wastewater treatment - val matic

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WastewaterTreatment

Society’s desire for a clean environmentshines light on the importance of under-

standing the essential role wastewater treatment plants have inour communities. Congress passed the Clean Water Act in 1972 tocontrol the discharge of effluent into water systems and water-ways, and provided grants to allow municipalities to meet thesenew requirements. Since then, technologies such as optimizedtreatment systems and automated valves have been used to makeour country’s wastewater plants technical marvels. The purpose ofthis article is to explain the various critical roles that valves playin the operation of typical wastewater plant processes.

THE BASICSA place to begin this understanding is to look at the overall pur-pose of a typical municipal wastewater system, which is to collectwastewater generated by residents, businesses and industries, and

BY JOHN V. BALLUN, P.E.

SUBJECT: Valves in wastewater must dealwith the challenges of turning whatmakes its way into our nation’s sewersinto water free of disease and ready forredistribution into waterways.

KEY ISSUES:

� Today’s plant processes

� The valves and where they work

� Primary, secondary and tertiary control

TAKE-AWAY: Special valves are required tohandle the debris and suspended matterin wastewater. However, other valves areused after the waste is removed—so theindustry has a wide range of valvepossibilities.

AWWA ball andbutterfly valves areused to pump reusewater in Waco, TX.

©2016 Valve Manufacturers Association. All rights reserved. Reprinted with permission.

WHEREVALVES

ARE USED

Executive Summary

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to process that wastewater into finaloutflow that meets federal and statewater quality standards. Treated watermeeting Environment ProtectionAgency requirements then can be safe-ly discharged into water reuse systemsor waterways. A successful wastewatersystem depends on cooperation andsupport from residents, municipalities,industries and regulators.

MEANS OF COLLECTIONAs cities grew in size in the U.S.,installing wastewater collection sys-tems became a necessity for prevent-ing waterborne disease. Achievingthis, in turn, facilitated acceleratedgrowth of those cities. By the year2000, about 208 million people in theU.S. were served by centralized waste-water collection systems.1

Depending on the geography of thearea, collection systems use gravity topass flow through sewers or use lift

stations and force mains to transmitwastewater over elevations and greatdistances to a centralized treatmentplant. When a plant is fed by gravitysewers, it also may be equipped withstation pumps to lift the wastewaterand start the gravity flow processthrough the plant.

Lift stations collect the wastewaterfrom a township or subdivision bygravity and then pump that waste-

water through a force main to a cen-tralized wastewater plant. These sta-tions can be designed as either a wetwell or a wet and dry well designwhere the dry well contains the pumpsand related equipment.

The valves in a lift station arelocated in the wastewater basin, drywell or a separate valve vault. Thethree types of valves typically foundin lift stations include check valves,shutoff valves and air valves. The pur-pose of the check valve is to preventreverse flow when the pump is turnedoff. Shutoff valves are used for isola-tion when repair or maintenance isneeded. Air valves expel air from thepump column and the force main toprovide flow efficiency and minimizesurges. Selecting valves for wastewaterapplications is similar to that ofselecting pumps in that considerationmust be given to the solids content ofthe flow media.2

CHECK VALVESCheck valves are essential in lift sta-tions for preventing reverse flow whenthe pumps are not in operation. Thereare as many types of check valves aspumps, so it is important to under-stand the essential characteristics thataffect performance in wastewater service. The swing check valve is thetraditional choice and is produced inaccordance with American WaterWorks Association (AWWA) C508.These valves are made of iron with cor-rosion-resistant internal mechanisms.Swing check valves use a 90-degreeseat and are typically provided with alever and weight to assist with closureand provide position indication. Thevalves also can be equipped withsprings, air cushions or oil dashpotarrangements to reduce the valve’spropensity to slam.

A variation of the traditional swingcheck is the resilient hinge design,which has a much shorter disc strokethat can greatly reduce the slammingproblems, especially for higher headapplications. Additional benefits ofthe resilient hinge design include acorrosion-resistant disc, an encapsu-lated hinge pin, the option for posi-tion indication and a top access coverfor ease of maintenance.

A ball check valve is commonly

� Submerged wastewater pumps in a wet well liftstation with a separate valve vault

COURTESY OF ROM

TEC UTILITIES

Wastewatertreatmentprocesses


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used on smaller systems where econo-my is important. This valve uses a ball(as compared to a disc) as its closuremember. The ball is lifted up and awayby the flow during system operationand falls back to the closed positionwhen the pump is shut down. Ballchecks can be mounted in both hori-zontal and vertical applications.

PUMP CONTROL CHECK VALVESWhen main pumping stations operateat high head or pump fluid through avery long force main (i.e., five miles),pump control check valves and specialsurge equipment may be neededinstead of traditional check valves.Quarter-turn plug or ball valvesequipped with electric, pneumatic orhydraulic-powered actuators and elec-trically connected to the pump circuitare used as pump control check valves.Pump control valves open and closeover several minutes to slowly changethe fluid velocity, thereby preventing

surges in long force mains. Moreover,the use of pump control check valvescan significantly save power consump-tion due to their low head loss.

SHUT OFF VALVESAll pumps and check valves should beequipped with a shutoff valve to allowisolation of the system and mainte-nance of the lift station components.Isolation or shutoff valves for waste-water service come in many varieties;however, they all must be designed toprevent clogging and wear from theflow of grit-containing fluid.

For small-diameter applications,threaded quarter-turn ball valves arean economical choice. The threaded orflanged body contains a floating ballthat seals against non-metallic seats inboth directions.

For larger applications, multi-turnknife or wedge gate valves are com-monly used. Gate valves are usuallyconstructed of iron with flanged con-

nections. These valves are produced inaccordance with several AWWA stan-dards, including AWWA C500, C509 andC515, and are available in both risingstem and non-rising stem models. Ris-ing stems are preferred because theyprovide indication of the valve posi-tion at all times.

A compact or short version of thegate valve is the knife gate, which isproduced in accordance with AWWAC520 and gets its name because thegate is a thin metal plate or blade.With wastewater, this gate can cutthrough sediment. Knife gates arecommonly used for suction isolation ofwastewater pumps because flow con-trol is not required. No gate valvesshould be used for throttling or flowcontrol because vibrations while thegate is partially open can damage thevalve.

Another shutoff valve for waste-water service is the quarter-turneccentric plug valve, which is built in

� Wastewater air valves isolated by gate valves are installed in a wastewater treatment plant.

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accordance with Manufacturers Stan-dardization Society (MSS) SP-108 orAWWA C517. The seat and plug face ofan eccentric plug valve is located off-set from the valve shaft and port sothat, as the plug is rotated out of theseat, it is pulled away rather thanscraping against that seat. This eccen-tric action prevents wear in abrasiveservice. Moreover, if wear does occur,the actuator can be adjusted, furtherclosing the plug to provide new seat-ing surface and a tight seal.

Plug valves can be furnished as adirect nut type for wrench operationor, in larger sizes, equipped with aquarter-turn worm gear actuator. Anadditional advantage of a plug valve isthat the valve can be used as a pumpcontrol valve by using electric/hydraulic actuation. These valves arealso excellent in throttling applicationsfor controlling the rate of flow.

AIR VALVESAutomatic air valves are installed onthe pump discharge and at high pointson the force main to prevent air pock-ets or vacuum conditions from formingin the force main. These valves areautomatic devices with floats thatopen to expel air when it collects inthe valve body. When wastewaterenters, the float lifts by buoyancy andcloses the orifice in the outlet of thevalve so the fluid is not expelled.Wastewater air valves often featureelongated or conical bodies to preventclogging, a sloped bottom to facilitatedrainage and Type 316 stainless-steelinternal components to withstand thecorrosive nature of wastewater andwastewater gasses.

The importance of air valves cannotbe overlooked. They not only maintainthe flow efficiency of a pipeline byventing accumulated air, but also per-form many other functions, includingsurge control after pump power failureby admitting air rapidly to prevent theformation of a vacuum pocket duringcolumn separation. Note, however,that maintaining equipment in waste-water service is always a challengingand dirty job. One field study demon-strated that air valve maintenance canbe reduced by the use of fusion-bond-ed interior coatings and Type 316stainless-steel trim.3

TREATMENT FACILITIESDomestic and industrial wastewatercollected from sewer systems and liftstations flows to a centralized waste-water treatment facility. The waste-water process is typically segregatedinto three phases: primary, secondaryand tertiary.

The primary treatment includesinlet bar screens to exclude physicaldebris such as rags and sticks from thewastewater flow stream. Often, severalsubmerged wastewater pumps lift thewastewater into grit tanks that slowthe velocity of the fluid so grit settlesto the bottom of the tank. Thesepumps and associated valves need tohave all of the characteristics associat-ed with lift stations.

The wastewater at this stage stillcontains sediment and organic con-stituents that are removed in a pri-mary settling tank using chemicalcoagulants. The constituents settle to

the bottom of the tanks as wastewaterprimary sludge. Sludge is pumped fromthe bottom of the tank at regularintervals to dewatering facilities. Thevalves associated with this processmust be designed to handle slurrieswith over 90% suspended solids.Industrial ball valves or eccentric plugvalves are used to stand up to thischallenge.

Some plants are faced with a seri-ous struvite (magnesium ammoniumphosphate) deposit problem in theirdigested sludge lines. Struvite crystalscan grow rapidly and form a concrete-hard crust on the inside of pipes andequipment, choking flow. Pipe andequipment subject to struvite serviceshould be glass-lined, which consistsof applying a 10-mils-thick ceramiccoating using a special high-tempera-ture process (1400°F or 760°C) forpipes, valves and pumps.4

The remaining organic matter is

� Centrifugal pump and resilient-hinge check valve in wastewater lift station dry well

Butterfly valves supplied in accordancewith AWWA C504 are often used [intertiary treatment] because of theircompact size and low cost, especially in large pipe sizes.


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then removed during the secondarytreatment using biological processes,often either a fixed film or a suspend-ed growth process. In a fixed filmprocess, the biological treatmentoccurs while immersed over filtermedia such as ground rock, plasticballs or corrugated plates. The organicmatter is consumed by bacteria, algaeand fungi, and converted into a bio-mass. A suspended growth processuses injected air added to the mixtureto support microbial growth and a cor-responding consumption of organicmatter.

Aeration systems frequently usehigh-power centrifugal air blowers andpower-actuated control valves, typical-ly wafer butterfly valves. The controlvalves for air service are designed fordry fluid service and high tempera-tures approaching 300°F (150°C).Additionally, blowers should be fittedwith check valves that have low open-ing or cracking pressure and are sizedso they will not chatter during low-flow operation.5

Tertiary treatment processes mayinclude biological or chemical treat-ment for nutrient removal or tertiaryfiltration for particulate removal. Ter-tiary treatment also includes disinfec-tion of the effluent by prolonged con-tact with a chemical such as chlorinein a contact basin before the outputwater is discharged. The final output

water will be dechlorinated and maybe pumped for reuse or simply dis-charged to a waterway. Since the sediment has been removed from thewastewater, other types of waterworksvalves may now be used. For example,butterfly valves supplied in accordancewith AWWA C504 are often used herebecause of their compact size and lowcost, especially in large pipe sizes.Waterworks gate valves also areemployed.

When pumping effluent for reuse,waterworks pumps, check valves andshut off valves can be used. Both but-terfly and ball valves are quarter-turnvalves that are reliable and simple toautomate for this service. Quarter-turnball valves supplied in accordance withAWWA C507 are used when head lossand energy savings are consideredimportant. A full port ball valve has a

head loss similar to a pipe of the samelength.

CONCLUSIONWhile many types of valves are used inwastewater treatment, one thing theyhave in common is that they all mustbe suited for fluids containing sus-pended solids. Some common valvessuch as silent check valves and butter-fly valves should not be used in rawwastewater service. Instead, speciallydesigned valves such as knife gatevalves and eccentric plug valves arethe go-to workhorses for wastewaterapplications. VM

JOHN V. BALLUN, president and CEO of Val-MaticValve (www.valmatic.com), is a regular contributor to VALVE Magazine. Reach him [email protected].

REFERENCES1. U.S. Environmental Protection Agency

(EPA), “Primer for Municipal WastewaterTreatment Systems,” Document EPA 832-R-04-001, September, 2004.

2. Submersible Wastewater Pump Associa-tion, “Submersible Sewage Pumping Sys-tems” Handbook, 4th ed., 2012.

3. Ballun, John V., “Coatings can Make a Dif-ference in Wastewater” VALVE Magazine;Summer, 2015.

4. Val-Matic Valve, “Mission Possible,” Water& Wastes Digest, October, 2004.

5. Aerzen USA Corporation (Aerzen), “Aera-tion Blowers in the Wastewater Industry inNorth America,” 2015.

� An eccentric plug valve (far right) isolates awastewater pump and check valve.

wastewater treatment - val matic

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