Andrew Randall | University of Central Florida (original) (raw)

Papers by Andrew Randall

Research paper thumbnail of Evaluation of Corrosion Inhibitors, Residual, Temperature, and Pipe Material on Bulk and Biofilm Heterotrophic Plate Counts Densities

The impact of corrosion inhibitors on biofilm and bulk heterotrophic plate counts (HPC) has been ... more The impact of corrosion inhibitors on biofilm and bulk heterotrophic plate counts (HPC) has been studied by a number of investigators and a review of the literature indicates a wide variety of seemingly contradictory results. Hozalski et al. (2005) observed an increase in bulk HPC levels when using phosphate based inhibitors. Miettinen et al. (1997) and Sathasivan et al. (1997) also observed full-scale systems where phosphate was a limiting nutrient and addition of it resulted in stimulation of bacterial growth. Appenzeller et al. (2001) observed a significant decrease in planktonic HPC when phosphate was added, but only when a highly corroded reactor was used. Evaluation of bacterial adhesion led Appenzeller et al. (2002) to conclude that the lower HPC were probably due to phosphate decreasing the ability of bacterial to adhere to corroded pipes due to phosphate sorption onto iron oxyhydroxides, which reversed their surface charge from positive to negative. In nonor lightly-corrode...

Research paper thumbnail of 水道管材料が微生物膜形成に及ぼす影響―特に米国における研究例―

Journal of Environmental Conservation Engineering, 2007

Research paper thumbnail of Effects of Reduced Ras Flows and Volume on Anaerobic Zone Performance for a Septic Wastewater Biological Phosphorous Removal System

Proceedings of the Water Environment Federation, 2003

Page 1. EFFECTS OF REDUCED RAS FLOWS AND VOLUME ON ANAEROBIC ZONE PERFORMANCE FOR A SEPTIC WASTEW... more Page 1. EFFECTS OF REDUCED RAS FLOWS AND VOLUME ON ANAEROBIC ZONE PERFORMANCE FOR A SEPTIC WASTEWATER BIOLOGICAL PHOSPHOROUS REMOVAL SYSTEM Daniel Magro1*, Steven L. Elias1, Andrew Amis Randall2 ...

Research paper thumbnail of Fouling control in activated sludge submerged hollow fiber membrane bioreactors

Desalination, 2002

The goal of this study is to determine the impact of various operating factors on membrane foulin... more The goal of this study is to determine the impact of various operating factors on membrane fouling in activated sludge membrane bioreactor (MBR) process, typically used for water reclamation. In this process, ultrafiltration (UF) and microfiltration (MF) hollow fiber membranes, submerged in the bioreactor, provided a solid-liquid separation by replacing gravity settling. Activated sludge from a food wastewater treatment plant was inoculated to purify synthetic wastewater consisting of glucose and (NH&SO, as a source of carbon and nitrogen, respectively. The results clearly showed that membrane fouling, defined as permeate flux decline due to accumulation of substances within membrane pores and/or onto membrane surface, was greatly influenced by membrane type and module configuration. It was also found that the rate and extent of permeate flux decline increased with increasing suction pressure (or initial operating flux) and with decreasing air-scouring rate. The mixed liquor suspended solids (MLSS) concentrations, however, exhibited very little influence on permeate flux for the range of 3600-8400 mgk. Another important finding of this investigation was that non-continuous membrane operation significantly improved membrane productivity. This observation can be explained by the enhanced back transport of foulants under pressure relaxation. During non-suction periods, the foulants not irreversibly attached to the membrane surface, diffused away from the membrane surface because of concentration gradient. Furthermore, the effectiveness of air scouring was greatly enhanced in the absence of transmembrane suction pressure, resulting in higher removal of foulants accumulated on the membrane surface. The use of intermittent suction operation may not be economically feasible at large-scale, but it may offer an effective fouling control means for small-scale MBR processes treating wastewaters with high fouling potential.

Research paper thumbnail of Aerobic production of activated sludge polyhydroxyalkanoates from nutrient deficient wastewaters

Water Science and Technology, 2006

It was found that aerobic strategies combined with multiple nutrient limitations produced greater... more It was found that aerobic strategies combined with multiple nutrient limitations produced greater quantities of polyhydroxyalkanoates (PHAs) than strategies relying on oxygen limitation (either micro-aerophilic or anaerobic/aerobic). This was true both for a synthetic wastewater composed of acetic and propionic acid, and also for a nutrient deficient industrial wastewater. PHA/substrate yields were shown to be comparable to axenic systems for many operating strategies analyzed, and it was found that PHA composition could be affected by process operational conditions. The molecular weight and melting point of the PHA produced were found to be in a desirable range with respect to material properties, which have not been well studied in the previous literature for mixed cultures (Salehizadeh and Van Loodsrecht, 2004). The effects of process staging, multiple treatment cycles, and inocula source were also addressed.

Research paper thumbnail of Modeling of organic substrate transformation in the high-rate activated sludge process

Water science and technology : a journal of the International Association on Water Pollution Research, 2015

This study describes the development of a modified activated sludge model No.1 framework to descr... more This study describes the development of a modified activated sludge model No.1 framework to describe the organic substrate transformation in the high-rate activated sludge (HRAS) process. New process mechanisms for dual soluble substrate utilization, production of extracellular polymeric substances (EPS), absorption of soluble substrate (storage), and adsorption of colloidal substrate were included in the modified model. Data from two HRAS pilot plants were investigated to calibrate and to validate the proposed model for HRAS systems. A subdivision of readily biodegradable soluble substrate into a slow and fast fraction were included to allow accurate description of effluent soluble chemical oxygen demand (COD) in HRAS versus longer solids retention time (SRT) systems. The modified model incorporates production of EPS and storage polymers as part of the aerobic growth transformation process on the soluble substrate and transformation processes for flocculation of colloidal COD to pa...

Research paper thumbnail of Reductive dechlorination of tetrachloroethylene (PCE) catalyzed by cyanocobalamin

Applied Biochemistry and Biotechnology, 1995

ABSTRACT A biomimetic system has been developed for the reductive dechlorination of tetrachloroet... more ABSTRACT A biomimetic system has been developed for the reductive dechlorination of tetrachloroethylene (PCE). PCE was dechlorinated to trichloroethylene (TCE) and 1,2-dichloroethylene (DCE) in the presence of dithiothreitol or Ti (III) citrate and catalytic amounts of cyanocobalamin in both homogeneous reaction mixtures and packed bed reactor systems. In packed bed reactors with Ti (III) citrate as the reductant, PCE (0.18 mM) conversion averaged 55% at residence times of 1.75 and 3.5 h. The product distribution was 94% TCE and 6% DCE at the lower residence time. DCE formation increased to 45% at the higher residence time. No reduction of PCE was observed in the absence of cyanocobalamin. This system may be useful as a means of pretreatment of halogenated aliphatic hydrocarbons in advance of biological treatment.

Research paper thumbnail of Optimization of Heterotrophic Denitrification Using Glycerol as a Sustainable External Carbon Substrate

Proceedings of 4th International Electronic Conference on Water Sciences, 2019

Nutrients removal from residential and industrial wastewaters are essential for environmental and... more Nutrients removal from residential and industrial wastewaters are essential for environmental and public health protection. Removal of nutrients from wastewater can be achieved chemically or biologically. Biological nutrient removal (BNR) is a series of anaerobic, anoxic, and aerobic zones to provide conditions for the biomass to uptake the nitrogen and phosphorus species, and comes in different configurations such as A/O, A2O, and 5-stage Bardenpho TM. However; BNR systems require a sufficient carbon source which most wastewaters lack. The goal of this study is to use a sustainable carbon source to optimize the 5-stage Bardenpho TM BNR systems and reduce the chemical cost. The experiments were carried out using two 5-stage Bardenpho TM BNR systems coupled with side-stream prefermenters. Glycerol, a biodiesel by-product, was used as a sustainable carbon source by direct addition or after fermentation. The results from both systems were beneficial to the BNR system and resulted in similar effluent quality. Both systems achieved complete denitrification and excellent phosphorus removal (82%-89%). Co-fermentation of glycerol and primary solids resulted in a significant increase in the volatile fatty acids (VFAs) loading beyond the estimated results, but did not correlate to better behavior between the two pilots since both systems achieved complete denitrification.

Research paper thumbnail of Impact of RO-desalted water on distribution water qualities

Water Science and Technology, 2005

A large-scale pilot distribution study was conducted to investigate the impacts of blending diffe... more A large-scale pilot distribution study was conducted to investigate the impacts of blending different source waters on distribution water qualities, with an emphasis on metal release (i.e. corrosion). The principal source waters investigated were conventionally treated ground water (G1), surface water processed by enhanced treatment (S1), and desalted seawater by reverse osmosis membranes (RO). Due to the nature of raw water quality and associated treatment processes, G1 water had high alkalinity, while S1 and RO sources were characterized as high sulfate and high chloride waters, respectively. The blending ratio of different treated waters determined the quality of finished waters. Iron release from aged cast iron pipes increased significantly when exposed to RO and SI waters: that is, the greater iron release was experienced with alkalinity reduced below the background of G1 water. Copper release to drinking water, however, increased with increasing alkalinity and decreasing pH. L...

Research paper thumbnail of Assimilable organic carbon and biodegradable organic carbon removal by nanofiltration: full and bench-scale evaluation

Water Science and Technology: Water Supply

The main objective of this research was to evaluate the effectiveness of nanofiltration (NF) at f... more The main objective of this research was to evaluate the effectiveness of nanofiltration (NF) at full and bench scale for controlling AOC and BDOC, which are the main indicators of biological stability of the finished potable water. One of the major observations from full-scale operation was that nanofiltration was a very effective means to reduce BDOC, but conversely, did not reject a significant fraction of AOC. The high BDOC rejection by nanofiltration (NF) membranes at full scale can be explained by size exclusion, since a significant fraction of BDOC consists of compounds, such as humic and fulvic acids, which are larger than the pores of NF membranes (molecular-weight cutoff ≃200 daltons). The insignificant AOC rejection observed in full-scale systems was probably due to the low pH, high hardness, and high ionic strength (TDS) of the raw water. Bench scale tests using simulated waters clearly demonstrated that AOC removal by NF membranes decreases markedly with decreasing pH, and increasing hardness and ionic strength, implying that electrostatic repulsion plays a significant role in AOC removal mechanisms. These solution environments repress the electrostatic interaction between charged organic compounds and membranes, allowing passage of small molecular weight compounds and thus reducing AOC rejection.

Research paper thumbnail of Case Study: Ozonation and distribution system biostability

Journal - American Water Works Association

ABSTRACT

Research paper thumbnail of Red Water Release in Drinking Water Distribution Systems

Journal - American Water Works Association

Research paper thumbnail of Effects of pipe-materials on microbial film formation in drinking water distribution system

Research paper thumbnail of High-Rate Activated Sludge System for Carbon Removal – Pilot Results and Crucial Process Parameters

Proceedings of the Water Environment Federation, 2013

Research paper thumbnail of Assimilable organic carbon (AOC) and biodegradable dissolved organic carbon (BDOC)

Water Research, 2001

FThe objective of this study was to evaluate the necessity of measuring both assimilable organic ... more FThe objective of this study was to evaluate the necessity of measuring both assimilable organic carbon (AOC) and biodegradable dissolved organic carbon (BDOC) as indicators of bacterial regrowth potential. AOC and BDOC have often been measured separately as indicators of bacterial regrowth, or together as indicators of bacterial regrowth and disinfection by-product formation potential, respectively. However, this study proposes that both AOC and BDOC should be used as complementary measurements of bacterial regrowth potential. In monitoring of full-scale membrane filtration, it was determined that nanofiltration (NF) removed over 90% of the BDOC while allowing the majority of the AOC through. Heterotrophic plate counts (HPC) remained low during the entire period of monitoring due to high additions of disinfectant residual. In a two-year monitoring of a water treatment plant that switched its treatment process from chlorination to chlorination and ozonation, it was observed that the plant effluent AOC increased by 127% while BDOC increased by 49% after the introduction of ozone. Even though AOC is a fraction of BDOC, measuring only one of these parameters can potentially under-or overestimate the bacterial regrowth potential of the water.

Research paper thumbnail of The efficiency of enhanced biological phosphorus removal from real wastewater affected by different ratios of acetic to propionic acid

Water Research, 2004

The effect of different ratios of propionic to acetic acid on the efficiency of enhanced biologic... more The effect of different ratios of propionic to acetic acid on the efficiency of enhanced biological phosphorus removal (EBPR) from real wastewater supplemented with volatile fatty acids (VFAs) was investigated. Two sequencing batch reactors (SBRs) were used to acclimate two types (SBR1 and SBR2) of biomass. They were cultured and studied using real wastewater with an average propionic to acetic acid carbon molar ratio of 0.16 and 2.06, respectively. The laboratory results showed that for a given long-term cultured biomass the more the soluble ortho-phosphate (SOP) was released in the anaerobic stage, the higher the SOP was taken up in the aerobic phase. However, the SBR2 biomass had a much greater SOP uptake to release ratio than SBR1, which resulted in a higher SOP removal efficiency than SBR1 (average 87.3% versus 76.9% in SBRs experiments, and 93.5% against 68.1% in batch tests). The SBR2 biomass therefore had a higher SOP uptake ability than the SBR1 for a given amount of SOP release. In addition, the SBR1 had a higher secondary SOP release following VFAs uptake. It was found that the SBR2 biomass synthesized and utilized less observable polyhydroxyalkanoates (PHAs) during the anaerobic and aerobic stage respectively than SBR1. The apparent PHAs utilization efficiency for SOP uptake with the SBR2 biomass was much greater than with the SBR1, and the SBR2 biomass synthesized less glycogen during aerobiosis than SBR1, which might mean a higher PHAs fraction was used for SOP removal, resulting in the increased efficiency with the long-term cultured SBR2 biomass. Higher propionic acid content led to superior EBPR in long-term cultivation, but was transiently detrimental in the short term.

Research paper thumbnail of Polyhydroxyalkanoates form potentially a key aspect of aerobic phosphorus uptake in enhanced biological phosphorus removal

Research paper thumbnail of Sample storage impact on the assimilable organic carbon (AOC) bioassay

Water Research, 2000

ÐThe eects of sample storage on the assimilable organic carbon (AOC) bioassay using Pseudomonas¯u... more ÐThe eects of sample storage on the assimilable organic carbon (AOC) bioassay using Pseudomonas¯uorescens strain P17 and Spirillum strain NOX have not been fully quanti®ed to date, and in the current Standard Method, it is stated that samples can``probably be held for several days'' (Standard Methods for the Examination of Water and Wastewater, ed. A. D. Eaton, L. S. Clesceri, A. E. Greenberg, 19th Edn., (1995)). Experiments were performed by splitting 22 samples after chlorine residual neutralization and pasteurization at 708C for 30 min, and holding one half of the replicate samples at 48C for one week prior to analysis. The majority of the samples were taken from a local water treatment plant and distribution system with source water from the deep Floridan aquifer. The others were taken from the laboratory tap water, whose source was also the Floridan aquifer. All collected samples were tested for eects due to storage, with each sample tested for AOC as soon as possible while an identical replicate was stored for one week. After one week, the AOC of the held samples was also determined. By comparing the AOC of samples that were not stored with samples that were stored, it was observed that after one week of storage, the AOC of the stored identical sample replicates increased by approximately 65%. This was determined to result from BOM (biodegradable organic matter) fermentation to AOC by a yeast, Cryptococcus neoformans. Of the 22 samples tested, only four displayed no signi®cant change in AOC and none displayed a signi®cant decrease in AOC. It was then determined that samples heat treated at 708C for 30 min could be stored for less than 2 days, but a modi®ed pasteurization of 728C for 30 min immediately followed by an ice bath for 30 min allowed storage for at least 7 days without signi®cant changes in AOC.

Research paper thumbnail of Anaerobic metabolic models for phosphorus- and glycogen-accumulating organisms with mixed acetic and propionic acids as carbon sources

Research paper thumbnail of The Role of Poly-hydroxy-alkanoate Form in Determining the Response of Enhanced Biological Phosphorus Removal Biomass to Volatile Fatty Acids

Water Environment Research, 2002

Anaerobic-aerobic batch experiments indicated that poly-hydroxy-alkanoate (PHA) form was importan... more Anaerobic-aerobic batch experiments indicated that poly-hydroxy-alkanoate (PHA) form was important in determining the net phosphorus removal resulting from different volatile fatty acids (VFAs). Poly-3-hydroxy-butyrate (3HB) content was found to correlate fairly well with higher observed aerobic phosphorus uptake per unit PHA carbon degraded. Poly-3-hydroxy-valerate (3HV) correlated with lower aerobic phosphorus uptakes per unit PHA carbon degraded. These experiments, conducted with synthetic wastewater, imply that VFA speciation might have a significant effect on aerobic phosphorus uptakes and net phosphorus removal. In addition, the model parameter fP.UPT (Barker and Dold, 1997) could vary with the proportion of acetic to propionic acid received (i.e., the acetic/propionic acid ratio may be an important parameter for these systems). Carbohydrate data implied that the lower aerobic phosphorus uptake resulting from 3HV might have been caused by a greater fraction of PHA carbon shunting to carbohydrate biosynthesis during aerobiosis.

Research paper thumbnail of Evaluation of Corrosion Inhibitors, Residual, Temperature, and Pipe Material on Bulk and Biofilm Heterotrophic Plate Counts Densities

The impact of corrosion inhibitors on biofilm and bulk heterotrophic plate counts (HPC) has been ... more The impact of corrosion inhibitors on biofilm and bulk heterotrophic plate counts (HPC) has been studied by a number of investigators and a review of the literature indicates a wide variety of seemingly contradictory results. Hozalski et al. (2005) observed an increase in bulk HPC levels when using phosphate based inhibitors. Miettinen et al. (1997) and Sathasivan et al. (1997) also observed full-scale systems where phosphate was a limiting nutrient and addition of it resulted in stimulation of bacterial growth. Appenzeller et al. (2001) observed a significant decrease in planktonic HPC when phosphate was added, but only when a highly corroded reactor was used. Evaluation of bacterial adhesion led Appenzeller et al. (2002) to conclude that the lower HPC were probably due to phosphate decreasing the ability of bacterial to adhere to corroded pipes due to phosphate sorption onto iron oxyhydroxides, which reversed their surface charge from positive to negative. In nonor lightly-corrode...

Research paper thumbnail of 水道管材料が微生物膜形成に及ぼす影響―特に米国における研究例―

Journal of Environmental Conservation Engineering, 2007

Research paper thumbnail of Effects of Reduced Ras Flows and Volume on Anaerobic Zone Performance for a Septic Wastewater Biological Phosphorous Removal System

Proceedings of the Water Environment Federation, 2003

Page 1. EFFECTS OF REDUCED RAS FLOWS AND VOLUME ON ANAEROBIC ZONE PERFORMANCE FOR A SEPTIC WASTEW... more Page 1. EFFECTS OF REDUCED RAS FLOWS AND VOLUME ON ANAEROBIC ZONE PERFORMANCE FOR A SEPTIC WASTEWATER BIOLOGICAL PHOSPHOROUS REMOVAL SYSTEM Daniel Magro1*, Steven L. Elias1, Andrew Amis Randall2 ...

Research paper thumbnail of Fouling control in activated sludge submerged hollow fiber membrane bioreactors

Desalination, 2002

The goal of this study is to determine the impact of various operating factors on membrane foulin... more The goal of this study is to determine the impact of various operating factors on membrane fouling in activated sludge membrane bioreactor (MBR) process, typically used for water reclamation. In this process, ultrafiltration (UF) and microfiltration (MF) hollow fiber membranes, submerged in the bioreactor, provided a solid-liquid separation by replacing gravity settling. Activated sludge from a food wastewater treatment plant was inoculated to purify synthetic wastewater consisting of glucose and (NH&SO, as a source of carbon and nitrogen, respectively. The results clearly showed that membrane fouling, defined as permeate flux decline due to accumulation of substances within membrane pores and/or onto membrane surface, was greatly influenced by membrane type and module configuration. It was also found that the rate and extent of permeate flux decline increased with increasing suction pressure (or initial operating flux) and with decreasing air-scouring rate. The mixed liquor suspended solids (MLSS) concentrations, however, exhibited very little influence on permeate flux for the range of 3600-8400 mgk. Another important finding of this investigation was that non-continuous membrane operation significantly improved membrane productivity. This observation can be explained by the enhanced back transport of foulants under pressure relaxation. During non-suction periods, the foulants not irreversibly attached to the membrane surface, diffused away from the membrane surface because of concentration gradient. Furthermore, the effectiveness of air scouring was greatly enhanced in the absence of transmembrane suction pressure, resulting in higher removal of foulants accumulated on the membrane surface. The use of intermittent suction operation may not be economically feasible at large-scale, but it may offer an effective fouling control means for small-scale MBR processes treating wastewaters with high fouling potential.

Research paper thumbnail of Aerobic production of activated sludge polyhydroxyalkanoates from nutrient deficient wastewaters

Water Science and Technology, 2006

It was found that aerobic strategies combined with multiple nutrient limitations produced greater... more It was found that aerobic strategies combined with multiple nutrient limitations produced greater quantities of polyhydroxyalkanoates (PHAs) than strategies relying on oxygen limitation (either micro-aerophilic or anaerobic/aerobic). This was true both for a synthetic wastewater composed of acetic and propionic acid, and also for a nutrient deficient industrial wastewater. PHA/substrate yields were shown to be comparable to axenic systems for many operating strategies analyzed, and it was found that PHA composition could be affected by process operational conditions. The molecular weight and melting point of the PHA produced were found to be in a desirable range with respect to material properties, which have not been well studied in the previous literature for mixed cultures (Salehizadeh and Van Loodsrecht, 2004). The effects of process staging, multiple treatment cycles, and inocula source were also addressed.

Research paper thumbnail of Modeling of organic substrate transformation in the high-rate activated sludge process

Water science and technology : a journal of the International Association on Water Pollution Research, 2015

This study describes the development of a modified activated sludge model No.1 framework to descr... more This study describes the development of a modified activated sludge model No.1 framework to describe the organic substrate transformation in the high-rate activated sludge (HRAS) process. New process mechanisms for dual soluble substrate utilization, production of extracellular polymeric substances (EPS), absorption of soluble substrate (storage), and adsorption of colloidal substrate were included in the modified model. Data from two HRAS pilot plants were investigated to calibrate and to validate the proposed model for HRAS systems. A subdivision of readily biodegradable soluble substrate into a slow and fast fraction were included to allow accurate description of effluent soluble chemical oxygen demand (COD) in HRAS versus longer solids retention time (SRT) systems. The modified model incorporates production of EPS and storage polymers as part of the aerobic growth transformation process on the soluble substrate and transformation processes for flocculation of colloidal COD to pa...

Research paper thumbnail of Reductive dechlorination of tetrachloroethylene (PCE) catalyzed by cyanocobalamin

Applied Biochemistry and Biotechnology, 1995

ABSTRACT A biomimetic system has been developed for the reductive dechlorination of tetrachloroet... more ABSTRACT A biomimetic system has been developed for the reductive dechlorination of tetrachloroethylene (PCE). PCE was dechlorinated to trichloroethylene (TCE) and 1,2-dichloroethylene (DCE) in the presence of dithiothreitol or Ti (III) citrate and catalytic amounts of cyanocobalamin in both homogeneous reaction mixtures and packed bed reactor systems. In packed bed reactors with Ti (III) citrate as the reductant, PCE (0.18 mM) conversion averaged 55% at residence times of 1.75 and 3.5 h. The product distribution was 94% TCE and 6% DCE at the lower residence time. DCE formation increased to 45% at the higher residence time. No reduction of PCE was observed in the absence of cyanocobalamin. This system may be useful as a means of pretreatment of halogenated aliphatic hydrocarbons in advance of biological treatment.

Research paper thumbnail of Optimization of Heterotrophic Denitrification Using Glycerol as a Sustainable External Carbon Substrate

Proceedings of 4th International Electronic Conference on Water Sciences, 2019

Nutrients removal from residential and industrial wastewaters are essential for environmental and... more Nutrients removal from residential and industrial wastewaters are essential for environmental and public health protection. Removal of nutrients from wastewater can be achieved chemically or biologically. Biological nutrient removal (BNR) is a series of anaerobic, anoxic, and aerobic zones to provide conditions for the biomass to uptake the nitrogen and phosphorus species, and comes in different configurations such as A/O, A2O, and 5-stage Bardenpho TM. However; BNR systems require a sufficient carbon source which most wastewaters lack. The goal of this study is to use a sustainable carbon source to optimize the 5-stage Bardenpho TM BNR systems and reduce the chemical cost. The experiments were carried out using two 5-stage Bardenpho TM BNR systems coupled with side-stream prefermenters. Glycerol, a biodiesel by-product, was used as a sustainable carbon source by direct addition or after fermentation. The results from both systems were beneficial to the BNR system and resulted in similar effluent quality. Both systems achieved complete denitrification and excellent phosphorus removal (82%-89%). Co-fermentation of glycerol and primary solids resulted in a significant increase in the volatile fatty acids (VFAs) loading beyond the estimated results, but did not correlate to better behavior between the two pilots since both systems achieved complete denitrification.

Research paper thumbnail of Impact of RO-desalted water on distribution water qualities

Water Science and Technology, 2005

A large-scale pilot distribution study was conducted to investigate the impacts of blending diffe... more A large-scale pilot distribution study was conducted to investigate the impacts of blending different source waters on distribution water qualities, with an emphasis on metal release (i.e. corrosion). The principal source waters investigated were conventionally treated ground water (G1), surface water processed by enhanced treatment (S1), and desalted seawater by reverse osmosis membranes (RO). Due to the nature of raw water quality and associated treatment processes, G1 water had high alkalinity, while S1 and RO sources were characterized as high sulfate and high chloride waters, respectively. The blending ratio of different treated waters determined the quality of finished waters. Iron release from aged cast iron pipes increased significantly when exposed to RO and SI waters: that is, the greater iron release was experienced with alkalinity reduced below the background of G1 water. Copper release to drinking water, however, increased with increasing alkalinity and decreasing pH. L...

Research paper thumbnail of Assimilable organic carbon and biodegradable organic carbon removal by nanofiltration: full and bench-scale evaluation

Water Science and Technology: Water Supply

The main objective of this research was to evaluate the effectiveness of nanofiltration (NF) at f... more The main objective of this research was to evaluate the effectiveness of nanofiltration (NF) at full and bench scale for controlling AOC and BDOC, which are the main indicators of biological stability of the finished potable water. One of the major observations from full-scale operation was that nanofiltration was a very effective means to reduce BDOC, but conversely, did not reject a significant fraction of AOC. The high BDOC rejection by nanofiltration (NF) membranes at full scale can be explained by size exclusion, since a significant fraction of BDOC consists of compounds, such as humic and fulvic acids, which are larger than the pores of NF membranes (molecular-weight cutoff ≃200 daltons). The insignificant AOC rejection observed in full-scale systems was probably due to the low pH, high hardness, and high ionic strength (TDS) of the raw water. Bench scale tests using simulated waters clearly demonstrated that AOC removal by NF membranes decreases markedly with decreasing pH, and increasing hardness and ionic strength, implying that electrostatic repulsion plays a significant role in AOC removal mechanisms. These solution environments repress the electrostatic interaction between charged organic compounds and membranes, allowing passage of small molecular weight compounds and thus reducing AOC rejection.

Research paper thumbnail of Case Study: Ozonation and distribution system biostability

Journal - American Water Works Association

ABSTRACT

Research paper thumbnail of Red Water Release in Drinking Water Distribution Systems

Journal - American Water Works Association

Research paper thumbnail of Effects of pipe-materials on microbial film formation in drinking water distribution system

Research paper thumbnail of High-Rate Activated Sludge System for Carbon Removal – Pilot Results and Crucial Process Parameters

Proceedings of the Water Environment Federation, 2013

Research paper thumbnail of Assimilable organic carbon (AOC) and biodegradable dissolved organic carbon (BDOC)

Water Research, 2001

FThe objective of this study was to evaluate the necessity of measuring both assimilable organic ... more FThe objective of this study was to evaluate the necessity of measuring both assimilable organic carbon (AOC) and biodegradable dissolved organic carbon (BDOC) as indicators of bacterial regrowth potential. AOC and BDOC have often been measured separately as indicators of bacterial regrowth, or together as indicators of bacterial regrowth and disinfection by-product formation potential, respectively. However, this study proposes that both AOC and BDOC should be used as complementary measurements of bacterial regrowth potential. In monitoring of full-scale membrane filtration, it was determined that nanofiltration (NF) removed over 90% of the BDOC while allowing the majority of the AOC through. Heterotrophic plate counts (HPC) remained low during the entire period of monitoring due to high additions of disinfectant residual. In a two-year monitoring of a water treatment plant that switched its treatment process from chlorination to chlorination and ozonation, it was observed that the plant effluent AOC increased by 127% while BDOC increased by 49% after the introduction of ozone. Even though AOC is a fraction of BDOC, measuring only one of these parameters can potentially under-or overestimate the bacterial regrowth potential of the water.

Research paper thumbnail of The efficiency of enhanced biological phosphorus removal from real wastewater affected by different ratios of acetic to propionic acid

Water Research, 2004

The effect of different ratios of propionic to acetic acid on the efficiency of enhanced biologic... more The effect of different ratios of propionic to acetic acid on the efficiency of enhanced biological phosphorus removal (EBPR) from real wastewater supplemented with volatile fatty acids (VFAs) was investigated. Two sequencing batch reactors (SBRs) were used to acclimate two types (SBR1 and SBR2) of biomass. They were cultured and studied using real wastewater with an average propionic to acetic acid carbon molar ratio of 0.16 and 2.06, respectively. The laboratory results showed that for a given long-term cultured biomass the more the soluble ortho-phosphate (SOP) was released in the anaerobic stage, the higher the SOP was taken up in the aerobic phase. However, the SBR2 biomass had a much greater SOP uptake to release ratio than SBR1, which resulted in a higher SOP removal efficiency than SBR1 (average 87.3% versus 76.9% in SBRs experiments, and 93.5% against 68.1% in batch tests). The SBR2 biomass therefore had a higher SOP uptake ability than the SBR1 for a given amount of SOP release. In addition, the SBR1 had a higher secondary SOP release following VFAs uptake. It was found that the SBR2 biomass synthesized and utilized less observable polyhydroxyalkanoates (PHAs) during the anaerobic and aerobic stage respectively than SBR1. The apparent PHAs utilization efficiency for SOP uptake with the SBR2 biomass was much greater than with the SBR1, and the SBR2 biomass synthesized less glycogen during aerobiosis than SBR1, which might mean a higher PHAs fraction was used for SOP removal, resulting in the increased efficiency with the long-term cultured SBR2 biomass. Higher propionic acid content led to superior EBPR in long-term cultivation, but was transiently detrimental in the short term.

Research paper thumbnail of Polyhydroxyalkanoates form potentially a key aspect of aerobic phosphorus uptake in enhanced biological phosphorus removal

Research paper thumbnail of Sample storage impact on the assimilable organic carbon (AOC) bioassay

Water Research, 2000

ÐThe eects of sample storage on the assimilable organic carbon (AOC) bioassay using Pseudomonas¯u... more ÐThe eects of sample storage on the assimilable organic carbon (AOC) bioassay using Pseudomonas¯uorescens strain P17 and Spirillum strain NOX have not been fully quanti®ed to date, and in the current Standard Method, it is stated that samples can``probably be held for several days'' (Standard Methods for the Examination of Water and Wastewater, ed. A. D. Eaton, L. S. Clesceri, A. E. Greenberg, 19th Edn., (1995)). Experiments were performed by splitting 22 samples after chlorine residual neutralization and pasteurization at 708C for 30 min, and holding one half of the replicate samples at 48C for one week prior to analysis. The majority of the samples were taken from a local water treatment plant and distribution system with source water from the deep Floridan aquifer. The others were taken from the laboratory tap water, whose source was also the Floridan aquifer. All collected samples were tested for eects due to storage, with each sample tested for AOC as soon as possible while an identical replicate was stored for one week. After one week, the AOC of the held samples was also determined. By comparing the AOC of samples that were not stored with samples that were stored, it was observed that after one week of storage, the AOC of the stored identical sample replicates increased by approximately 65%. This was determined to result from BOM (biodegradable organic matter) fermentation to AOC by a yeast, Cryptococcus neoformans. Of the 22 samples tested, only four displayed no signi®cant change in AOC and none displayed a signi®cant decrease in AOC. It was then determined that samples heat treated at 708C for 30 min could be stored for less than 2 days, but a modi®ed pasteurization of 728C for 30 min immediately followed by an ice bath for 30 min allowed storage for at least 7 days without signi®cant changes in AOC.

Research paper thumbnail of Anaerobic metabolic models for phosphorus- and glycogen-accumulating organisms with mixed acetic and propionic acids as carbon sources

Research paper thumbnail of The Role of Poly-hydroxy-alkanoate Form in Determining the Response of Enhanced Biological Phosphorus Removal Biomass to Volatile Fatty Acids

Water Environment Research, 2002

Anaerobic-aerobic batch experiments indicated that poly-hydroxy-alkanoate (PHA) form was importan... more Anaerobic-aerobic batch experiments indicated that poly-hydroxy-alkanoate (PHA) form was important in determining the net phosphorus removal resulting from different volatile fatty acids (VFAs). Poly-3-hydroxy-butyrate (3HB) content was found to correlate fairly well with higher observed aerobic phosphorus uptake per unit PHA carbon degraded. Poly-3-hydroxy-valerate (3HV) correlated with lower aerobic phosphorus uptakes per unit PHA carbon degraded. These experiments, conducted with synthetic wastewater, imply that VFA speciation might have a significant effect on aerobic phosphorus uptakes and net phosphorus removal. In addition, the model parameter fP.UPT (Barker and Dold, 1997) could vary with the proportion of acetic to propionic acid received (i.e., the acetic/propionic acid ratio may be an important parameter for these systems). Carbohydrate data implied that the lower aerobic phosphorus uptake resulting from 3HV might have been caused by a greater fraction of PHA carbon shunting to carbohydrate biosynthesis during aerobiosis.