4 Introduction to Process Analysis and Selection Treatment methods in which the application of physical forces predominate are known as physical unit operations Examples of physical unit operations include screening, mixing, sedimentation, gas transfer, filtration, and adsorption. Treatment methods in which the removal or conversion of constituents is brought about by the addition of chemicals or by other chemical reactions are known as chemical unit processes Examples of chemical unit processes include disinfection, oXidation, and precipitation Treatment methods in which the removal of constituents is brought about by biological activity are known as biological unit processes
4 Introduction to Process Analysis and Selection Treatment methods in which the application of physical forces predominate are known as physical unit operations. Examples of physical unit operations include screening, mixing, sedimentation, gas transfer, filtration, and adsorption. Treatment methods in which the removal or conversion of constituents is brought about by the addition of chemicals or by other chemical reactions are known as chemical unit processes. Examples of chemical unit processes include disinfection, oxidation, and precipitation. Treatment methods in which the removal of constituents is brought about by biological activity are known as biological unit processes
Unit operations and processes occur in a variety of combinations in treatment flow diagrams The rate at which reactions and conversions occur and the degree of their completion, is generally a function of the constituents invol ved, the temperature, and the type of reactor (i.e. container or tank in which the reactions take place) The fundamental basis for the analysis of the physical chemical, and biological unit operations and processes used for wastewater treatment is the materials mass balance principle in which an accounting of mass is made before and after reactions and conversions have taken place
Unit operations and processes occur in a variety of combinations in treatment flow diagrams. The rate at which reactions and conversions occur, and the degree of their completion, is generally a function of the constituents involved, the temperature, and the type of reactor (i.e., container or tank in which the reactions take place). The fundamental basis for the analysis of the physical, chemical, and biological unit operations and processes used for wastewater treatment is the materials mass balance principle in which an accounting of mass is made before and after reactions and conversions have taken place
Chlorine contact basin Gravity thickeners nd gravity bell thickener building ry clarifiers Dechlorination Final post-aeration iquid biosolids and effluent pumping BNR Anaerobic Influent pump Actors biosolids Septage station and storage pond receiving screening Fig 4-1 Overview of a biological nutrient removal(Bnr wastewater-treatment plant
Fig. 4-1 Overview of a biological nutrient removal(BNR) wastewater-treatment plant
4-1 Reactors used for the Treatment of Wastewater Types ofReactors Fig. 4-2 Definition sketch for various types of reactors used for wastewater treatment he principal types of reactors used for the treatment of wastewater. are )the batch reactor, 2) the complete-mix reactor(also known as the continuous flow stirred-tank reactor (CFSTR) in the chemical engineering literature) 3)the plug-flow reactor (also known as a tubular-flow reactor (4)complete-mix reactors in series (5) the packed-bed reactor (6)the fluidized-bed reactor
4-1 Reactors used for the Treatment of Wastewater Types of Reactors Fig. 4-2 Definition sketch for various types of reactors used for wastewater treatment The principal types of reactors used for the treatment of wastewater, are (1) the batch reactor, (2) the complete-mix reactor (also known as the continuousflow stirred-tank reactor (CFSTR) in the chemical engineering literature), (3) the plug-flow reactor (also known as a tubular-flow reactor), (4) complete-mix reactors in series, (5) the packed-bed reactor, (6) the fluidized-bed reactor
Batch reactor In the batch reactor, flow is neither entering nor leaving the reactor(i.e, flow enters, is treated, and then is discharged and the cycle repeats) The bod test is carried out in a batch reactor that are often used to blend chemicals or to dilute concentrated chemicals
Batch Reactor In the batch reactor, flow is neither entering nor leaving the reactor (i.e, flow enters, is treated, and then is discharged, and the cycle repeats). The BOD test is carried out in a batch reactor that are often used to blend chemicals or to dilute concentrated chemicals
Complete-Mix Reactor Fluid particles leave the reactor in proportion to their statistical population. Complete mixing can be accomplished in round or square reactors if the contents of the reactor are uniformly and continuously redistributed. The actual time required to achieve completely mixed conditions will depend on the reactor geometry and the power Input
Complete-Mix Reactor Fluid particles leave the reactor in proportion to their statistical population. Complete mixing can be accomplished in round or square reactors if the contents of the reactor are uniformly and continuously redistributed. The actual time required to achieve completely mixed conditions will depend on the reactor geometry and the power input
Plug-Flow Reactor Fluid particles pass through the reactor with little in the same sequence in which they entered Reactor or no longitudinal mixing and exit from the The particles retain their identity and remain in the reactor for a time equal to the theoretical detention time
Plug-Flow Reactor Fluid particles pass through the reactor with little or no longitudinal mixing and exit from the reactor in the same sequence in which they entered. The particles retain their identity and remain in the reactor for a time equal to the theoretical detention time
Complete-Mix Reactors in Series The series of complete-mix reactors is used to model the flow regime that exists between the ideal hydraulic flow patterns corresponding to the complete-mix and plug-flow reactors. If the series s composed of one reactor, the complete-mix regime prevails If the series consists of an infinite number of reactors in series, the plug- flow regime prevails
Complete-Mix Reactors in Series The series of complete-mix reactors is used to model the flow regime that exists between the ideal hydraulic flow patterns corresponding to the complete-mix and plug-flow reactors. If the series is composed of one reactor, the complete-mix regime prevails. If the series consists of an infinite number of reactors in series, the plug-flow regime prevails
Packed-Bed reactors Dosing can be continuous or intermittent(e.g, trickling filter). The packing material in packed-bed reactors can be continuous or arranged in multiple stages, with flow from one stage to another Fluidized-Bed reactor The fluidized-bed reactor is similar to the packed-bed reactor in many respects, but the packing material is expanded by the upward movement of fluid(air or water) through the bed. The expanded porosity of the fluidized bed packing material can be varied by controlling the flowrate of the fluid
Packed-Bed Reactors Dosing can be continuous or intermittent (e.g., trickling filter). The packing material in packed-bed reactors can be continuous or arranged in multiple stages, with flow from one stage to another. Fluidized-Bed Reactor The fluidized-bed reactor is similar to the packed-bed reactor in many respects, but the packing material is expanded by the upward movement of fluid (air or water) through the bed. The expanded porosity of the fluidizedbed packing material can be varied by controlling the flowrate of the fluid
Application of reactors Tab. 4-1 Principal applications of reactor types used for wastewater treatment Operational factors that must be considered in the selection of the type of reactor or reactors to be used in the treatment process include I) the nature of the wastewater to be treated (2 )the nature of the reaction (i.e, homogeneous or heterogeneous ()the reaction kinetics governing the treatment proces (4)the process performance requirements, (5)local environmental conditions. In practice, the construction costs and operation and maintenance costs also affect reactor selection
Application of Reactors Tab. 4-1 Principal applications of reactor types used for wastewater treatment Operational factors that must be considered in the selection of the type of reactor or reactors to be used in the treatment process include (1) the nature of the wastewater to be treated, (2)the nature of the reaction (i.e., homogeneous or heterogeneous), (3) the reaction kinetics governing the treatment process, (4) the process performance requirements, (5)local environmental conditions. In practice, the construction costs and operation and maintenance costs also affect reactor selection
