Certain plumbing design choices and building contractor practices can promote the growth of microorganisms in new plumbing systems. This can lead to corrosion of metals, increased metals concentration in the drinking water, holes in pipe walls, and waterborne illnesses. Basic steps can prevent the problem from occurring in the first place. INTRODUCTION TO DISASTER Read more
Water Quality
Certain plumbing design choices and building contractor practices can promote the growth of microorganisms in new plumbing systems. This can lead to corrosion of metals, increased metals concentration in the drinking water, holes in pipe walls, and waterborne illnesses. Basic steps can prevent the problem from occurring in the first place.
INTRODUCTION TO DISASTER
The story is repeated over and over. Occupants of a new building notice either discolored water coming from the water faucets or a “rotten egg” odor coming from the hot water.
Typically, what will happen next is that the plumbing contractor, realizing that corrosion is occurring, will pull the sacrificial anode rod from the hot water storage tank. The rod in a hot water storage tank is there to slowly corrode over many years, with the rod’s metallic properties diverting the flow of electrons to sacrifice itself to corrosion and protect the storage tank. But, in these cases, the anode rod has greatly corroded over a few weeks or months. The plumbing contractor will replace the rod, only to see the new rod corrode quickly again.
Stray electrical currents or the connection of dissimilar metals are then blamed for the system-wide corrosion. Wires are added to connect various parts of the piping system for diverting electrons to a different path.
The problem persists.
MICROORGANISMS AT WORK
What most people don’t know is that the problem is of microbiological origin. Microbiologically influenced corrosion (MIC) has not been appropriately understood or acknowledged in the drinking water industry—in municipal water systems or in plumbing systems.
Microorganisms are everywhere, and there are many different types of them. Some directly cause human illness and some do not. All waterborne microorganisms can grow into out-of-control populations when there are long periods of water stagnation or low flow and when disinfection chemicals are in inadequate concentrations. Under such conditions, microorganisms attach to plumbing system surfaces, both metal and non-metal. The microorganisms secrete an enzyme that forms a protective barrier around them, and they begin to multiply. This buildup of enzyme and microorganism colonies on surfaces is called a biofilm.
The biofilm is acidic and can create conditions at the pipe wall that allow metal to corrode. Metals that the plumbing sys- tem is made of, such as copper, iron, and even lead, have been found to corrode and their concentrations found to be increased in the drinking water when biofilms are present. Pinhole leaks in copper pipes have also been found. In addition, lower doses of chlorine and other disinfectants cannot reach the microorganisms protected in the biofilms. Instead, disinfectants get used up by reactions with the surface of the biofilms. This creates the environment for the growth of microorganisms that cause human illness if they are accidentally introduced into the water system.
Once a biofilm is firmly in place in a plumbing system, it is very difficult, if not impossible, to remove. It cannot be flushed with high-velocity water because the required water flows and pressures cannot be achieved in plumbing systems. The biofilm cannot be removed by disinfection because many modern plumbing materials, such as PEX® piping, cannot come in contact with the high concentrations of disinfection that are needed.
PREVENTIVE MEASURES IN PLUMBING DESIGN
Proper plumbing design is the first line of defense against the growth of microorganisms in a plumbing system. In general, in water with low or no disinfection, whenever an excessive quantity of water is stored and excessive surface area is available in the plumbing system, microorganisms can get the upper hand and form biofilms.
Plumbing designers should carefully plan the capacity of the water system. In modern plumbing systems, the high hot waterflow demands of large bathtubs and Jacuzzis control the plumbing system design. This leads to installation of large water softeners and hot water storage tanks which are oversized for typical water usage in the building when the tubs are not in use. This creates a long residence time for water inside the plumbing system.
Another area where biofilm development is typically found is in hot water recirculation systems. In larger residences and buildings, hot water is re-circulated between the faucets throughout the building and the storage tank in order to provide water at the desired elevated temperature immediately when a faucet is opened. The recirculation piping adds extra storage of water and residence time in the plumbing system and helps spread microorganisms from a location of biofilm development to other parts of the hot water system.
Water conservation devices also increase the time that water spends in the plumbing system.
Water treatment devices cause issues in that many remove disinfection from the water, provide a large volume of water storage, and provide greatly increased surface area on the treatment media, such as on physical filters, granular activated carbon, and softener resin.
There is no room in this article to discuss plumbing design details. Just be aware in plumbing design that disinfected water should flow in the plumbing system with minimum residence time and minimum surface area contact.
PREVENTIVE MEASURES DURING CONSTRUCTION
Construction of a building takes months and sometimes over a year or more. During this time, any water that has been introduced into the water service line and the interior plumbing system is stagnating in the pipelines and forming biofilms. Building contractors need to be aware of this. Routine flushing and disinfection of all on-site pipelines should be performed. The disinfection concentration, and even the microbiological activity, can be measured and documented to show that no problems occurred under the building contractor’s watch.
Although there are many details that can help prevent microorganism growth, generally be aware that flushing, disinfection, and monitoring can prevent the growth of microorganisms and the development of biofilms in the piping system.
SUMMARY
Everyone involved in the design and construction of buildings should be aware that microorganisms can and do significantly affect water quality in plumbing systems and can even weaken the pipe itself. Modern plumbing systems with large bathtubs, increased use of water treatment devices, materials of construction that cannot come in contact with high disinfection concentrations, and water conservation devices contribute to the likelihood that microorganisms will grow in the plumbing system and form biofilms on pipe and tank surfaces.
Plumbing designers can do their part in preventing the growth of microorganisms and the development of biofilms by minimizing the residence time of water in the plumbing system and the surface area that the water contacts. Building con- tractors can do their part by routinely flushing the pipelines, disinfecting the water, and documenting disinfection concentration and microbiological activity.
Bio
Abigail Cantor is the founder of Process Research Solutions, LLC, a chemical engineering consulting firm specializing in drinking water quality issues.
Contact Info
Phone: 608-233-3011
Email: info@processresearch.net
Website: ProcessResearch.net
Ecolab Equipment Care and Green Turtle Americas Announce Exclusive Distribution Partnership Company’s Equipment Care division becomes sole vendor and installer of Green Turtle’s Retroceptor™ and Microceptor™ in-kitchen wastewater treatment solutions ST. PAUL, Minn. – Oct. 29, 2013 – Ecolab’s Equipment Care division and Green Turtle Americas have formed an exclusive distribution agreement to provide innovative Read more
Ecolab Equipment Care and Green Turtle Americas Announce Exclusive Distribution Partnership
Company’s Equipment Care division becomes sole vendor and installer of Green Turtle’s Retroceptor™ and Microceptor™ in-kitchen wastewater treatment solutions
ST. PAUL, Minn. – Oct. 29, 2013 – Ecolab’s Equipment Care division and Green Turtle Americas have formed an exclusive distribution agreement to provide innovative in-kitchen wastewater treatment solutions to the U.S. restaurant and food service industry. Through the partnership, Green Turtle’s line of Retroceptor™ under-sink grease interceptors and Microceptor™ drain-line coffee ground interceptors will be sold and installed exclusively by Ecolab’s Equipment Care division.
“Ecolab customers appreciate innovative solutions that solve specific pain-points within their operations, and the in-kitchen wastewater treatment solutions we are offering with Green Turtle do just that,” said Mike Goede, vice president of Sales and Service, Ecolab Equipment Care. “This distribution partnership extends our product and service portfolio and will help food service establishments throughout the U.S. increase wastewater pre-treatment compliance and improve operational efficiency.”
Green Turtle’s certified Retroceptor grease interceptors have been engineered to efficiently treat greasy wastewater at the source, in the kitchen. Retroceptor systems eliminate drain-line blockages and help reduce the occurrence of sanitary sewer overflows. They deliver improved water quality to comply with local effluent regulations.
Microceptor drain-line coffee ground interceptors install easily under the sink to keep lines free from coffee ground build-up and help eliminate sink back-ups, preventing costly emergency plumber calls and drain-line maintenance.
About Ecolab
A trusted partner at more than one million customer locations, Ecolab (ECL) is the global leader in water, hygiene and energy technologies and services that protect people and vital resources. With 2012 sales of $12 billion and 44,000 associates, Ecolab delivers comprehensive solutions and on-site service to promote safe food, maintain clean environments, optimize water and energy use and improve operational efficiencies for customers in the food, healthcare, energy, hospitality and industrial markets in more than 170 countries around the world.
About Green Turtle
Green Turtle works with commercial and industrial customers to deliver innovative rainwater harvesting and wastewater pre-treatment solutions with industry-leading warranties. Their systems are flexible, easy to install and simple to maintain. Visit them at www.greenturtletech.com or call them at (877) 428-8187 (USA) or 1-877-966-9444 (Canada).
New Signet Optical Dissolved Oxygen Sensor Features Expanded Communication Capabilities GF Piping Systems has introduced the Signet 2610-41 Optical Dissolved Oxygen Sensor featuring expanded communication protocol capabilities. The 2610-41 Sensor utilizes optical technology to measure dissolved oxygen with high reliability and accuracy in a wide variety of applications. The new sensor model incorporates the Signet Read more
New Signet Optical Dissolved Oxygen Sensor Features Expanded Communication Capabilities
GF Piping Systems has introduced the Signet 2610-41 Optical Dissolved Oxygen Sensor featuring expanded communication protocol capabilities. The 2610-41 Sensor utilizes optical technology to measure dissolved oxygen with high reliability and accuracy in a wide variety of applications.
The new sensor model incorporates the Signet Sensor System Link (S3L) digital communication link that allows direct connection to the Signet 9900 SmartPro® Transmitter Generation III as well as to the Signet 8900 Multi-Parameter Controller. These connection capabilities provide enhanced system control and versatility.
The company’s Signet 9900 Transmitter Generation III supports the new sensor with a dedicated Dissolved Oxygen (DO) instrument that allows for selection of measurement type, ppm, percent saturation, or partial pressure of oxygen. The transmitter also allows for setting of system specific parameters to increase the accuracy of the dissolved oxygen measurement.
“The 2610-41 DO Sensor when used in conjunction with the 9900 Transmitter, provides an excellent cost-effective dissolved oxygen monitoring system,” says Dave Vollaire, Instrumentation Product Manager. “Plus, GF Piping’s optical dissolved oxygen technology requires no membranes or filling solutions that in other technologies need frequent replacing. This helps reduce maintenance costs.”
The 2610-41 incorporates all the inherent advantages of the original model including rugged materials of construction that can withstand the harsh environments of both fresh and saltwater applications. A built-in Modbus RS485 and 4 to 20 mA current loop outputs provide ease of interface to existing control systems. Operating capabilities feature a measurement range of 0 to 20 mg/L, 0 to 200% saturation, and accuracies of ± 0.1 mg/L for 0 to 8 mg/L and ±0.2 mg/L for 8 to 20 mg/L. An optical sensor cap with built-in calibration eliminates the need for field calibration and has a one year lifetime compared to membrane life, which is typically three to six months. The sensor is CE and FCC approved and available with two week lead-time.
The Signet Dissolved Oxygen Sensor is suitable for use in a wide range of applications including municipal and industrial wastewater treatment, drinking water reservoir monitoring, environmental water discharge monitoring and aquaculture and aquatic life support.
By Dave Duren Believe it or not…when I’m out in the field as I’m headed to San Diego right now…the most asked question I’ll get is “what exactly is softening?” And if they don’t asked…I’ll be bringing it up! If you asked 99% of the legitimate water treatment companies and or manufacturers; they respond by Read more
By Dave Duren
Believe it or not…when I’m out in the field as I’m headed to San Diego right now…the most asked question I’ll get is “what exactly is softening?” And if they don’t asked…I’ll be bringing it up!
If you asked 99% of the legitimate water treatment companies and or manufacturers; they respond by saying…Water softening is the “removal of mineral” from the water….plan and simple.
And mineral for the purpose of this article is mostly calcium and magnesium. (Other metals are also removed by the ion exchange process)I’m going to be talking about ion exchange process from here on out for clarification. So let’s review what is actually going on in that what softener. Inside of a water softener are millions of tiny beads that are man-made of a plastic material. They have a negative charge. Mineral has a positive charge. Water with mineral in it passed through the bed of “resin” and the mineral clings to these beads. As they cling, they release some sodium ions. This is where the term “exchange” comes into play. After a certain period of time the beads become full of mineral or as we say the bed becomes exhausted and it needs to regenerate. This process involves drawing a brine (“salty”) solution into the bed which flushes the mineral away and down the drain while allowing more sodium ions to cling to the beads to get ready for more actual softening.
There are basically three ways this whole process occurs. The first way is manually. Someone tells the unit the time when to start and stop. The second way is with an automatic time clock. The time clock is set to regenerate every certain amount of days. A couple of reliable industry valves have a 12 day wheel on them to control this period. This involves sliding out pins that trip the unit into the process every set amount of days, like every third day or so. The third and probably most popular these days is a metered system. This involves some type of water meter that will kick the unit into regeneration when a set amount of water has passed through it.
So to continue, if mineral is not REMOVED from water through ion exchange softening then some other method is used to try to prevent it from sticking to surfaces, (inside of pipes, inside of heaters and exchangers, showerheads, shower doors..etc.) And you might ask WHY it is sticking to surfaces anyway. This is due to the positive valence or polarity of the mineral itself. Many of the reputable companies use the term “Conditioning” or “Management” but do not say softening in their explanation as to how this gets done. So with that, I’ve broken this down into 4 general methods that are used although there may be other methods out there.
- Magnets and electricity
- Adding polyphosphates
- Creating acid water, mostly using citric acid
- Media based methods
Let’s talk about these in a general way. First magnets and electricity are merely an attempt to change the polarity of the mineral elements in the water. They are not easily changed and many revert back to their original state if ever changed in the first place.
Secondly are polyphosphates. They have been around a good long while. This product coats the inside of the pipes and anything downstream with a thin layer of itself situating itself between the water and surface. It also coats the mineral element and prevents it from attaching to other things. This method is good in some applications.
Thirdly, acid water created by using citric acid or other chemical is added to the water to reduce the ph of the water making it “acidic”. Acidic water then has a tendency to make the mineral not want to stick to surfaces. This method can work at times but also reduces all of the water’s ph and now introduces acid water to the entire plumbing system.
The fourth method is using medias. There are a few different ones on the market and they basically create an atmosphere wherein that the mineral either sticks to it or sticks to itself or another particle of something that is introduced into the water.
None of the above methods removes or even reduces mineral from the water but once again, merely tries to “control” the mineral’s positive polarity and prevent it from sticking to surfaces. Either inside the plumbing system on a surface (shower doors, dishes, showerheads, etc.) Some with some success and others with zero success. This is why “SALT-FREE SOFTENING” does not exist except in a few extreme cases using very expensive equipment and seldom seen in residential applications. It is also worth mentioning that NSF, National Sanitation Foundation and WQA, Water Quality Association both have standards and protocols for testing Ion exchange softeners. So as I’ve stated before, this is a very good way to tell if the equipment you’re being asked about or you yourself is trying to sell, is legitimate. Going to either website would also be a great way of learning more about what they do as organizations.
All of the above areas would command their own article or series of articles so take this as an overview. I think that you as a contractor need to at least be aware of the terms and methods because you will probably be asked by a customer. I think that when asked “what is softening?” you can simply say….”it’s REMOVAL of mineral from the water and the best and most economical, tried and true method is an ion exchange softener. I think it would be perfectly OK for you to tell your customer “Buyer Beware”…especially if they are asking or maybe even trying to tell you about some super wiz product they found on the internet or so slick guy called and tried to sell them over the phone.
I’d like to add that research and development continues to look for another method of SOFTENING water for residential use that will be efficient and affordable (which is what?….RIGHT!…REMOVING MINERAL FROM THE WATER!) as growing demand for this type of system exists. Until then ion exchange softening is the way to go to get the desired effects of actual SOFT WATER. Until next time…happy selling!
Microorganisms: The effects of on-site water treatment by Abigail Cantor, P.E. This article is part of a series discussing the growth of microorganisms in plumbing systems. As previously noted, many types of on-site water treatment equipment create conditions for microorganisms to grow and thrive by increasing the residence time of the water in the plumbing Read more
Microorganisms: The effects of on-site water treatment
by Abigail Cantor, P.E.
This article is part of a series discussing the growth of microorganisms in plumbing systems. As previously noted, many types of on-site water treatment equipment create conditions for microorganisms to grow and thrive by increasing the residence time of the water in the plumbing system with extra water storage volume, providing additional surface area for microorganisms to form biofilms on, and removing or using up any available disinfection to fight microorganisms.
The best practice in plumbing design is to provide on-site water treatment only when it is absolutely necessary to do so. It is also important to select the appropriate treatment system, to determine a proper location for the equipment in the plumbing system, and to size the equipment so that volume and surface area are minimized. Finally, automatic clean-in-place systems or manual cleaning protocols must be utilized to keep the equipment free of biofilms.
Determining Necessary Water Treatment
The first step in plumbing design is to determine specifically what contaminants, if any, are of concern in a building’s water source. To do this, one must consider that there are numerous chemical compounds and types of microorganisms that can potentially contaminate drinking water. Contaminants are identified and regulated in the United States with separate standards for municipal water systems, private water systems, and bottled water. See Table 1.
If the building is connected to a public water system, the water has already been rigorously tested for the list of contaminants listed in Tables 2 and 3. The results of those tests are public record, available at the regulatory agency that governs the state or territory where the building is located. The results are also sent to each water utility customer annually in the Consumer Confidence Report. There might be local issues to be concerned about, such as increasing concentrations of an industrial chemical in a public well. In that case, the property owner should keep track of water utility plans to resolve the problem and attend water commission meetings, read the water utility website, or call the water quality manager. If a building owner is not comfortable with the utility’s approach to removing the contaminant threat, then an on-site water treatment device should be used for removal. It would be a rare and special case to need such a device.
It is possible for building plumbing systems to receive debris from municipal water distribution system piping. Debris occurs in the distribution system when particles, like sand, settle out and when dissolved chemicals in the water, like manganese, iron, or aluminum, chemically precipitate out. The possibility varies with the nature of the water and the water utility’s pipe cleaning and replacement program. Debris can temporarily be entrained in the water during utility or road construction; it can happen seasonally due to water main flushing and other routine maintenance activities. If a property owner experiences discolored water at an intolerable frequency, then on-site removal of the debris may be desired.
There is also the possibility that a building’s plumbing system leaches contaminants into the water. Lead, copper, and iron are known to transfer from piping materials into water to varying degrees depending on characteristics of the individual water system.
If the property owner owns the water source, such as a private well, they must take the responsibilities of a water utility manager. After complying with any state regulations on water quality for private water sources, the property owner must decide what other contaminants they might want to test for and, if significant, remove. See Tables 2 and 3. A common issue for private wells is high iron concentrations which can precipitate out and stain sinks and laundry.
For both private water sources and municipal water, the hardness of the water can be an issue. Water hardness is mostly a measure of calcium and magnesium concentrations in the water. Depending on other characteristics of the water, including temperature, the calcium and magnesium can precipitate out of the water as solid compounds. The solids can cover heating surfaces in hot water heating systems, which in turn, will require more energy to heat the water; the buildup of solids will also reduce the life of the hot water heating tank. For this reason, it is more economical to remove hardness from water where hardness is greater than about 120 mg/L as calcium carbonate (7 grains of hardness). Many people argue that hard water for cold domestic use should be softened; they state that hard water will clog pipes, create spots on glass shower doors, and react with soap so that it will not lather. These are debatable arguments. Even in locations with very high hardness (300 to 500 mg/L as calcium carbonate or 17.5 to 30 grains), cold un-softened water does not typically cause these severe problems. Older residences in those locations only use softened water for the hot water system. It is only recently, with modern plumbing practices, that cold water is also softened.
Determining Type of Water Treatment System
When specific contaminants have been identified in the water, then the proper contaminant removal technique can be selected. The proper technique is the one that removes all contaminants of concern at the highest efficiency for the lowest financial and environmental costs. Below are descriptions of common on-site treatment techniques.
Activated carbon filters
Activated carbon is carbon, typically from charcoal, that has been processed to make it very porous. The more pores in the carbon, the higher the surface area. The higher the surface area, the more specific contaminants can be pulled from the water to adhere to the carbon, a process called “adsorption”.
Different chemicals have different attractions to the carbon. For example, heavier compounds have a greater attraction than lighter compounds. This means carbon filters will not remove every type of contaminant. In addition, the carbon can become saturated with contaminants and stop removing them. Most importantly, just before the saturation point, the concentration of contaminants in the water flowing out of the filter begins increasing at a rapid rate. Therefore, a carbon filter must be removed before the “breakpoint” of the least adsorptive contaminant or else the consumer will be drinking high levels of the contaminant that they intended to remove. Filter manufacturers make assumptions as to what contaminants might typically be in water and set a common time when filters should be changed. This may or may not be applicable in individual water systems.
Some carbon filters, such as certain ones that attach to sink faucets, are manufactured so that they combine treatment techniques within a small block of carbon. Like other activated carbon filters, they have their limitations as to what contaminants can be treated and for how long. In addition, the filters, themselves, can add contaminants to the water, based on compounds in the manufactured filter material. There are research projects looking into this phenomenon.
Reverse osmosis and other membrane technologies
Reverse osmosis is a treatment technique that places a membrane barrier in the water. The membrane is made of synthetic organic materials that do not have straight-through pores like a filter. Instead, the pores are like a microscopic maze that can prevent many dissolved contaminants from passing through. High pressure on the upstream side pushes the water, minus many of the contaminants, through the membrane.
There are other membrane technologies where the pores are straighter but very small. Those technologies remove specific contaminants at lower pressures than reverse osmosis.
Membrane technologies prevent a percentage of the incoming water from going through the membrane, and instead, the water is sent down the drain to waste with the rejected contaminants. The technique is not practical when it is too expensive to waste a percentage of the available water. In addition, the synthetic organic membranes can dissolve in contact with some chemicals that might be in the water. Chlorine used for disinfection is one of the chemicals and it is typically removed in a carbon filter upstream of the membrane.
Physical filters
Physical filters provide a physical barrier that can remove particles from water. The filters can be made of sand or flossy material that will not allow particles of a certain size to pass through.
Ion exchange/water softeners
Ion exchange is a treatment process where one ion is taken out of the water and others are put into the water in its place. An ion is an atom or molecule with either additional electrons or missing electrons; this gives the atom or molecule a negative or positive electric charge. Water softeners are an example of an ion exchange process. Here, calcium and magnesium, dissolved in the water as positively-charged ions, are “stuck to” negatively-charged ions. When in contact with the ion exchange material, they are attracted and adhere to the material. In exchange, the material releases two sodium ions for every calcium or magnesium ion; the sodium ions, then, form a union with the negatively-charged ions that were left behind in the water. In the case of softening, the sodium concentration increases in the water.
At certain intervals, the ion exchange material must be cleaned to knock off the exchanged ions and replenish the original type of ions on the material. In the case of water softeners, a solution of sodium chloride (brine) is used to flush out the ion exchange material. This regeneration process creates a waste stream of chloride-laden water that is sent down the drain and out to the wastewater treatment plant.
Iron and manganese removal
Dissolved iron and manganese in the water eventually react with an oxidant like oxygen or chlorine in the water and precipitate out as a solid on pipe walls, sinks, and laundry. To remove dissolved iron and manganese before it drops out elsewhere, an oxidant is pumped or bubbled into the water. After a certain contact time, the iron and manganese are oxidized to a solid form and the particles are filtered out in a sand filter.
The filter must be backwashed periodically to clean the solids out and send them in a waste stream down the drain.
Sequestering
Sequestering is used to hold metals like iron and manganese in the water and prevent them from precipitating out as solids. Traditionally, polyphosphate chemical products have been used in water systems to hold the metals in the water. This is especially done when a small water utility or private property owner cannot afford a treatment process to remove iron and manganese.
It is now known that the use of polyphosphates carries negative side effects. The polyphosphates not only can hold iron and manganese in the water but can also pull lead, copper, and iron from pipes and hold those metals in solution as well. The consumer drinks any concentration of the metals being held in the water. Polyphosphates also provide an essential nutrient, phosphorus, for the growth of microorganisms and in doing so, can aid in biofilm formation. Finally, as the phosphorus from the polyphosphates eventually flows to waste, the wastewater treatment plants struggle with meeting stringent phosphorus discharge limits.
Disinfection
This series of articles on the growth of microorganisms and the formation of biofilms in piping systems has emphasized that disinfection of water is a main weapon against microorganisms. With a clean piping system, it typically only takes a low dose of disinfection (0.3 to 0.5 mg/L free chlorine) to fight off intruding microorganisms and keep the piping system clean.
When on-site water treatment systems remove or use up disinfection in the incoming water, a dosing system should be added to replenish the disinfection in the water. For owners of private water sources, continuous disinfection of the water before and after any treatment should be considered.
Some people complain about the taste of chlorine in their water. If that is in issue, then drinking water can be left in a big pot open to the air or with cheesecloth covering it to allow the chlorine to transfer from the water into the air. Alternatively, chlorine can be removed by a carbon filter at the drinking water faucet. (Refer to the carbon filter discussion above.)
A more serious negative effect of disinfection is the possible formation of carcinogenic disinfection by-products. This can occur when the water has high naturally-occurring organic carbon compounds that react with the chlorine. If water is received from a municipal water system, disinfection by-products are tracked and minimized by regulation (Table 2); the property owner should re-chlorinate water within the concentration boundaries of the municipal utility. For private water sources, the owner should become familiar with the disinfection by-product forming potential in the water and chlorinate accordingly.
Determining the Location of the Water Treatment System
Treatment systems located at the point in the plumbing where the water enters the building is called a point-of-entry water system. Treatment systems located at the drinking water faucet are called point-of-use systems. The location of on-site water treatment in a building’s plumbing system is a critical design decision.
Point-of-entry systems treat the complete water flow to the building and are subsequently larger in size than point-of-use systems. This creates a greater possibility of biofilm formation in the treatment equipment from increased surface area and retention of water. It also increases the volume of water needed to clean and maintain the treatment system. Many point-of-entry systems remove or use up incoming disinfection and so all of the piping downstream of the treatment system is not protected from the growth of microorganisms unless a disinfection dosing system is added.
Although smaller with little or no waste streams, point-of-use treatment systems must be installed for every drinking water faucet, while point-of-entry systems are installed at one location only.
Water treatment equipment for specific needs, such as water softeners for hot water, should be located as close to the specific need as possible. Water softeners are typically located in a mechanical room adjacent to the water heating system.
Sizing Water Treatment Equipment
The goal of proper modern plumbing design should be to minimize volume of water retained and surface area of the treatment equipment. The larger the size of the water treatment equipment, the more volume of water is retained on-site and the more surface area is available for biofilm formation. As already discussed, one way to minimize volume is to eliminate treatment equipment unless absolutely necessary. In addition, the volume of water to be treated should be carefully considered. Divide the estimated total water use into: water for drinking/cooking, water for cleaning, and water for any significant purpose such as filling large bathtubs. Design separate pipelines and treatment strategies for each purpose.
Cleaning Water Treatment Equipment
Various types of water treatment systems have cleaning cycles. Sand filters must be backwashed to remove trapped solids. Ion exchange material must be backwashed to remove solids and must be regenerated to replace ions. Water treatment of this type has automatic clean-in-place cycles. The cleaning water can be chlorinated to disinfect and fight developing biofilms routinely. It is critical to work with the equipment manufacturer in setting up a cleaning water disinfection system; chlorine in too high a dose can destroy the treatment material.
Filters that require replacement of filter cartridges should be changed before or at the time recommended by the manufacturer to prevent breakthrough of contaminants and the development of biofilms.
Summary
This article continues the series warning against the growth of microorganisms and the formation of biofilms in plumbing systems. On-site water treatment systems can contribute to the growth of microorganisms by increasing the retention time of water, increasing the surface area where biofilms can form, and by removing or using up disinfection in the water.
The first step in plumbing system design is to determine which contaminants in the water are essential to remove on-site. In many buildings that receive municipal water, additional water treatment is not necessary. There is a greater need for on-site water treatment when the building is served by a private water source where the property owner must manage their own personal water utility. There are also special needs for water treatment such as the need to soften hard water before it enters a hot water heating system.
After it is determined what contaminants must be removed, the best removal system must be selected. Every treatment system has advantages and disadvantages and has specific removal efficiencies for each individual contaminant. The sizing of the water treatment equipment and its location in the plumbing system are also critical design choices affecting the growth of microorganisms.
Finally, all water treatment equipment must be cleaned and disinfected or filter cartridges replaced routinely to clean out and prevent the formation of biofilms.
Maintaining a high water quality, including the elimination of microbiological growth, is a very delicate balancing act that should be given the highest priority when designing a plumbing system.