Digging Deep into Water Treatment

Discussion in 'Grain, Hops, Yeast & Water' started by strange-steve, Oct 18, 2019.

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  1. Oct 18, 2019 #1

    strange-steve

    strange-steve

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    For a while now I've been thinking about writing a more in depth look at some of the various aspects of water treatment. The problem with that though, is that I'm not a chemist, or a scientist of any kind in fact, and so my understanding of this very complex subject is pretty superficial, other than a casual interest in general chemistry. So I decided to do some digging, reading lots of information and generally geeking out on the more technical aspects of water treatment, starting initially with chlorine removal (part 2 will deal with alkalinity adjustment and part 3 will be about additions of calcium salts, although I haven't started those parts yet so don't hold your breath waiting).

    I started taking a few notes, researching until I understood the processes (to some extent at least), then tried to piece it all together in a coherent way and this is the result. Now the fact that I don't have a science background means that there's a good chance of a few errors in this, in which case feel free to point and laugh, but also let me know so that I can correct them. Also note that obviously none of this is based on my own research, so I've listed all of my references at the end.

    If you're new to brewing water treatment, this probably isn't for you (have a look at the beginners guide instead). In fact this type of post probably has a fairly niche audience, but I've no doubt that there are others who like to understand the theory behind the advice we receive, and those people might find this interesting. There is however a TL;DR bullet point version at the end if you want to skip the chemistry and maths, but where's the fun in that. Get comfortable because this is a long one, and without further ado…
     
    Last edited: Oct 18, 2019
  2. Oct 18, 2019 #2

    strange-steve

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    Part 1 - Removal of Chlorine and Chloramine

    Water Chlorination
    No doubt we're all familiar with chlorine to some extent. It's a highly reactive element and a strong oxidising agent, widely used as a water treatment agent due to its biocidal qualities as well as a disinfectant in the form of bleach (sodium hypochlorite solution). Before we get into the reasons why removal is so important for brewing water, let’s look at the chemistry of chlorination which will then help us understand the mechanisms at work during dechlorination.

    So chlorine is typically added to water supplies in the form of either elemental gas or sodium hypochlorite. When chlorine gas is dissolved in water it forms hydrochloric acid (HCl) and hypochlorous acid (HOCl) [1]:

    Cl₂ + H₂O ⇌ HCl + HOCl

    The hydrochloric acid will then dissociate to H⁺ and chloride (Cl⁻) ions, so you get this:

    Cl₂ + H₂O ⇌ H⁺ + Cl⁻ + HOCl

    Hypochlorous acid is a weak acid, so the amount of ionisation (into H⁺ and hypochlorite (OCl⁻) ions) is pH dependant. Below pH 6 there will be no ionisation, but at a typical tap water pH of 7.3, around half of the chlorine will be in the form of hypochlorous acid, and half will be in the form of hypochlorite anions, and so you're left with this reaction:

    2Cl₂ + 2H₂O ⇌ 3H⁺ + 2C⁻- + HOCl + OCl⁻

    This is interesting (maybe pushing the definition of interesting there) because hypochlorous acid has much more (about 60-80 times more) disinfection ability than hypochlorite ion does, which is why acidified bleach is significantly better for disinfection than standard bleach.

    If chlorine is added by the water company in the form of sodium hypochlorite rather than chlorine gas, the reaction is similar except that sodium hydroxide (NaOH) is formed instead of hydrochloric acid:

    2NaOCl + 2H₂O ⇌ 2NaOH + HOCl + OCl⁻ + H⁺

    Sodium hydroxide (aka caustic soda) is an alkali, raising the pH of the solution, meaning that there will be less hypochlorous acid and more hypochlorite ion compared to chlorine addition through elemental gas.

    Water Chloramination
    Chloramine may not be as well known as chlorine, however the distinctive "swimming pool" aroma typically associated with chlorine is actually the aroma of chloramine. Chloramine (typically monochloramine) is a compound formed from the reaction of ammonia and chlorine (NH₂Cl). This can occur naturally in chlorinated water supplied when free chlorine present in water (in the form of HOCl or OC⁻) reacts with ammonia derivatives, known as amines, from organic substances.

    Chloramination is also sometimes used as an alternative to chlorination of tap water, because it is more stable than chlorine and produces fewer disinfection byproducts. As far as I can tell (which actually isn't very far) most water authorities in the UK don't use chloramine (yet) but there are some who do, and it seems to be getting more common. As mentioned above though, even if it's not used by your water supplier, monochloramine can form in your water supply if there is naturally occurring ammonia from organic substances (amines).
     
    Last edited: Oct 19, 2019
  3. Oct 18, 2019 #3

    strange-steve

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    Chlorophenols
    The reason that this is relevant to brewing, is that free chlorine in the form of hypochlorous acid and hypochlorite ion, and chloramine can react with substances found in wort and beer, namely phenols, to produce particularly unpleasant off-flavours. The reaction between chlorine and phenolics produces chlorinated phenols (no surprise), also known as chlorophenols.

    These substances have a distinctive "antiseptic" aroma, often described as medicinal, band aid, plastic, mouthwash etc. If you've ever smelt TCP then you know what chlorophenols smell like, because it's essentially a mixture of halogenated (eg chlorinated) phenols.

    The unfortunate thing about chlorophenols is that they have a tiny taste threshold, measured in parts per billion (in fact Randy Mosher suggests that 0.5 ppb is enough to ruin your beer!) and once they're in your beer, they're there for good [2]. This isn't an off flavour that will be fixed by aging.

    Phenols are aromatic compounds found in beer and they have various sources throughout the brewing process, and this is actually a huge topic in itself, but we won't go down that rabbit hole here (if you want an excellent article on beer phenols see reference 17).

    I've heard that chlorophenol off flavours are more likely to occur when fermenting with a POF+ yeast strain, which may sound plausible initially. A POF+ (phenolic off flavour positive) yeast strain is one which carries the gene that enables it to excrete a ferulic acid enzyme, catalysing the reaction which converts ferulic acid into the phenol 4VG, which has a spicy, clove-like flavour found in German and some Belgian style beers [3].

    The problem with this theory however, is that the amount of phenols produced by the yeast is tiny in comparison to the amount which comes from the malt during mashing, and from the hops during the boil. It also seems to ignore the fact that ferulic acid is itself a phenolic compound, even before conversion by the yeast. That being said however, there may be other factors and mechanisms at work here (such as transformation of phenol compounds) and it's difficult to find much more than anecdotal evidence on this theory.

    Either way though, there are plenty of sources of phenols to react with free chlorine and chloramine if it's present in the water, there have been 67 identified basic phenols in beer and hundreds of phenol complexes [17].

    The point is that you can't keep phenols out of your beer (nor would you want to, phenols have many positive as well as negative flavour impacts on beer), but you can eliminate the chlorine, thereby avoiding spoiling your brew with chlorophenols. So let's now look at some of the methods that can be employed to remove chlorine and chloramine.
     
    Last edited: Oct 18, 2019
  4. Oct 18, 2019 #4

    strange-steve

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    Evaporation
    The first and most simple method used is the evaporation method, collect the full volume of water and leave it uncovered overnight to allow the free chlorine to dissipate. This occurs because the water is no longer under mains pressure (Henry's Law), however, is this an effective method?

    Well, there was a clue there, free chlorine, which doesn't include chloramine. So while this may be an effective way to remove free chlorine (HOCl and OCl⁻) it's less effective for chloramine which is more stable. In fact, this is why it's used by some water suppliers.

    There are various factors involved in the rate of chlorine evaporation, such as aeration, circulation, volume, surface area, temperature etc. so it's difficult to determine exactly how long this method of dechlorination takes. There's a nice table in reference 18 which shows some experimental data on this subject, but just to pull some figures from it:

    At a typical tap water chlorination dosage of 0.5 ppm free chlorine, it could take up to 27.5 hours for complete evaporation from 38L of undisturbed water. Aeration and circulation of the water speeds this up to about 4.5 hours.

    Chloramine at the same dosage however can take up to 86.5 hours for complete evaporation in undisturbed water and about 34 hours in aerated and circulated water.

    Note that 0.5 ppm is typical for free chlorine in tap water in the UK, but that's not to say it won't be higher than this. Although there is no PCV limit for free chlorine, the WHO recommended maximum is 5 ppm [4].From looking at my own water report the maximum recorded value is just over 1 ppm (although the average is indeed 0.5 ppm). In those instances the time periods above would need to be significantly higher for effective dechlorination and dechloramination, so from a time efficiency perspective this may not be the most effective method to use. Note also that these timings could vary greatly depending on other variables as mentioned above.

    Exposure to sunlight is one method of speeding this process up. Photolysis of hypochlorous acid and hypochlorite ion will break these down into hydrochloric acid and chloride respectively plus oxygen gas. Again, this will work on chloramine also, but at a much slower rate [5].

    Boiling
    Another method of dechlorination is boiling of the water prior to use. This is related to the above method as similar mechanisms are at work, however boiling speeds up the process because gas solubility decreases as temperature increases. The article in reference 18 shows that there is, as expected, a dramatic reduction in the length of time required to remove both chlorine and chloramine when the water is boiled. Again with 0.5 ppm free chlorine in 38L of water it took less than 2 mins of boiling for dechlorination. However with the same amount of chloramine it took around 32 mins of boiling for dechloramination. (For some more in depth research on this see reference 19, where it's shown that chloramine has a half-life almost 15 times greater than free chlorine in boiling water).

    So these two methods, leaving the water exposed for several hours or boiling the water, while effective may not be the most time or energy efficient methods for removal of chlorine and chloramine. There are some other options available, so let's look at those.
     
    Last edited: Oct 19, 2019
  5. Oct 18, 2019 #5

    strange-steve

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    Ascorbic Acid
    Ascorbic acid addition is another method which is effective for removal of both free chlorine and chloramine. Ascorbic acid (aka vitamin C) dechlorination is superior to the previous methods, from a time efficiency perspective at least, because the reaction is almost instantaneous, however there are other aspects to consider. The reactions with free chlorine are as follows [6], I've left out the chemical formulas here because they're quite long:

    Ascorbic acid + hypochlorous acid = dehydroascorbic acid + hydrochloric acid + water

    Ascorbic acid + hypochlorite = dehydroascorbic acid + chloride + water

    But what about those products? Well hydrochloric acid will dissociate to H⁺ and chloride, meaning a slight reduction in alkalinity (very slight given the small quantities we're working with here) and increase in chloride, a desirable ion in brewing water. Dehydroascorbic acid is basically an oxidised version of ascorbic acid which is sometimes used as a vitamin C supplement, so again nothing to worry about there, especially in such small quantities as we'll see.

    How about the more tenacious chloramine? Again ascorbic acid works well as a dechloramination agent, although the reaction is slower. The reaction is:

    Ascorbic acid + monochloramine = dehydroascorbic acid + ammonium + chloride

    As for that ammonium product, from a brewing perspective this is no bad thing, ammonium in small amounts is a yeast nutrient as it acts as a nitrogen source for yeast growth but we can see now how small the dosing is…

    Applying a little stoichiometry to the equations we can determine that 0.5 ppm of free chlorine or chloramine would require an addition of around 1.7 ppm ascorbic acid for complete removal, which would leave after reaction a little less than 1.7 ppm dehydroascorbic acid, 0.3 ppm chloride, and 0.2 ppm ammonium. If you're unsure of your chlorine levels then as you can see, overdosing just to be safe could be a reasonable option with no ill effects, in fact some brewers add much more than this to their beer due to the antioxidant properties of ascorbic acid [14]. Practically speaking, trying to measure out <0.1 g of ascorbic acid to dechlorinate 35L of water isn't going to be terribly precise anyhow, so a small pinch would be reasonable amount.

    This may be an efficient option for homebrewers, you can buy 100 g of ascorbic acid (probably a lifetime supply) for only a few pounds and the reaction is quick enough that it wouldn't disrupt your brew day.
     
    Last edited: Oct 19, 2019
  6. Oct 18, 2019 #6

    strange-steve

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    Activated Carbon
    The next method to look at is activated carbon filtration. A common type of water filter in the UK is the Brita filter, which is a combined activated charcoal and ion exchange filter. The fact that there is an ion exchange resin in the filter means that these types of filter are quite unsuitable for brewing water.

    An ion exchange works (as the name suggests) by removing ions responsible for water hardness, ie calcium and magnesium, and replacing them with another ion, typically sodium, which does not contribute to water hardness. The water flows through a column of sodium-saturated polymer beads, designed to attract calcium and magnesium more strongly than sodium, and so when these ions bind to the polymer sodium is displaced into the water to maintain a zero net charge.

    The issue with this type of filter, from a brewing perspective of course, is that calcium and, to a lesser extent, magnesium are desirable ions whereas sodium is generally best kept at a relatively low concentration. In other words, an ion exchange filter removes the good stuff and replaces it with bad (or probably more accurately "less good") stuff. (Note this will be explored more in part 3.)

    You can get, however, activated carbon filters without the ion exchange resin and these are a very effective dechlorination method. So what's actually happening? Well activated carbon is usually sourced from coconut shells (at least for home water filters) which are exposed to high temperatures for carbonisation, and then processed to increase surface area. It's this high surface area, microporous property which makes it "active", commonly known as granulated activated carbon (GAC).

    The mechanism at work during dechlorination is, rather than absorption of the free chlorine, a redox reaction between the carbon and hypochlorous acid and hypochlorite ion [8]. The reactions are:

    C* + HOCl => C*O (oxidised carbon) + H⁺ + Cl⁻

    C* + OCl⁻ => C*O + Cl⁻

    So the only products of these reactions are hydrogen and chloride ions (the oxidised carbons are surface sites on the GAC particles and are not released into the outgoing water). Interestingly in the case of chloramine, there are two reactions which take place, depending on the amount of oxidation of the carbon. With a new filter the top reaction takes place, but as the activated carbon is oxidised the second reaction takes place. The more oxidised carbon there is (ie the more the filter has been used) the more the ratio will swing towards the second reaction:

    C* + NH₂Cl + H₂O => C*O + NH₃ + Cl⁻ + H⁺

    C*O + 2NH₂Cl => N₂ + H₂O + 2Cl⁻ + 2H⁺ + C

    As you can see the first reaction produces ammonia and chloride, whereas the second one produces nitrogen and chloride. Nitrogen is certainly more preferable than ammonia, but practically speaking we're dealing with very tiny amounts so there isn't really any issue for us.

    There are several variables which impact the speed of dechlorination and dechloramination, such as particle size of the GAC (smaller particles means greater surface area and therefore faster dechlorination), water temperature (higher means faster reaction), and pH (lower means faster reaction) for example [7]. However another very important factor in this is the length of time the water is in contact with the GAC, known as empty bed contact time (EBCT). This is equal to the volume of GAC (L) divided by the flow rate (L/min).

    It's the EBCT that will determine the effectiveness of chlorine/chloramine removal. As you might expect, the reaction with chlorine happens pretty quickly, but chloramine takes considerably longer, probably at least 4 times longer. The recommended EBCT for chlorine removal is about 30-40 seconds which will reduce free chlorine by about 95%, and around 6 minutes for chloramine.

    Converting these to flow rate is obviously dependent on the size of the filter, the larger the volume of GAC, the faster the flow rate will be for the same EBCT. However, a typical 10” GAC filter for domestic use (like this one https://www.uk-water-filters.co.uk/...-replacement.html#product_tabs_video_contents) may require a flow rate of around 4 L/min for effective chlorine removal, which is very reasonable, but a flow rate of around 400 ml/min or less might be necessary for dechloramination [9]. This may not be practical (or even possible) and so this may not be the most efficient option for brewers.
     
  7. Oct 18, 2019 #7

    strange-steve

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    Metabisulphite
    Another method of dechlorination is a metabisulphite addition, typically in the form of sodium metabisulphite (SMBS) or potassium metabisulphite (PMBS). [Note that for this discussion I'll be talking about SMBS, but PMBS can for our purposes be used interchangeably because it's the anion, ie the metabisulphite part, that's the active ingredient as far as we're concerned. The only real difference is residual potassium rather than sodium, but these are trace amounts and so not of any practical concern.] This is commonly sold by homebrew stores as Campden tablets, which were originally developed in the 1920s in Chipping Campden (hence the name) as a simple method of fruit preservation, and SMBS is primarily used today as a food preservative and antioxidant [10].

    So first of all, let's look at the rather complex chemistry of the humble little Campden tablet. Sodium metabisulphite (Na₂S₂O₅) is typically used as a source of sulphur dioxide (SO₂) due to its biocidal qualities. The fact that bacteria and certain wild yeast strains, such as the apiculate yeasts found on grapes, are very susceptible to SO₂ while Saccharomyces strains are much more resilient makes this a very useful substance for wine and cider makers. But it's the dechlorination effect that we're interested in for now, so what's actually happening?

    Well the sulphur dioxide is released when the Campden tablet is dissolved in water, along with sodium and hydroxide ions [11]:

    Na₂S₂O₅ + H₂O = 2SO₂ + 2Na⁺ + 2OH⁻

    The sulphur dioxide in solution forms sulphurous acid (H₂SO₃) which partially dissociates to form bisulphite (HSO₃⁻) and sulphite (SO₃⁻²) anions, along with H⁺ cations:

    SO2 + H₂O -> H₂SO₃ -> (H⁺ + HSO₃⁻) + (2H⁺ + SO3-2)

    The actual relative concentrations of sulphurous acid, bisulphite, and sulphite are dependant on pH and temperature, and it makes the actual dechlorination/dechloramination process rather complex because you end up with many different chain reactions taking place [12]. So for the sake of simplicity let's skip those intermediate reactions and also isolate the chlorine from the hypochlorous acid and hypochlorite ion. In practice the products are the same, but we can leave out some of the irrelevant hydrogens and oxygens from the equations, and just be aware that this is the simplified version.

    So the basic reaction of SMBS in solution with chlorine can be written [13]:

    Na₂S₂O₅ + 3H₂O + 2Cl₂ = 2Na⁺ + 6H⁺ + 2SO₄⁻² + 4Cl⁻

    SMBS + water + chlorine = sodium + hydrogen ion + sulphate + chloride

    And the reaction with chloramine is:

    Na₂S₂O₅ + 3H₂O + 2NH₂Cl = 2Na⁺ + 2H⁺ + 2SO₄⁻² + 2Cl⁻ + 2NH₄⁺

    SMBS + water + chloramine = sodium + hydrogen ion + sulphate + chloride + ammonium

    So the products are sulphate and chloride (both of which are often added to brewing water for their positive flavour contributions), sodium (again this is sometimes added in small amounts for its flavour effects), ammonium (yeast nutrient as a source of nitrogen), and hydrogen ions (which increase acidity, although we're using very small amounts so the actual effect on pH will be tiny).

    Using the equations above, we can determine the amount of SMBS required for dechlorination per 1 ppm like so:

    0.25 mol SMBS (190.11 g/mol) reduces 1 mol of chlorine (35.45 g/mol)

    1 ppm chlorine = 0.0282 mmol/l (1 / 35.45)

    0.0282 mmol SMBS = 5.36 mg (0.0282 x 190.11)

    5.36 x 0.25 = 1.34 mg

    So 1.34 mg of SMBS will reduce 1 mg of free chlorine. To convert that to the real world, I weighed some Campden tablets on my jewellery scales (0.01g resolution) and believe it or not they weighed exactly 0.5 g each. That means that one tablet will dechlorinate 746 litres of water with a typical free chlorine level of 0.5 ppm! So for a 20L batch of beer you might use 35L of water, which would require a SMBS addition of 23 mg.

    Obviously it's not really practical to try to use 1/20th of a tablet, plus (as mentioned earlier) although 0.5 ppm is a typical level of free chlorine, levels of double this (and more) aren't uncommon, so let's take a look now at the effects of overdosing your water with SMBS, what impact would it have to add half a tablet to 35L of water? Well this is equivalent to roughly 7 mg/l which would add the following to your water:

    Sodium ~ 2 ppm
    Sulphate ~ 7 ppm (assuming complete reaction, but in practice it will almost certainly be less than this)
    Chloride - this will be equivalent to the level of free chlorine or chloramine reduced, so probably < 2 ppm
    Hydrogen ions < 1 ppm which will reduce alkalinity by a tiny amount
    Ammonium ~ 1 ppm (dechloramination only)

    So even though half a tablet per 35L is much more than required, you can see that the residual products are negligible, plus this amount will ensure dechlorination up to 5.2 ppm of free chlorine, as well as being easy to measure out, so I would suggest this as a good dosage to use. Any surplus unreacted bisulphite and sulphite will not have any adverse effects, and in fact may have some benefits in terms of reducing dissolved oxygen in the water [14].

    With regards to chloramine, twice as much SMBS is required per 1 ppm compared to chlorine, and so the suggested dose of half a tablet per 35L will be effective up to a residual chloramine level of 2.6 ppm, which is more than the typical level found in drinking water even when chloramine is used as the primary disinfectant [15].

    So campden tablets seem like they could be the most efficient option for both dechlorination and dechloramination, the reaction takes place very quickly (2 minutes contact time is more than enough [13]) and currently 100 tablets (enough for 7000L of water at the recommended dose) cost around £3.
     
    Last edited: Oct 19, 2019
  8. Oct 18, 2019 #8

    strange-steve

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    Summary
    Yikers, this has ended up being much longer than I expected when I started, so let’s try to summarise some of the main points from above as a TL;DR version:

    • Most water suppliers in the UK use chlorine rather than chloramine as the primary disinfectant, but chloramination is becoming more common (for example some suppliers which do use chloramine in at least some of their treatment plants are BWH Water, Dee Valley, Sutton and East Surrey, Thames Water, Welsh Water, Yorkshire Water [16])
    • Even if chloramine isn’t used as a disinfectant by your water supplier it can still form in the water through reaction with amines from organic sources (this is what causes the strong “chlorine” smell, which is actually chloramine, in public swimming pools)
    • Tap water typically has a free chlorine concentration of ~ 0.5 ppm, however it can be higher than this (the maximum allowable concentration in drinking water as recommended by WHO is 5 ppm)
    • Chloramine concentrations in tap water will typically be < 1 ppm
    • Reactions between chlorine/chloramine and phenols supplied by malt, hops, and yeast creates chlorophenols which will ruin your beer and have a tiny taste threshold of just a few parts per billion
    • The evaporation method (leaving the water sitting exposed for several hours) is effective for removing chlorine but not chloramine, which could take several days of exposure
    • Boiling the water prior to use is again very effective for chlorine removal, requiring only a couple of minutes, but less so for chloramine which could take half an hour or more of boiling
    • Ascorbic acid is very effective for removing both chlorine and chloramine. A very small addition of 3.4 ppm (34 mg per 10L) will remove up to 1 ppm of chlorine/chloramine with only trace amounts of by products
    • Ion exchange filters will not remove chlorine or chloramine, but they will remove useful stuff like calcium and magnesium. Don’t use an ion exchange filter for brewing water.
    • Activated carbon filtering will remove both chlorine and chloramine, but might require a very low flow rate (less than 0.5 L/min) for successful dechloramination
    • Metabisulphite (usually in the form of Campden tablets) is a cheap, quick, and effective method of dechlorination/dechloramination. Dosing at 7 ppm (0.25 g or half a tablet per 35 L) will remove up to 5.2 ppm free chlorine or 2.6 ppm chloramine and leave only trace amounts of byproducts
     
    Last edited: Oct 19, 2019
  9. Oct 18, 2019 #9

    strange-steve

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  10. Oct 18, 2019 #10

    Chippy_Tea

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    A well deserved sticky thread. clapa
     
  11. Oct 18, 2019 #11

    Lee Brown

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    Holy moly! You are Albert Einstein reincarnated. I am blinded by Science...and slightly aroused too - in a geeky way.
     

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