EP0690944A1

EP0690944A1 - Method of cleaning and maintaining potable water distribution pipe systems

Info

Publication number: EP0690944A1
Application number: EP94912283A
Authority: EP
Inventors: Allen C. Hieatt; Jerome H. Ludwig
Original assignee: HERC Inc; HERC Products Inc
Current assignee: HERC Products Inc
Priority date: 1993-03-23
Filing date: 1994-03-22
Publication date: 1996-01-10
Anticipated expiration: 2014-03-22
Also published as: CA2157916A1; CA2157916C; BR9406139A; AU6490394A; JP3597193B2; ATE170583T1; DE69413017T2; AU673426B2; EP0690944B1; DE69413017D1; WO1994021865A1; JPH08509908A

Abstract

A method of cleaning and maintaining potable water distribution system which have reduced flow due to an increase of water scale deposits, sediment, and the like on the inside surface of the pipe is disclosed. An aqueous acidic cleaning solution (12) is introduced and circulated through the pipe (25) to be treated for a sufficient time to dissolve and loosen the scale and sediment, and the spent solution containing dissolved or suspended scale and sediment is flushed from the pipe (25) to provide a cleaned pipe with improved water flow. It is also desirable to flush the water distribution pipe system with high pressure water after the treatment to remove loosened scale and sediment that was not removed during the circulation and flushing of the treating solution (12).

Description

METHOD OF CLEANING AND MAINTAINING POTABLE WATER DISTRIBUTION PIPE SYSTEMS

RELATED APPLICATIONS

This application is a continuation-in-part of Application Serial No. 08/036,188, filed March 23, 1993, and also claims the benefit of Application Serial No. 07/700,780, filed May 16, 1991, and the disclosures of both of these applications are incorporated herein in their entireties by reference. BACKGROUND OF THE INVENTION

It is well known that hardness and suspended solids in water sources vary widely in composition depending on the source and will result in scale deposition and sedimentation on surfaces wherever water is used. Scale deposition and sedimentation is particularly troublesome in water distribution pipe systems which service the residential and commercial customers of municipalities, private water companies and the like along with industrial process water distribution pipe systems as found in the mining, petroleum, agriculture and the like industries. In these systems, the formation of scale and sediment can reduce the water flow through the pipe system whic will limit the capacity of the pipe to service the requirements of the customers or to provide the required water necessary for an industrial process, irrigation, etc. For instance, in municipal systems an increase in the fire risk would be obvious if the fire hydrant did not supply sufficient water to extinguish the fire due to scale and sediment deposits in the feed pipe line. At some point, the water distribution pipe would have to be replaced due to these restrictions at a high cost and with prolonged interruption of service.

Additionally, scale and sedimentation will increase the possibility of corrosion in the water distribution pipe along with promoting the growth of organisms. The organisms also can be a health hazard, promoting corrosion and biomass which binds scale and sediment together and to the surfaces of the system. Corrosion will eventually lead to the leakage of the system and the necessity to replace the leaking section.

Strong acids have been used to clean water wells, however, submersible pumps are removed prior to treatment to prevent corrosion by the acids employed. Also, organic acids, mixtures of mineral acids and organic acids or inhibited acid compositions have been found to clean water wells without the necessity of removing the pumps or other equipment. These methods for cleaning water wells have involved static an surging treatment.

A proper cleaning and maintenance program fo water distribution systems will prevent decreased wate flow capacity, corrosion and the necessity to replac the system or portions thereof. A simple and effectiv method for cleaning and maintaining these systems i needed. SUMMARY OF THE INVENTION This invention is directed to a method o cleaning and maintaining water distribution systems Water systems having interior scale and sedimen deposits are cleaned by introducing and circulating a effective amount of an aqueous treatment solution fo a sufficient period of time which results in th solution, loosening and suspension of the undesire scale and sediment. Thereafter, the spent treatin solution containing the dissolved or suspended scal and sediment is flushed from the water distributio system to provide a clean system with improved wate flow and operation. Additionally, further flushin with high pressure water will also remove additiona scale that had been loosened by the treating solution.

The cleaning solution may be acidic, neutra or basic. In the most preferred form, in potable wate pipe systems, mineral acids or organic acids, an mixtures thereof, are employed as acidic treatmen solutions. The acidic treatment solution may contai further additives such as inhibitors, chelating agents, penetrating and/or dispersing agents to assist in the removal of scale and sediment and to minimize any adverse effects on the pipes, valves, or other system surfaces due to the acids employed.

This invention provides a simple, low cost and effective method of removing water scale and sediment from water distribution systems in order to maintain proper water flow, operation and to prevent corrosion of the system which would require the high cost and inconvenience of replacement.

Other advantages and objectives of this invention will be further understood with reference to the following detailed description and drawings. DETAILED DESCRIPTION OF THE INVENTION

Among the acidic treatment solutions found to be useful in practicing the method of this invention are aqueous solutions of mineral acids such as hydrochloric, nitric, phosphoric, polyphosphoric, hydrofluoric, boric, sulfuric, sulfurous, and the like. Aqueous solutions of mono-, di- and polybasic organic acids have also been found to be useful and include formic, acetic, propionic, citric, glycolic, lactic, tartaric, polyacrylic, succinic, p-toluenesulfonic, and the like. The useful treatment solutions may also be aqueous mixtures of the above mineral and organic acids. Alkaline, acid, or neutral cleaning solutions may also be employed, as indicated above, dependin upon the type of scale that needs to be removed. Sequestering or chelating agents such as EDT (ethylenediamine tetraacetic acid) , NT (nitrilotriacetic acid), and derivatives, i.e., basic alkali salts, and the like have also been found to be useful in the treatment solution in certain cases.

The acidic treatment solution may also contain acid inhibitors which substantially reduce the acidic action on metal surfaces of the water distribution system, particularly valves, fire hydrants, etc. , and these various inhibitors for acids have been well documented in the patent art. Typical, but not necessarily all inclusive, examples of acid inhibitors are disclosed in the following U.S. Patents:

2,758,970; 2,807,585; 2,941,949; 3,077,454; 3,607,781;

3,668,137; 3,885,913; 4,089,795; 4,199,469; 4,310,435;

4,541,945; 4,554,090; 4,587,030; 4,614,600; 4,637,899; 4,670,186; 4,780,150 and 4,851,149 which are incorporated herein by reference.

The treatment solution may also contain dispersing, penetrating or emulsifying agents to assist in the removal of the scale and sediment. These surface active agents may be anionic, cationic, nonionic or amphoteric as defined in the art. Compounds such as alkyl ether sulfates, alkyl or aryl sulfates, alkanolamines, ethoxylated alkanolamides, a ine oxides, ammonium and alkali soaps, betaines, hydrotropes such as sodium aryl sulfonates; ethoxylated and propoxylated fatty alcohols and sugars, ethoxylated and propoxylated alkylphenols, sulfonates, phosphate esters, quarternaries, sulfosuccinates, and mixtures thereof, have been found to be useful in admixture with the acid treating solution. DRAWINGS AND OPERATING EXAMPLES

Fig. 1 is a schematic of a laboratory test system illustrating the method of this invention.

Fig. 2 is a diagram of a field system for cleaning a potable water distribution system.

With reference to Fig. 1, a laboratory test system is shown to evaluate the removal of scale and sediment by acidic treating solutions from a test pipe sample taken from a water distribution system. This system includes a 15 gallon acidic treating solution reservoir 5, submersible acidic treating solution circulation pump 6 rated at 1200 gallons per hour, 1" inlet transfer line 7, drain valve 8, heavy rubber diaphragm seals 9 for the ends of the test pipe specimen 10, 1" outlet transfer line 11 and the treating solution 12. The test pipe specimen 10 is mounted at about a 30 degree angle so that the test solution will contact essentially the entire inner pipe surface to be treated.

A laboratory test, for example, was run on a four foot section of 6" diameter pipe which had been removed from a potabl i water distribution system tha had been used for over 40 years. The scale on th inside of the pipe consisted of nodules of up to 1 t 1% inches in height covering 100% of the inside pip surface which had substantially reduced the openin inside the pipe for water to flow. Analysis of th scale indicated it consisted of primarily iron wit some calcium, magnesium and manganese in the for oxides, hydroxides and carbonates along with fin mineral acid insoluble solids and some "biomass". This is typical scale associated with sulfate-reducing an iron bacteria along with the associated corrosion.

About 10 gallons of a 12.5% aqueous inhibite hydrochloric/glycolic acid solution containing penetrating agent was placed in the reservoir 5 an circulated through the test pipe 10 for a period of 24 hours. After 2 hours of circulation, particles of th scale were breaking loose and could be heard in th outlet transfer line 11 and observed entering th reservoir 5. The color of the treating solution als became increasingly darker with circulation time. After 24 hours the circulation was stopped and th system was drained of the treating solution. Th diaphragms 9 were removed and the inside of the tes p pe was observed to be about 80% cleaned of scale an sediment solids.

On treating the test pipe with a secon identical treating solution for a period of 21.5 hours. about 80% of the interior surface of the test pipe wa observed to still be covered over with a scale and/o sediment that was a soft and paste-like semi-soli which contained some grit and could be easily remove with a probe. The remaining scale nodules had bee substantially reduced in size since the end of th first treatment. It was concluded that the secon treatment would probably not be necessary if a hig pressure water flush was employed to remove th insoluble soft sediment which had coated the remainin scale nodules after the first treatment.

With reference to Fig. 2, a field equipment and system diagram is shown which may be employed i the cleaning of a potable water pipe distributio system. Two 500 gallon treating solution reservoir tanks 20 and 21 along with a 100 gallon per minut circulation pump 22 and sight glass 23 are mounted o a flat bed truck (not shown) . In this example, a 2% inlet pipe 24 is secured to a 650 foot section of 6" water distribution pipe 25 after the main shut off valve 26. The fire hydrant 27 and fire hose 28 were employed for the acidic treating solution return to tanks 20 and 21.

The section of pipe 25 to be treated was isolated by closing off the two water main shut-off valves 26 and 29 along with all service line valves, typically 30 and 31. With valves 32 and 33 closed, 1000 gallons of acidic treating solution was prepared in tanks 20 and 21. With the coupling 34 open, th treating solution was allowed to enter the system b opening valves 33 and 35 and turning on the circulatio pump 22. The pH of the water coming from the ope coupling was then monitored until a decrease was note which indicated the acid treating solution ha displaced the water in the section to be treated. Th circulation pump 22 was turned off and the coupling 34 connected. Valves 36 and 37 were then closed and valv 32 opened for circulation. The circulation pump 22 was then started again for the treatment period. Valve 37 was closed to allow for scale solids to accumulate i tank 20 while the treating solution could overflow a 38 to tank 21 which reduces the chances of pluggin during treatment.

The treating solution was then circulated i the system of Fig. 2 for a period of 5 hours. Observation of the treating solution through the sigh glass 23 showed an increasingly darker discoloratio with time. At the end of the treatment period, th circulation pump 22 was turned off, and valves 33 an 35 were closed. The main shut-off valve 26 was slowl opened and fresh water allowed to enter the syste until the treating solution was displaced as noted whe the tanks 20 and 21 were full. Valve 32 was the closed. The fire hose 28 was then disconnected fro the fire hydrant 27 and the main shut-off valve 2 opened full to allow high pressure flushing of th treated water main 25. As the flush water emerged fr the fire hydrant 27 it was dark in color wi considerable scale and sediment solids. Flushi continued until the flush water was clean of solids f 5 a period of time prior to putting the treated secti of the water distribution system back into service.

The flow rate through the fire hydrant 2 prior to treatment had been determined by a Pitot Gau to be 588 gallons per minute. After treatment, t

10 flow rate was determined to be 790 gallons per minute This was an increase of 34.5%.

Also, improved mechanical operations of t hydrants and valves of the system were achieved. T flow of cleaning solution may also be reversed in t

15 system to further improve cleaning efficiency. T above cleaning solutions met the requirements of t National Sanitation Foundation (NSF International, A Arbor, Michigan) . Standard 60 for potable wate distribution systems.

20 Other examples of cleaning solutions may employed as follows:

Preblend Ingredients % bv wt

31% Hydrochloric acid in water 87.14 +/- 2%

70% Glycolic acid in water 5.27 +/- 0.3%

25 40% Sodium xylene sulfonate in water 2.06 +/- 0.2%

Triethanolamine and diethanolamine 2.96 +/- 0.2% mixture (85%/15%)

Water 2.57 +/- 0.2%

In a preferred form of the invention, th

30 above preblended cleaning solution is used in an amoun of about 12.5% by weight with water in the field fo cleaning an underground potable water distribution pip system. However, more generally, the solution may b employed in amounts of from about 5 to about 50% b weight with water in the field, depending upon suc variables as the amount of scale, pipe volume to b cleaned, circulation time and other factors. Th amounts of anhydrous chemicals in a broader range o ingredients are about 1% to 27% HC1, 0.1% to 4 glycolic acid, 0.04% to 1% sodium xylene sulfonate an a b o u t 0 . 1 % t o 2 . 5 % o f t h triethanolamine/diethanolomine mixture (hereinafte referred to as "TEA") .

It should be understood that the abov chemical ingredients may be blended in the field fo cleaning the underground potable pipes, for example, hydrochloric acid may be added to a concentrate of th glycolic acid, sodium xylene sulfonate and TEA. In th potable water distribution systems, an undergroun section of the pipe to be cleaned is sealed off fro the rest of the system. As illustrated above in Fig. 2, the cleaning solution is then introduced from a tan into the pipe section and, if water is in that sectio of pipe, it is removed upon the introduction of th cleaning solution. After the cleaning solution ha been introduced into the pipe section, circulation o the cleaning solution through the underground pipe i initiated for a sufficient period of time fo solubilization, loosening and/or suspension of th scale and sediments.

In the above preblends, a soap having a 1:1 stoichiometric equivalent of the acid (HC1 and glycolic acid) and TEA base is formed with an excess of the acid. This composition has been found to work effectively in the field for the removal of scale associated with sulfate-reducing and iron bacteria consisting primarily of iron oxide, biomass and sediment. These 1:1 soaps have also been described in the above referred to co-pending Application Serial No. 07/700,780, filed May 16, 1991, now U.S. Patent No. and the disclosure thereof is incorporated herein in its entirety by reference. These soaps may be more generally categorized as soaps of mineral and/or organic acids and a base such as an amine and ammonia. Further examples of these soaps include 1:1 soaps of TEA and glycolic acid (also known as hydroxyacetic acid) ; TEA and acetic acid; TEA and citric acid; TEA and benzoic acid; hydrochloric acid and ammonia; sulfuric acid and ammonia; nitric acid and ammonia; TEA and hydrochloric acid; TEA and sulfuric acid; TEA and nitric acid; ammonia and glycolic acid; ammonia and benzoic acid; and ammonia and p- toluenesulfonic acid. Accordingly, it will be understood that other cleaning solutions of the acidic type employing 1:1 soaps may be employed to effectively solubilize, loosen and/or suspend the scale and sediment from the potable pipe in accordance with th principles of this invention.

In view of the above detailed description other method variations to clean domestic an industrial water distribution systems, like houses hotels, plants, offices, etc., will be apparent to person of ordinary skill in the art without departin from the scope of this invention. The method i especially advantageous in cleaning underground potabl water distribution systems having scale associated wit sulfate-reducing and iron bacteria consisting primaril of iron oxide, biomass and sediment.

What is claimed is:

Claims

(1) A method for cleaning a potable wate distribution system comprising introducing an effective amount of an aqueous cleaning solution for the removal of scale associate with sulfate-reducing and iron bacteria consistin primarily of iron oxide, biomass and sediment fro inside surfaces of a potable water distribution system, said solution selected from the group consisting of acidic, neutral and basic solution, sealing off a section of pipe in said system for circulation of said cleaning solution therethrough, circulating said cleaning solution through said pipe system for a sufficient period of time for solubilization, loosening and/or suspension of said scale and sediment, flushing said cleaning solution containing solubilized, loosened or suspended scale and sediment from said system.

(2) The method of claim 1 comprising the furthe step of flushing said system with clean water after th removal of the spent cleaning solution.

(3) The method of claim 1 comprising the furthe step of flushing said system with high pressure wate for the removal of any spent cleaning solution, scal and/or sediment.

(4) The method of claim 1 wherein said aqueou treatment solution is acidic.

(5) The method of claim 4 wherein said aci solution contains further additives selected from th group consisting of acid inhibitors, chelating agents, surfactants, penetrating agents and dispersing agents, and mixtures thereof to assist in the removal of sai scale and sediment.

(6) The method of claim 4 wherein said acid i selected from the group consisting of mineral an organic acids and mixtures thereof.

(7) The method of claim 6 wherein said minera acid is selected from the group consisting o hydrochloric, nitric, phosphoric, polyphosphoric, hydrofluoric, boric, sulfuric, and sulfurous, an mixtures thereof.

(8) The method of claim 6 wherein said organi acid is selected from the group consisting of formic acetic, propionic, citric, glycolic, lactic, tartaric polyacrylic, succinic, p-toluenesulfonic, and mixture

5 thereof.

(9) The method of claim 6 wherein said solutio further contains an additive from the group consistin of acid inhibitors, chelating agents, surfactants penetrating agents and dispersing agents, and mixture

10 thereof to assist in the removal of said scale an sediment.

(10) The method of claim 1 wherein said cleanin solution is a mixture of hydrochloric acid, glycoli acid, and alkanolamine and a surfactant.

15

(11) The method of claim 10 wherein said mixtur is employed in a preblend as the aqueous cleanin solution.

(12) The method of claim 1 wherein said cleanin solution contains a soap having a 1:1 stoichiometri equivalent of an acid and a base wherein said acid i selected from the group consisting a mineral acid an an organic acid and said base is selected from a grou consisting of an amine and ammonia, where an effectiv amount of free acid is present in the solution to reac with said scale.

(13) A method for cleaning a potable wate distribution pipe system comprising providing a reservoir for containing a aqueous acidic cleaning solution for the removal o scale associated with sulfate-reducing and iro bacteria consisting primarily of iron oxide, biomas and sediment from inside pipe surfaces of a potabl water distribution pipe system, sealing off a section of pipe in said syste for circulation of said cleaning solution therethrough circulating said cleaning solution from sai reservoir through said pipe section and returning sai solution to said reservoir for the removal of sai scale and sediment.

(14) The method of claim 13 wherein said cleanin solution is a mixture of hydrochloric acid, glycoli acid, and alkanolamine and a surfactant.

(15) The method of claim 13 wherein said cleanin solution contains a soap having a 1:1 stoichiometri equivalent of an acid and a base wherein said acid i selected from the group consisting a mineral acid an an organic acid and said base is selected from a grou consisting of an amine and ammonia, where an effectiv amount of free acid is present in the solution to reac with said scale.

(16) The method of claim 13 wherein said reservoir is truck mounted for makeup, storage and disposal of cleaning solution.

(17) The method of claim 13 by sealing said pipe section between two fire hydrants and circulating said cleaning solution by connecting one of said fire hydrants to said reservoir for pumping said cleaning solution therethrough.

(18) The method of claim 13 wherein said pipe distribution system is domestic or industrial water distribution system.

(19) The method of claim 13 comprising the further step of flushing said pipe system with clean water after the removal of spent cleaning solution.

(20) A method of claim 15 wherein said mineral acid is selected from a group consisting of hydrochloric, nitric, phosphoric, polyphosphoric, hydrofluoric, boric, sulfuric and sulphurous, mixtures thereof, and said organic acid as selected from the group consisting of formic, acetic, propionic, citric, glycolic, lactic, tartaric, polyacrylic, succinic, poly-toluenesulfonic and mixtures thereof. (21) The method of claim 13 wherein said aqueo treatment solution meets the requirements of t National Sanitation Foundation Standard 60 for potabl water distribution systems.