Easy Test for ORP


Posted November 30th, 2019

 

 Testing for ORP with Potassium Permanganate

Editor’s Note: The instructions below, which we’ve modified a bit, were prepared by the original manufacturer of Filox-R iron removal media. The purpose is to provide a quick and easy way to determine if your water can be treated by standard manganese dioxide-based iron filter media like Filox without the use of additional oxidizers like chlorine, air, ozone, hydrogen peroxide or potassium permanganate. 

 

Oxidation Reduction Potential (ORP) can be the most important factor to take into consideration in certain waters. Highly reducing waters may cause premature exhaustion or even destruction of the Filox-R bed.

 

Precautions can be taken prior to installation that can prevent ORP problems. Use one of the screening tests and follow the instructions below if the subject water has reducing properties that will require additional oxidants. 

 

 The Simple Test

 

Mix 1.75 ounces (50 grams) water with 0.75 ounces (22 grams) of potassium permanganate crystals. Then take 2 drops of the mixture and stir into a fresh ¼ gallon (1 liter) sample of the subject water. Let the subject water stand for 15 minutes. If the pink color remains, Filox-R can be installed without additional oxidants. If the pink color disappears, additional oxidants will be needed for Filox-R to function properly.

 

The ORP Test with a Meter

 

Note: Must use a calibrated ORP meter. Any reading that is above a negative 170 millivolts indicates that Filox-R can be used effectively without additional oxidants. Any reading falling below a negative 170 millivolts indicates that additional oxidants will be required.

 

The amount of oxidant required for proper installation can be determined by measuring the amount of oxidant added to a specific volume of subject water until the solution remains pink or the meter reads at negative 170 millivolts or above. An extrapolation can then be made to determine the correct feed rate for the oxidant with respect to the subject water flow rate. Once installed, sample the solution after the injector and mixer and repeat the above test to confirm that the feed rate is correct.

 

How to Pick the Best Filter Cartridge

The “best” water filter cartridge is not necessarily the one that removes most contaminants or the one that treats the most gallons of water or the one that has the least pressure drop. The best for you is the one that does what is needed in your application.

This article makes some generalizations about water filter cartridges to help clarify what performance information provided by manufacturers means to the filter customer. We’re using “whole house” carbon filter cartridges, 4.5″ X 20″, treating chlorine and chloramine, to illustrate, but the principles apply as well to other filters, like sediment filters and “media” cartridges that are intended for problems like iron, turbidity, lead,  and nitrate reduction.

In general terms, the more tightly the filter media is packed together, the more effective the filter is at removing contaminants, but the more it restricts the flow of water through it and the more likely it is to become clogged by particles. The looser the media is packed, the less effective the filter is at contaminant removal, but the less it restricts the flow of water and the less likely it is to be clogged. Tighter means more effective performance but greater pressure loss.

Another generalization that’s true of most cartridges is that the slower the water goes through the filter, the more effectively it treats contaminants, the longer it lasts, and the less water pressure is lost. Conversely, the faster the flow, the poorer the performance, the greater the pressure loss, and the shorter the lifespan of the filter.

The art of selecting a filter, then, is to choose one that’s tight enough to be effective but not so tight that it restricts service flow or stops up easily. It must also be large enough to accommodate the needed service flow rate. Sometimes with cartridge filters to get a larger filter the most practical approach is to install 2 or more filters in parallel.  (See the picture below.)

To see how pressure drop, capacity, and micron size are related, here is a comparison of chlorine treatment figures for  two 4.5″ X 20″ MatriKX carbon blocks, identical except in tightness. (Micron size is the way filter makers state tightness: the lower the micron number, the tighter the filter.)

Two Identical Carbon Block Filters of Different Micron Ratings: Chlorine Reduction

MatriKX CTO MatriKX CTO+
Filter Type Coconut Shell Carbon Block Coconut Shell Carbon Block
Micron Rating Nominal 5 microns Nominal 1 micron
Chlorine Removal Capacity 34,000 gallons @ 7 gpm 160,000 gallons @ 7 gpm
Pressure Drop 8 psi @ 7 gpm 16 psi @ 7 gpm
Current Retail Price $68.00 $89.00

Considerations

The very tight CTO+ would seem like the better value in terms of gallons treated per cost, but it is very unlikely that in residential use such a tight filter would treat 160,000 before it stops up. Also, the excessive pressure drop gets even worse as the filter picks up particulate. Its performance is remarkable, but it probably is not the better choice for whole house residential treatment of chlorine.

The looser CTO has half the pressure drop. Most residential water use is at a rate below 7 gpm, so you can expect the 34K capacity of the CTO to go up. We’ve found the CTO to be an excellent residential filter for water treated with chlorine.

The pair of filters compared below are identical “radial flow” granular filters. Though both are rated at 25 microns, the chloramine filter evidently uses a finer carbon and is therefore a bit more restrictive.  These are very high grade radial flow cartridges, not to be confused with the standard axial flow cartridges that normally use regular-grind (not powdered) carbon and have much lower performance numbers.  (Axial vs. radial explained.)

Similar Radial Flow Granular Carbon Filters: One for Chlorine, the other for Chloramine

Pentek RFC20BB—Chlorine Grade Pentek CRFC20BB –Chloramine Grade
Filter Type Radial Flow GAC (powdered) Radial Flow Catalytic GAC (powdered)
Micron Rating 25 Microns 25 Microns
Chlorine Removal Capacity 70,000 gallons @ 4 gpm Unknown
Chloramine Removal Capacity Unknown

10,000 gallons @ 5 gpm

25,000 gallons @ 2.5 gpm

Pressure Drop

0.9 psi @ 4 gpm

2 psi@ 7 gpm

4 psi @ 11 gpm

1 psi @ 2.5 gpm

2.5 psi @ 5 gpm

5 psi @ 7 gpm

Current Retail Price $95.00 $168.00

Considerations

Reducing the flow rate more than doubles the lifespan of the chloramine cartridge. While this ratio doesn’t apply everywhere, as a general rule cutting the flow rate through the filter significantly adds to its life expectancy, adds to its efficiency, and reduces pressure drop. Therefore, running two filters in parallel more than doubles the valve of a single filter. In many cases using multiple filters actually costs less than using one, plus you get lower pressure drop.

doublecarbonfilter02

 Split installation: each filter gets half the flow rate. Efficiency goes up, pressure drop goes down, and cost goes down.

With a flow rate of 5 gpm, one filter treats 10,000 gallons with a pressure drop of 2.5 psi, but two filters treat 50,000 gallons with a pressure drop of 1 psi. What’s more, operation cost is 1.6 cents per gallon for one filter and 0.66 cents for two.

Flow rate matters!

Ultrafiltration Problems


Posted November 12th, 2019

Common Problems Of Ultrafiltration System Operations

By Nick Nicholas

Gazette Introductory Note: This article is being reprinted because it presents a concise, easy-to-understand explanation of the ultrafiltration process. It concerns use of UF for wastewater treatment, but the problems it raises–membrane fouling and scaling, waste stream disposal, etc.–apply as well to residential applications. We (Pure Water Products) do not currently offer residential ultrafiltration units for the whole home partly because the issues detailed in the article should be addressed by professionals rather than home owners, our main customers. –Gene Franks.

One facet of technological advancement is attempting to mitigate the more glaring issues that consistently crop up due to the nature of a system process. Of course, even with decades of improvement nothing is infallible. In this article, we will discuss the common issues that can occur using UF filtration systems.

Ultrafiltration is a pressure driven membrane separation technology that is a compact and refined filtration method utilized in drinking water and tertiary wastewater reuse applications. Its semipermeable membrane can remove solids as small as 0.01 microns, including silt and viruses. However, membrane filtration technologies will have problems without proper care for appropriate pretreatment, operation, and maintenance.

UF filter systems are typically affected by three main issues:

Membrane Fouling

UF filtration, like any other membrane separation technology including reverse osmosis, is susceptible to what is known as membrane fouling. In simple terms, fouling is what happens when particulate matter adheres to the surface of a membrane. The unchecked buildup will eventually cause reduced efficiency, a pressure drop, and increased energy consumption.

There are a few different types of fouling that can occur. Each has its own cause as well as some differences in effects. Of these membrane foulants, some are reversible and others are irreversible.

Solids

Suspended solids and colloidal particles collect on the surface of the ultrafiltration membrane as well as within its pores, preventing the flow of water through the membrane. This fouling occurs more commonly in applications with high turbidity and suspended solids without appropriate pretreatment.

Scaling

Membrane scaling is not unlike what happens in pipes that carry water with high concentrations of hardness materials. When the concentration of these dissolved minerals is high enough to surpass the saturation limit of the solvent solution, they begin to precipitate out of solution onto the surface of the membrane. These minerals can crystalize, which makes them nearly impossible to remove without some sort of chemical cleaning or antiscalant pretreatment. Calcium and magnesium are two primary minerals that can cause scaling to occur on the UF filter system’s membranes.

Microbiological

Biological contaminants like algae and microorganisms are often found in surface water sources. Provided with a warm environment and low flow rates, these contaminants will attach themselves to the surface of a membrane and begin multiplying. Over time, they can form a film that will prevent water from passing through the membrane and cause an increase in the trans membrane pressure differential. This increased pressure differential will put more strain on the pumps and increase the amount of energy they draw.

Waste Stream Disposal

This relates to the UF filter concentrate discharge. The filtration system did what it’s supposed to do and you have clean water that you can safely discharge into an outdoor stream without having to pay any environmental regulation fines. Or maybe you are going to reuse it somehow. Regardless of what is going to happen to it, you have this water resource.

However, what about all that contaminants that were removed? Sadly, this concentrate stream didn’t disappear into thin air, never to be dealt with again. Nope. It’s still there, whether it’s stuck to the membrane or sitting in a concentrate waste tank, and something needs to be done about it.

The problem is, you can’t just toss it out the window and call it a day. This reject wastewater is a concentrated form of whatever was in the feedwater. Therefore, in some cases, it may be safe enough to discharge into the environment; however, in others, the facility would be charged a hefty fine if it contains harmful pollutants.

Increased Permeate Contamination

This point is pretty rare for systems that are well maintained and monitored. To reiterate, permeate refers to the water that has been separated from the contaminating solids. It’s the clean water that you get out of this filtration process. Therefore, it’s definitely an issue when you start noticing that the quality of your permeate water is getting worse. Either there are larger solids or bacteria that should have been retained by the membrane contaminating the water.

This decrease in removal efficiency is usually indicative of a compromised membrane. Polymeric membranes can get worn out over time. High temperature or pH levels can degrade them pretty quickly, and without a decent pretreatment regime, rough particles can damage the inner pores of the membrane. To state the obvious, membranes do not work very well if they are full of additional holes (other than their pores of course). And now the system isn’t meeting it’s designed specifications and you have to replace the membrane and recirculate the contaminated permeate.

Source: Water Online.

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1,4-Dioxane


Posted November 10th, 2019

 

Residential Water Treatment for 1,4-Dioxane

by Gene Franks

dioxaneskull02

 

As with many contaminants, most of the research done on 1,4-dioxane treatment is focused on large applications like wastewater treatment plants and municipal water suppliers.  Often, methods that prove effective for large operations are impossible to apply to residential treatment. In the case of dioxane, advanced oxidation processes involving hydrogen peroxide with ultraviolet (UV) light or ozone and anion exchange with specialty resins are used with some success to treat 1,4-dioxane. These large-scale methods are not practical for residential users.

Information about 1,4-dioxane as a residential contaminant and how to treat it is scarce and inconsistent.  For residential treatment the old standby products carbon filtration and reverse osmosis seem to be the best things available, although very little actual testing seems to have been done to establish their effectiveness.
One North Carolina State University researcher says, “Most in-home water filters, including activated carbon filters, don’t remove 1,4-dioxane effectively. Reverse osmosis filters are better, removing a significant portion of the chemical from tap water, but still fall short.”  Not exactly helpful if you’re designing a home treatment strategy, but typical of the information available. One leading internet vendor recommends whole house reverse osmosis at $10,000. Between the lines reading of the not-very-helpful advice on residential treatment indicates that filter carbon works, but not as well as one would hope, that it works best if there is long contact time (large filters and reduced flow rates), and that nutshell carbon seems to work better than coal-based. As for reverse osmosis, everyone agrees that it is effective but no one has established any hard information about rejection percentages.

To plan residential treatment for any contaminant, one needs to consider first  how the contaminant is taken in by humans. In this area, too, there is a disturbing lack of information and a lot of contradictory information about dioxane. Water contaminants can be ingested by drinking contaminated water, or breathed in as a vapor or taken in through the skin. Showering is a common hazard since the contaminant can be taken in through the skin or breathed in if it vaporizes.  Arsenic, to illustrate,  does not evaporate into the air and is not easily absorbed through the skin, so there is little need for “whole house” treatment. Chlorine, conversely, vaporizes easily in the shower and also penetrates the skin, so whole house chlorine treatment is important.

Information about dermal and inhalation exposure to dioxane varies so much that it is essentially useless. The consensus is that it evaporates so quickly that dermal uptake is minimal; but this, of course, makes it more likely that it is breathed in during showering. To complicate the issue, because so many bath products are possible sources of the chemical, it is hard to know how much exposure is avoided by treating the water itself. It certainly makes no sense to install an elaborate and expensive system to remove 1, 4-dioxane from the water you shower with and then use a shampoo that contains the contaminant.

Treatment

Our recommendation for residential 1,4-dioxane protection is the same as for contaminants like fluoride, arsenic, and chromium. Install a high quality reverse osmosis unit that has at least two carbon stages for drinking water. An undersink  RO unit should be a standard feature in all homes.  For the whole house, carbon filtration, either as carbon block cartridge filters or a tank-style backwashing filter, provides broad protection against most contaminants and should reduce exposure to dioxane. We do not believe that installation of over-sized carbon tanks just to treat dioxane is advisable.

dioxanewastedrums

Leaking underground storage tanks at hazardous waste sites and discharges from manufacturing plants are important sources of 1,4-dioxane water contamination. Other significant sources of exposure to the chemical include personal care products like shampoos, deodorants and lotions as well as laundry products and household cleaning products. 

 

 

 

 

 

 

 

 

“Whole House” Reverse Osmosis for Less than $2500

 

The usual operating setup for “whole house” reverse osmosis is to allow the RO unit to produce water into an atmospheric (non- pressurized) storage tank and then use a pump to send the water into the home. This arrangement provides a large storage capacity for treated water (300 to 500 gallons is typical for residences). Standard whole house RO units might be capable of producing up to 1000 gallons or more per day to top off the storage tank as water is withdrawn and pumped to the home. Such setups require pretreatment and posttreatment for the RO unit and a shutoff system for the storage tank, plus the re-pressurization pump to deliver water to the point of use.

The system described on this page is a simple RO unit that uses a pressure tank which is very large version of the storage tanks used on undersink RO units. It is designed for use only in small homes — one or two people with low water use–or in other low use applications like offices, medical offices, or large homes with multiple sinks fed by a single RO unit.

This system features a ready-to-use Axeon 300 gallon-per-day RO unit that includes pre-treatment for sediment and chemicals and has carbon post-filtration built in. It is coupled with a high capacity pressurized RO storage tank.  No RO shut-off or re- pressurization pump is needed. The pressurized storage tank sends water to the point of use and the RO unit turns on automatically to refill the tank.
lt30020

The classy Axeon L1-300 RO unit uses standard-sized housings and membrane for easy replacement. It is a fully automatic unit that shuts off and turns on in response to changes in tank pressure. It is shown here with an optional mounting stand but can also be wall mounted.

 

Installation consists of connecting the RO unit to the storage tank.  We furnish the tee that joins the tank to the RO unit and sends water to the point of use.  Tanks come in 40, 60, and 80 gallon sizes.

 

romate80

ROMate 80 gallon pressurized RO storage tank. Large fiberglass reinforced RO tanks function exactly like well tanks. Water goes in and out through the single pipe at the bottom. 

 

Pages with more information:

Axion L1-300 RO Unit.

RO Tanks.

 

 

EPA Proposes New Regulations For Lead In Drinking Water

  by Paolo Zialcita

This is a National Public Radio news report, issued in late October 2019.

leadpipefromnewark

The Environmental Protection Agency has announced a new proposal that would change how communities test for lead in drinking water. It’s the first major update to the Lead and Copper Rule in nearly 30 years, but it does not go as far as many health advocates had hoped.

The regulations are aimed at stopping people’s water from being contaminated through lead pipes that connect public water supplies to homes. The EPA’s website points out that ingesting lead “can be harmful to human health even at low exposure levels.”

The proposal that was announced Thursday would require water systems to keep a public inventory of where those lead service lines are and help homeowners replace them if their water is found to be contaminated with lead.

If a water test shows dangerous lead levels, utilities would also have to notify their customers within 24 hours.

“By improving protocols for identifying lead, expanding sampling, and strengthening treatment requirements, our proposal would ensure that more water systems proactively take actions to prevent lead exposure, especially in schools, child care facilities, and the most at-risk communities,” EPA Administrator Andrew Wheeler said.

 

Elizabeth Warren Joins Bernie Sanders In Opposition To Water Privatization

by Peter Chawaga

Gazette Editor’s Note:  Politics aside, we’re reprinting this article because it presents water issues that should be part of our national political discussion. Private/public ownership of water supplies, regulation of emerging contaminants like PFAS,  the Waters of the United States rule, and development and maintenance of water infrastructure should all be important campaign topics. We should not let political candidates continue to ignore them. 

There’s little doubt that the field of candidates vying for U.S. presidential election in 2020 represents a wide array of views on nearly every issue. But two Democratic frontrunners now appear unified on at least one major issue: the privatization of water systems.

Elizabeth Warren, a Democratic presidential nominee who leads her colleague according to some polls, released an environmental plan that emphasized the need for the nation’s water systems to be run publicly, among other things.

“America’s water is a public asset and should be owned by and for the public,” according to Warren’s plan. “A Warren Administration will end decades of disinvestment and privatization of our nation’s water system — our government at every level should invest in safe, affordable drinking water for all of us.”

More specifically, Warren advocates for harsher federal classification of per- and polyfluoroalkyl substances (PFAS), the reinstatement of the Waters of the United States (WOTUS) rule, and investment into public water system infrastructure.

The emphasis on public water system management puts Warren firmly in alliance with Bernie Sanders, who has advocated for the same approach in the WATER Act that he released in February 2019 and in the Green New Deal, an expansive legislative proposal to revamp the country’s approach to environmental issues.

“Sanders introduced the WATER Act, which would help municipalities or state agencies bring treatment works back into public ownership,” per Common Dreams. “Months earlier, in November 2018, Sanders gave a forceful rejection of privately controlled water after voters in Baltimore easily passed Question E, which bans the privatization of the municipal water and sewer systems.”

By discouraging private water systems, both Warren and Sanders are highlighting research that indicates this management structure is less safe for consumers than public utility management.

“The private water industry serves 73 million Americans, according to National Association of Water Companies data,” The Huffington Post reported in a story on Warren’s climate plan. “For-profit water services put public health at risk, a 66-page paper by University of Louisville law professor Craig Anthony Arnold argues, because the profit motive incentivizes companies to provide better services to customers who pay more and to maintain infrastructure with an eye to the length of the firm’s contract.”

While Warren alluded to these inherent flaws with privately-run drinking water systems, her plan did not outline whether or not she’d actively work against their formation as president. But it did make clear that if Warren were to become the next president of the United States, privately-run water systems would become far less common.

“[The] proposal did not make clear whether a Warren White House would take explicit steps to discourage municipalities from switching to private water,” per The Huffington Post. “But the campaign said an influx of federal funding to overhaul water infrastructure should make switching to private water services far less appealing.”

Article Source:  Water Online.

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Ultrafiltration


Posted October 12th, 2019

Ultrafiltration: Between Conventional Filters and Reverse Osmosis

by Gene Franks

In water treatment, the term “ultrafiltration” is used to describe a filtration process that separates out particles down into the 0.1 to 0.001 micron range.

That’s extremely small when compared with conventional filtration, but it’s large when compared with nanofiltration and reverse osmosis. Ultrafiltration is tight enough to strain out pesky colloidal particles that conventional filters can’t hold, and it rejects both organic and inorganic large molecule substances. It cannot, however, remove ions and organics with low molecular weights (sodium, calcium, sulfate, for example), which are readily removed by reverse osmosis.

Molecular weight, in fact, is the yardstick by which ultrafiltration systems are usually measured. For example, an ultrafiltration membrane that removes dissolved solids with molecular weights of 10,000 is said to have a molecular weight cutoff of 10,000. Such a membrane has a nominal pore size of about 0.003 micron.

Compared with reverse osmosis, ultrafiltration membranes have extremely high flux rates. (Think of flux as the speed that the product water goes through the membrane.) They can also be operated at much lower pressure. As with reverse osmosis, temperature can have a great effect on performance, with lower temperature resulting in reduced flux rate.

Unlike conventional filters, ultrafiltration membranes do not trap and hold contaminants but like the reverse osmosis membranes they act as a barrier, holding contaminants until they are washed away. Ultrafiltration works in the same cross-flow separation method as reverse osmosis.

Ultrafiltration membranes do not trap and hold contaminants but like the reverse osmosis membranes they act as a barrier, blocking out contaminants until they are washed away. Ultrafiltration works in the same cross-flow separation method as reverse osmosis.

One great advantage of ultrafiltration membranes is that they can operate at pressures much lower than those required for reverse osmosis. In fact, UF systems usually operate at pressures below 100 psi, and 50 psi operation is common.

 

How Buying a Reverse Osmosis Unit Can Make You Rich

richandpoor

Guess which man owns a reverse osmosis unit.

We usually just assume that ingesting water contaminants like lead and arsenic is not a good idea. We don’t think about the economic implications.  We want our kids to be as smart and as healthy as they can be without having to put a dollar sign on the loss in IQ points that could result from their consuming water that is tainted with lead.

A recent study conducted by researchers from the University of Arizona and funded by the Water Quality Research Foundation (WQRF) sought to do just that: to determine the economic benefits of using point-of-use (POU) devices to reduce health risks in drinking water. The study was designed to put a dollar value on the benefits of treating five drinking water contaminant categories–microorganisms, arsenic, lead, disinfection byproducts, nitrates and chromium–with POU equipment.

Lead was considered apart from the other contaminants, since the Flint, MI ordeal offered a convenient way to study lead exposure. Here’s what resulted, as reported by Water Quality Products magazine:

In the case of the water emergency in Flint, the study assumed all of the 98,310 Flint residents were exposed to lead levels of 25 µg/L in drinking water, and 20% of lead in drinking water is manifested in the body as blood lead levels. This corresponded to an average blood lead level of 0.5 µg/dL and a loss of 0.257 IQ points. Using the blood lead level to lifetime economic impact model, this corresponds to a lifetime loss of $5,381 per person and a total community cost of $435 million. The average household size in Flint is 2.42 persons, which equates to 40,064 houses. A five-year community wide intervention using one activated carbon filter with lead adsorption capabilities per household would have cost $11.1 million. A five-year POU RO implemented in every home would have cost $26 million. 

This seems to mean that if each of the 40,064 houses had an RO unit that cost $648.96 to buy and maintain, and each of the 2.42 persons who lived in that home saved the $5,381 that would have been lost because of ingestion of lead, the per household profit resulting from RO ownership would be $12,265 from lead-avoidance alone. What is more, if instead of the RO unit the home installed an activated carbon filter with lead adsorption capabilities, which costs only $277, profit (savings less the cost of the filter) for the 2.42-person home would be even more, $12,637!

Clearly, the filter is the better choice since you can get the same dollar savings from lead removal that you would from the RO unit at a lower purchase price. More bang for your lead-removal buck. Of course, if you factor in the costs of exposure to arsenic, nitrates, chromium, fluoride, sodium, and more–items the RO removes but the filter doesn’t–the extra $400 you pay for the reverse osmosis unit doesn’t look all that bad.

richroowner

 A reverse osmosis unit is like money in the bank. The more contaminants they find in the water, the more you save.

The Water Quality Products article suggests that the cost saving figures that resulted from the Arizona study can be “leveraged” by water treatment professionals “to talk to their regulators and utilities about this study and encourage the acceptance of POU devices as a risk mitigation strategy.”

We at Pure Water Products will probably leave the leveraging to others and stick to our usual strategy of pointing out that with or without the dollar consideration, and whether you live in a 2.42-person home or a 6.79-person home, an undersink reverse osmosis unit should be a standard household appliance, not an optional item. What a great value! A device that produces pure, great tasting, contaminant-free water at a small cost. Getting rich in the process is just icing on the cake.

Reference Source: Water Quality Products.

 

Researchers find antibiotic resistant genes prevalent in groundwater

Historically, indirect reuse treatment methods in which an environmental barrier is an intermediary step in the water cleaning process have been more popular than the direct “toilet to tap” process. While indirect methods of water reuse treatment were, from a public perception and appetite, considered more reliable, it is actually direct reuse “toilet to tap” approaches which do not introduce an environmental buffer that produce safer, more pure water for potability. The reason for this lies in the way ARGs in the environment can contaminate potable reuse water. These findings were highlighted in a study published in Environmental Science & Technology Letters.

How ARGs Spread through Water Treatment Systems

While some ARGs are naturally occurring in microbial communities, antibiotics, ARGs and antibiotic resistant pathogens are on the rise in water sources as a result of the overuse of antibiotics in general. In a typical water treatment cycle, wastewater is treated first at a wastewater treatment facility. The study found that this water remains high in ARGs, as they persist throughout the treatment process. From here, water intended for potable reuse is further purified using advanced physical and chemical techniques including reverse osmosis—a process that uses a partially permeable membrane to purify drinking water.

In an indirect reuse schema, the purified water will be infused back into an environmental buffer, like a groundwater aquifer. Later, water is pulled from the aquifer and further treated at a drinking water treatment plant before being added to the public water supply. In contrast, in direct reuse approaches, purified water does not return to an environmental buffer, but instead, remains within the engineered water cycle, going from the wastewater treatment plant to the water reuse plant to the drinking water treatment plant and then out to your tap

Looking at the differences in ARGs between various water sources is incredibly important in considering future health hazards, like development of super bugs, said Smith. Since wastewater treatment plants are not generally designed for removal of micro-pollutants like antibiotics, they tend to persist in treatment systems, leading to high densities of ARG resistant bacteria at different stages of treatment. When this water is introduced into an aquifer, where ARGs are already naturally occurring, it can become contaminated with ARGs and antibiotic resistant bacteria. To further complicate the issue, ARGs are easily transferred through horizontal gene transfer, increasing the risk for antibiotic resistant pathogens.

“ARGs are not regulated in any way and are a challenging emerging contaminant of concern due to our reliance on biological treatment in the engineered water cycle,” Smith said. “Because they are biological contaminants—small fragments of DNA that are released to the environment—bacteria present in receiving environments can uptake them, becoming resistant themselves, and further perpetuating the spread of resistance.”

Wastewater reuse is the prevailing option for dealing with a mounting pressure on global water supply and might be preferable to options like desalination, which is expensive and energy inefficient by comparison. However, the danger of spreading antibiotic resistance is one that should inform which methodologies gain more traction and investment as we look ahead Smith said. Eliminating unknowns that persist in the environmental water buffers could be one way to ensure water that reaches our taps is clean of ARGs and other harmful contaminants.

“Lessening the global spread of antibiotic resistance will require an interdisciplinary approach that spans environmental and clinical systems. We must act fast before we enter a so called ‘post-antibiotic world’ where bacterial infections become impossible to treat,” Smith said.

 

Source: University of  Southern California.

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