Particle size distribution of the particulates is an essential characteristic of the wastewater quality. Particle size distribution has been used to predict COD, suspended solids, color, and turbidity. The understanding of particle size distribution contributed to the better understanding of soluble and particulate COD fractions and benefited the modeling of activated sludge process. Particle size distribution of wastewater particles was used to improve the understanding of both primary treatment and secondary treatment. Particle size of activated sludge flocs may affect key sludge handling processes including sedimentation, thickening, digestion, and dewatering. Particle size distribution of secondary effluent is also an important consideration for the design of tertiary treatment such as filtration and disinfection. Several design and operational parameters, e.g. mixing, aeration, flocculation, and SRT, may affect particle size distribution of activated sludge. Previous results strongly suggest that SRT is an important parameter affecting particle size distribution in activated sludge process. However, direct comparison of different wastewater treatment plants could not rule out possible confounders such as sheer force in aeration basin, doses of coagulants, and variation of organic loadings. The objective of this study is to investigate particle size distribution of activated sludge flocs under different SRTs and treatment processes. Particle size distribution of lab-scale MLE reactor and IFAS reactor were studied under various SRTs and carbon sources. Five full-scale wastewater treatment plants were surveyed for detailed understanding of the change of particle size distribution from raw wastewater to secondary effluent. Chapter 2 investigates the impact of SRT on particle size distribution, sludge settleability, effluent turbidity, and removals of COD and NH4+-N. A MLE reactor is established with 16L of operational volume. Settling test, water quality analyses, and microscopic examination are applied to evaluate the impact of different SRTs. Particle size of activated sludge flocs are analyzed at different controlled SRTs. Particles with different size ranges were evaluated at various SRTs. Chapter 3 focuses on the impact of SRT on particle size distribution, sludge settleability, effluent turbidity, and removals of COD, NH4+-N in a lab-scale Integrated Fixed Film Activated Sludge (IFAS) reactor. Chapter 3 further investigates the impact of difference carbon sources (Glucose vs. Sodium Acetate) on particle size distribution and reactor performance in the IFAS reactor. Settling test, water quality analyses, and microscopic examination are applied to evaluate the impact of different SRTs. Particle size distribution of the mixed liquor in the IFAS reactor is compared with that in MLE reactor operated at similar SRTs for suspended solids. Chapter 4 surveys particle size distribution in 5 full-scale WWTPs with different SRTs and treatment processes in the Los Angeles County. Particles size distribution profiles from primary influent to secondary effluent are fully evaluated. The relationship between SRT and particle size of activated sludge in biological process and sedimentation process are studied in detail.

A bench-scale treatment system with external clarifier was used to determine the effects of solids retention time (SRT) and temperature on treatment performance while simulating the full scale activated sludge process. Four bench-scale reactors, operating at SRTs of 20, 10, 5 and 2 days, were fed settled municipal wastewater collected after primary clarification from the Kuwahee wastewater treatment plant in Knoxville, TN. Three operational temperatures were investigated during this study, 22°C, 12°C and 7°C. The order and duration of operation at each temperature was first 22°C for 61 days, next 7°C for 47 days and lastly 12°C for 105 days. Experimental results indicate that carbon treatment performance improved, on average with increasing SRT; however, carbon treatment performance was not effected by operational temperatures studied to the same extent. On average, carbon oxidation improved with increasing SRT at each operational temperature; however, carbon oxidation was more efficient at 12°C than 22°C. CODT treatment performance at 7°C was poor irrespective of SRT. The difference in performance between 22°C and 12°C was attributed to acclimation of biomass from startup at 22°C to operation at 12°C beginning at 108 days. Sludge volume index (SVI) and effluent suspended solids (ESS) values also indicated that SRT had a greater impact on biosolids settling than did temperature. During this study, nitrification was observed to be viable at 22°C and 12°C despite reported sensitivity of lower SRTs (2 and 5 days) to process changes and low operational temperature. According to these observations, higher SRTs would be recommended for full-scale treatment especially during wintertime or sub-optimum temperatures. Nitrification at 7°C was observed to be almost nonexistent for all SRTs studied during this research. Based on the data presented in this study, an SRT of 5 days and a process temperature of 12°C are necessary to achieve effective carbon treatment, biosolids settling, and nitrification. A comparison of the full and bench scale (5-day SRT) systems, based on the operational and environmental parameters considered in this study revealed inadequacies of the bench scale system in simulating the full scale facility. Carbon treatment performance as well as MLSS levels, differed in the two systems. The full scale facility consistently discharged significantly lower carbon levels than did the bench scale system. Additionally MLSS levels were significantly higher in the full scale facility. Nitrification performance was better in the bench scale system at temperatures above 12°C but were significantly poorer at 7°C.

Contents: Process Theory Kinetics and Sludge Quality Control: Activated Sludge Process - Process Theory - Activated Sludge Separation Problems - References Activated Sludge Treatment of Municipal Wastewater U.S.A. Practice: General Approach - Clarifier Design - Aeration Tank (Reactor) Design - Appurtenance Design - Configurations - ReferencesEurope

The activated sludge process is the most versatile, commonly used wastewater treatment system in North America; however, many activated sludge processes frequently experience operational problems related to poor compaction or settleability of secondary solids and loss of secondary solids from the clarifier. Eschewing the technical jargon and copious chemical equations found in the majority of wastewater studies, Settleability Problems and Loss of Solids in the Activated Sludge Process speaks directly to plant operators, showing them how to identify and solve common problems and achieve maximum efficiency. Michael H. Gerardi’s hands-on guide addresses the most common plant operational problems, such as increased costs, loss of treatment efficiency, and permit violations. Using numerous tables and illustrations, Settleability Problems provides microscopic and analytical techniques for troubleshooting and identifying the conditions responsible for settleability problems and loss of solids. It includes pictures of wet mounts and smears of acceptable and unacceptable microscopic conditions of the activated sludge and presents corrective measures for operational problems. Chapters include: Undesired Filamentous Growth Nutrient-Deficient Floc Particles Denitrification Slug Discharge of Soluble cBOD Viscous Bulking or Zoogloeal Growth Production and Accumulation of Foam and Scum Volume II in the series, Settleability Problems will prove to be of unparalleled value to wastewater treatment plant operators as well as students of wastewater microbiology.

This book provides a thorough overview of respirometry and its scientific and engineering basis. The book describes the fundamentals of biological waste treatment, development of predictive models for system design and operation, and how respirometry fits in with these operations. It also presents case studies, which give you concrete examples of the application of respirometry. This book will help activated sludge process control designers, operators, and managers of biological wastewater treatment facilitieslearn how to improve methods for the analysis of biological wastewater systems, enhance design and treatability projects, optimize and troubleshoot plant operations, and accurately predict the impact of new loads or streams on biological wastewater facilities.