pH Increase in Desalinated Water in Water Transmission Pipeline
Published on by Mohsan Ali Chaudhry in Academic
Does anyone know the reason why the pH of water increases after it travels through a water transmission pipeline of 20 km?
The pH of desalinated water changes from 7.1 to 9.8-10.01 after 20 km before reaching a storage reservoir.
To normalize the pH, we are using the citric acid at end-point of the storage reservoir, before the water is distributed.
What could be the reason for the change in water pH and how can we regulate this?
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28 Answers
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Everybody is focusing on Pipe leaks, but there is no mention of such problem on the text. From the "leak" theorist, I must assume that you are saying that it is INWARDS, creating contamination. I don´t really see how a flow reduction can create a pH change. So let us focus on a non-leaking pipe scenario and provide answers, not comments: What is the pipe material? I am suspecting concrete. The best way is CO2, because in fact you are "eating up" your pipe, something that sounds even more pausible when starting the journey at 7.1 pH. Happened in Ryihad years ago but not a single "gurú" would accept that possibility... until we fixed it. HEY, CO2 is a very misunderstood product. be very suspicious of the "expert" solutions coming from the guys that will sell you gas.
Just to be sure: Are you SURE your alkalinity at entry is good?
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Langelier saturation index (LSI) is the most widely used index in water treatment and distribution field. The index is based on the effect of pH on the equilibrium of calcium carbonate, CaCO3. LSI is the difference between the measured (actual) pH of water and the hypothetical value when water is in equilibrium with solid calcium carbonate. This value is known as pHs. LSI is defined by the following equation:
LSI = pH - pHs
At saturation, calcium carbonate is neither deposited nor dissolved. So LSI=0 and water believed to be stable. At super-saturation, LSI >0 , and water tends to precipitate calcium carbonate . It is called protective or precipitated and non-corrosive water. When pH is less than pHs then LSI1 Comment
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May i know detail how can we control PH by Controlling & measuring LSI.....
3 Comment replies
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Very clear water, like RO permeate, has high tendency for dilluting anything is in contact with. So, if pipes are made from concrete, is very likely to dissolve carbonates consistently its pH raising.
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pH measurement of low TDS water has to be performed immediatelly after sampling and using a low impedance glass electrode. Otherwise sample's pH is tending to neutral, measurement takes long time to stabilized and electrode is destroyed.
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pH is controlled by addition of an appropriate acid or alkali.
LSI is a mathematic formula calculated by Ca, TDS, temperature, Alkalinity.
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I have problem on posting answer. It is not fully posted.......
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In order to measure accurately the pH of a pure water (Conductivity < 100 μS/cm) you have to use low impedance sensitive glass membrane(
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Possibilities:
Cement Concrete pipelines if eroded can leach calcium carbonate which may increase the pH.
Contamination of wastes of alkaline nature from outside the pipeline (breakage, if any) some where along the 20km stretch needs to be explored.
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Dear Mr. Ali,
The only way for you to confirm there is no leakage is to fix a flow meter at the beginning and at the end of the 20 km line and compare these 2 readings. Settlement and leakage of underground water pipes is a very common problem. In North America they run water pipes under residential houses, eventually these pipes leak, and even the residential houses are only one ground floor, these houses are showing cracked walls.
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Theoretically its not possible to any change in pH until & unless there is contamination. Check the pipeline.
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Dr T K Sinha . Hydro Environmental Disaster Geologist and President Parayavaran Chetana Peeth ,Varanasi, India.---------pH of Surface and Ground water + Soil of way must be check, , there is contamination of high pH at any place .
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Ya , there may be mixing of high pH Water in way of 20 Km. by leakage in pipeline . It may be find out to take every 100 Mt ground water sample and at the junction of any cut ( junction ) or nearest surface water . it must be check pH at the spot , if not traced , check 50 Mt interval sample and so on . Also must check soil type also , may be mixing / transmitting water of such high pH quality of water in way.
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A full CHEMICAL ANALYSIS of the water at the start point and the end point where the pH has this high value will answer all your questions. Everything else is simply HYPOTHESIS....
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Is the result of pH done by the same lab?
is there more than one entrance?
is the quantity cubic feet per second the same at entrance and exit.
logicaly saline water is added s one where along the line, maybe illegally which chemicals are greater at the exit compared to the entrance. Get an engineer for such answers!
1 Comment
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Same other lab other types of Meters,
Same quantity inlet & outlet,
working pressure 11 bar, no entrance saline water due to pressure in line
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Dear Mr. Ali,
In very simple words, your pipeline might be running underground and leaking in sensible length of the pipeline, consequently your water runs for a considerable length of the pipeline in contact with underground soil, causing this increase in pH.
2 Comments
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High pressure pipeline, 14 Bar pressure , with flow 1000m3/hr, 800,600mm DI pipelines, not possible
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No leakage.
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Here are a couple articles for you! Blessings!
May I request your connection?
https://www.facebook.com/EndingWorldwideFreshWaterShortages/
Ending Worldwide Fresh Water Shortages Using Ocean, Hydrogels, AWGs
https://www.linkedin.com/pulse/ending-worldwide-fresh-water-shortages-using-ocean-potable-hart
@EndingWorldwideFreshWaterShortages
http://www.gaiam.com/discover/185/article/increase-alkalinity-water/
The Water Network:
Lets understand what is pH?
pH is a numeric scale that indicates the acidity of an aqueous solution.
It is the negative logarithm to base 10 of the molar concentration of hydrogen ions, measured in units of mol/l.
The pH scale has a range from 0 to 14, with the 7 indicating a neutral point.
Solutions with a pH below 7 are acids.
Solutions with a pH above 7 are bases.
Distilled, pure water is neutral, neither acid nor a base, and has a pH of 7.
Pure water is neutral, but when it is mixed with chemicals it can change its acidity. Additionally, mixing acids and bases can neutralize their effects.
Causes of pH variations in water:
Soil composition through which the water moves, in its bed and as groundwater. Certain rocks can neutralize the acid while others have no effect.
Limestone can buffer – neutralize the acidification of freshwater. Number of plants and organic matter in the water. Carbon dioxide is released when they decompose, and if forms the carbonic acid as it combines with water. It is a weak acid but in greater amounts in will lower the water pH.
Chemicals in the water released by industries or individuals. Industrial effluents that are released in the environment, therefore, are required to have a certain pH value.
Acid precipitation. Acid rain occurs when nitrogen oxides (NOx) and sulfur dioxide (SO2) in the air are combined with water vapor. They are products of car fumes and emissions from coal-fired power plants.
Coal mine drainage. Sulfuric acid is formed when iron sulfide, which is found around coal mines, is combined with water.
pH standards for drinking water:
Environmental Protection Agency (EPA) maintains strict standards for appropriate pH levels in drinking water. Consuming excessively acidic or alkaline water is harmful, warns the EPA. Drinking water must have a pH value of 6.5-8.5 to fall within the EPA standards , and they further note that even within the acceptable pH range, slightly high- or low-pH water can be unappealing for several reasons. High-pH water has a slippery feel, tastes a bit like baking soda, and may leave deposits on fixtures, according to the EPA website. Low-pH water, on the other hand, may have a bitter or metallic taste, and may contribute to fixture corrosion.
pH adjustment systems:
There are two primary types of system design for pH adjustments – continuous and batch.
Continuous flow
Diagram 1: Continuous flow system.
Source: phadjustment.comThe tank is constantly full – the amount of influent entering it equal to the treated effluent exiting the tank.
The advantage of this system is that can handle relatively high flows. However, it is not certain that the effluent will always be in range.
Batch
Diagram 2: Batch adjustment system
Source: phadjustment.comThe batch has a fixed water volume, which is discharged only after fulfilling the criteria.
The influent enters the tank anywhere convenient and exits due to gravity near the bottom, where the port is located.
The batch volume is treated in one cycle.
** The systems shown here are simplified.
pH adjusting methods:
Raising the pH
Lowering the pH
Neutralizing filters
Acid injections
MgO beads
CO2
Soda ash/sodium hydroxide injections
Neutralizing filters
Neutralizing filters are used if drinking water is acidic.
The pH is increased by the addition of the neutralizing material.
It is important to highlight that the water hardness may increase.
(Water hardness is the amount of dissolved calcium and magnesium in the water - dissolved bicarbonate minerals - calcium bicarbonate and magnesium bicarbonate.) Neutralizing filters are point-of-entry devices.
Water with pH greater than 6 is treated with calcium carbonate (limestone) and water with the pH below 6 is treated with the synthetic magnesium oxide.
Untreated water passes through a filter filled with either calcium carbonate or a synthetic magnesium oxide medium and the material dissolves in the water therefore raising the pH level.
The flow rate should not the greater than 2 l/s·m2. The bed should be deep enough to provide sufficient contact time.
The material in the neutralizing filter need refilling and regular backwaching.
If cartridge filters, that retain solids from passing through, are installed before the neutralizing filters, the neutralizing filters will last longer.
After the neutralizing filter a water softener can be added to regulate the water hardness.
The neutralizing filter may result in pressure loss, since the water passes through the finely ground neutralizing material.
The corrosion of the pressure tank and the well pump may occur since the neutralizing filters are installed after the pressure tank.
In case of a high flow rate, liquid injection systems are a better solution.
Magnesium oxide beads in combination
Prill MgO beads are used when the water pH needs to be rasied.
They should be used after reverse osmosis.
Osmosis is a spontaneous movement of the molecules in the solvent through a semi-permeable membrane. The molecules tend to "go" to the in that direction that will equalize the concentrations of the two sides. Reverse osmosis is a process in which the particles move in the opposite direction than in natural osmosis. The contaminated fluid passes through the membrane and the suspended particles are separated from the liquid. For this process, pressure is needed – the hydrostatic pressure needs to be greater than the osmotic pressure.
Prilly Pure Water Beads raise and balance pH levels of the water to 8,7 without any chemicals.
The beads are made from magnesium oxide which is produced from naturally occurring salts of magnesium found in rich brine deposits located approximately 2,500 feet below ground. The resulting magnesium oxide is ‘prilled’ into small, hard pellets by a high temperature firing process which turns them into small ceramic-like pellets.
In addition to adjusting the pH, the beads lower the surface tension of water, remove toxins and pull out heavy metals from water.
Prilly Pure Water Beads last forever and never need to be replaced.
Injection systems:
I Soda ash/sodium hydroxide injection
Soda ash/sodium hydroxide injections are used if the water is acidic.
When injected into a water system, soda ash (sodium carbonate) and sodium hydroxide raise the pH of water.
Injection systems are a point-of-entry system.
Soda ash or sodium hydroxide solution are injected in the water by a corrosion-resistant chemical feed pump.
The injections are installed before the pressure tank so that the tank ant plumbing systems are protected from corrosion.
Dual treatment is used if the water needs to be disinfected, in addition to being neutralized. A chlorine solution is added with the neutralizing chemical.
With the injection systems water with low pH can be effectively treated – as low as 4.
The chemical storage tanks need to be refilled occasionally.
II Acid injection
Acid injection is used for water with a high pH.
Water with a higher pH can have a soda-like taste that is eliminated with this treatment and the chlorination is improved.
Acid injection is a point-of-entry system.
Acid injection reduces pipe corrosion, since water with the pH above 9 corrodes brass, copper, zinc, aluminum and iron.
A solution of acetic acid is injected into water. Usually white vinegar is used, as it is the cheapest, but citric acid and alum are also an option, as well as more hazardous weak solutions of hydrochloric acid or sulfuric acid if the pH is above 11.
The chemicals need to be refilled occasionally, while wearing the protective goggles, gloves and clothing.
Carbon dioxide
Carbon dioxide is used to reduce pH in alkaline water.
Carbon dioxide, CO2, is a colorless and odorless gas. It is a chemical compound composed of a carbon atom covalently double bonded to two oxygen atoms.
It is used as a pretreatment and sulfuric acid is added in the second step. The main purpose of this secondary acidification is to reduce the bicarbonate content and avoid calcium carbonate precipitation.
Carbon dioxide does not corrode the pipes and the equipment.
It was gives better control of pH than sulfuric acid. It shows self-buffering when reaching neutral pH levels. The self-buffering enables precise end-point control eliminating the danger of lowering the pH too much.
It can be utilized via a completely automated system.
Documents on TWN about pH and drinking water standards:
WHO guidelines for drinking-water quality
EPA drinking water standards and health advisories table
pH Control in WTP by the Addition of CO2
Drinking Water Treatment - pH Adjustment
pH Requirements of Freshwater Aquatic Life
What is pH and How is it Measured?
http://www.gaiam.com/discover/185/article/increase-alkalinity-water/
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Dear Mohsan
We need more informations on concentrations of some ions (Ca++, Na+, HCO-, CO3-, SO4-- and Cl-) corresponding to PH 7.1 and PH 9.8 to 10.1, and saturation Index vis a vis of Calcite and Dolomite.
The increasing of PH during the transportation can suggest loss or degasing of CO2 in the pipe. At PH 9.8 to 10.1 we have precipitation of Calcite and dolomite. So, concentration of Ca++ and Mg++ decrease in water.
Please let us have more informations on these ions.
Thanks.
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Knowing the material makeup of the pipe is important. Knowing if groundwater is entering the pipe anywhere is important. It could be very important to have toxic metals tested for in the source water compared to end of pipe sampling.
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Dear Mohsan,
Water stability, tendency of water to scale or corrode, depends on the pH value. Saturation pHs depends on total alkalinity, calcium hardness, total dissolved solids and temperature. Monitoring the pH will give an idea about the water stability.
Following are reason in long line.
1. Small increase in the total alkalinity noticed with an appreciable value of phenolphthalein alkalinity which reflects the formation of carbonate toward the end of the carrying pipes. This may increase in the pH and LSI values.
2. Corrosion of the pipe line.
3. Increase of Iron Ion.
4.Minor leakage in pipe line (ejector effect)
5. Dissolve O2 Iron Get passivate.
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Concrete?
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I would suggest take a sample of your water after the pH measuring point. In the lab stir it continuously in a beaker and check the pH for the same residence time as the fluid spends in the pipeline. If the pH rises its an ongoing chemical reaction most likely from the pH correction. If not then your problem is most likely leaching of salts from the pipeline materials or corrossion by products. Of course as previously suggested you should ensure that the pH meters at both ends are calibrated correctly.
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It is important to know what is Conductivity of water entering the pipe and exiting the pipe. The water is definitely picking up something inside the pipe. I would suggest maintain Positive, +, LSI of water entering into the pipe.
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Considering that the PH values are measured at sample points situated at the beginning of pipeline and at the end of the pipeline. The variance in PH reading from 7.1 to 9.8-10.01 is only possible when this desalinated water reacts with the pipe material assuming there is no leakage in the pipeline.
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It is important to know the material of pipe as already pointed out desalinated water is highly corrosive and if pipe is MS/CS/CI and uncoated, corrosion products could be dissolving in water.
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Dear Mohsan Ali,
It could be basic however would like to point out (sometimes sampling points's selection plays a vital role);
Please check if your pH meter is calibrated (must be installed at Product of RO or RO Product Tank)
Please check your pH meter is calibrated at Receiving End means if it is coming into a Reservoir (20km Away).
Check your RO Product Tank Reservoir if not having any infiltration of the ground as instantly coming out of your RO pH might be around 6 - 7 and you might be measuring at that point but look into the Product Tank (reservoir from where you are pumping towards 20km).
Check your Receiving End Reservoir (20km Away) if it is not having infiltration or leakages.
Check pH just from the pump discharge from RO Product and pH at the reception tank inlet pipe before entering into the reception tank.
The above checks will ensure if we need to look into the pipe line or not, first ensure these points. I strongly feel your sampling point will play a vital role.
If all are Ok on these, then there must be Pressure Release Valves/Surge Release Valves on elevated points of pipeline due to topography , please check any of these points are intact or are not the reason for any infiltration.
Please check further detailed analysis of water for RO Product, RO Product Reservoir, Before Entering Reception (20km away) and from Reception Reservoir;
pH
TDS
Conductivity
Hardness
Alkalinity (Methyl Orange Alkalinity)
Phenolphthalein Alkalinity
This will help you if other parameters are also not changed.
Hope you will find now the main cause and solve this issue. Please share your findings.
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Dissolution of salts deposited in the inner walls of the pipe could be a reason. Measuring EC of water prior to and after passage through pipe network could verify this hypothesis.
Slight acidification of water before transmissipn could be persisted till EC of transmitted water reduces to desired levels.
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If the pipe line laid below the ground and pressure and flow of the water transmission line are not stable through out the process , then definitely the your water is continuously contacted with foreign material.
Try chlorine dosing to regulate your pH, it will gives you other benefits too I guess.
1 Comment
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Normal chlorine dosing for disinfection purposes has a small effect on pH. If it's gas chlorine will slightly lower, if it's sodium hypochlorite will sligtly increase it. Chlorine is a disinfectant and not a pH-regulator.
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The material of the transmission line is PVC or metal?
1 Comment
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Inside the Pump Station MS pipes but all over in Transmission DI Pipeline.
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Is the pipe cement mortar lined?
2 Comments
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We had same experience with cement mortar lined steel pipe. It was temporary and after months lowering the quality of water declined. Finally, the quality stayed stable.
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Yes..... Cement-mortar lined ductile iron pipe
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One likely cause is leaching from the inside surface of the pipeline if it is cementitious? If this is the case it is unlikely to change with time to any extent and it could lead to erosion of the pipeline. It may be possible to reduce the buffering capacity of the water or alternatively to consider lining the pipeline with a coating such as an epoxy resin. Or you could draw a polyethylene pipe inside the existing - sliplining. Logistics and size will govern the decision.
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Has the water already treated ( remineralized)?
Material of the pipeline?
Perhaps, if water hasn't been remineralized it is substracting minerals from the pipe. Desalinizated water trends to be very corrosive
1 Comment
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CO2 change ?
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