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All Fouled Up - Investigating PTFE Layered EPDM Membranes (Part 2) |
April 24, 2007 |
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Posted by Barry Nagassar at 09:49 PM | Comments (0) | TrackBack (0) |
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This is the second of a two part series on the adoption of PTFE layered EPDM membranes for wastewater aeration systems. We will continue by looking at more data. The empirical data collected by SSI to date the applications where PTFE layered EPDM has been installed as a replacement for conventional plain EPDM membranes, or side by side with conventional plain EPDM membranes is limited to two example applications, though we are attempting to collect additional information from both independent pilot studies and research, through our own tests, and through outreach to plants which replaced old technology with PTFE layered EPDM to learn from their experiences.
The two specific cases are the Agropur Dairy Cooperative in Quebec, Canada, and the Ringkobing Water Purification Plant in Denmark. In the case of Agropur, the plant has 4 basins of equal size in parallel flow, and has used EPDM membranes from 3 manufacturers, as well waxy bloom EPDM, silicone blended EPDM, and most recently PTFE layered EPDM from December 2004.
At the Agropur plant, after ten months of use the PTFE membranes showed less fouling than EDPM, as shown in the picture. With PTFE membranes maintenance frequency declined and a higher oxygen transfer for a longer time period was achieved. It is the first time the plant went more than a year without maintenance. In Figure 2 (left), the left side is typical of a plain EPDM membrane which must be acid soaked to clean, and a photo of a PTFE membrane which has been wiped clean with a stroke of a towel.
At Ringkobing another brand's diffuser had been installed.* The plant ordered SSI brand PTFE 
layered EPDM replacement membranes to retrofit into the existing plastic diffuser holders. We confirm that SSI PTFE membranes have been working for six months without clogging problems. Before the plant had to clean the EPDM membranes every 3-4 weeks! Figure 3 (right) shows the SSI PTFE membrane inside of the existing diffuser holder. The lines illustrate where the operator ran his finger along the surface and was able to clean the surface residue. It also illustrates that little to no fouling occurred in the slits.
Figure 4 (left) shows the PTFE membrane bubbling in a tank of clean water before the surface was wiped clean.
In both of the above cases, it was explained to SSI that the diffusers did not require cleaning, however it was the operator’s curiosity to look at the diffusers that drove them to drain the tanks and inspect them. In both cases, the surface bubble pattern was consistent with new and clean diffusers, the dissolved oxygen concentrations had not changed from new, and the diffuser headloss appeared not to have changed significantly.
It should be noted that both of the above are extreme examples of industrial plants with highly concentrated wastewater and proven foulants.
Over the course of the next few years, SSI believes that it can prove that in a typical municipal plant there is little to no change in alpha between a new PTFE and an aged PTFE membrane, and there is little to no change in delta P, with the help of independent research and the addition of further empirical examples. If this can be proven, wastewater plants of all sorts that install PTFE layered membranes will be looking at energy savings over the operating life of the plant of 30 to 40% with the added benefit of reduced maintenance and perhaps less frequent replacement requirements.
* The diffuser plastic holders shown in Figs. 2 and 3 were manufactured by the Nopon Group. SSI manufactured the membrane only and retrofitted our PTFE layered EPDM membrane into the existing holder. SSI is not related to any other diffuser company.
About the Author
Mr. Tom Frankle
Stamford Scientific International Inc.
4 Tucker Drive
Poughkeepsie, NY 12603
Telephone: 845.454.8171
Fax: 845.454.8094
Email: info@stamfordscientific.com
Web site: http://www.stamfordscientific.com/
Mr. Frankle is part of Stamford Scientific International Inc. which maintains production and support facilities for various products including: fine bubble diffuser, square diffuser, and tube diffuser and aeration systems.
All Fouled Up - Investigating PTFE Layered EPDM Membranes |
April 16, 2007 |
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Posted by Barry Nagassar at 11:51 AM | Comments (1) | TrackBack (0) |
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In the aeration basin of a typical wastewater treatment plant there are both organic and inorganic matter which can impair, over time, the function of fine bubble diffusers, thus requiring either additional energy to overcome high membrane headloss, or reducing the oxygen mass transfer to the process.
The rate and type of fouling depend on whether the plant is treating industrial or municipal wastewater, as well as on the process. Typically diffusers types foul more rapidly in low MCRT plants such as non nitrifying conventional processes than in high MCRT plants such as in nutrient removal processes like oxidation ditch, BNR and SBR.
Diffuser media which have been readily available in the market include porous types such as aluminum oxide, porcelain, ABS and Polyethylene, and non-porous types EPDM, Silicone and Polyurethane.
Most diffuser manufacturers have taken a targeted rather than blanket approach to diffuser fouling problems. For example, in a dairy WWTP, it is expected that there will be significant calcium fouling, therefore it is common to use a flexible membrane diffuser rather than a hard porous type which may prove more difficult to keep clean.
In some cases manufacturers have recommended lower roughness coefficient materials such as PU rather than EPDM in such applications to reduce surface adhesion of calcium, gypsum, and silicas to the membrane. However there have always been trade-offs in the selection of a diffuser media other than porous types or EPDM.
For example PU and Silicone formulations that have been used often have a relatively high headloss and lower SOTE than EPDM, and Silicone is prone to tear propagation, while most PU is resistant to only 40 C. Only EPDM provides desirable physical properties and bubble sizes consistent with high SOTE.
In Figure 1, see the proximity of SOTE of EPDM and PTFE layered EPDM in an independent test conducted by ATC, SA of Spain on SSI disc diffusers1. It should be noted that any result above 7% SOTE/m is considered high, and these tests were conducted at a diffuser submergence of 4.7m.
PTFE layered EPDM membranes were introduced in late 2004 and were installed throughout the course of 2005 in two dairies, one paper mill, one post aeration basin, a brewery, a landfill leachate treatment plant, and a number of municipal sewage treatment plants. In most of the cases, PTFE layered EPDM was selected due to the failure of previous technologies to avoid fouling to a sufficient degree that the plant could operate efficiently.
Rosso and Stenstrom have empirically studied the extent of fouling and cleaning intervals of various diffuser media in a wide array of municipal sewage treatment plants and have found that F rates between cleanings of membranes even in municipal plants are much greater than common perception, dropping from an average alpha in a low MCRT plant of 0.50 to less than 0.40 after up to 2 years and stabilizing to less than 0.35 thereafter.2 At this time specifically in low MCRT plants they have found that the difference in a F between porous and non-porous fine bubble media do not vary significantly.
This is the first of a two part series on wastewater management solutions. Part two will look at more empirical evidence in support of PTFE layered EPDM membranes.
About the Author
Mr. Tom Frankle
Stamford Scientific International Inc.
4 Tucker Drive
Poughkeepsie, NY 12603
Telephone: 845.454.8171
Fax: 845.454.8094
Email: info@stamfordscientific.com
Web site: http://www.stamfordscientific.com/
Mr. Frankle is part of Stamford Scientific International Inc. which maintains production and support facilities for various products including: fine bubble diffusers, disc diffusers, and tube diffusers.
Notes:
1. “Clean Water Oxygen Transfer Tests, Scientific International”, October 2005, by Ian Trillo of Asesoria Tecnica y Control, S.A. Clean water tests were commissioned by SSI.
2. “Economics of Fine Pore Diffuser Aging”, by Diego Rosso and Michael Stenstrom, Accepted for Publication Water Environment Research.
Hero or Chicken - Risk Perception in Macho Territory |
April 15, 2007 |
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Posted by Joseph Taylor at 06:09 PM | Comments (0) | TrackBack (0) |
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Lessons Learned from Fatal Events - Alternatives and consequences
Industrial Accident Analysis Dichotomy
• Search for the real cause and implement effective corrective actions
• Or find the “appropriate person to blame” and do nothing else
Based in the article See & Flee in the Petrochemical Industry, by Jim Whiting and on 32 years of personal experience in design start-up, operation, and troubleshooting of direct reduction plants worldwide.
Investigations on fatal events in industrial plants in Mexico, Malaysia, Indonesia, India, and the North Sea, as well as in Australia according to Jim Whiting, bring a question to mind.
Were the workers aware that the mine conditions were unsafe and was that awareness translated into actions to reduce the risk? Or was the risk accepted as part of the job?
Especially after the recent evidence at Pasta de Conchos (explosion in a coal mine in Northern Mexico), and the “heroic” declarations of some politicians: “We will not rest until we have found and punished the person responsible!”
Particularly, in one of the companies where I was employed, a few years ago, two operators died in an explosion, there was a ball a fire that covered them during one of the product discharges. Unfortunately this was not an isolated event.
I remember the work environment and the spirit that moved us. Production is first, personal security was never mentioned, even though the official speech would say otherwise. We thought we were expected to be “machos”.
Nobody wanted to appear as a “chicken”.
In that period, even the use of dust masks was socially unacceptable. The use of fall arresting harnesses indicated fear or insecurity, and was taken as a bad example for the rest of the workers.
“Nothing is going to happen! We have worked like this for more than 35 years; we are not going to back up now, are we?” This was said to me by one of the company’s VP’s, when he wanted to install a video camera in the open discharge of one of the new reactors. When I was explaining to him that the camera had open electronic components and that the atmosphere was explosive, and that the dust was electrically conductive, he said to me “we’re not going to chicken-out, are we?”
I had to think fast and melt the fuses in the camera, so that we could not use it. I then designed a rig to put the camera in with minimum risk. The end result was there was indeed an explosion, but, fortunately, nobody was hurt, as they were using the appropriate equipment.
I lost the opportunity to move up in the administrative ladder, as there were two Vice Presidents and one Manager looking down into the reactor that day!
Explosions in the reactor’s charge and discharge were frequent; the balls of fire were, literally, fireworks. The personnel would play, throwing objects from high platforms to the new engineers. We would laugh at their fear when they heard an unexpected (for them), explosion.
Intoxicated employees and flames during maintenance and operation were part of the environmental conditions, especially in some of the loading bins and quench towers, where, more than once, we retrieved unconscious, burnt and, sometimes, deceased personnel.
Reports and discussions were confronted with opinions from people in higher positions with no on-site experience, or that were so brave as to not visualize the danger. A report on a risky situation was a sign of not wearing the company’s T-shirt, and it was a terminal career move.
But we never ran, we would always return to work, once the ball of flame had passed. Actually, we were really never afraid. Nobody reported anything, we all knew the environment we worked in and we considered it exciting and part of our work. Those who would stay away were criticized and stigmatized.
The question now is, how do we train the operators and maintenance personnel on when to run or when to be “macho”?
When is it OK to be afraid?
Unfortunately, in Mexico, the consequences for a fatal accident in a company are few, even though the official speech may deny it. So there are hardly any effective motivational and disciplinary policies, besides signs and useless statistics.
In some cases, the consequences have been limited to the loss of production, during the time it took to clean-up.
In Australia, in comparison, a plant can be shut-down indefinitely.
In other countries, the insurance company can refuse to pay de damages, and fines for a fatality are charged automatically, even before the investigation, and they can be considerable.
Even so, “the culture of production is first”, it is universal… and it extends to nuclear installations and even to NASA.
And the phobia to use the emergency shut-down button also.
Many years ago, when we were beginning to make use of computers to control chemical plant operations, we decided to install controlled shut-down buttons, baptized as “the panic” buttons.
Few of us could clearly see the conditions under which they should be activated.
We only knew that shutting down a complex installation without assistance from the control system was very difficult, due to the number of variables that the operator had to have in mind. (This button was installed after a catastrophic incident, similar, in sequence, but not in consequence, to the one in Chernovyl.)
Each operator would establish the criteria for activating the “panic” button.
An unfortunate name as it implied the lack of ability of the person who activated it. Our people were reluctant to activate the “panic” button, as it meant that they were afraid of something.
Years later an effort was made to change its name to CSB (Controlled Shutdown Button), a difficult task in the petrochemical industry. At least the name was changed in some drawings!
Later on, due to the persistence of one of the production managers, the shutdown button was used every time they had to shutdown the plant. So the “panic” part of activating the button was finally lost, and became a very comfortable addition to the operation environment.
A related incident happened not long ago, two operators followed by a Manager went to a platform to correct a problem. They all knew they could have the option of shutting down the plant, nevertheless, they decided to solve the problem, without using the panic button.
The apparent process control loss and the record of recent repeated plant shutdowns made them take a high risk decision that took their lives.
The situation had never been analyzed or drilled.
They made the wrong decision as a team (they did not work as a team; they supported the wrong decision due to an incorrect concept of solidarity.
The technical problem was finally tracked to a poor control loop tuning (the plant had been built using multiple contractors, each one supplying its own control system); the conflicts between control systems led them to block all but one computer during start-up, a shortcut that would cost them dearly.
But the issue here is, what led them to decide to put their lives on the line, when there was the option of shutting down the plant and starting-up again?
As with all investigations, pertaining to human performance problems, the principal challenge is to:
• Analyze which were the “good reasons” that made them take that risk.
• See what they took into account that made them believe that their opportunities of winning were better than those of loosing.
All this behavior depends on the perception of risk. Which was and is the perception of risk of the miners in the coal mine industry?
Three perceptions have been considered for this incident, at least, to try to interpret the motivation of the operators that died and the rest of the personnel involved.
1. One setting could be that they intentionally, or unintentionally, did, or did not do something that had created the problem, and they believed that they could correct the problem before anyone else could find out, possibly to avoid a professionally embarrassing situation or for fear of disciplinary actions. To activate a stop button and shutdown the plant would make everyone aware of the problem. They believed that, if they could solve the problem without stopping the process, then nobody would find out what had happened. In that particular case somebody had pushed the start-up button again, resetting the computer block-out during start-up. (The buttons were too close together and the operator’s attention was on controlling a dome.)
2. The second setting is that the emergency stop button had been given the name of “panic button” or “chicken button”. During our investigations we discovered:
• That there was a cultural expectation established among all the workers and management process, that the plant should not shut down for any change, unless you were “chicken”.
• Management would award those who were known to have been able to make a change without shutting down the plant. (They would also give more importance to the people who spoke English, no matter how inefficient they were.)
• This perception was reinforced when management would give contradictory or ambiguous messages referring to when to use the emergency stop button or the shutdown control button to stop the plant.
• Management honestly said that they had never told the operators not to use the stop button, and they probably frequently said otherwise, “your safety is more important than the process”, you have the power to shutdown the plant when you consider it necessary” and other similar euphemisms.
• BUT there had been some previous incidents when someone had shut the plant down and management had commented almost simultaneously, “Yes, you should have pressed the stop button, BUT we lost $250,000 Dollars worth of production”. The message that was relayed to the operators was ambiguous and they were left with a feeling that they had done something wrong.
• Adding to this, the personal image of the plant manager was that of a GI at work, people were afraid of discussing any issue with him.
You will agree that, frequently, the influence or pressure of our peers or bosses can have a great effect on how we perceive risk and how we perform in our jobs.
The third perception is familiar to all who have started plants up. There are many actions required in a plant start-up. There is much equipment involved and, normally, few people on hand. Therefore, the decision to shut-down the plant also takes into consideration the perception of the amount of work and time it takes to re-start it.
3. This third perception could be the main reason why the organization, not to say the operators, avoided activating the controlled shutdown button and do whatever possible to maintain the plant operating; in many cases not having the foresight of the risk that is being taken.
The message should be clear – and should be clear in the minds of Management, that all levels of the organization should frequently discuss the risk perceptions and risk expectations, as to how to handle tolerable/intolerable risk situations for special and real settings in their immediate work environments.
Fatal accidents, in particular, project a provocative and valuable concept, to be considered always in the meetings prior to the work and risk evaluation. Although we cannot give the names of companies or people that are involved, we can describe the conditions that gave origin, and their consequences, hoping the lessons will be useful for all, and hoping that you will never need to live these situations.
One of these could illustrate the case.
The operators knew, through smell, sounds and vibrations that an explosion was imminent and “saw and fled”; the supervisors stayed behind and died.
a) What determined that the supervisors should stay behind?
b) What was their perception of risk, conscious or subconscious?
c) And, their perception of duty?
d) What finally determined their behavior, and why did they stay?
e) Why do only the good employees get hurt and, sometimes, die?
f) Did the supervisors relieve that their boss’ wanted them to stay and die?
g) Did the supervisors ignore the risk?
h) Did they accept it consciously?
Some questions come to mind:
1) Was this discussed at any moment, among themselves, as to when they should stay and solve the problems, or when to run? Was this ever on the agenda?
2) Did their bosses ever discuss and analyze this setting at a previous meeting?
3) Did the operators consider themselves less responsible for the plant security and therefore ran?
4) Did they ever have a meeting with Management addressing this situation explicitly?
5) Was the company implicitly encouraging the supervisors to be in risky situations?
Using the knowledge we have gained after the incident, we ask:
Why didn’t we do what we were supposed to have done?
And now that we know what we have to do, why are we not doing it?
Confucius said at one point:
“If you know what you need to do and you do not do it,
then you are worst than before “
“To see what is right and not to do it, is want of courage”
The questions are actually simple.
From the answers, we should obtain actions to carry out, and not only assign guilt.
Actually, finding a guilty person or persons serves to satisfy the desire of vengeance; to try to destroy the opponent’s image little by little, will not reflect in substantial improvements.
The person selected as guilty will simply be substituted by someone else, possibly with less training and surely with less experience, who will be afraid of taking any decision.
Some questions that can be asked are:
• How many more settings of “see and flee” can be identified in our work places before having to take that decision when the time comes?
• Is there a trans-functional communication protocol that will inform us of other dangerous conditions?
All these questions should be made and discussed regularly, evaluating the answers, planning, practicing and stage-managing the actions and reactions within the work groups in your installation.
In the theatre, war and emergencies…
“You are what you drill”
• A systematic incident analysis tool used in many nuclear plants and employed to find root causes and the appropriate solutions, has proven over and over, how useful it is in the proactive risk evaluating process. For more information check their site www.taproot.com
A final challenge to be used in safety and hygiene group discussions at work is, what it means to be a hero (especially in the case of underground mining management and nuclear and petrochemical operations):
• Have you taken risks you should not have taken?
• Have you not reported deviations that could cause a tragedy, for fear of being seen as a coward?
To center a fatal incident analysis, in the search of someone to blame and to finish the analysis when that person is found, is a recipe for disaster.
Finding the root cause and taking the appropriate corrective actions is the only way out of the spiral. Closely following the corrective actions, and making sure they have done their job properly, will be the first step. If the information flow channel is kept open and objective between operation and management, this will insure further improvement, and a safer working environment.
Article by:
M. C. Marco A. Flores V.
tecmen1@gmail.com
TECMEN SA de CV
Applied Innovation
and
J.F.(Jim) Whiting
jim@workplaces.com.au
Risk@Workplaces Pty. Ltd.
Inherent Safer Technology: Onsite production of 12% hypo |
April 07, 2007 |
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Posted by EM Cudworth at 05:24 PM | Comments (0) |
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CASE STUDY: KLORIGEN™ SYSTEM PERFORMANCE Background Des Moines Water Works (DMWW) plays a key role in providing the city of Prior to selection, DMWW performed an economic evaluation of the various technology alternatives that were available to replace their liquid chlorine system, which then consisted of multiple one-ton cylinders of compressed elemental chlorine gas. Alternatives that were evaluated included: · Traditional high strength (12.5%) sodium hypochlorite (“bleach”) storage system dependent on frequent deliveries from third party suppliers using large tank trucks; · On-site electrochemical generation of commercial strength (12.5%) bleach using salt; and · On-site generation of low strength bleach (0.8%) that also used salt. DMWW made their decision in favor of a Klorigen™ on-site electrochemical system manufactured by Electrolytic Technologies Corporation, for the following reasons: a. production cost was originally projected (and continues) to be significantly less than the prevailing market price of commercially-supplied bulk hypo; b. on-site generated bleach produced by the Klorigen™ system was compatible with conventional commercial strength monitoring, measurement, pumping and storage systems; c. the Klorigen™ produced hypo was to be of equal - if not better quality than that commercially available and provide a consistent high concentration (at least 12.5%); d. compared to the low strength (0.8%) alternative, storage requirements for the high strength solution were was less - by a factor of 15; e. On-site production removed the risk of an accident from transporting hypo through the local community; and f. The Klorigen™ hypo product met the requirements for NSF/ANSI 60 certification. The final selection comprised a Klorigen™ system rated at 1,500 gpd of 12.5 trade % sodium hypochlorite and two 5,000 gallon storage tanks. Due to Klorigen’s unique modular design, DMWW was able to design their own OSG facility and managed the installation with internal personnel at minimal cost. The Klorigen™ on-site sodium hypochlorite generating system at DMWW was commissioned in the 1st quarter of 2004. Data depicting the performance of the Klorigen™ system was compiled using DMWW’s SCADA system. The system data collection began in the 3rd quarter of 2004 and the results in this study have been compiled through the 4th quarter of 2006. Table 1 shows the DMWW hypochlorite system production for a period of 30 months. The water plant sodium hypochlorite usage varies according to the time of year, with the highest sodium hypochlorite production requirement occurring during the summer months. Table1. DMWW Klorigen™ System hypochlorite production graph (30 month period) DMWW 12.5% Sodium Hypochlorite Generation Costs Table 1. DMWW Klorigen™ system quarterly operating costs for producing sodium hypochlorite versus the price for local sodium hypochlorite delivery. Table 1 above and Figure 1 below show the combined chemical and power operating costs per gallon of the DMWW Klorigen™ System for 12.5 trade% sodium hypochlorite over a ten calendar quarter (30 month) period. The chemical raw material pricing increased by about 20% in 2006 (salt, NaOH, HCl, and bisulfite) and is depicted as an increase in $/gal (2006) column. Figure 1. DMWW Klorigen™ system quarterly operating costs showing a base operating cost (2004-2005 pricing) and the impact of the raw material price increases in 2006. DMWW On-Site Sodium Hypochlorite Generation - Operating Cost Reductions Table 2 depicts the calculated quarterly Klorigen™ System operating costs and Figure 2 shows the cost savings over purchased sodium hypochlorite that the DMWW facility has had over ten calendar quarters of operation. The cost savings after only ten operating quarters have been nearly $360,000 and are already approaching the original capital cost for the system. Table 2. DMWW Klorigen™ System quarterly operating costs and calculated cost savings over purchased sodium hypochlorite. Figure 2. DMWW Klorigen™ System quarterly hypochlorite operating costs and savings in comparison to delivered purchased hypochlorite over ten quarters (30 months) of operation. {For a complete version of this report which includes photos, figures and tables, please contact: info@electrolytictech.com}
Iowa with a safe, clean and healthy water supply. The DMWW operates two water treatment plants in central
Fleur Drive in
Des Moines and the second one at Maffitt Reservoir, located southwest of the metropolitan area. Des Moines Water Works is an independently operated public utility providing drinking water to a population in excess of 300,000 in
Iowa , one of the largest 100 utilities in the country and nationally recognized as a water industry leader.
Des Moines Water Works' Fleur Drive facility is a surface water treatment facility rated for 100 million gallons per day (mgd) and pumps on average, 43 mgd. It draws water from three sources: the Raccoon River, the
Des Moines River and an infiltration gallery. The infiltration gallery is a large horizontal well that lies in sand and gravel sediment adjacent to the
Raccoon River . This source yields approximately 15 mgd of clean, naturally filtered river and ground water. The remaining demand is obtained from either the Raccoon or
Des Moines rivers. The selection of river water is based primarily on source water quality and the ability to treat substances in the water. Treatment strategy and design must accommodate rapid changes in river quality and water demand.
Powdered activated carbon is first fed into the selected river water for removal of man-made and naturally occurring organic chemicals. The water is then treated to remove dirt and debris and combined with water from the infiltration gallery system. The combined water then flows into softening basins. The pH of the water is then adjusted before the final filtering process. The water is passed through layers of sand and various sizes of gravel to remove any remaining particles. During periods of possible increases in nitrate levels, Des Moines Water Works activates its nitrate removal facility to remove this contaminant. Next, fluoride is added to aid in the prevention of tooth decay and then chlorine (in the form of solution sodium hypo-chlorite) is added as a disinfectant to kill bacteria. Finally, the now clean water is stored in a clear-well until pumped into the pipes of the distribution system.
