Reactor Analysis

Reactor is a device or vessel within which chemical processes are carried out for experimental or manufacturing purposes. The most common basic types of reactors are tanks (where the reactants mix in the whole volume) and pipes or tubes (for laminar flow reactors and plug flow reactors). Both types can be used as continuous reactors or batch reactors, and either may accommodate one or more solids (reagents, catalysts, or inert materials), but the reagents and products are typically fluids (liquids or gases). Reactors in continuous processes are typically run at steady-state, whereas reactors in batch processes are necessarily operated in a transient state. When a reactor is brought into operation, either for the first time or after a shutdown, it is in a transient state, and key process variables change with time. The purpose of this chapter is to discuss the types of the reactors used in the wastewater treatment, modeling ideal, non-ideal flows in the reactor and treatment kinetics. Furthermore, the chapter considers both kinetic and hydrodynamic aspect while designing the reactor.

Wastewater Treatment Operations

Sewage is treated by a variety of methods to make it suitable for its intended use, be it for spraying onto irrigation fields (for watering crops) or be it for human consumption. Sewage treatment mainly takes place in two main stages: primary and secondary treatment. In arid areas, where there is not enough water, sewage also undergoes a tertiary treatment to meet the demands of the drinking water supply. During primary treatment, the suspended solids are separated from the water and the BOD (biochemical oxygen demand) of the water is reduced, preparing it for the next stage in wastewater treatment. Secondary treatment consists of aeration and settling tank. This process removes 75-95% of the BOD. In case of trickling filter, BOD removal is up to 80%-85%. The water is then disinfected, mostly by chlorination, and released into flowing streams or oceans. Therefore, the main objective of this chapter is to provide a deeper insight into preliminary, primary, secondary, and tertiary treatment of wastewater and furthermore provide cognizance concerning design considerations of treatment units.

Characteristics of Wastewater

Wastewater is defined as any water that has been negatively affected in quality by humans and is a complex mixture of inorganic and organic materials. Wastewater is used water from any combination of domestic, industrial, commercial or agricultural activities, surface runoff or stormwater, and any sewer inflow or sewer infiltration. As technological changes take place in manufacturing, changes also occur in the compounds discharged and resulting wastewater characteristics. High amounts of inorganic and organic matter discharged via process effluent can seriously impair water sources or result in toxic levels in soil. Therefore, the purpose of this wastewater characterization chapter is to provide a plan for sampling and analysis of the wastewater to obtain baseline data for an expanded list of wastewater characteristics. The characterization results will assist in further identifying locations of concern and any additional pollutants that may require control or could interfere with wastewater operations.

Digestion and Disposal of Primary and Secondary Sludge

Sewage sludge is the solid, semisolid, or slurry residual material that is produced as a byproduct of wastewater treatment processes. This residue is commonly classified as primary and secondary sludge. Primary sludge is generated from chemical precipitation, sedimentation, and other primary processes, whereas secondary sludge is the activated waste biomass resulting from biological treatments. Quite often the sludges are combined together for further treatment and disposal. Sludge from biological treatment operations is sometimes referred to as wastewater biosolids. Of the constituents removed by the treatment, solids and biosolids are by far the largest in volume, and their processing, reuse, and disposal present perhaps the most challenging environmental problem and complex problem in wastewater treatment processes. Therefore, the chapter is devoted to the discussion of the sources, characteristics, quantities, disposal, digestion, and stabilization of sludge so as to present background data and information on these topics that will serve as a basis for the designing of sludge processing, treatment, and disposal facilities.

Advanced Wastewater Treatments

Advanced wastewater treatment is the process that reduces the level of impurities in wastewater below that attainable through conventional secondary or biological treatment. It includes the removal of nutrients such as phosphorus and nitrogen and a high percentage of suspended solids. The removal of nitrogen and phosphorus from wastewater has become an emerging worldwide concern because these compounds cause eutrophication in natural water. A post-treatment process is therefore required to remove nitrogen and phosphorus from the effluent. Therefore, the purpose of this chapter is to provide the deeper knowledge of membrane technology, membrane bioreactor, sequential batch reactor, moving bed biofilm reactor, nitrification, denitrification, phosphorus removal from wastewater, carbon adsorption, and provide a design of a sewage treatment plant using moving bed biofilm reactor technology.