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Design of Water and Wastewater Systems II

by: Savanna Cruickshank

Design of Water and Wastewater Systems II CE 432

Marketplace > University of Idaho > Civil Engineering > CE 432 > Design of Water and Wastewater Systems II
Savanna Cruickshank
GPA 3.54


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Class Notes
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This 6 page Class Notes was uploaded by Savanna Cruickshank on Friday October 23, 2015. The Class Notes belongs to CE 432 at University of Idaho taught by Staff in Fall. Since its upload, it has received 17 views. For similar materials see /class/227787/ce-432-university-of-idaho in Civil Engineering at University of Idaho.


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Date Created: 10/23/15
e dents 151econfain d th e l ve s or11tf1r icouldfail 39 Dam bwgongmmnwisem w e39 al39fel ctron39 cceptor whehquot o39xfdi39zi ompdundg quot are moieyul ab1 to 01 other in u n e 39 a 3901jj1d39beth e tcit uffer39as air s uitVt th 39 nwfonm ht 39 gen DO l e39v li Which is atdb low j pawn W his oohigh39or39i06391dw or th i u e Of potgntlally ih re se mthe 1 cdnc nhauonww u uglHL u mnyr m bgenw during whole ef uent toxicity t stjhg in 39 15 below 27 C the NOE popu39latlo39ri will ag AOB population during startupb cause NQBs e d nitriteas an39energy source 1 quot These quotrelationships show that en Virbnm cdndi dns couldvcaus nitrit I39d mclpdzdglqwno iy39oerH j in gayanay mmwmmgmamm x 39sdurc s1ch I gt chljb fixyle f sed ffOrytfilamefttO39 v s e opd39ai39y39 chloriha d a L quotEllow p bEC us of nit ca op n WWa st wa ers if e39WasteWater ont i1n gt quot quot quot asscaiceium arbo a 39 I Io39iihe39 consumption boring Nitrite Lock Milligrams per Liter 83 9M2 5 q 3 a b b b q 2 95quot 6quot 36 9 a n bnd9at at 35 f9 9 5 gr 35 1 3 9quot 95 solids MLSS rose from about 62 to 65 The pure oxygen system was converted to air 2 days before the activated sludge process was started up and continued to operate in parallel with the trickling filter until full TFAS operations began I When covered pure oxygen basins typically have lower pH than air activated sludge because of the high partial pressure n NitriteN o AmmoniaN Chlorlne Usage pounds 39 of carbon dioxide in the headspace Case Studies The following examples illustrate various causes and effects of nitrite lock that wastewater treatment professionals have learned during 19 years of experience The rst two case studies are based on forensic analyses of historical data the other two were assessed when the nitrite lock occurred Salem Ore In 1988 the Willow Lake Wastewater Treatment Plant in Salem Ore switched its activated sludge process from pure oxygen to diffused air and converted it to operate in series with the trickling lter rather than in parallel The newly combined trickling filter activated sludge TFAS process had nitrite lock for about 2 weeks during startup Historical data show that the secondary ef uent contained 4 to 5 mgL of nitrite nitrogen requiring the addition of up to 10 times more chlorine than normal Figure 2 Secondary Effluent Nitrite Nitrogen and pH Comparison Once the TFAS process was brought on line nitri cation increased in the secondary process even though MLSS and DO concentrations steadily declined Nitrification began to decrease about Feb 12 The trickling lter s load had doubled when the plant switched over to the TF AS process seeding the airactivated sludge process with nitrifiers High MLSS and DO concentrations promoted nitrification The data suggest that DO was the key limiting factor because the MLSS concentration increased dramatically on Feb 17 with no corresponding change in nitrification As the MLSS s pH increased during the 2 month period the nitrite nitrogen concentration decreased see Figure 2 below The increasing pH correlated to the decreasing nitrite concentration suggesting that nitrite lock was caused by low pH particularly below 67 see Figure 1 above The reactions between nitrite and chlorine consumed 6 7 the chlorine and resulted 5 OO 390 O O O 69 in poor disinfection and 3 to 00 octane o 0 was higher operating costs 3 4 39 I quotCIED67 The data also show that g 0 555 5349 5 50 pogo c cry 0 J 55 chlorine use decreased 3 0m 5030 CDT 7 39Ijiii 3 n 435 5 as the ammonia nitrogen Ziamo Q s f 54 levelsinsecondaryeffluent g 4 63 increased because 1 i i 1amp2 chloraminesdonotreadily o H I 61 react with nitrites 1 q 3 g g 6 q q q 39 In addition when the 1 a a iei la activated sludge basin was Converted from pure 1 NitriteN o MLSSpH uNitriieN Trendline MLSSpHTrendllne oxygen to finepore air diffusion the pH of the WEampT WWWWEFORGMAGAZINE mixed liquor suspended Figure 3 s condaiy l iue t N39itri telNitrdgenf2quot Milligrams por thnr 3w 5 sum D 3 Q Q Q D Q B Q S D Q Q es 3 as as Kg as 3 3955 55 39 35 99 as as as 9 e a 9 9 9 o a a a lt9 a gt 16 9 a 5 s a x a a a Nd 9 s 5 Ne s 9 s s Troubleshooters initially suspected that the cause was the low alkalinity s effect on pH until both sides had similar nitrification rates and alkalinity levels at the end of the month Ef uent nitrite levels remained 39 basically stable in side 2 but continued to uctuate in side 1 Also the MLSS s pH on side 1 ranged from 67 to 72 only one data point was below 68 which should not inhibit NOB So the nitrite lock was not caused by low Also Willow Lake s in uent alkalinity was low 130 to 150 mgL When the process was completely nitrifying AOB consumed enough alkalinity to lower the MLSS39s pH and thereby inhibit NOBBecause the facility was neither required nor designed to nitrify no additional alkalinity was available This example demonstrates two important aspects of nitrite lock 39 Low pH can inhibit NOB 0 Chloramines do not readily react with nitrite Durham Ore In October 1990 nitrite lock occurred intermittently in a secondary treatment train at the Durham Ore Wastewater Treatment Plant owned by Clean Water Services formerly the Unified Sewerage Agency At the time the plant had two parallel but independent secondary treatment trains At rst side 1 was carrying about 15 more biological mass than side 2 resulting in a higher yet inconsistent nitri cation rate About midmonth side pH Troubleshooters eventually determined that the most likely cause was low DO According to a monthly process summary memorandum Uni ed Sewerage Agency 1990 The aeration basin dissolved oxygen problems gradually were xed during the month The system is now back to normal Early in the month microscopic examination revealed that Side 2 looked very healthy but Side 1 was lousy As the aeration system problems which mainly affected Side 1 were xed Side 1 bugs gradually improved during the mom This example illustrates that nitrite lock can be induced by processspecific variables NOB and ACE require oxygen to thrive IasVegas In December 1994 nitrite lock occurred during the startup of a nitri cation system at the City of Las Vegas Water Pollution Control Facility Ef uent Figure 4 Progression of Nitrification Dining Startup 2 s mass began to increase 25 as did its nitrification rate I Interestingly side 1 s ef uent nitrite nitrogen levels fluctuated significantly while side 239s effluent nitrite nitrogen levels remained fairly stable even when its nitrification rate rose see Figure 3 above This discrepancy suggested Mllllgrams per Liter December 1994 that srde 1 s nitrite lock was caused by something 0 lnfluent AmmonlaN Efluent AmmoniaN E luent NitratemltrlteN specific to the treatment train DECEMBER 2007 3T0 RegairijplilorinelResidua l Figure 5 Am m39o hia39concentr39ation I M the chlorine demand associated with nitrite lock Nltrogenlvlllllgrams per Liter 1610 1650 1730 December 17 1994 El Paso Texas In 1999 an airactivated sludge process that could provide full nitrification began operating at the Haskell R Street Wastewater Treatment Plant which is owned by El Paso Water Utilities EPWU Nitrite lock was expected during startup so the project 1805 team developed a strategy to minimize it The strategy O AmmonlaN a NltrltaN a Chlorine Residual i involved increasing MISS slowly to ensure that ammonia concentrations were decreasing the combined effluent nitrite and nitrate concentration was increasing and disinfection effectiveness was lost see Figure 4 p 85 Effluent fecal coliform concentrations began to increase significantly on Dec 14 On Dec 16 lab analysis confirmed that nitrite lock was occurring Comparisons of prechlorination nitrite concentrations with postchlorination chlorine residual showed that chlorine was reacting with nitrite Because chloramines do not react readily with nitrite troubleshooters mixed a nonnitri ed ef uent with the nitriteladen one Raising the ammonia concentration above the nitrite concentration quickly produced a measurable chlorine residual see Figure 5 above but this solution was unsustainable because of hydraulic constraints Fortunately the NOB population was large enough by Dec 24 to oxidize the nitrite to nitrate for effective disinfection 4 This example illustrates three important aspects of nitrite lock 39 Nitrite lock can occur during the startup of a nitrification process Nitrite nitrogen and nitrate nitrogen should be analyzed separately Chloramines can significantly reduce AmmoniaN mgIL O 2 0 9 9 9 9 9 9 Q 9 A q I39 l39 the ammonia nitrogen concentration always exceeded the nitrite nitrogen concentration in secondary ef uent Nevertheless the first two attempts resulted in nitrite lock The team suspected toxic inhibition was causing the problem because the process variables were within nitrification ranges Unlike most facilities the EPWU plant s discharge 39 permit required a minimum chlorine residual of 10 mgL so it used more chlorine than would be expected Nitrite lock further increased chlorine demand straining the chlorination system until it could not supply enough chemical to the chlorine contact tank to meet demand and maintain the required residual Adding calcium hypochlorite only helped somewhat so the team tried intermittently adding chlorine solution to one of the secondary clarifier s weir chlorination rings Figure 6 secondary Effluent AmmoniaNitrogen and Nitrite Nitrogen H Nitri cation lost on second attempt OI Chlorine feed to secondary clari er stopped N b NitriteN mglL l O a 9 9 a 9 a q 99 9 e 9 e 9 a 9 a 9 9quot if at atquot 3 quot 9 or at cit9 wear WWWWEFORGMAGAZlNE Clarifier 1 Clarifier 2 The water in that clarifier turned green on Aug 20 The team measured the clarifier s chlorine residual and found that concentrations were as high as 35 mgL So the team immediately stopped adding chlorine to the weir chlorination ring Within a week full nitrification was achieved The team suspected that the chlorine had inhibited NOB in the clarifier s sludge blanket When chlorine feed to the chlorination rings was stopped the third attempt to achieve nitrification was successful see Figure 6 p 86 This example illustrates how onsite sources of toxicity can cause nitrite lock In this case toxic concentrations of chlorine were being introduced to the return activated sludge thereby inhibitingNOB Useful Observation The observation that nitrite chlorine reactions turned the EPWU plant s water green was useful less than 2 weeks later at awastewater treatment plant in Hawaii The Hawaii plant has two secondary clari ers that operate in parallel see Figure 7 above both are fed mixed liquor from one aeration basin Both clarifiers were producing excellent ef uent with little turbidity but clarifier 1 s water was green while clarifier 2 s was not An analysis of the MLSS indicated that nitrites were present concentrations were not quantified Both clarifiers have chlorination rings around the weirs that are used to inject chlorine into the water for disinfection Clarifier 1 s chlorine ring is above the water surface and injects chlorine down into the water via multiple points Clarifier 2 s chlorine ring is just below the water surface and the chlorine is injected laterally against the clarifier wall Discussions with plant staff indicated that clari er 1 turned green shortly after scale buildup was removed from the chlorine ring s nozzles The team suspected that removing the scale allowed most if not all of the chlorine feed to be directed to clarifier 1 The team also suspected that chlorine was inhibiting NOB in clarifier 1 s sludge blanket just as it had at the EPWU plant When the chlorine was shifted from the clari er chlorine rings to an ef uent junction box the green color appeared immediately at the junction box and disappeared from clari er 1 within 24 hours Within a week full nitri cation was achieved Woodie Mark Muirhead is a vice president in the Honolulu of ce and Ron Appleton is regional process engineer in the headquarters office of Brown and Caldwell Walnut Creek Calif The authors thank Keith Chapman City of Salem Ore Vic Pedregon El Paso Texas Water Utilities and Rob Baur Clean Water Services Hillsboro Ore for their help in preparing this article


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