Enteroviruses, hepatitis A virus (HAV) and other enteric viruses can survive wastewater treatment processes, even after chlorination, and are found in the final effluents. These viruses can be detected by cell culture techniques with observations for cytopathic effect (CPE). Recently molecular detection of viral nucleic acids has been used. Most viruses found in wastewater are RNA viruses and RT-PCR is a rapid and sensitive method to detect these single-strand RNA enteric viruses. This methodology does not distinguish between infectious and non-infectious viruses. Viruses inactivated in the treatment process can be detected but do not pose a public health threat. Methods are needed to quickly distinguish the infectious viruses from inactivated viruses, both of which may be present in effluents. In this project we investigated the use of a method that combines cell culture and molecular detection. If a sample contains viruses that replicate in cell culture even without CPE, the proof of replication can be demonstrated by the detection of a replicative form (RF) in cell culture that is only present during replication of infectious RNA viruses. A negative sense strand of RNA is generated from the viral positive strand virus, and these two are found primarily bound in a replicative form. This RNA was specifically detected by RT-PCR, including the positive and negative strands. This assay was developed and explored for the detection of low levels of CVB3 and HAV laboratory strains first and then for low levels of wild-type enteroviruses isolated from sewage samples. As few as four infectious units of wild-type enteroviruses, contained in 2.0 ml of water concentrate prepared from 600 ml of treated wastewater effluent, could be detected within two days. Treated wastewater effluents were collected weekly over an 18 months period, and viruses were concentrated with a developed method. About 7% of the final effluent wastewater samples were found positive for infectious enterovirus with the developed RF method, although only 1% of the samples were positive by presence of cytopathic effect. This method avoids the use of two complete cycles of cell culture to detect infectious virus, while confirming infectivity with a molecular method.

Plant-availability of metals in biosolids-treated soils may be mathematically described by M t = C x 1 - e - (k x t) ] where M t (mg kg -1 ) is the cumulative metal removal from the biosolids-treated soils by growing and harvesting plants for t years, C is the total phytoavailable metal pool of the soil (mg kg -1 ) at t = 0, and k is the metal absorption rate coefficient (yr -1 ). The total available metal pool, C, is defined as metals extractable by organic acids in the rhizosphere of growing plants and k is related to the kinetics of metal release by organic acids. Half-life of the available metals in biosolids-amended soils may be derived from k. Experiments were conducted to characterize the concentration and composition of the organic acids. A successive extraction method was used to extract metals from biosolids-treated soils for determinging C and k. In this manner, the plant available metals of the bioslids-treated soils are defined by the total avialble metals, half-life, and duration of plant growing. Examples showed that the total available metals of the biosolids-amended were 18 to 39, 0.12 to 2.0, 7.4 to 13, 24 to 46, 1.2 to 2.1, and 43 to 53% of the total Cd, Cr, Cu, Ni. Pb, and Zn in the soils. This publication can also be purchased and downloaded via Pay Per View on Water Intelligence Online - click on the Pay Per View icon below

This highly technical work is at the leading edge of spatial analysis. It covers the Global Monitoring for Environment and Security (GMES) initiative in the international context of access to environmental data. This book identifies the data policy issues, such as intellectual property rights, privacy, licensing and archiving policies, that affect environmental monitoring organisations, statistical institutes, mapping agencies, institutes for natural resources and Earth observation. It recommends courses of action to improve information services in GMES and assesses the impact of data policy on access to and cost-efficient use of information services in GMES.

This title will be essential reading for government institutions such as mapping organisations, space agencies, environmental departments, military and defence departments; it will also be useful to students of environmental policies and industries involved in mapping, cartography, aerial surveys and the space industry.

Intensifying Activated Sludge Using Media-Supported Biofilms will be of interest to practicing wastewater treatment process designers, along with those seeking more compact and energy-efficient wastewater treatment options. The advantages of Moving Bed Biological Reactor (MBBR)-based hybrid processes are now well-established in practice, leading to their increased use in the field. Membrane Aerated Biofilm Reactor (MABR)-based hybrid processes are much newer and offer further systematic process and energy advantages. This book examines the evolution of hybrid technologies as well as the potential for continued improvement of biological wastewater treatment techniques. Features: Reviews current approaches for intensifying biological wastewater treatment processes and their mechanistic bases. Examines hybrid suspended growth/biofilm-based wastewater treatment processes, including the newly-developed MABR-based processes, and their unique dynamic performance characteristics. Presents a novel method for characterizing the performance and process intensification advantages of hybrid processes. Provides guidance for simulating the performance of hybrid processes, including oxygen transfer in MABR hybrid processes.

Rural-Urban Water Struggles compiles diverse analyses of rural-urban water connections, discourses, identities and struggles evolving in the context of urbanization around the world. Departing from an understanding of urbanization as a process of constant making and remaking of multi-scalar territorial interactions that extend beyond traditional city boundaries and that deeply reconfigure rural-urban hydrosocial territories and interlinkages, the chapters demonstrate the need to reconsider and trouble the rural-urban dichotomy. The contributors scrutinize how existing approaches for securing urban water supply - ranging from water transfers to payments for ecosystem services - all rely on a myriad of techniques: they are produced by, and embedded in, specific institutional and legal arrangements, actor alliances, discourses, interests and technologies entwining local, regional and global scales. The different chapters show the need to better understand on-the-ground realities, taking account of inequalities in water access and control, as well as representation and cultural-political recognition among rural and urban subjects. Rural-Urban Water Struggles will be of great use to scholars of water governance and justice, environmental justice and political ecology. This book was originally published as a special issue of Water International.

This is the first monograph in English on the topic of the sienese acqueducts. The book reviews scholarly literature and archival sources including maps and diagrams, to better situate Siena's achievement in urban history and broadens our understanding of medieval technology and urban life. Michael P. Kucher argues that urban patronage of anonymous craftsmen provided the cultural foundations for the careers of better known engineers like Francesco di Giorgio and Leonardo da Vinci. The book joins the rapidly expanding field of works that focus on urban technology to shed new light on daily life in the medieval city.

Nitrification kinetics were evaluated in bench-scale batch reactors fed with a synthetic wastewater containing approximately 1,000 mg ammonia-nitrogen (NH3-N)/L operated at 5, 10, and 20 day solids retention times (SRTs) and with dewatered biosolids supernatant (1,126 to 1,680 mg NH3-N/L) operated at a 20-day SRT. For the 5- and 10-day SRTs, complete nitrification appeared to be inhibited by the presence of un-ionized ammonia and un-ionized nitrous acid. For the 20-day SRT, near complete nitrification was observed for both substrates. Observed ammonium oxidation rates decreased with increasing SRT. Observed yield coefficients were similar for all SRTs and substrates. Fully established steady-state conditions were observed at higher SRTs despite process start-up and operational considerations. Although it may be possible to culture a nitrifier population capable of near-complete nitrification at lower SRTs, the design configuration and operational strategy must mitigate the potential for un-ionized ammonia and un-ionized nitrous acid inhibition (e.g. process start-up at lower concentration with gradual increase to higher concentration, continuous feed operation, etc.). Batch bioaugmentation analyses were conducted in the mixed liquor suspended solids and final clarifier effluent from a non-nitrifying activated sludge with seed nitrifiers developed from the 20-day SRT reactors and with biomass from a nitrifying trickling filter facility. Ammonia removal was observed in all bioaugmentation analyses with no apparent lag or acclimation period. Observed ammonium oxidation rates were not significantly different between the seed and batch bioaugmentation reactors. Acclimation does not appear to be a critical obstacle for nitrifier bioaugmentation when environmental conditions (e.g. temperature, pH, etc.) between the seed and bioaugmentation processes are not significantly different.

Over the past 20 years, the use of Best Management Practices (BMPs) in the United States has been instrumental in reducing both the detrimental impacts to receiving water quality and the exacerbated flooding caused by urbanization and storm water drainage. More recently, Sustainable Urban Drainage Systems (SUDS) have started to be used in the United Kingdom. Both SUDS and BMPs attempt to mimic the drainage patterns of the natural watershed, and can also provide a degree of treatment needed to improve the quality of the water discharged to an acceptable level. The costs of conventional stormwater collection systems are determined primarily in terms of initial capital expenditure. Long-term maintenance costs are absorbed by stormwater authorities that are responsible for maintaining their infrastructure as part of their 'asset base'. Currently, only a few of these responsibilities exist for BMPs and SUDS, which generally incorporate surface components and are often dependent on landscaping rather than on traditional construction techniques, but may require significant regular maintenance. Any potential adopting organization will require guidance on the maintenance regimes of different types of systems and how such regimes translate into long-term adoption costs. The project is being conducted in two phases. Phase 1, which is the subject of this report, includes a literature review and a survey of stormwater authorities and organizations in the U.S. and U.K. to identify the most commonly used BMPs and SUDS and to determine the availability of data on their cost and performance. Phase 1 also involves establishment of protocols for whole-life costs and performance data for BMPs and SUDS. Protocols for whole-life costs will be published separately. An additional outcome of Phase 1 will be the selection of a limited number of BMPs and SUDS authorities or sites for qualitative or quantitative monitoring and further assessment during Phase 2.As part of Phase 2, the operation of selected BMPs and SUDS will be monitored over a one-year period in terms of pollutant removal and hydrologic/hydraulic efficiency, and applicability of their design criteria and maintenance regime. The protocols developed in Phase 1 will be used to assess BMPs/SUDS performance and whole-life costs.

The main objective of this project is to demonstrate that the technology of on line monitoring of waterborne metals by X-ray Fluorescence (XRF) at part per billion (ppb) and sub-ppb levels, which has been successfully applied in the power industry for several years, can be applied to water and wastewater treatment plants. A specially designed on line XRF monitor was assembled, tested in the laboratory, and used at the City of Alliance, Ohio Wastewater and Water Treatment Plants from July 2002 until March 2004. At various times through this project, the metals monitored included iron, copper, chromium, nickel, zinc, manganese, arsenic, cadmium, mercury and lead. The results indicate that XRF on line monitoring of waterborne metals at trace levels is feasible for the influent and effluent of water treatment plants, and the effluent of wastewater treatment plants.

With contributions from an international team of experts, this book offers planners, engineers, and designers guidelines for using recycled water in landscape and agricultural applications. The book thoroughly covers all of the relevant technical, economic, financial, agronomic, health, environmental, regulatory, and social issues. It covers how to develop, implement, and operate wastewater reuse systems based on rigorous, best management practices that maximize efficiency, reliability, and economy while minimizing the potential for adverse effects to the environment and human health. Comprehensive tables, charts, figures, photographs, and case-studies make the information easy to find. Lazarova; Valentina Suez Environment Services Locaux, CIRSEE, Le Pecq, France,Akissa; Bahri INRGREE, Ariana, Tunisia

Sustainable Water Services: A Procedural Guide is the result of the Sustainable Water industry Asset Resource Decisions (SWARD) project, undertaken by a consortium of UK academics in collaboration with water service providers in Scotland, England and Romania. It has been developed to act as a practical tool to assist with the explicit inclusion of ?sustainability? in the decision-making processes of those responsible for providing water services. The book contains a framework that comprises a set of decision support processes that can be used by water service providers to explicitly incorporate sustainability considerations into their decision-making procedures, through the use of sustainability principles, criteria, indicators and processes. These principles and criteria can be applied at an overall corporate strategic level, for example in the service provider?s mission statement, or at an application level, where these strategic principles are being applied to a particular decision. Sustainable Water Services is designed to inform and to provide support for strategic activity, both as a resource containing information about sustainability, and by employing feedback from application to inform the strategic processes of the water service provider. Presents an inclusive and generic set of sustainability criteria for use in water industry decision making processes; Discusses the legislative drivers for sustainable decision making for the UK water industry; Presents clear case study examples of the sustainability framework in action; Discusses the use and applicability of a wide range of tools and techniques for undertaking environmental, economic and social analyses, e.g. life cycle assessment, multi-criteria analysis.

Drinking water provides an efficient source for the spread of gastrointestinal microbial pathogens capable of causing serious human disease. The massive death toll and burden of disease worldwide caused by unsafe drinking water is a compelling reason to value the privilege of having safe drinking water delivered to individual homes. On rare occasions, that privilege has been undermined in affluent nations by waterborne disease outbreaks traced to the water supply. Using the rich and detailed perspectives offered by the evidence and reports from the Canadian public inquiries into the Walkerton (2000) and North Battleford (2001) outbreaks to develop templates for understanding their key dimensions, over 60 waterborne outbreaks from 15 affluent countries over the past 30 years are explored as individual case studies. Recurring themes and patterns are revealed and the critical human dimensions are highlighted suggesting insights for more effective and more individualized preventive strategies, personnel training, management, and regulatory control. Safe Drinking Water aims to raise understanding and awareness of those factors that have most commonly contributed to or caused drinking-water-transmitted disease outbreaks - essentially a case-history analysis within the multi-barrier framework. It contains detailed analysis of the failures underlying drinking-water-transmitted disease epidemics that have been documented in the open literature, by public inquiry, in investigation reports, in surveillance databases and other reliable information sources. The book adopts a theme of 'converting hindsight into foresight', to inform drinking-water and health professionals including operators, managers, engineers, chemists and microbiologists, regulators, as well as undergraduates and graduates at specialty level. Key Features: Contains details and perspectives of major outbreaks not widely known or understood beyond those directly involved in the investigations. Technical and scientific background associated with case studies is offered in an accessible summary form. Does not require specialist training or experience to comprehend the details of the numerous outbreaks reviewed. By providing a broad-spectrum review using a consistent approach, several key recurring themes are revealed that offer insights for developing localized, tailor-made prevention strategies.

One approach to the introduction of computational material to the classroom is to supplement a textbook with modern computer codes. Unfortunately most codes are expensive, designed for commercial use, without source code and may require special software. Visual Hydrology provides a cheaper and simpler alternative, supplying computational exercises that can be fully assimilated by students, and allowing them to activate, understand and reproduce modern computer code. Visual Hydrology aims to: explain the structure of modern object-oriented computer code provide the source code for worked examples numerically check the worked examples used in text show how worked examples can be used with alternative data describe and reference the underlying theory provide additional exercises with each worked example use Microsoft Excel software alone Requiring only a basic knowledge of Microsoft Excel, this Primer teaches the use of modern and readily-available computer code for engineering computation. Visual Hydrology demonstrates codes for common and practical examples used in hydrological engineering, and will be a valuable resource to students, research workers and consulting engineers in the water-related sector. Examples of source code to accompany this publication can be downloaded by clicking here.

A new development for the treatment of domestic wastewater is a technology based on aerobic granular sludge. Granular sludge can be developed under specific process conditions and, because of its unique properties, high volumetric loading rates of aeration tanks can be applied. Thanks to excellent settling properties, the separation of treated wastewater and granular sludge can take place at high hydraulic loading rates. Depending on the process configuration chosen, good effluent quality can be obtained, complying with stringent effluent requirements regarding nitrogen and phosphorus, which can be expected in the future. In this way, aerobic granular sludge has the potential to contribute significantly to wastewater treatment management.This report describes the results of research carried out at the Technical University of Delft.IWA Publishing Water and Wastewater Practitioner Series: STOWA Report

The ability to measure sludge network strength is important in sludge dewatering applications because it can be used to determine optimum polymer dose for conditioning to achieve good dewaterability. This was demonstrated in laboratory and in full-scale dewatering and thickening. The network strength increased as the polymer dose was increased, however, at the optimum dose a "drop" in the network strength occurred. Further research is needed to verify this concept at full scale and to provide a robust technology to the water and wastewater treatment industry. A second phase is sought through WERF funding. Rheometry was used for determining the sludge network strength. This report also formulated and demonstrated a standard protocol for measuring network strength in terms of energy dissipated in a certain volume of sludge. Two protocols for measuring network strengths by either torque or concentric cylinder rheometers are described in this report. A mathematical derivation has shown that area under rheograms, namely the curves which were developed by plotting shear rate (1/sec) versus shear stress (Pa) and time (sec) versus torque (mNm), indicated the rate of energy dissipation within the sludge system and the total dissipated energy was related to the network strength. The research did not intend to measure the "absolute" network strength, rather a comparative strength of different aggregates using the same instrument and under the same measuring conditions.

Mathematical modeling is a useful tool for the design, analysis and control of wastewater treatment systems. The activated sludge process is one of the most common processes used in wastewater treatment, and therefore is a particularly important candidate for the application of mathematical models. In the 1980s, a task group organized by the International Association on Water Quality (IAWQ) developed a conceptual model of the activated sludge process, which has become an industry-wide standard for the development of computer-based activated sludge models. A recent version of the IAWQ model incorporates 19 components, 17 processes, and numerous rate and stoichiometric coefficients. It is difficult and costly to quantify all of the necessary coefficients for any given application of the model; consequently, it is important to identify the most critical wastewater and biomass components and the relevant coefficients to be quantified for the most common uses of the model. It is also important to provide guidance to potential model users on the use of default and/or estimated values for the remaining parameters.

Uncontrolled spreading of waste materials leads to health problems and environmental damage. To prevent these problems a waste management infrastructure has been set to collect and dispose of the waste, based on a hierarchy of three principles: waste prevention, recycling/reuse, and final disposal. Final disposal is the least desirable as it causes massive emissions, to the atmosphere, water bodies and the subsoil. The emission of methane to the atmosphere is an important source of greenhouse gasses. Organic waste therefore gets a lot of attention in waste management, which for Europe can be illustrated by the issue of the Landfill Directive (99/31/EC) and the Sewage Sludge Directive (86/278/EEC). Proper treatment of organic waste may however turn this burden into an asset. In particular, biological treatment may help in developing more effective resource management and sustainable development. The following advantages may be listed: The greenhouse effect is tackled as methane emissions from landfilling are prevented Soil quality can be restored or enhanced by the use of compost in agriculture Compost may replace peat in horticulture and home gardening, reducing greenhouse emissions and wetland exploitation Anaerobic digestion has the additional benefit of producing biogas that may be used as a fuel Pesticide use can be reduced by proper use of the disease suppressive properties of compost Resource Recovery and Reuse in Organic Solid Waste Management disseminates at advanced scientific level the potential of environmental biotechnology for the recovery and reuse of products from solid waste. Several options to recover energy out of organic solid waste from domestic, agricultural and industrial origin are presented and discussed and existing economically feasible treatment systems that produce energy out of solid waste and recover useful by-products in the form of fertiliser or soil conditioner are demonstrated. The potential of environmental biotechnology is highlighted from different perspectives: societal, technological and practical.

This project was undertaken in response to needs by the wastewater treatment industry to better understand the generation of odors from biosolids produced by wastewater treatment plants (WWTPs). Its primary objective is to begin to establish relationships between WWTP process parameters and biosolids odors, so that more effective techniques for minimizing biosolids odors can be developed. The project consisted of a detailed field study involving extensive sampling and analyses at 11 WWTPs across North America with capacities from 13 to 350 million gallons per day (mgd). Biosolids samples were collected from the WWTPs at a number of sampling points, which were chosen to represent a complete snapshot of biosolids generation and handling at each WWTP. The sampling points started with influent wastewater, proceeded through primary and secondary clarification, and continued through digestion, dewatering, and onsite storage of dewatered biosolids cake. Laboratory-scale anaerobic storage tests were conducted to simulate odor development of biosolids in storage, prior to their beneficial reuse or disposal. A battery of analyses were performed on the biosolids samples by the participating utility laboratories, commercial laboratories, and specialized university laboratories. The analytical data were evaluated and compared with process and operation parameters at each participating WWTP.

The objective of this project was to develop and evaluate a practical technique to indicate the probability of the presence of bacterial pathogens in receiving waters. A "practical" method was defined as one that would limit the use of defined culture-based microbiological methods, and would be based on: (1) validating indicator organisms that predicted the presence of pathogens, or (2) detection of pathogens by polymerase chain reaction (PCR)-based assays. The study also assessed the utility of PCR-based technology for bacterial pathogen detection with respect to technology transfer to a wider range of water and wastewater facilities.

These proceedings present state-of-the-art papers on mine and mill tailings and mine waste as well as current and future issues facing the mining and environmental communities. This includes matters dealing with technical capabilities and developments, regulations, and environmental concerns. Papers include topics related to site characterization and monitoring, reclamation and remediation, protective liners, covers, and barriers, design, operation and disposal, groundwater and surface water quality and modeling, geotechnical and geochemical aspects, reprocessing, utilization and treatment, radioactivity and risk, new technologies and paste technology, and case histories.

Cyanide occurs in many industrial and municipal wastewaters and is often an expected constituent of typical treatment plant wastewater streams. However, a growing number of wastewater treatment plants (WWTPs) across the USA have detected cyanide in cholorinated effluents at levels exceeding influent concentrations. Because water quality criteria and related discharge limits are typically low some of these WWTPs periodically exceed effluent cyanide standards. Potential causes include cyanide formation during wastewater cholrination processes, the presence of interferences that cause false negatives, and false positives caused by artifacts of sample handling or analytical techniques. The possible causes of the apparent cyanide formation phenomenon were investigated in this study. This publication can also be purchased and downloaded via Pay Per View on Water Intelligence Online - click on the Pay Per View icon below

A general review of literature published from 1990 to 2000 and unpublished (gray) literature on odors associated with municipal wastewater collection systems and treatment facilities, including biosolids handling. The literature review focused on several areas including odor characterization technology, odor sampling, analysis, measurement technology, and odor mitigation (control) technology.

Anaerobic/aerobic (AnA) and completely aerobic (CA) laboratory-scale sequencing batch reactors operating on an acetate- and casamino acids-based synthetic wastewater were used to investigate the suitability of the AnA process for treating nutrient?deficient wastewaters in plants that have stringent effluent nutrient requirements. Of particular interest is the case where phosphorus (P)-deficient wastewaters with highly variable influent COD loading are being treated to meet both effluent TSS and P limits. At a 4 d mean cell residence time, AnA activated sludge had an approx. 20% lower P requirement than CA activated sludge. The difference between the end-of-aerobic cycle polyhydroxyalkanoate and carbohydrate contents of the sludges indicated that the AnAsludge used more influent carbon than the CA sludge for synthesis of non-P-containing storage products. The nitrogen requirements of AnA sludge were similar to those of the CA sludge. The AnA and CA SBRs were subjected to three different transient influent COD loading patterns that simulated (#1) daily COD Loading fluctuations, (#2) low weekend COD loading, and (#3) extended low COD loading periods. During the Loading Pattern #1 experiment, the average effluent soluble P concentrations for the AnA and CA SBRs were 0.4 and 1.0 mgP/L respectively, and complete removal of influent acetate was observed. During the Loading Pattern #2 experiment, the average effluent soluble P concentrations for the AnA and CA SBRs were 0.3 and 0.9 mgP/L respectively, but effluent acetate was detected during the first high COD loading cycle following the low weekend COD loading period. During the Loading Pattern #3 experiment, the VSS content of both reactors dropped sharply, effluent acetate breakthrough occurred, and effluent P concentrations exceeding 1 mgP/L were detected in both the AnA and CA SBRs. Based on these findings, the AnA process has potential as a technologically and economically superior alternative for wastewater treatment plants treating P-deficient wastewasters to meet stringent effluent TSS and P limits. This publication can also be purchased and downloaded via Pay Per View on Water Intelligence Online - click on the Pay Per View icon below

The purpose of this research was to evaluate and compare various thermophilic anaerobic digestion processes for meeting U.S. EPA biosolids Class A pathogen standards. The project was split into three phases. Phase 1 screened three bench-scale thermophilic anaerobic process configurations at three different thermophilic temperatures based on their fecal coliform destruction efficiency. All three of the thermophilic process configurations tested were capable of achieving the Class A fecal coliform standard and were included in Phase 2. In Phase 2, bench-scale anaerobic digesters were fed primary sludge seeded with E.coli, helminth ova, poliovirus, and Salmonella to evaluate pathogen destruction. Two process configurations, the thermophilic single-stage and the two-stage mesophilic acid-phase/thermophilic methane-phase system, met Class A requirements at 50oC. In Phase 3, the single-stage thermophilic anaerobic digestion process was compared to the single-stage mesophilic process at full scale (1.5-MG digesters) based on fecal coliform and pathogen destruction, process performance, digested sludge dewaterability, and odor generation.Pathogen destruction and process performance comparisons of the various process configurations are presented for each phase of the study. Based on the fecal coliform data presented here, an empirical model was developed for quantitatively comparing multiple stage and single-stage thermophilic anaerobic digester performance. The model demonstrates that various combinations of thermophilic temperatures, staging, and residence times can achieve the Class A fecal coliform requirement. This study also suggests that anaerobic digesters operating in the lower thermophilic temperature range (approximately 50degreeC) are not only capable of achieving Class A requirements but may also produce digested sludges with less odor and lower volatile solids than digesters operating at higher thermophilic temperatures.

This research attempts to evaluate nitrification treatment performance in combined carbon/nitrogen municipal wastewater reactors using traditional physical/chemical methods and modern molecular techniques. Bench scale activated sludge reactors were operated at different SRTs under varying DO levels and temperatures over a 21-month period. Real-time PCR assays were used to determine cell concentrations of total bacterial 16S rDNA, a gross measure of biomass content, the amoA gene, a measure of ammonia-oxidizing bacteria (AOB), and the Nitrospira 16S rDNA gene, a measure of nitrite-oxidizing bacteria (NOB). As expected, gravimetric biomass and total bacterial 16S rDNA levels increased with increasing SRT. Ammonia oxidation rates and N. oligotropha-type AOB concentrations did not follow similar trends with respect to changes in SRT, temperature, and DO nor were they highly correlated. The concentration of available nitrite and SRT were positively correlated with Nitrospira cell densities, while DO concentration and temperature were negatively correlated with NOB levels. The percentage of the total population comprised of AOB and NOB obtained with the real-time PCR assays were compared to predicted values estimated from design equations using typical kinetic parameters. While the percentages of NOB measured using the real-time PCR assay corresponded very well with the predicted values, the measured percentages of AOB were much lower than those estimated from the design equations, suggesting that N. oligotropha-type AOB were not the dominant ammonia-oxidizing species in these reactors. This publication can be purchased and downloaded via Pay Per View on Water Intelligence Online - click on the Pay Per View icon below