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WATER QUALITY VARIATIONS DURING NITRIFICATION IN DRINKING WATER DISTRIBUTION SYSTEMS
Title
WATER QUALITY VARIATIONS DURING NITRIFICATION IN DRINKING WATER DISTRIBUTION SYSTEMS.
Creator
Webb, David W, Taylor, James S., University of Central Florida
Abstract / Description
This thesis documents the relationship among the major water quality parametersduring a nitrification episode. Nitrification unexpectedly occurred in a chloraminated pilotdrinking water distribution system practicing with a 4.0 mg/L as Cl2 residual dosed at 4.5:1Cl2:NH3-N. Surface, ground and sea water were treated and disinfected withmonochloramines to produce finished water quality similar to regional utility water quality.PVC, galvanized, unlined cast iron and lined iron pipes were...
Show moreThis thesis documents the relationship among the major water quality parametersduring a nitrification episode. Nitrification unexpectedly occurred in a chloraminated pilotdrinking water distribution system practicing with a 4.0 mg/L as Cl2 residual dosed at 4.5:1Cl2:NH3-N. Surface, ground and sea water were treated and disinfected withmonochloramines to produce finished water quality similar to regional utility water quality.PVC, galvanized, unlined cast iron and lined iron pipes were harvested from regionaldistribution systems and used to build eighteen pilot distribution systems (PDSs). The PDSswere operated at a 5-day hydraulic residence time (HRT) and ambient temperatures.As seasonal temperatures increased the rate of monochloramine dissipation increaseduntil effluent PDS residuals were zero. PDSs effluent water quality parameters chloraminesresidual, dissolved oxygen, heterotrophic plate counts (HPCs), pH, alkalinity, and nitrogenspecies were monitored and found to vary as expected by stoichiometry associated withtheoretical biological reactions excepting alkalinity. Nitrification was confirmed in thePDSs. The occurrence in the PDSs was not isolated to any particular source water.Ammonia for nitrification came from degraded chloramines, which was common among allfinished waters. Consistent with nitrification trends of dissolved oxygen consumption,ammonia consumption, nitrite and nitrate production were clearly observed in the PDSs bulkwater quality profiles. Trends of pH and alkalinity were less apparent. To controlnitrification: residual was increased to 4.5 mg/L as Cl2 at 5:1 Cl2:NH3-N dosing ratio, and theHRT was reduced from 5 to 2 days. Elimination of the nitrification episode was achievedafter a 1 week free chlorine burn.
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Date Issued
2004
Identifier
CFE0000063, ucf:46118
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0000063
MODELING FREE CHLORINE AND CHLORAMINE DECAY IN A PILOT DISTRIBUTION SYSTEM
Title
MODELING FREE CHLORINE AND CHLORAMINE DECAY IN A PILOT DISTRIBUTION SYSTEM.
Creator
Arevalo, Jorge, Taylor, James, University of Central Florida
Abstract / Description
The purpose of this study was to identify the effect that water quality, pipe material, pipe size, flow conditions and the use of corrosion inhibitors would have on the rate of free chlorine and chloramine decay in distribution systems. Empirical models were developed to predict the disinfectant residual concentration with time based on the parameters that affected it. Different water treatment processes were used to treat groundwater and surface water to obtain 7 types of finished waters...
Show moreThe purpose of this study was to identify the effect that water quality, pipe material, pipe size, flow conditions and the use of corrosion inhibitors would have on the rate of free chlorine and chloramine decay in distribution systems. Empirical models were developed to predict the disinfectant residual concentration with time based on the parameters that affected it. Different water treatment processes were used to treat groundwater and surface water to obtain 7 types of finished waters with a wide range of water quality characteristics. The groundwater was treated either by conventional treatment by aeration (G1) or softening (G2) or high pressure reverse osmosis (RO) and the surface water was treated either by enhanced coagulation, ozonation and GAC filtration (CSF-O3-GAC or S1) or an integrated membrane system (CSF-NF or S2). The remaining two water types were obtained by treating a blend of G1, S1 and RO by softening (S2) and nanofiltration (G4). A pilot distribution systems (PDS) consisting of eighteen (18) lines was built using old pipes obtained from existing distribution system. The pipe materials used were polyvinyl chloride (PVC), lined cast iron (LCI), unlined cast iron (UCI) and galvanized steel (G). During the first stage of the study, the 7 types of water were blended and fed to the PDS to study the effect of feed water quality changes on PDS effluent water quality, and specifically disinfectant residual. Both free chlorine and chloramines were used as disinfectant and the PDSs were operated at hydraulic retention times (HRT) of 2 and 5 days. The PDSs were periodically tested for free and combined chlorine, organic content, temperature, pH, turbidity and color. The data obtained were used to develop separate models for free chlorine and chloramines. The best fit model was a first-order kinetic model with respect to initial disinfectant concentration that is dependent on the pipe material, pipe diameter and the organic content and temperature of the water. Turbidity, color and pH were found to be not significant for the range of values observed. The models contain two decay constants, the first constant (KB) accounts for the decay due to reaction in the bulk liquid and is affected by the organics and temperature while the second constant, KW, represents the reactions at the pipe wall and is affected by the temperature of the water and the pipe material and diameter. The rate of free chlorine and chloramine decay was found to be highly affected by the pipe material, the decay was faster in unlined metallic pipes (UCI and G) and slower in the synthetic (PVC) and lined pipes (LCI). The models showed that the rate of disinfectant residual loss increases with the increase of temperature or the organics in the water irrespective of pipe material. During the second part of the study, corrosion control inhibitors were added to a blend of S1, G1 and RO that fed all the hybrid PDSs. The inhibitors used were: orthophosphate, blended ortho-polyphosphate, zinc orthophosphate and sodium silicate. Three PDSs were used for each inhibitor type, for a total of 12 PDSs, to study the effect of low, medium and high dose on water quality. Two PDSs were used as control, fed with the blend without any inhibitor addition. The control PDSs were used to observe the effect of pH control on water quality and compare to the inhibitor use. One of the control PDSs (called PDS 13) had the pH adjusted to be equal to the saturation pH in relation to calcium carbonate precipitation (pHs) while the pH of the other control PDS (PDS 14) was adjusted to be 0.3 pH units above the pHs. The disinfectant used for this part of the study was chloramine and the flow rates were set to obtain a HRT of 2 days. The chloramine demand was the same for PDS 14 and all the PDSs receiving inhibitors. PDS 13 had a chloramine demand greater than any other PDS. The lowest chloramine demand was observed in PDS 12, which received silicate inhibitor at a dose of 12 mg/L, and presented the highest pH. The elevation of pH of the water seems to reduce the rate of decay of chloramines while the use of corrosion inhibitors did not have any effect. on the rate of chloramine decay. The PDS were monitored for chloramine residual, temperature, pH, phosphate, reactive silica, and organic content. Empirical models were developed for the dissipation of chloramine in the pilot distribution systems as a function of time, pipe material, pipe diameter and water quality. Terms accounting for the effect of pH and the type and dose of corrosion inhibitor were included in the model. The use of phosphate-based or silica-based corrosion inhibitors was found to have no effect on the rate of chloramine dissipation in any of the pipe materials. Only the increase of pH was found to decrease the rate of chloramine decay. The model to best describe the decay of chloramine in the pilot distribution systems was a first-order kinetic model containing separate rate constants for the bulk reactions, pH effect and the pipe wall reactions. The rate of chloramine decay was dependent on the material and diameter of the pipe, and the temperature, pH and organic content of the water. The rate of chloramine decay was low for PVC and LCI, and more elevated in UCI and G pipes. Small diameter pipes and higher temperatures increase the rate of chlorine decay irrespective of pipe material. Additional experiments were conducted to evaluate the effect of flow velocity on chloramine decay in a pilot distribution system (PDS) for different pipe materials and water qualities. The experiments were done using the single material lines and the flow velocity of the water was varied to obtain Reynolds' numbers from 50 to 8000. A subset of experiments included the addition of blended orthophosphate corrosion inhibitor (BOP) at a dose of 1.0 mg/L as P to evaluate the effect of the inhibitor on chloramine decay. The effect of Reynolds' number on the overall chloramine decay rate (K) and the wall decay rate constant (W) was assessed for PVC, LCI, UCI, and G pipes. PVC and LCI showed no change on the rate of chloramine decay at any flow velocity. UCI and G pipes showed a rapid increase on the wall decay rate under laminar conditions (Re < 500) followed by a more gradual increase under fully turbulent flow conditions (Re > 2000). The use of the BOP inhibitor did not have an effect on the rate of chloramine decay for any of the pipe materials studied. Linear correlations were developed to adjust the rate of chloramine decay at the pipe wall for UCI and G depending on the Reynolds' number.
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Date Issued
2007
Identifier
CFE0001863, ucf:47400
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0001863
NITRIFICATION INVESTIGATION AND MODELING IN THE CHLORAMINATED DRINKING WATER DISTRIBUTION SYSTEM
Title
NITRIFICATION INVESTIGATION AND MODELING IN THE CHLORAMINATED DRINKING WATER DISTRIBUTION SYSTEM.
Creator
Liu, Suibing, Taylor, James, University of Central Florida
Abstract / Description
This dissertation consists of five papers concerning nitrification in chloraminated drinking water distribution systems in a one and a half year field study. Seven finished waters were produced from different treatment processes and distributed to eighteen pilot distribution systems (PDSs) that were made pipes taken from actual distribution systems. Unlined cast iron (UCI), galvanized steel (G), lined cast iron (LCI), and PVC pipes were used to build the PDSs. All finished waters were...
Show moreThis dissertation consists of five papers concerning nitrification in chloraminated drinking water distribution systems in a one and a half year field study. Seven finished waters were produced from different treatment processes and distributed to eighteen pilot distribution systems (PDSs) that were made pipes taken from actual distribution systems. Unlined cast iron (UCI), galvanized steel (G), lined cast iron (LCI), and PVC pipes were used to build the PDSs. All finished waters were stabilized and chloraminated before entering the PDSs. This dissertation consists of five major parts.(1) System variations of nitrates, nitrites, DO, pH, alkalinity, temperature, chloramine residuals and hydraulic residence times (HRT) during biological nitrification are interrelated and discussed relative to nitrification, which demonstrated Stoichiometric relationships associated with conventional biochemical nitrification reactions. Ammonia is always released when chloramines are used for residual maintenance in drinking water distribution systems, which practically insures the occurrence of biological nitrification to some degree. Biological nitrification was initiated by a loss of chloramine residual brought about by increasing temperatures at a five day HRT, which was accompanied by DO loss and slightly decreased pH. Ammonia increased due to chloramine decomposition and then decreased as nitrification began. Nitrites and nitrates increased initially with time after the chloramine residual was lost but decreased if denitrification began. Dissolved oxygen limited nitrifier growth and nitrification. No significant alkalinity variation was observed during nitrification. Residual and nitrites are key parameters for monitoring nitrification in drinking water distribution systems.(2) Using Monod kinetics, a steady state plug-flow kinetics model was developed to describe the variations of ammonia, nitrite and nitrate-N concentrations in a chloraminated distribution system. Active AOB and NOB biomass in the distribution system was determined using predictive equations within the model. The kinetic model used numerical analysis and was solved by C language to predict ammonia, nitrite, nitrate variation.(3) Nitrification control strategies were investigated during an unexpected episode and controlled study in a field study. Once nitrification began, increasing chloramine dose from 4.0 to 4.5 mg/L as Cl2 and Cl2:N ratio from 4/1 to 5/1 did not stop nitrification. Nitrification was significantly reduced but not stopped, when the distribution system hydraulic retention time was decreased from 5 to 2 days. A free chlorine burn for one week at 5 mg/L Cl2 stopped nitrification. In a controlled nitrification study, nitrification increased with increasing free ammonia and Cl2:N ratios less than 5. Flushing with increased chloramine concentration reduced nitrification, but varying flush frequency from 1 to 2 weeks had no effect on nitrification.(4) HPC variations in a chloraminated drinking water distribution system were investigated. Results showed average residual and temperature were the only water quality variables shown to affect HPC change at a five day distribution system hydraulic residence time was five days. Once nitrification began, HPC change was correlated to HRT, average residual and generated nitrite-N in the distribution system. (5) Biostability was assessed for water treatment processes and distribution system pipe by AOCs, BDOCs, and HPCs of the bulk water, and by PEPAs of the attached biofilms. All membrane finished waters were more likely to be biologically stable as indicated by lower AOCs. RO produced the lowest AOC. The order of biofilm growth by pipe material was UCI > G > LCI > PVC. Biostability decreased as temperature increased.
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Date Issued
2004
Identifier
CFE0000039, ucf:46151
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0000039
THE EFFECT OF FREE CHLORINE AND CHLORAMINES ON LEAD RELEASE IN A DISTRIBUTION SYSTEM
Title
THE EFFECT OF FREE CHLORINE AND CHLORAMINES ON LEAD RELEASE IN A DISTRIBUTION SYSTEM.
Creator
Vasquez, Ferdinand, Taylor, James, University of Central Florida
Abstract / Description
Total lead release in drinking water in the presence of free chlorine and chloramine residuals was investigated in field, laboratory and fundamental investigations for finished waters produced from ground (GW), surface (SW), saline (RO) and blended (B) sources. Field investigations found more total lead was released in the presence of chloramines than in the presence of free chlorine for RO and blended finished waters; however, there were no statistical differences in total lead release to...
Show moreTotal lead release in drinking water in the presence of free chlorine and chloramine residuals was investigated in field, laboratory and fundamental investigations for finished waters produced from ground (GW), surface (SW), saline (RO) and blended (B) sources. Field investigations found more total lead was released in the presence of chloramines than in the presence of free chlorine for RO and blended finished waters; however, there were no statistical differences in total lead release to finished GW and SW. Laboratory measurements of finished waters oxidation-reduction potential (ORP) were equivalent by source and were not affected by the addition of more than 100 mg/L of sulfates or chlorides, but were significantly higher in the presence of free chlorine relative to chloramines. Development of Pourbaix diagrams revealed the PbO2 was the controlling solid phase at the higher ORP in the presence of free chlorine and Pb3(CO3)2(OH)2(s) (hydrocerussite) was the controlling solid phase in the presence of chloramines at the lower ORP, which mechanistically accounted for the observed release of total lead as PbO2 is much less soluble than hydrocerussite. The lack of differences in total lead release to finished GW and SW was attributed to differences in water quality and intermittent behavior of particulate release from controlling solid films.
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Date Issued
2005
Identifier
CFE0000533, ucf:46427
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0000533