Basic unit processes and operations for water treatment
Answers
Answer:
This stage involves several unit operations such as screening, comminution, sedimentation for grit removal, skimming, and flow equalization. 2. Primary treatment: unit operations such as sedimentation and flotation are employed to remove the suspended and colloid fractions of the effluent. . Secondary treatment: it aims to remove organic material through biological processes. 4. Tertiary or advanced treatment: it aims to remove nutrients such as nitrogen and phosphorous, residual suspended solids, inorganics and toxic and refractory organics that have escaped from previous stages. This can be done through physical (e.g., filtration, screening, air stripping, adsorption, ion exchange), chemical (precipitation, oxidation), or biological processes. However, with the exception of very few countries that have nutrient removal regulations for ecological reasons, typical WWTPs do not go beyond secondary treatment. 5. Disinfection removes water pathogens by chemical (e.g., chlorination or ozonation) or physical processes (e.g., UV irradiation).
Answer:
Municipal wastewater treatment typically comprises a string of physical, chemical, and biological processes aimed at the removal of the polluting load and the production of a final product that can safely be disposed of in watercourses and=or reused. Of the various processes involved, physical processes, which are also commonly referred to as unit operations, play a major role throughout the various treatment stages. In a conventional wastewater treatment plant (WWTP), which is schematically illustrated in Figure 3.1, one can easily identify several such stages and typical efficiencies in terms of biochemical oxygen demand (BOD) and suspended solids (SS) removal. 1. Preliminary treatment (also referred to as pretreatment): it aims to remove bulky and large solids, thus preconditioning the effluent prior to the remainder of the treatment. This stage involves several unit operations such as screening, comminution, sedimentation for grit removal, skimming, and flow equalization. 2. Primary treatment: unit operations such as sedimentation and flotation are employed to remove the suspended and colloid fractions of the effluent. 3. Secondary treatment: it aims to remove organic material through biological processes. 4. Tertiary or advanced treatment: it aims to remove nutrients such as nitrogen and phosphorous, residual suspended solids, inorganics and toxic and refractory organics that have escaped from previous stages. This can be done through physical (e.g., filtration, screening, air stripping, adsorption, ion exchange), chemical (precipitation, oxidation), or biological processes. However, with the exception of very few countries that have nutrient removal regulations for ecological reasons, typical WWTPs do not go beyond secondary treatment. 5. Disinfection removes water pathogens by chemical (e.g., chlorination or ozonation) or physical processes (e.g., UV irradiation)