Reprinted from October 2004

LCPPJOURNAL OF PROTECTIVE COATINGS & LININGS

J

Out of Sight,

Out of Mind,

and Often Out of Order:

The Problems with Protecting Wastewater

Treatment Plants

Out of Sight,

Out of Mind,

and Often Out of Order:

The Problems with Protecting Wastewater

Treatment PlantsBy Gary Hall, Sauereisen, Inc.

Winner of the

2006 Outstanding

SSPC Publication Award

waterWaste solids + microbes H2S + polythionates + sulfates

agitation

ollections. Drains. SewerLines. By whatevername they are called,they and their associatedtreatment plants presentunique protection and

maintenance challenges. Imagine beingasked to put a coating on concrete thatis saturated with water, covered withgrease and a nasty biofilm, heavilyattacked by sulfuric acid, and contami-nated with bacteria. Imagine, too, thatsurface preparation techniques at bestremove degradated concrete and sur-face contaminants but have no effect onthe level of moisture in the substrate orthe degree of subsurface microbial colo-nization. Suppose your coating has tocure at cool temperatures in an environ-ment that is at more than 90% RH andfilled with hydrogen sulfide. That isenough to make even hardened coatingapplicators nervous and the best coat-ing formulator sweat. Yet those are pre-cisely the conditions found in waste-water collection and treatment systems.

A system that is out of sight and outof mind is often out of order. To saythere are “coating issues” in wastewatertreatment systems is a classic under-

J P C L / O c t o b e r 2 0 0 4 / P C E

statement. Contributing to those issuesare two underlying factors—a basic lackof understanding of the cause of deterio-ration on the part of the industry andits specification writers, and an all toocommon material specification for theconcrete that demonstrates the com-bined effects of insufficient informationand a resistance to change. This articlehighlights these issues, outlines the cor-rosion mechanisms involved, and dis-cusses substrate specifications and coat-ing selection, including properties andchemistry.

Germs and Other NastiesAs one would suppose, the environ-ment of a sewage collection system isone of the least sterile imaginable.Perversely, it is the very lack of sterili-

ty that at once makes the system workas efficiently as it does and that is thecause of myriad problems. The processbegins with decomposition of solidwastes in the sewage. To travel fromany particular home or building on thesystem to the wastewater treatmentplant (WWTP) requires several days,on average. During this time, anaerobicbacteria, which function in an airlessenvironment, are present in the solidwastes, along with water-aided dissolu-tion and agitation due to flowing andtumbling through the pipeline. Thesefactors cause the waste solids to breakup. The microbes release hydrogen sul-fide (H2S) as they form sulfate-contain-ing organic compounds:

The bacterial digestion of the solidsforms polythionates and other sulfates,

The Problems with Protecting WastewaterTreatment Plants

By Gary Hall, Sauereisen, Inc.C

Out of Sight, Out of Mind, and Often Out of Order:

(above) Large wastewater treatment in Arizona with(tan) epoxy liner applied

(above) Gravity thickener tank(rehab.) lined with 20 mils(1⁄2 mm) of epoxy(left) Underground clarifier lined with 1⁄4-inch (6-mm)epoxy mortarPhotos courtesy of the author

2

surface pH begins to drop. Unhindered,these reactions will eventually lowerthe pH to about 8.

Also ubiquitous in the air space arethe Thiobacillus bacteria. As the pluralform indicates, there are more thanone type, or strain, of Thiobacillus,

including one called Th.Concretivorous, or “concretedevouring” Thiobacillus. Thesebacteria respire H2S and con-sume polythionates. Theymetabolically reduce thesesulfates and produce sulfuricacid (H2SO4), which has a con-centration that is straindependent. The concentrationof H2SO4 ranges from 1.6% to60.40%. Our friend Th.Concretivorous secretes>40wt% H2SO4. This sulfate-reducing bacteria (SRB) is aer-obic, functioning in a gaseousenvironment, usually one thatincludes oxygen. The SRBlodge on the concrete abovethe sewage, where theysecrete their H2SO4 waste. Ofcourse, the H2SO4 greatlyaccelerates the corrosionprocess, the rate of which isultimately dependent uponthe strain of bacteria presentand how successful it hasbeen at proliferation. This

phenomenon is also MIC.

An Underlying Problem After WWII, specification writersbegan to call for the use of Type IIportland cement in concrete sewerpipes and appurtenances. Type II port-land, a so-called “sulfate-resistant”cement, was chosen with the mistakenbelief that it would withstand acidsbetter than Type I, the “standard”cement used in construction. ASTM C-150, Specification for PortlandCement, does promote the resistanceof Type II to neutral and alkaline sul-fates common to ground water.

some of which are deposited on theconcrete.

In the air spaces above the sewage,water vapor (H2O) and carbon dioxide(CO2) are ubiquitous. Collecting on theconcrete, the condensed H2O dissolvesboth the CO2 and H2S, resulting in asolution of H2S and carbonicacid (H2CO3).

Metals are also used in variousways throughout wastewatertreatment systems. Concreteusually contains metallic rein-forcement (rebar). Ladders, sluicegates, and other metallic sub-strates offer opportunities forcorrosion. Microbiologicallyinfluenced corrosion (MIC) onmetals is no different than anyother electrochemical attack. Themicroorganisms involved cancause the same sort of corrosionproblems seen in other environ-ments. They may accelerate cor-rosion from other sources, suchas industrial discharges.Corrosion phenomena such aspitting, gaseous concentrationcells, crevice corrosion, exfolia-tion, and selective de-alloying areall found with MIC.

Most instances of MIC resultfrom highly complex interac-tions between groups ofmicroorganisms, not all ofwhich are bacteria. Molds, mildew,fungi and yeasts, and many species ofbacteria can contribute to corrosion.Due to this multiple organism environ-ment, simply testing a material’s resis-tance to H2SO4 or one microbe doesnot replicate field conditions. The onlymeaningful test is in fact multiple fieldexposures in a variety of locales andsystems.

The presence of multiple species ofmicroorganisms may complicate sur-face preparation. Some microorganismsare anaerobic and may infiltrate con-crete, which typically has upwards of10% total porosity as measured by

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ASTM C-20, Test Methods forApparent Porosity, Water Absorption,Apparent Specific Gravity, and BulkDensity of Burned Refractory Brickand Shapes by Boiling Water.

Different microbial species willintroduce other chemical species. For

example, halophillic bacteria may beassociated with chlorides or other halo-gens. Due to the highly complex interac-tions between groups of microorgan-isms, the chemistry at the substrate/biofilm interface is far different than ifthe biofilm was not present. The differ-ences may include pH, dissolved oxy-gen, organic and inorganic compounds,and entrapped/ dissolved gases such asH2S.

Virgin concrete, dependent upon themix design and degree of carbonation,has a pH of 12.5 to 13.5. The alkalineconcrete begins to react with the car-bonic acid/ H2S condensate and the

Concrete Pipe

CondensedH20, H2C03, H2S

Released H2S

Waste Solids

Different microbial species will introduce other chemical species

Same surface after filling voids/bug-holes with epoxy filler compound

New concrete after abrasive blasting toremove laitance and expose bugholes

3

However, all portland cement is strongly alkaline and willreadily react with even the weakest H2SO4. A study pub-lished in 1993 by the author1 and G. Maloney illustratesthat Type II deteriorates to a greater degree than Type Iafter 6 months’ exposure to a H2SO4 solution that wasonly 5wt%. After one year the Type II had suffered signifi-cantly more strength and mass loss than Type I, which wasitself essentially destroyed. Figures 1 and 2 illustrate theeffect of an even weaker 1% H2SO4 solution on Types I & IIportland. Figure 3 is a control mix of Type II unexposed.Figures 4 and 5 demonstrate the effect on calcium alumi-nate cements. As can be seen in Fig. 5, the calcium alumi-nate cements are rapidly attacked at 40% H2SO4, the acidconcentration secreted by Th. Concretivorous.

Much of the municipal collection infrastructure in theUnited States and elsewhere has suffered significant corro-sion loss because of the initial ignorance of the propertiesof portland cement, in general, and of Type II, in particular,and a misunderstanding of the overall destructive mecha-nism including the microbial role. Many large sewer lineshave collapsed as a result. Inertia has kept the process run-ning. Inertia on the part of industry “experts” has keptthem from correcting past errors in design specificationsand material choices. Inertia on the part of system owners,because the system is “out of sight,” has created chronicfunding shortfalls and an unwarranted and ultimatelyunwise dependence upon contractors for material selectionrather than qualified engineers. The municipalities andtheir design engineers should have the ultimate objective ofobtaining the lowest total cost/unit area over the structure’sexpected life. In reality, they often jointly conspire with thecontractor to obtain the lowest installed cost/unit area. Theformer is good engineering practice and money manage-ment. The latter ignores known facts and is a gamble thattoo often proves costly.

To Coat or Not To Coat?The environment and the elements of the corrosion processexist throughout the collection system. Moreover, theyexist from one system to another in areas as different asAlaska, Puerto Rico, and Arizona. Regardless of locale, thesame microbes are present; H2S is given off; polythionatesare formed; and H2O is present. Yet some systems have lit-tle or no corrosion while others lose six or more inches ofconcrete in less than four years. In some systems, one areaexhibits severe corrosion while another shows none. Giventhis, how do we decide whether to coat or not to coat?With what do we coat? How do we specify the coating?

J P C L / O c t o b e r 2 0 0 4 / P C E

What properties are needed? How do we rehabilitate sub-strates prior to protecting them?

History is a valuable tool. History can provide clues thatenable us to evaluate data, much of it anecdotal in our case.The history of a given collection system will obviously indi-cate where the effects of corrosion have been observed. Thatis one prong of the multi-pronged problem. Until relativelyrecently, most pipeline interiors were rarely if ever seen onceplaced in the ground. We only knew about problems whenthey produced observable effects like collapse and leakage.Today, the means exist to visually inspect pipeline interiors inplace. This allows for the collection of data and decision mak-ing based upon this data.

Some industrial companies and a few technical organiza-tions have taken the lead in determining the cause of corro-

Figure 1: Effect of Weak H2SO4 on Weight of Types I and IIPortland Cement over Time

Figure 2: Effect of Weak H2SO4 on Compressive Strength of Types I and IIPortland Cement over Time

1% H2SO4

1% H2SO4

% c

hang

e in

wei

ght

% c

hang

e in

com

pres

sive

stre

ngth

Type #1 Type #2

Type #1 Type #2

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Out of Sight, Out of Mind, and Often Out of Order

sion and developing data or means to combat the corrosion orprevent it. Organizations such as NACE International, WaterEnvironment Federation (WEF), and the InternationalConcrete Repair Institute (ICRI) have provided a public forumto help elucidate the problems, causes, effective remediation,and quality control. Others such as SSPC: The Society forProtective Coatings have helped train the industry and its con-sultants and contractors to correctly specify and apply coat-ings for corrosion protection.

We now recognize and understand the conditions that leadto MIC and the mechanisms involved. Where do we applyprotective coatings? As stated above, within one collectionsystem, there can be some areas exhibiting severe corrosionand others exhibiting very little or even none. Examination ofhundreds of systems, in person or by video, has given usenough data to make some generalizations about the condi-tions and locations likely to corrode. One very importantcaveat underlying these generalizations is that fixing theproblem in one area may exacerbate the situation down-stream. The bacteria may prefer one area to another due to alocalized variable such as a higher H2S concentration.Eliminating their growth support platform, for example, byapplying a coating, may cause them to move on to a lessdesirable area. Being highly adaptable, they lodge, proliferate,and start the MIC process in a new area. Table 1 lists some ofthe Th. bacteria and their ideal growth conditions; Table 2lists some areas especially prone to MIC.

As mentioned above, some parts of the wastewater treat-ment system will not be subject to corrosion. Indeed, some-times an entire collection and treatment system may haveonly limited corrosion. Why does one system in Vermontshow no corrosion, yet a system in Florida shows severe cor-rosion? We now know that systems with forced-mains willundergo much less MIC compared to gravity-flow systems.When sewage is pumped through forced-main systems, thepipe is full and the pressure of the flowing water helps todilute any acid present and to remove biofilms. The more often

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7000

6000

5000

4000

3000

2000

1000

01 3 7 14 21 28

Com

pres

sive

Stre

ngth

(psi

)

Time (Days)

+ 50

- 5-10-15-20-25-30-35-40-45-50

1 3 7 14 21 28

Com

pres

sive

Stre

ngth

(%)

Time (Days)

Fig. 4: Change in Strength of Calcium Aluminate Cementvs Time for 37.5% HCI Immersion

Fig. 5: Change in Strength of Calcium Aluminate Cement vs Time for 40% H2S04 Immersion

+ 50

- 5-10-15-20-25-30-35-40-45-50

1 3 7 14 21 28

Com

pres

sive

Stre

ngth

(%)

Time (Days)

Bottom side view of 12-inch x 12-inch x 6-inch (30-cm x 30-cm x 15-cm)rein-forced concrete steel beam in wet well. Six years’ service in Louisiana waste-water treatment collection system. Concrete loss is greater than 4 in. (10 cm)

Fig. 3: Change in Strength vs Time

Concrete comparator panels from ICRI being used to determine adequacy of surface preparation

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Out of Sight, Out of Mind, and Often Out of Order

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the forced-main runs full, the less the likelihood of corrosion.Some very old systems have very little MIC, even if they

are gravity-flow systems. The daily load is sufficient to keepthe pipes fairly full. This has a similar effect as seen in forced-main systems. Conversely, a new system may exhibit severecorrosion. This is a result of designing the system to handleanticipated volumes when the population density increases.Until such time, the lines rarely if ever experience full loadconditions. The crown of the pipe in this scenario becomeshighly susceptible to MIC.

Areas where sewage flow is slowed are at risk of MIC.Sewage fermentation continues regardless of flow rates.

When the solid wastes are allowed toremain or collect in one area, the con-centration of H2S in the air spaceabove the sewage increases. The higherH2S concentration allows for more effi-cient proliferation of the microbes. Asmicrobial proliferation increases, sodoes MIC. Gravity-flow lines and gritchambers are two such examples.

When the turbulence of the sewageincreases, dissolved H2S comes out ofsolution. This too increases the H2Sconcentration above the sewage, lead-ing to greater MIC rates. Drop man-holes, pump stations, changes in planewithin a line, and junction boxes aresome examples.

The locale can have a significant

Parameter

Metabolicprocess

pHInitialOptimum GrowthSlow GrowthTemperature

Optimum Growth

Slow Growth

Thiobacillusconcretivorous

Oxidizes thiosulfateselemental sulfur, sulfides

7 to 8

2 to 4<1

50–75 F (10–24 C)85–98.6 F (29–37 C)75–85 F (24–29 C)

Thiobacillusthiooxidans

Oxidizes thiosulfateselemental sulfur, sulfides

7 to 8

>0.6>5

50–75 F (10–24 C)85–98.6 F (29–37 C)75–85 F (24–29 C)

Thiobacillusthioparans

Oxidizes thiosulfatesto elemental sulfur

and sulfate 7 to 8

4 to 5>9, <5

50–75 F (10–24 C)85–98.6 F (29–37 C)75–85 F (24–29 C)

Table 1: Environmental Conditions Promoting Thiobacillus Growth

• Manholes

• Lift Stations/Pumping Stations

• Grit Chambers

• Junction Boxes

• Drop Manholes

• Digesters

• Clarifiers

• Sludge Houses

• Wet Wells

• Aeration Basins

Table 2: Areas in Wastewater Collection andTreatment Systems Prone to Corrosion

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Out of Sight, Out of Mind, and Often Out of Order

being touted for service in municipal wastewater systems.Some are coatings already in use in other industries. A man-ufacturer with little or no knowledge of the issues will thenbegin to recommend such systems for the severe environ-ments of wastewater treatment plants. Other coatings weredeveloped specifically for this market with full knowledge ofthe MIC process and application and cure challengesinvolved. Still others are copies of other manufacturers’products, offering no technology base other than some skillin cook-book blending. Specifiers of coatings and systemowners have only a limited ability to evaluate the success ofthe many coatings available, much less the technologybehind the coating or its chemistry—thus the need for strict-ly enforced specifications.

At this junction, some system owners and consulting engi-neers take a step down a slippery slope by asking their con-tractors to choose a coating. Sometimes the contractor evendetermines substrate repair and acceptability. As skilled assome contractors are, especially those who are SSPC-trainedand certified, they are not qualified to make recommenda-tions on matters needing a scientific background. When thecontractor becomes the coating consultant, concerns aboutchemistry, materials science, corrosion science, microbiology,and civil engineering are ignored. Other issues, such as coat-ing cost, ease of use, and personal/ business relationshipsbecome the overriding ones.

While cost issues and applicator friendliness are legiti-mate concerns, they are merely additional factors. When acoating is chosen by price alone, a prime responsibility ofengineers and managers is compromised. A financial analy-sis that ignores cost/ unit area/year of service life is at bestan analysis of questionable worth.

As for user friendliness, the author’s experience has been

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Property

Compressive Strength

Flexural Strength

Modulus of Elasticity, Flex

Tensile Strength

Tensile Elongation

Hardness

Bond

WVT/Permeability

Coating #1

C-579

C-580

D-522

C-307/D-638

D-638

D-2240

D-4542

D-1653

Coating #2

D-695 (Property not

needed)

D-790

—

D-638

D-638

D-2240

D-4541

D-1653

Table 3: Properties and Test Methods Specified for 65-Mil (1.5-mm) Coating

Rehabilitation of a brick manhole—counterclockwise, from left top (p. 44):Brick manhole with severely deteriorated mortar joints; lined with cement-based epoxy repair material at approximately 1/4-inch (6 mm); being coatedwith rotary spray-applied epoxy at approximately 125 mils (3 mm); complet-ed rehabilitation

effect. Table I lists the environmental conditions most favor-able for Thiobacillus growth. If one system is exposed to sig-nificantly warmer temperatures, the bacteria proliferatemore efficiently than in a cooler climate. For example, asystem in Vermont may see only 50 F (10 C) or more threemonths/year, while the same size system in Puerto Ricomay never fall below 50 F (10 C). The Puerto Rico systemwill see significantly increased corrosion compared to theVermont system.

Some locales have high levels of sulfur and H2S in theirwater supply. Coastal areas may have chloride in the sys-tem. Farming communities will have phosphates andnitrates from fertilizers. Each of these scenarios creates anadditional potential for MIC. Halophilic bacteria will gener-ate HCl, while others utilize the phosphates and nitrates.

Recently, the industry has seen a proliferation of coatings

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Out of Sight, Out of Mind, and Often Out of Order

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that most coating manufacturers makecoatings that are simple enough toallow for proper application easily.Failure to do so is tantamount to guar-anteeing a poor sales growth. The prob-lem in this regard usually relates to oneof four factors.• A preferred contractor or low-bidderdoes not have the required equipment.• A preferred contractor or low bidderdoes not have the required skill levels orexperience.• The contractor does not have sufficientmoney in his bid to support materials ofrequired/specified quality.• The contractor does not have a pre-ferred contractor discount available withthe specified coating manufacturer.

PropertiesEngineering consultants or system own-ers specify the properties of the materi-als to be used along with “appropriate”test methodology. Table 3 shows twodifferent sets of engineering specifiedproperties and the ASTM test methodsused by their respective manufacturers.

Both are for a 65-mil (1.5-mm) spray-applied epoxy coating for manholerepair. The set of properties on the leftis generated via ASTM methods pre-dominantly under ASTM committees C-3, Committee on Chemical-ResistantNonmetallic Materials, and D-1, Paintand Related Coatings, Materials, andApplications. The set on the rightincludes types of data generated viamethods for molded plastics and pre-formed plastics under D-20, on plastics.“So what,” you say. The method bywhich a given mechanical property isdetermined has a statistically profoundeffect upon the result. Factors such assample shape, size, sample preparation,surface area/volume ratio, speed atwhich loads are applied, and the man-ner of testing all have an effect on theresults obtained. The different ASTM

OrganismAchromocacter Spp.Aerobacter Spp.

Aerobacter aerogenesAlcaligenesBacillus Spp.

Bacillus cereusBacillus subtilis

BeggiatoaChromobacteriumClostridium Spp.CrenothrixDesulfotomaculum Spp.

Desulfotomaculum nigrificansDesulfotomaculum orientis

Desulfovibrio Spp.Desulfovibrio africannusDesulfovibriodesulfuricansDesulfovibrio salexigensDesulfovibrio vulgaris

Diplicoccus Spp.Diplicoccus pneumoniae

Escherichia Spp.Escherichia coliEscherichia freundii

Ferrobacillus ferrooxidansFlavobacterium Spp.

Flavobacterium hydrophiliumGallionella ferrugineaKlebsiella Spp.Klebsiella pneumoniaeLactobacillusLepthothrix

OrganismMicrococcusMicrospiraNocardia Spp.Paracolobactrum Spp.Proteus Spp.

Proteus morganiiProteus vulgaris

Pseudomonas Spp.Pseudomonas aeruginosaPseudomonas oleovorans

Salmonella Spp.Sarcina Spp.Shigella Spp.SphaerotilusSpirillumSporovibrioStaphylococcus Spp.

Staphylococcus albusStaphylococcus aureauStaphylococcus citreus

Streptociccus Spp.Thiobacillus Spp.

Thiobacillus concretivorousThiobacillus thiooxidansThiobacillus thioparus

ThiothrixVibrio Spp.YeastFungi

Cladsporium resinaeCephalosporium Spp.

Table 4: Compilation of Microbiological Species Identifiedin Environments Associated with Corrosion Fouling

methods utilize different testing tech-niques and sample preparation meth-ods, and are unable to determine prop-erties at a specific age. In addition,machining of samples introduces poten-tial error due to the effect of frictionalforces with a cutting device. This

means that a particular property mea-sured by a D-20 method will not neces-sarily correspond to the same propertymeasured by a C-3 methodolgy.

Which methods are appropriate? Weare dealing with a corrosion-resistantcoating, not a molded or machined plas-

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Out of Sight, Out of Mind, and Often Out of Order

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tic part. Therefore, the methodologiesof C-3 and D-1 pertain. Plastic testmethods are wholly inappropriate andmisleading. The properties requiringspecification are those important to theperformance in service. Let’s examinesome properties, needed values, andtheir appropriateness to their perfor-mance in service.• Thickness—usually less than 125mils (3 mm)— is an important propertybecause some other properties aredirectly proportional to the thickness,e.g., wear, permeability, microbial barri-er efficiency, and completeness of cov-erage. Thickness should always be spec-ified as dry film thickness (DFT). Onnew, smooth concrete, a thickness of30–40 mils (~1 mm) will work well.When the concrete is rougher than a36-grit sandpaper, thickness needs tobe increased to 60–120 mils (1.5–3mm).• Compressive strength—Since appliedcoatings in wastewater treatment sys-tems are not subjected to more thanminor levels of compressive forces, thisproperty is not one that is truly need-ed. Its value lies in the fact that engi-neers think they understand its mean-ing and it is a cheap and easy test torun as a QC/QA test. But we are deal-ing with coatings, high-build paint, ifyou will. It makes no more sense tospeak of the compressive strength ofthese coatings than it does for paint.• Flexural strength—Since flexing andvertical misalignment occur regularlyin buried wastewater treatment andcollection systems, both the flexuralstrength and the tangent flexural mod-ulus of elasticity are valuable proper-ties to know. These can be accuratelydetermined for coatings at thicknessesof 50 mils (1.2 mm) or greater. Valuesof 4,000 psi or greater for flexuralstrength and 5 x 106 psi or less forflexural modulus are good.

Tensile strength—One of the mostimportant of mechanical properties,tensile strength is needed to calculateoverburden-bearing capacity and is ofparamount importance to resistance toground water infiltration. Tensilestrengths of 1,800 psi are consideredexcellent.• Bond strength—The bond of thecoating to the substrate is perhaps thekey element to achieving a long servicelife. Loss of bond is the most commonmode of failure for coatings. Bondstrength to wet concrete should exceedthe cohesive strength of the concrete,usually above 400 psi.• Permeability—Calculated from watervapor transmission (WVT) rates andpermeance, permeability is the proper-ty that controls passage of corrodentsthrough the coating to the substrate. Ifall other properties and chemistry areequivalent, the coating exhibiting thehighest permeability will typically failfirst. A permeability of <10-6 perm-inches is recommended.

Two other critical properties arechemical resistance and resistance tomicrobial growth. Since the chemistryin a sewer system is a true witches’brew, including microbe-generated sul-furic acid up to 60wt% and organiccompounds, the chosen lining mustpossess excellent chemical resistance.Depending upon locale, other chemicalspecies such as chlorides, nitrates, andphosphates may also be present.

It is also important for the coating toresist microbial growth. If the coatingcontains compounds that microbes canuse, or if it is porous enough to allowmicrobes to penetrate, then the coatingwill fail prematurely. But one has to becareful in adding bacteriacides towastewater treatment coatings. Whenthe bacteriacide leaches, it will reachthe WWTP. At the WWTP, the sameSRB’s are deliberately introduced in

the digester in order to complete thedegradation of suspended waste solids.Bacteriacides entering the WWTP willcreate havoc. Once the bacteriacidesenter the digester, they kill off thedeliberately introduced bacteria, thusreducing the efficiency of the digestionprocess. Further, since the WWTPprocesses will not remove or destroythe bacteriacide, they are dischargedwith the treated wastewater intowaterways. This practice requires EPAapproval and much testing.

Thus far, we have not discussedindustrial wastewater treatment sys-tems or municipal systems that allowpre-treated industrial waste. The con-cerns are the same as described hereto-fore with the additional corrosionpotential represented by these dis-charges. Sometimes these industrialdischarges destroy bacteria; sometimesthey create conditions more favorablefor bacteria proliferation; and, at othertimes, they create conditions favorablefor different types of bacteria than theTh.

Each situation requires an analysisof the conditions present in order tomake an appropriate coating recom-mendation. Some conditions may war-rant a novolac epoxy, others a vinylester or some other coating chemistry.

For example, a treatment plant inwestern Virginia receives dischargesfrom four chemical plants upstream ofthe treatment plant. Even though thesedischarges are partially pre-treated bythe chemical companies, they still con-tain aggressive chemical species suchas chlorides and organometal com-pounds. The combination of com-pounds dictates either an inorganic sili-cate refractory or a vinyl ester coating.The vinyl ester coating is more eco-nomical and was chosen in this case.

We have discussed aerobic bacteriaand their role, but there are anaerobic

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Out of Sight, Out of Mind, and Often Out of Order

Gary Hall is currentlyManager of OrganicTechnology andManager of Environ-ment, Health andSafety at Sauereisen,Inc. (Pittsburgh, PA).Sauereisen manufac-tures ceramics, refrac-tories, cements, and

coatings. Mr. Hall is responsible for productdevelopment and improvement forSauereisen and manages the Research andDevelopment efforts for the organic productline. He has been with Sauereisen for 36-years and is a graduate chemist from theUniversity of Pittsburgh. He is active in theNational Association of Concrete Engineers,several ASTM Committees, AmericanInstitute of Chemical Engineers, and theElectrostatic Discharge Association. Mr. Hallis also a contributing editor for JPCL and hastwice been the recipient of the JPCL Editors’Award. His areas of special interest includecement and concrete technology, corrosionscience and control, polymer science, andnanotechnology.

J P C L / O c t o b e r 2 0 0 4 / P C E

microbes at work as well. For example,Desulfovibriodesulfuricans actuallymigrate through capillary and gel poresin the concrete to lodge on embeddedreinforcement. These SRB use iron (Fe)to catalyze the reduction of polythion-ates to H2SO4. The H2SO4 is secreteddirectly on the iron and causes it to cor-rode and expand as it does. The volu-metric expansion can be up to twelvetimes the original volume of the rein-forcement. This expansion can generatetremendous stresses in the concrete,causing it to crack concurrent with thereinforcement. When this occurs, thereinforcement must be exposed, cleanedand repaired, grouted for stress relief atsplices, and recoated with concrete. Tocoat the concrete without doing so is tovirtually guarantee future failure. Theconcrete on both sides of the reinforce-ment needs to be repaired.

Although not specifically discussedin this paper, many microorganismshave been associated with corrosion,and the reader should be aware ofthem. Table 4 lists some of thesemicroorganisms.

CoatingsNow we know what happened andwhy, and we have discussed neededphysical properties, corrosion resis-tance, and substrate issues. It is time toconsider coating types. For municipalcollection systems without industrialdischarge, a high quality bisphenol Aepoxy cured with a cycloaliphaticamine or equivalent will performadmirably for many years. The authorhas personally inspected such linings inservice for more than 20 years withoutany maintenance. Today, plural-compo-nent spray-applied polyureas are beingused in a few municipalities. They havehad adhesion problems due to the factthat they cure so rapidly that they can-not adequately wet the concrete and

develop the needed adhesion. Some arenot of sufficient quality to withstandhydrolysis—dissolution by water.Several companies are working onthese problems with varying degrees ofsuccess. Polyurethanes are also beinglooked at for this application. Somecoatings based on novolac epoxy resinsare being installed. While these resinswill resist higher concentrations ofmost acids, they do have a potentiallyserious drawback. Permeability testingshows that novolac epoxies are actual-ly more likely to be permeable to H2Sthan are bisphenol A epoxies.

ConclusionWastewater collection and treatmentsystems present very difficult challengesto stakeholders such as owners, engi-neers, coatings manufacturers, andinstallers. This article has outlined someof these naturally occurring challenges. Itis the responsibility of each of thesestakeholders to become aware of thesechallenges and incorporate the necessarytechnology to withstand the difficultenvironments. The owner must ensurethat cost/unit area/year of service isthe determining factor in awarding bids.Owners need to be more judicious incontractor selection. Engineers need tobecome familiar with the conditions pre-sent and research available materials toensure quality specifications. Engineersneed also to apply their knowledge andskill in evaluating reported propertiesand test methodologies. Contractorsneed to develop the necessary skill set toapply the specified coatings or theyshould not be allowed to bid a project.Only an unwise contractor voluntarilyplaces himself at risk by becoming the defacto consultant. He isn’t being paid totake that financial risk or to risk civilpenalties for failure. The coatings manu-facturer has to know the exposure condi-tions, application and cure conditions,

Gary R. Hall

and required properties in order todevelop a quality coating. He needs tohave a knowledge of coatings chemistryand to be able to evaluate the effect ofthe environment upon the coating. Thecoatings manufacturer also needs tounderstand materials science in order todetermine what properties are neededand to choose the correct methodology.

Short cuts lead to short coating ser-vice life.

Reference1. G. Hall and G. Maloney, “CorrosionRates of Uncoated Concrete for SelectedCorrodents,” Journal of Protective Coatings& Linings, December 1993, p. 61.

10

Out of Sight, Out of Mind, and Often Out of Order

PRODUCTS FOR RESTORATION AND PROTECTION OF WASTEWATER INFRASTRUCTURES

LININGS – INFILTRATION AND CORROSION PROTECTION

SewerGard Epoxy Systems No. 210Self priming, moisture tolerant epoxy systems that are completely resistant to the micro-biologically induced corrosion common to munic-ipal wastewater applications as well as provide an infiltration barrier. They are available in aggregate filled trowel (No. 210T) and rotaryspray (No. 210RS) versions, as well as a fiber-filled airless spray version (No. 210S). The No. 210RS allows manholes to be efficientlylined from street level with minimal entry into the manhole. These products will bond to damp concrete and cure in the presence of mois-ture. An optional topcoat (210G) provides a more smooth surface for greater cleanability. This 100% solids product can be economicallyrolled or sprayed.

SewerSeal No. F-170Single component, high strength, 100% calcium aluminate based product for use in manholes and other wastewater structures. This mate-rial will restore structural integrity, prevent infiltration and resist mild acids and alkalies on concrete, brick, and steel structures. SewerSealis designed for rotary and straight shot spray applications and can be applied at various thickness’ in one pass.

H2OPruf No. F-190Two component cementitious based negative side waterproofing system specifically designed to withstand hydrostatic pressures thatcause water seepage in below grade structures. Two 1/16-inch coats will withstand up to 70 feet of water head pressure. It can be appliedby brush or spray, including rotary spray equipment used for manholes.

SUBSTRATE REPAIR

Underlayment and Repair Mortar No. F-120Single component, high strength, rapid set Portland cement based repair mortar that is available in trowel, castable and gunite grades.The trowel grade can be applied vertically and overhead and can be topcoated with epoxy in 5 hours.

Substrate Resurfacer No. F-121Single component, high strength, rapid set Portland cement based product for repairing, resurfacing, and waterproofing masonry struc-tures. This material will restore structural integrity and prevent water infiltration into concrete and brick structures. It is designed for rotaryand straight shot spray applications and can be applied at various thicknesses in one pass.

Filler Compound No. 209Three component, epoxy formulation that is specifically designed to fill voids, irregularities, and air pockets in concrete. No. 209 will pro-vide a smooth surface ready for application of protective compounds in 3 hours. This material is also available in a fast setting grade thatcan be topcoated in 1 hour. Either formulation is suitable for application over damp or dry concrete. Application is performed with a rub-ber K&R trowel.

ACTIVE INFLOW AND WATERSTOP PRODUCTS

Manhole ChimneySeal No. F-88Elastomeric lining composed of fiber-reinforced, asphalt-modified urethane. Two component, chemical resistant seal that can be appliedby a gloved hand onto the chimney sections of manholes to prevent water inflow. As a high solids elastomer, Chimney Seal maintainsexcellent elasticity and adhesion over a temperature range of -30ÐF to 250ÐF while resisting acids, alkalies, and salts.

InstaPlug No. F-180Rapid setting hydraulic water plug that will seal active water leaks and allow continuous rehabilitation work on concrete structures. Thismaterial will set in 60 – 90 seconds and cure completely in one hour. It is also used to fill small voids and for anchoring applications.

Hydroactive Polyurethane Grout No. F-370Catalyzed hydrophobic grout that reacts with moisture and expands to 20 times its volume to seal leaks, cracks, joints and voids. It bondstenaciously to practically any substrate, wet or dry, it has excellent chemical resistance and it is safe for potable water.

SPECIALTY

PenePrime No. 500Two component water-borne epoxy primer that is specially formulated to work in conjunction with other Sauereisen products. PenePrimepenetrates deep into the concrete substrate to seal porous substrates and reduce off-gassing from concrete. This product is manufacturedto ensure maximum adhesion of the specified protective coating. Application is performed by brush, roll or spray.

160 Gamma Drive - Pittsburgh, Pennsylvania 15238-2989 - 412.963.0303 - Fax: 412.963.7620www.sauereisen.com - e-mail: questions@sauereisen.com