Every wastewater treatment plant is comprised of a collection of individual unit processes, each of which serves a unique purpose, with a specific goal or treatment objective. Some unit processes, such as API separators or grit chambers, for example, have minimal constraints, only needing to be operated at or below a maximum velocity, aided by the powerful force of gravity, to work well. Other processes, such as the activated sludge process, are faced with many potential constraints, needing a large oxygen input, lots of mixing, desirable food source, sufficient macronutrients (nitrogen and phosphorus), and a fairly narrow range of pH, temperature, and other factors to work well, and these many and highly variable requirements can significantly complicate the operation of biological unit processes.
A range of unit processes are discussed here with varying degrees of detail. The unit processes currently available for review are: 1) Gravity Separators with a focus on refinery API Separators, 2) Equalization Tanks, 3) Oxidation Ditches, 4) Primary Clarifiers, 5) Secondary Clarifiers, and 6) Wet Gas Scrubbers. Additional unit processes will be added over time so check back every now and then for updates.