biofouling in raw water supply wells and its impact

8/13/2019 Biofouling in Raw Water Supply Wells and Its Impact

1/7

Biofouling in Raw Water Supply Wells and Its Impact

Frederick Bloetscher, P.E., erhardt !. Witt, P.. and Ro"ert E. Fergan, P.E.

#cto"er $%, &''$

Face"ook(witter)inkedIn

!em"rane *oncerns

!any coastal water utilities across the +nited States are striing to find additional sources of

water to meet the demands of "urgeoning populations and hae limited freshwater

aaila"ility. In many cases, this freshwater is threatened "y saltwater intrusion from

deelopment that has reduced historical a-uifer heads. Surficial a-uifer sources also may

hae water -uality concerns caused "y a high organic content and the potential for pollution.

(his is especially pro"lematic in coastal Florida.

In order to meet drinking water standards, many utilities hae pursued mem"rane processes

for organic and hardness remoal. (he finished water -uality of mem"rane softened waternanofiltration/ is significantly "etter than the -uality of water from more traditional lime

softening treatment processes. *omparisons of recent "ids hae indicated that the

construction costs for mem"rane systems hae reduced su"stantially, while more traditional

treatment costs hae increased to meet drinking water regulations. 0oweer, as the

mem"rane systems hae "ecome operational, it has "ecome clear that more care needs to "e

taken in well construction and in the reiew of micro"iological contaminants.

Raw Water 1uality *oncerns

For years, +S EP2 and other agencies hae "een concerned with contamination of water

supplies "y industrial users or commercial carrier accidents. E3tensie efforts are ongoing to

protect watersheds and proide for wellfield protection 4ones. 2s a result of findings

concerning well contamination and the introduction of pathogenic "acteria in watersheds oer

the past 5' years, engineers and scientists hae found that "etter raw water -uality contri"utes

to less e3pensie, "etter -uality finished water.

#ther inestigations hae indicated that while many wellfields may not "e threatened "y

chemical contaminants, other concerns e3ist. For e3ample, plugging and fouling pro"lems

occur. (hese plugging and fouling pro"lems are caused "y a num"er of hydrogeologic,geologic, engineering and construction related factors including the following.

6 0ydrogeologic constraints that are unassessed at the time of design and7or change oer

time. For e3ample, sand, clay or rock layers that are unsta"le and collapse into the well "ores8

naturally occurring and7or man9made fracturing7faulting8 long term water -uality changes

caused "y changes to the hydraulic regime such as dams8 water hammer to the

a-uifer7formation8 man9induced influences mining the a-uifer, introduction of chemicals

and7or microorganisms/8 and naturally occurring phenomena sinkholes, karst terrain features

and7or faulting/.
http://facebook.com/sharer.php?u=http://www.wwdmag.com/water/biofouling-raw-water-supply-wells-and-its-impact&t=Biofouling+in+Raw+Water+Supply+Wells+and+Its+Impacthttp://twitter.com/intent/tweet?text=Biofouling+in+Raw+Water+Supply+Wells+and+Its+Impact&url=http://www.wwdmag.com/water/biofouling-raw-water-supply-wells-and-its-impacthttp://www.linkedin.com/shareArticle?url=http://www.wwdmag.com/water/biofouling-raw-water-supply-wells-and-its-impact&mini=true&title=Biofouling+in+Raw+Water+Supply+Wells+and+Its+Impact&ro=false&summary=Many+coastal+water+utilities+across+the+United+...&source=http://facebook.com/sharer.php?u=http://www.wwdmag.com/water/biofouling-raw-water-supply-wells-and-its-impact&t=Biofouling+in+Raw+Water+Supply+Wells+and+Its+Impacthttp://twitter.com/intent/tweet?text=Biofouling+in+Raw+Water+Supply+Wells+and+Its+Impact&url=http://www.wwdmag.com/water/biofouling-raw-water-supply-wells-and-its-impacthttp://www.linkedin.com/shareArticle?url=http://www.wwdmag.com/water/biofouling-raw-water-supply-wells-and-its-impact&mini=true&title=Biofouling+in+Raw+Water+Supply+Wells+and+Its+Impact&ro=false&summary=Many+coastal+water+utilities+across+the+United+...&source=


2/7

6 Poor well design and7or construction practices including insufficient placement of grout,

improper design of pumps, ales and fittings8 and e3cessie drawdown allowances.

6 Poor operating and7or maintenance procedures.

6 !echanical failures including failures of electrical motors, pumps and ales.

6 0igh silt or sand content caused "y failure to deelop the wells fully, or interfingered sand

or silt layers that hae not or cannot "e sealed off from the "orehole or corrected in well

design.

6 !icro"iological fouling pro"lems.

(he first fie contri"ute to sand, silt and other physical deterioration in the wells and the

downstream treatment system. In deeloping water sources for mem"rane processes,

engineers typically hae "een concerned with the a"ility of mem"ranes to remoe impurities

such as organics and hardness with concerns a"out the leels of iron, sand and silt in the rawwater. 2S(! has deeloped standards for conducting water -uality analyses for reerse

osmosis applications 2S(! :5$%;9


3/7

Sulfur reducing "acteria often are responsi"le for the hydrogen sulfide smell released when

raw water is aerated. (hese "acteria are common where sulfur naturally e3ists in the

formation, and will tend to form "lack colonies on pipe surfaces. While anaero"ic, they will

e3ist in enironments where aero"ic conditions that can lead to sym"iotic relationships with

aero"ic organisms e3ist.

Slime producing "acteria are found in surface waters and in soil. !em"ers of this genre often

are used to protect farm crops from fungal growth, and as a result are to "e e3pected in

groundwater that has organics. 0oweer, these "acteria are highly adaptie. Research seeral

years ago indicated that the "acteria would grow in any enironment into which they were

introduced. (he Pseudomonas genera are facultatie anaero"es that can persist in o3ygen

depleted enironments "y "reaking down comple3 hydrocar"ons for the o3ygen. In some

circumstances, they will use nitrogen in the a"sence of o3ygen.

Pseudomonas "acteria can permanently affi3 themseles to laser9polished >$?) stainless steel

in a matter of hours, so attaching to steel or lower grades of stainless steel is easily

accomplished. ien that the Pseudomonas sp. are adhering "acteria, they are capa"le ofproducing a polysaccharide matri3 "iofilm/ that can act as a "arrier protecting the "acteria

incorporated in the films from harmful su"stances such as disinfectants and, in some cases,

o3ygen. Biofilms also act to protect the "acteria from the shearing effect of tur"ulent flow,

and can proide an enironment for other species. Periodic sloughing occurs when the

"iofilm gets too thick.

(he micro"iological accumulations7 "iofilms pose seeral significant concerns. First, the

accumulations on the metallic surfaces create anodes and, in con@unction with reactions

caused "y dissimilar metals, can lead to a steady cathodic deterioration oer time with or

without iron "acteria/. Since the Pseudomonads are acid formers, ferrous materials are

particularly ulnera"le to deterioration, especially in the presence of iron "acteria.

(he sloughing eents pose a significant fouling concern for "oth the mem"rane softening and

reerse osmosis mem"ranes and could lead to some "reaching of the mem"ranes "y the

"acteria, where"y the "acteria could su"se-uently enter the distri"ution system. Because of

the si4e of the openings in the mem"ranes, it has "een assumed that the mem"ranes will filter

out the "acteria, "ut the seals in the system may allow some leakage, allowing the permeate

to "e e3posed to the raw water.

(he accumulation of "acteria in the concentrate causes concern from the standpoint of a point

source discharge, as well as the potential for seere corrosion caused "y concentration ofinorganic salts and organic acids caused "y the "acteria. (he corrosion of the steel pipe at

lime softening plants also could "e partially attri"uted to the "acteria "eing "rought in with

the raw water.

2nalysis of treatment processes indicates that lime softening does a relatiely good @o" at

remoing the "acteria "ecause of the mi3ing of lime and raw water that occurs and the

=sticky= constituency of the "acteria. 0oweer, the proposed mem"rane softening process

would not "e as effectie in the remoal of the "acteria.

0ow to See If Aou 0ae the Pro"lem


4/7

Routine monitoring of "ackground "acteria, especially iron and slime9producing species,

should "e performed "y all utilities, whether water is o"tained from a groundwater source or

a surface water source. Raw water samples must "e collected and analy4ed to determine the

speciation of "acteria, fungi and other organisms. (his cannot "e done "y simply using

B2R( or other tests although they can proide a preliminary indication of species of

concern "eing present/8 it must "e done in a micro"iological la". (he samples should "ecollected using one gallon sterili4ed plastic "ottles. (he wells should "e shut down for seeral

days. (he sample tap must "e sterili4ed in a manner similar to distri"ution system samples,

since many of the organisms are common on the hands of people. (he wells then should "e

turned on and samples collected. (he samples must "e placed on ice and sent to a la"oratory

within four hours of sampling.

Sampling protocol is important. If samples are collected from wells that hae "een running,

the samples will "e less representatie of the "acterial matri3 "ecause of the potential for not

o"taining a sloughing eent.

#nce deliered to the micro"iological la", the samples are analy4ed for heterotrophic "acteriaplate count, fecal and non9fecal coliform "acteria plate count and identification of species and

algae. (he standard industry practice for water distri"ution systems is that the presence of

coliform "acteria is an indicator of a sanitary ha4ard. 0oweer, this ignores other "acteria

that are known pathogens, and also are e3tremely detrimental to functions of the mem"rane

process.

If undesira"le "acteria are found in the wells, distri"ution system sampling should occur to

proide some comfort that the pro"lem has not moed "eyond the plant itself. (he presence

or relatie a"sence of microorganisms should determine the fre-uency of testing, "ut utilities

must monitor this pro"lem.

If Aou 0ae It, (hen What

2ll parties must understand that as utilities moe toward more adanced treatment methods,

more knowledge must "e gained a"out the -uality of the raw water. Where "acteria e3ist,

nonferrous materials should "e used for the wells and the raw water lines where possi"le. If

ferrous materials are used, it is ital that dissimilar metal conditions not e3ist, as these will

encourage fouling or lead to deterioration due to cathodic reactions, and may encourage

"iological growth.

It is recommended that utilities that are in the process of designing or constructing new

production wells or plants study the raw water -uality, potential plugging and fouling

pro"lems, and the geologic formations prior to completing design and construction of the new

facility. (est wells should "e checked for microorganisms and colloidal, sand and silt

production. +se of sand separators, well disinfection programs and conersion of well

construction materials from ferrous products to polyinyl chloride PC*/, fi"erglass and

"ron4e must "e factored into the life9cycle cost of the treatment process and the capital

program. (he need to make ma@or modifications to the wellfield often is oerlooked in the

life9cycle cost of a new mem"rane facility.


5/7

*hoosing the correct materials in the design of the plants, wells and pipelines is essential to

sae considera"le maintenance costs in the future. *areful start9up of new facilities and the

acknowledgment and inestigation/ of the potential for "iofouling will help engineers aoid

the traditional startup fouling pro"lems encountered "y many mem"rane facilities in the past.

If changes to the wells cannot "e made, you can change the plant design or attend to the"acteria pro"lem in9situ. *hanging the design may "e the less e3pensie option, "ut will

come with a time and treatment -uality penalty. In9situ treatment may "e the ne3t "est option.

(reatment is routinely conducted using high concentrations of acid and chlorine, with the

intent to shock the "acteria, "y causing rapid changes in their enironment ia p0 changes

and o3idants. 0igh concentrations of acid, in con@unction with high chlorine concentrations

up to ?,''' mg7)/, hae "een found to "e effectie, "ut the heat generated limits the

applica"ility to non9ferrous wells. 2 reiew of the cement grout also should "e undertaken.

#ther treatment methods hae included lining wells with lesser disinfection fre-uency/,

hydrogen pero3ide in some circumstances/ and ariations of the p0 ad@ustment. (hey all

hae met with arying degrees of success in controlling micro"iological growth. #3ygenatedcompounds should "e used with caution gien the a"ility of the "acteria to meta"oli4e the

o3ygen from the chemical compounds.

*ity of 0ollywood

2 >' mgd mem"rane treatment plant recently was constructed for the *ity of 0ollywood

Fla./ to house $? mgd of softening mem"ranes to treat Biscayne a-uifer water currently $5

mgd is installed/, and $5 mgd of reerse osmosis mem"ranes to treat the "rackish raw water

from the Floridan 2-uifer System 5.' mgd of reerse osmosis mem"ranes currently are

installed/. (hese processes e3ist on the same site as the *ityDs mgd lime softening facility that

uses Spiractor treatment units with a sand catalyst/ to treat relatiely good -uality Biscayne

water for many years. 2ll three processes are com"ined on9site to produce high -uality water.

(he Biscayne 2-uifer is significantly affected "y rainfall. In addition, at one time, most of

the surface was coered with the Eerglades, so significant -uantities of organics are found.

2s a result, it should "e no surprise that the *ityDs raw water and wells contain aero"ic iron

"acteria, anaero"ic sulfur9reducing "acteria and slime producing "acteria that cause

su"stantial damage to well e-uipment and column pipes, necessitating fre-uent maintenance.

(he enironment within the a-uifer causes these "acteria to "e e3tremely aggressie towardiron pipe, including (ype >'5 and (ype >$?) stainless steel. (he *ity first noticed seere

corrosion pro"lems in its wells during the $%%; e3pansion of its water treatment plant.

Because the lime softening reactions do a good @o" at remoing the "acterial colonies, this

was not an issue that the operations staff had focused on preiously.

2dditional damage was noted during inestigations of the older iron well casings, pipes,

pump "odies and fittings. In addition, iron "acteria staining and pitting were found on the

stainless steel piping used for the raw water line on the plant site and for the mem"rane

intakes. (esting of the cartridge filters showed effects from the "acteria in the *ityDs wells.

(hus, the *ity has em"arked on a program to minimi4e the impact of the "acteria. (he *ityfirst initiated a program to treat all the wells with acid and ?,''' mg7) of chlorine. It was


6/7

determined that growth in the e3isting wells would occur within %' days, so o3ygen treatment

was necessary. (he program went on to include new material specifications, pump

changeouts, disinfection of the wells, replacement of iron9"ased parts, sliplining,

a"andonment and drilling of new wells. Seeral fi"erglass column pipes were installed to

correct corrosion pro"lems. While no o"sera"le damage was eident to the fi"erglass, these

column pipes showed a "right orange slime layer when withdrawn from the wells afterseeral years. (he *ity found that the orange slime was caused "y an iron "acterial growth,

with the consistent presence of Pseudomonas sp.

*ollier *ounty

In $%%', the *ollier *ounty Water9Sewer :istrict decided to proceed with the design of a $&

mgd mem"rane softening nanofiltration/ facility located fie miles north of its e3isting $&

mgd lime softening plant. Finished water from the two plants was proposed to "e manifolded

together prior to entering the distri"ution system. Both treatment plants were to use the samewellfield a )ower (amiami a-uifer wellfield that had sered the utility system for oer ten

years/. (he production 4one is a semi9confined 4one "etween ?' and $5' feet. E3cept for the

first fie wells, all wells were of polyinyl chloride PC*/ construction with "ron4e pumps

and stainless steel column pipes. 0oweer, seere deterioration of the stainless steel column

pipes installed in the late $%' years. (he cleaning process

may cause damage to the mem"ranes and reduce the life of the mem"ranes and7or the plant.

*onclusions

Plugging and "iofouling pro"lems in wells are prealent throughout South Florida and other

areas of the country. +nfortunately, despite the num"er of systems utili4ing wells, the focus

of operations personnel is more on the mechanical and electrical failures that routinely plague

operators than on root causes of long9term deterioration such as colloidal, silt, sand, pump

and well design and installation and "iofouling.

*onclusions from the case studies are that long9term micro"iological pro"lems may go

unnoticed, undiagnosed or improperly diagnosed. *athodic reactions from dissimilar metals

pose significant risk to the long9term maintenance of the wellfield and may "e enhanced and

e3acer"ated "y micro"iological action. 2 complete inestigation and proper analysis of the


7/7

raw water supply including silt, sand and micro"iological analyses are re-uired prior to

design of mem"rane processes.

eologic pro"lems can go unnoticed during the initial startup of the wells. 0oweer,

geologic pro"lems, sand, silt or micro"iological clogging of a grael pack or open hole/ are

significant issues that are generally ignored "y design engineers, construction engineers andcontractors, leaing the operations staff with a pro"lem shortly after start9up of the facility.

2cknowledgement

!r. Bloetscher was preiously the 2ssistant +tilities 2dministrator for the *ollier *ounty

Water9Sewer :istrict, and the :eputy Pu"lic +tilities :irector for the *ity of 0ollywood,

Fla.

Frederick Bloetscher, P.E., is director of engineering, operations and planning for Pu"lic+tility !anagement and Planning Serices, Inc. P+!PS, Inc./, :ania Beach, Fla.

erhardt !. Witt, P.., is the principal of erhardt !. Witt 2ssociates, Inc., West Palm

Beach, Fla.

Ro"ert E. Fergan, P.E., is an engineer with 0a4en Sawyer, Raleigh, .*.

biofouling in raw water supply wells and its impact

Documents