries] at 07:53 14 November 2014
water supplies, have several disadvantages. The main disadvantage is associated with the fact that oxidation of hydrogen sulfide requires a ratio of 6 g of KMnO4 to 1 g of H2S. If influent H2S levels are high, (in the range of 1-5 mg/1 per liter), the resulting floe concentration may be as high as 30 mg/1 per liter of suspended solids. As a result, the filtration/oxidation demands on a batchwise regenerated column are high. If the filter is regenerated by the home owner, it requires a great deal of time and is wasteful of chemicals. On the other hand, if the units are regenerated by a commercial supplier, the replacement frequency is high, consequently, use of these filters is expensive. The third commercially available alternative is the automatic batchwise regenerating units which are available at prices ranging up to $2,000 per unit, in addition to the monthly cost of chemicals. Therefore, the purpose of this study was to develop a design, and operating procedure for a more cost effective oxidizing filter by applying the common municipal practice of continuously regenerated greensand filters to small or single family water systems.
REGENERATED GREENSAND FILTER.
7
DESIGN METHODS AND MATERIALS Systems Design The overall study consisted of two parts. The first part dealt with
Downloaded by [York University Libraries] at 07:53 14 November 2014
filtration characteristics of greensand and the second part dealt with the actual system design.
Details of the greensand filtration
characteristics are available in Perez7. Design considerations are the primary point of this discussion. The design of the filtration apparatus was based on two considerations; 1) to use materials of construction which were locally available and 2) to address specific problem areas, arising in commercially available filtration units such as malfunctions of automatic valving, and difficulty in properly backwashing the unit. Commercial units will typically be designed to provide one-half square foot (0.05 square meter) of filtration surface area. At typical filtration rates of 5-10 gallons per minute per square foot (203-407 liters per minute per square meter) this gives a household yield of 2.5 to 5 gallons per minute (9.5 to 18.9 liters per minute) which is adequate for most home needs. However, filter backwash rates required to remove the sulfur and MnO2 floe may range as high as 15 gallons per minute per square foot (609 liters per minute per square meter). Therefore, these units are often too large to backwash properly with the water flow rates available from wells serving single family dwellings.
8
BRUNE AND PEREZ
These problems were solved by using manually-operated parallel flow units. This design, illustrated in Figures la and lb, consists of three flow units made from sections of 6-inch (15.2-cm), high pressure
Downloaded by [York University Libraries] at 07:53 14 November 2014
PVC pipe with inlet caps on either end. The overall height of the unit is approximately 4 feet (1.3 meters). The inlet cap is covered with a screen strainer to provide better inlet water distribution and to prevent media loss during backwashing. The outlet cap is fitted with a stainless steel micro screen and a 3/8-inch (9.5-mm) thick stainless steel screen retainer plate. The column is filled with 3 inches (7.6cm) of washed pea gravel covered by 3 feet (0 9-m) of greensahd. Water distribution to the filter is controlled by a manifold consisting of 1/2-inch (1.3-cm) copper tubing and eleven 1/2 inch (1.3-cm) brass gate valves. Each filtration tube has an inlet and outlet valve to allow each unit to be isolated during backwash. In addition, there must be an inlet and outlet shutoff valve as well as backwash discharge valve and filtrate discharge valve. The inlet and outlet lines are connected to the PVC unit by taping and installing a 1/2 inch (1.3-cm) compression fitting in each PVC end cap. The bottom of the filter unit (discharge) is connected to the manifold by means of individual flexible rubber lines. Inlet and outlet lines are equipped with pressure gages for monitoring filter pressure drop.
REGENERATED GREENSAND FILTER
9
System Operation The system is operated as a continuously regenerated greensand bed, with the solution of KMnO4 injected prior to the water
Downloaded by [York University Libraries] at 07:53 14 November 2014
pressurization tank with a chemical feed pump (refer to Figure 2). A number of pumps of various designs are available for this purpose. The pump chosen for this application was a proportioning pump available from Merit Industries, Inc., Cranston, Rhode Island. This pump injects solution at a fixed ratio of 160 to 1 (flow volume to injected volume). This type of pump offers the advantages of not requiring electrical installation yet, providing reliable performance combined with relatively inexpensive cost. When operated in this manner, the primary role of the greensand filter unit is to trap the suspended solids resulting from the reaction of hydrogen sulfide and KMnO4 or to oxidize excess H2S. Excess H2S may be produced as a result of fluctuations in influent hydrogen sulfide levels or fluctuations in either the concentration or injection rate of KMnO
